EFFECT OF SOIL APPLIED POTASSIUM SILICATE ON PAPAYA (Carica papaya L.) PLANT GROWTH, DEVELOPMENT, YIELDS, PHYSIOLOGY AND, POSTHARVEST FRUIT QUALITY

By

OCTAVIO A. MENOCAL BARBERENA

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2014

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© 2014 Octavio A. Menocal Barberena

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Blessed is the man who finds wisdom, the man who gains understanding (Proverbs 3:13). The man could not step in the same rivers twice, for other waters are ever flowing on (Heraclitus of Ephesus). God our Lord planted many fruit trees in the ‘Garden of Eden’, took man and put him to work and take care of it, and man with all his forces has done it for making a better world (Genesis 2:10-11). God has given to man the most powerful gift: “Hope”. With hope, man work and do research on the land of God and produce the best fruits to feed mankind. Octavio A. Menocal [adapted from Hope International: ‘Hope’

This dissertation is dedicated with all my heart to my lovely wife Norma del Socorro Sandoval-Balladares and our two wonderful children Octavio Augusto and Norman Francisco. My wife always trusted my decisions, supported everything I wanted to do and has inspired me every single day I have spent at the University of Florida in Gainesville and Homestead. In addition, I would like to acknowledge my children’s support whom endured many sacrifices and who have provided me and their mother their continuous love and encouragement during my Ph.D. graduate program. This is also dedicated to my mother Nelcys Barberena-Valladares with all my love for her brave and unwavering support during this difficult time of her life. Last but not least, to Dr. William (Bill) Castle for his teachings and having trained me as a professional.

3 ACKNOWLEDGMENTS

First, I would like to thank Almighty God for guiding me and helping, leading, and protecting me and my family. Thank God for his blessings and for everything he did for my family.

I would like to thank and express my deep appreciation to my entire committee: Dr.

Jonathan H. Crane, Dr. Jeffrey K. Brecht, Dr. Bruce A. Schaffer, Dr. Yuncong Li and Dr. Kati

W. Migliaccio for their advice. I want to give very special thanks to my major professor Dr.

Jonathan H. Crane for his guidance and support. He also provided me with excellent technical and academic advice. Dr. Crane not only believed in me, but also spent many hours, and much energy and effort, trying to give me the best while showing his true respect, concern, and friendship toward me. I express my deepest gratitude to Dr. Jeffrey K. Brecht for his willingness to participate on my supervisory committee. Dr. Brecht believed in me and encouraged me to develop my research, and provided me his critical advice. He also provided me his friendship, guidance, support, confidence, and illuminated my way during my economical struggles. I also express my gratitude to Dr. Bruce A. Schaffer for his advice and invaluable knowledge and motivation during the process of my statistical analyses. I also thank Dr. Yuncong Li for his friendship, support and his invaluable and critical inputs. I also want to thank Dr. Migliaccio for her advice and guidance in the establishment of and functioning of the irrigation system utilized in my field work.

Special thanks to Dr. Wanda Montas for her unconditional support and cooperation during the time I conducted my field research at the Tropical Research and Education Center

(TREC-UF), in Homestead, FL. I also want to thank Ms. Ana Vargas for her support and friendship. Special thanks to TREC’s field crew for their work during the time I was conducting my field research.

4 I would also like to thank the Everglades Soil Testing Laboratory, Soil and Water Science

Department at the Everglades Research and Education Center of the University of Florida (UF-

EREC), Belle Glade, under the direction of Dr. Alan Wright, particularly Dr. Yigang Luo for the arduous and tremendous work he did by analyzing my soil and papaya tissue samples.

I am indebted to Ms. María I. Cruz and Ms. Ana Zometa for their support since the beginning of my educational journey, for their friendship, guidance and encouragement during the time I was a student at the University of Florida. I want to express my deepest gratitude for their help and confidence. Special thanks to my very old friend Eng. MSc. Jaime A. Cuadra-

Miranda and his wife Ms. Ena for their support, confidence, and friendship. I also want to thank

Eng. Armando Bendaña-López and Dr. Leonardo Green for their support and friendship.

I also give thanks to my friends: Ms. Adrian Berry and Ms. Kim Cordasco, Walter and

Elena (Peruvian), Pavlos, Alexandra and Angelos (Greeks), Xheng-Ke Zhang and Yinyan Guo

(Rep. of China), for their friendship at the beginning of my doctoral studies. Thanks to my classmates and very good friends Francisco Loayza (Perú) and Darío Chávez (Ecuador). Thanks to my friends, mentors and excellent professors Eng. Eddy Castellón-Sanabria, Dr. José Ramón

Peralta-Videa, Eng. MSc. Miguel López-Guadamuz, Eng. MSc. Aleyda Juárez-Moya, Eng. MSc.

Agustín Castillo-Gómez and Eng. MSc. Gerardo Medrano-Morales who believed in me and encouraged me to pursue my doctoral degree, and to my professors Eng. MSc. Ernesto Terán-

Hernández and Eng. MSc. Silvio Echaverry-Briceño, In Memoriam (R.I.P).

Thanks to my Nicaraguan friends and colleagues: Henner Obregón-Olivas, Dr. Elide

Valencia, Carlos and Marthelena Guerrero-Manfut, Rosa Inés Carrillo, Leonardo Omar and Frida

Aguilar-Weiss, Marco Pacheco Gómez, William and Adela Chamorro, Nestor and Jaime Bonilla,

Matilde Somarriba-Chang, María Lourdes Espinosa, Joel Reyes, Carmen Gutiérrez, Jellin Pavón,

5 Ms. Eva Webster, Martín Mena, José Filipone and Ms. Emilia Sandoval, Eddy and Ms. Martina

Thomas, Mario Torres-Molina and Ms. Nidia Gutiérrez-Chamorro for their friendship.

Thanks to my family, for all their love and patience, especially to my mother Nelcys

Barberena-Valladares and my sister Nelcys Alicia who supported me throughout my graduate studies. Thanks to my sisters Nelcys Evaclemencia and Nelcys René because they cared for my family while I was away. Thanks to my brother Octavio Anastacio because he was the medical doctor for my family and my younger brother Marcos Antonio for his support.

To my parents-in-law, my deepest appreciation for taking care of my wife and my kids during the time I was away from home. Special gratitude to my mother-in-law, Ms. Nereyda

Sandoval for her support, help, and love for my family. Her love was invaluable and I am in deepest debt to you, as to my father-in-law Mr. Francisco (‘Pancho’) Sandoval. Thanks to my brothers and sisters-in-law Ernesto Espinoza, Julio Delgado, Mario Alvarenga, Ileana Cordero,

Marlon-, Victor-, Allan-, Marisol-, and Yessenia Sandoval-Balladares for their support.

My highest gratitude is reserved for my wife, Norma del Socorro Sandoval-Balladares, for her support, help, patience, and deepest love which allowed me to complete my doctoral studies. Although, she could not be with me in the U.S. she stood by me and her unconditional support and love throughout my graduate studies at the University of Florida was tremendously valuable for me because without her, I would not be what I am. Thus, all my love goes to my lovely wife because she is everything to me as well as my children Octavio Augusto and Norman

Francisco, who are the reasons for my life. Norma, with all my heart I will always love you.

6 TABLE OF CONTENTS

page

ACKNOWLEDGMENTS ...... 4

LIST OF TABLES ...... 11

LIST OF FIGURES ...... 18

ABSTRACT ...... 19

CHAPTER

1 INTRODUCTION ...... 21

Assumptions ...... 26 Objectives ...... 26 General ...... 26 Specific ...... 26

2 LITERATURE REVIEW ...... 27

General Description ...... 27 Factors Affecting Papaya Production ...... 30 Environmental Conditions ...... 32 Drought ...... 32 Flooding ...... 32 Temperature ...... 32 Wind ...... 33 Insect Pests and Diseases Affecting Papaya Production ...... 33 Insect pests ...... 33 Diseases ...... 34 Plant Nutrients ...... 34 Silicic Acid (Silicate) ...... 42 General biogeological description and cycle...... 42 The benefits of silicon ...... 43 Silicon Uptake, Transport, Distribution and Accumulation in Plant Organs ...... 45 Quantifying silicate in soil and water ...... 51 Quantifying silicate in plants ...... 52 Potential Plant Growth and Physiological Effects of Silicic Acid ...... 53 Plant growth and physiological effects ...... 53 Growth and yields ...... 54 Silicon Effect on Plant Tolerance to Environmental Stress ...... 58 Drought stress ...... 58 Flood stress ...... 60 Wind stress ...... 61 Cold stress ...... 62

7 Salinity stress ...... 63 Silicon Effect on Plant Tolerance to Biotic Stress ...... 63 Silicon’s role in insect pest tolerance ...... 63 Silicon’s role in disease resistance ...... 65 Effect of Silicate Applications on Postharvest Physiology ...... 66

3 EFFECT OF SOIL DRENCH AND FOLIARLY APPLIED POTASSIUM SILICATE RATE ON PAPAYA LEAF GAS EXCHANGE AND GROWTH AND DEVELOPMENT UNDER WELL-WATERED AND DROUGHT STRESSED GREENHOUSE AND PLASTIC-HOUSE CONDITIONS ...... 69

Overview ...... 69 Materials and Methods ...... 72 Research Site and Location ...... 72 Plant Selection, Soil Sampling and Processing, and Crop Management ...... 72 Plant measurements ...... 76 Plant leaf gas exchange measurements ...... 76 Soil sampling, processing and nutrient analysis ...... 77 Analysis of tissue sample for silicon available content ...... 78 Statistical Analysis ...... 79 Results and Discussion ...... 80 Effect of K2SiO3 Soil Drench Applications Under Well-Watered Soil Conditions ...... 80 Plant height and diameter measurements ...... 80 Plant fresh and dry weights ...... 81 Plant gas exchange ...... 81 Soil and plant tissue nutrient and Si content ...... 82 Effect of Foliar K2SiO3 Applications Under Well-Watered Soil Conditions ...... 84 Plant height and diameter measurements ...... 84 Plant fresh and dry weights ...... 84 Plant gas exchange ...... 85 Soil and plant tissue nutrient and Si content ...... 85 Effect of Foliarly Applied K2SiO3 on Container-Grown Well-Watered and Drought Stressed Papaya Plants ...... 87 Plant height and diameter measurements ...... 87 Plant fresh and dry weights ...... 88 SPAD values ...... 88 Soil and plant tissue nutrient and Si content ...... 89 Conclusions...... 90

4 EFFECT OF SILICATE APPLICATION RATES ON PAPAYA GAS EXCHANGE, GROWTH AND YIELDS UNDER FIELD CONDITIONS IN SOUTH FLORIDA ...... 91

Overview ...... 91 Materials and Methods ...... 93 Research Site and Location ...... 93 Plant Selection and Crop Management ...... 93 Plant measurements ...... 96

8 Plant leaf gas exchange measurements ...... 97 Soil sampling, processing and nutrient analysis ...... 98 Analysis of tissue sample for silicon available content ...... 99 Fruit yield ...... 100 Statistical Analysis ...... 100 Results and Discussion ...... 100 Ambient Air and Soil Temperatures and Rainfall ...... 100 Plant Growth Measurements ...... 101 Plant Gas Exchange ...... 103 Soil, Plant Petiole, and Lamina Tissue Nutrient Content ...... 104 Soil nutrients ...... 104 Plant leaf petiole nutrients ...... 107 Plant leaf petiole and lamina silicon ...... 107 Fruit number and fruit weight per plant ...... 109 Conclusions...... 110

5 EFFECT OF POTASSIUM SILICATE SOIL APPLICATIONS ON POSTHARVEST QUALITY OF X17-2 x T5 PAPAYA FRUIT ...... 113

Overview ...... 113 Materials and Methods ...... 122 Fruit Selection ...... 122 Postharvest Fruit Evaluation ...... 123 Analysis of Tissue Samples for Available Silicon Content ...... 125 Statistical Analysis ...... 126 Results and Discussion ...... 126 Conclusions...... 130

6 SUMMARY AND CONCLUSIONS ...... 132

APPENDIX

A CRITICAL PETIOLE RANGES FOR NITROGEN (N), PHOSPHORUS (P), AND POTASSIUM (K) LEVELS IN PAPAYA ...... 137

B CONCENTRATIONS OF CONSTITUENTS AND TOTAL MINERAL ELEMENTSz IN THREE COMMERCIAL ARTIFICIAL SOIL MEDIA ...... 138

C CONCENTRATIONS OF CONSTITUENTS AND SOIL PLANT AVAILABLE NUTRIENT ELEMENTSz IN THREE COMMERCIAL ARTIFICIAL SOIL MEDIA .....139

D MONTHLY MINIMUM, MAXIMUM AND AVERAGE AIR AND SOIL TEMPERATURES (OC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION ...... 140

E MONTHLY MINIMUM, MAXIMUM AND AVERAGE AIR TEMPERATURES (oC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION ...... 142

9 F MONTHLY MINIMUM, MAXIMUM AND AVERAGE SOIL TEMPERATURES (oC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION ...... 144

G SCHEDULE OF POTASSIUM SILICATE SOIL DRENCH APPLICATIONS ON X- 17-2 x T5 TRANSGENIC BISEXUAL AND FEMALE PAPAYA PLANTS GROWN UNDER WILL-WATERED FIELD CONDITIONS ...... 146

H AVERAGE FRUIT FRESH WEIGHT OF POTASSIUM SILICATE SOIL DRENCH APPLICATIONS ON X17-2 x T5 TRANSGENIC PAPAYA PLANTS GROWN IN A KROME VERY GRAVELLY SANDY SOIL UNDER WELL-WATERED FIELD CONDITIONS ...... 147

I ADDITIONAL TABLES FOR CHAPTER 3 ...... 149

J ADDITIONAL TABLES FOR CHAPTER 4 ...... 219

K ADDITIONAL TABLES FOR CHAPTER 5 ...... 262

LIST OF REFERENCES ...... 276

BIOGRAPHICAL SKETCH ...... 312

10 LIST OF TABLES

Table page

-1 I-1 Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant height ...150

-1 I-2 Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant height ...151

-1 I-3 Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter .152

-1 I-4 Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter .153

-1 I-5 Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight ...... 154

-1 I-6 Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight ...... 155

-1 I-7 Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight...... 156

-1 I-8 Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight...... 157

-1 I-9 Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) ...... 158

-1 I-10 Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) ...... 159

-1 I-11 Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) ...... 160

-1 I-12 Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) ...... 161

-1 I-13 Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) ...... 162

-1 I-14 Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) ...... 163

-1 I-15 Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values ...164

11 -1 I-16 Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values ...165

I-17 Concentration of constituent and total mineral elementsz of Krome soil (n = 2) prior to soil drench K2SiO3 applications to ‘Red Lady’ papaya (C. papaya L.) plants ...... 166

I-18 Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to soil drench K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants ...... 167

I-19 Soil pH, OM, concentration of total mineral elementsz and Si of Krome soil (n = 2) collected after 11 soil drench K2SiO3 applications (Exp. 1) to ‘Red Lady’ papaya ...... 168

I-20 Soil pH, OM, concentration of total mineral elementsz and Si of Krome soil (n = 2) collected after 9 soil drench K2SiO3 applications (Exp. 2) to ‘Red Lady’ papaya ...... 169

I-21 Concentration of constituent and plant available nutrient elementsz and Si of Krome soil after 11 soil drench K2SiO3 applications (Exp. 1) to ‘Red Lady’ papaya plants ...... 170

I-22 Concentration of constituent and plant available nutrient elementsz and Si of Krome soil after 9 soil drench K2SiO3 applications (Exp. 2) to ‘Red Lady’ papaya plants ...... 171

I-23 Silicon concentration in Krome soil samples (n = 2) collected at 0, and after 6 and 11 soil drench applications of K2SiO3 (Exp. 1) to ‘Red Lady’ papaya plants ...... 172

I-24 Silicon concentration in Krome soil samples (n = 2) collected at 0, and after 5 and 9 soil drench applications of K2SiO3 (Exp. 2) to ‘Red Lady’ papaya plants ...... 173

I-25 Effect of 11 soild drench potassium silicate applications at a 0, 60, 120, and 240 g plant-1application-1 (Exp. 1) on ‘Red Lady’ papaya plant tissue silicon content (n=4) ...174

I-26 Effect of 9 soil drench potassium silicate applications at a 0, 60, 120, and 240 g plant-1application-1 (Exp. 2) on ‘Red Lady’ papaya plant tissue silicon content (n=4) ...175

-1 I-27 Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant height ...... 176

-1 I-28 Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant height ...... 177

-1 I-29 Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter ..178

-1 I-30 Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter ..179

-1 I-31 Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight ...... 180

12 -1 I-32 Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight ...... 181

-1 I-33 Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight ...... 182

-1 I-34 Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight ...... 183

-1 I-35 Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) ...... 184

-1 I-36 Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) ...... 185

-1 I-37 Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) ...... 186

-1 I-38 Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) ...... 187

-1 I-39 Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) values ...... 188

-1 I-40 Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) values ...... 189

-1 I-41 Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values ...190

-1 I-42 Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) SPAD ...... 191

I-43 Concentration of constituent and total mineral elementsz of Krome soil (n = 2) prior to K2SiO3 foliar applications to ‘Red Lady’ papaya (Carica papaya L.) plants ...... 192

I-44 Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to K2SiO3 foliar applications of ‘Red Lady’ papaya (Carica papaya L.) plants ...... 193

I-45 Soil pH, OM and concentration of total mineral elementsz and Si of Krome soil (n=2) collected after 13 K2SiO3 foliar applications (Exp. 3) to ‘Red Lady’ papaya plants ...... 194

I-46 Soil pH, OM and concentration of total mineral elementsz and Si of Krome soil (n=2) collected after 16 K2SiO3 foliar applications (Exp. 4) to ‘Red Lady’ papaya plants ...... 195

I-47 Concentration of constituent and plant available nutrient elementsz and Si of Krome soil collected after 13 K2SiO3 foliar applications (Exp 3) to ‘Red Lady’ papaya plants .196

13 I-48 Concentration of constituent and plant available nutrient elementsz and Si of Krome soil collected after 16 K2SiO3 foliar applications (Exp 4) to ‘Red Lady’ papaya plants .197

I-49 Silicon concentration in Krome soil samples (n = 2) collected at 0, and after 7 and 13 K2SiO3 foliar applications (Exp. 3) to ‘Red Lady’ papaya (Carica papaya L.) plants ...198

I-50 Silicon concentration in Krome soil samples (n = 2) collected at 0, and after 9 and 16 K2SiO3 foliar applications (Exp. 4) to ‘Red Lady’ papaya (Carica papaya L.) plants ...199

I-51 Effect of 13 potassium silicate (K2SiO3) foliar applications at a 0, 2.5, 5, and 10 g plant-1application-1 (Exp. 3) to ‘Red Lady’ papaya plant tissue silicon content (n = 4) ..200

I-52 Effect of 16 potassium silicate (K2SiO3) foliar applications at a 0, 2.5, 5, and 10 g plant-1application-1 (Exp. 4) to ‘Red Lady’ papaya plant tissue silicon content (n = 4) ..201

I-53 Comparison of the effect of 9 foliar applications of K2SiO3 at 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya (Carica papaya L.) plant height (Exp. 5) ....202

I-54 Comparison of the effect of 9 foliar applications of K2SiO3 at 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya plant trunk diameter (Exp. 5) ...... 205

I-55 Comparison of the effect of 9 foliar applications of K2SiO3 at 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya plant tissue fresh weight (Exp. 5) ...... 208

I-56 Comparison of the effect of 9 foliar applications of K2SiO3 at 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya plant dry weight (Exp. 5) ...... 209

I-57 Comparison of the effect of 9 foliar applications of K2SiO3 at 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya (Carica papaya L.) SPAD values (Exp. 5) ...210

I-58 Concentration of constituents and total mineral elementsz of Krome soil (n = 2) prior to foliar K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants ...... 213

I-59 Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to foliar K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants ...... 214

I-60 Soil pH, organic matter (OM) and concentration of total mineral elementsz and Si of Krome soil collected after 9 K2SiO3 foliar applications to ‘Red Lady’ papaya plants ....215

I-61 Concentration of constituents and plant available nutrient elementsz and Si of Krome soil (n = 2) collected after 9 K2SiO3 foliar applications to ‘Red Lady’ papaya plants ....216

I-62 Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and 5 and after 9 K2SiO3 foliar applications to ‘Red Lady’ papaya plants ...... 217

I-63 Effect of 9 potassium silicate (K2SiO3, 25% Si) foliar applications at a 0, 2.5, 5, and 10 g plant-1application-1 to ‘Red Lady’ papaya plant tissue silicon content (n = 3) ...... 218

14 -1 -1 J-1 Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya plant height ...... 220

-1 -1 J-2 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant trunk diameter .....221

-1 -1 J-3 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant leaf expansion area ...... 222

-1 -1 J-4 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant leaf expansion area...... 223

-1 -1 J-5 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant leaf expansion area ...... 224

-1 -1 J-6 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant leaf expansion area...... 225

-1 -1 J-7 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya plant leaf abscission number ...... 226

-1 -1 J-8 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya plant leaf abscission number ...... 227

-1 -1 J-9 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya plant leaf abscission number ...... 228

-1 -1 J-10 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) petiole fresh weight ...... 229

-1 -1 J-11 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) lamina fresh weight ...... 232

-1 -1 J-12 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) petiole dry weight ...... 235

-1 -1 J-13 Effect of 0, 500, and 1,000 kg ha year K2SiO soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) lamina dry weight ...... 238

-1 -1 J-14 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) stomatal conductance (gs) ...... 241

-1 -1 J-15 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) stomatal conductance (gs) ...... 242

-1 -1 J-16 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant transpiration (E) ...... 243

15 -1 -1 J-17 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant transpiration (E) ...... 244

-1 -1 J-18 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2- T5 transgenic bisexual papaya (Carica papaya L.) net CO2 assimilation (A) ...... 245

-1 -1 J-19 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2- T5 transgenic female papaya (Carica papaya L.) net CO2 assimilation (A) ...... 246

-1 -1 J-20 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant SPAD values ...... 247

-1 -1 J-21 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant SPAD values ...... 248

J-22 Concentration of constituents, total mineral, and plant available nutrient elementsz of Krome soil prior to K2SiO3 soil drench applications to X17-2 x T5 transgenic papaya .249

J-23 Concentration of constituent and total mineral elementsz of Krome soil collected after 25 K2SiO3 soil drench applications to X17-2 x T5 transgenic papaya plants ...... 250

J-24 Concentration of constituent and plant available nutrient elementsz of Krome soil collected after 25 K2SiO3 soil drench applications to X17-2 x T5 transgenic papaya ....251

J-25 Concentration of nutrients and total available Si nutrient leaf petiole content of bisexual X17-2 x T5 transgenic papaya plants grown in Krome soil after 25 Si applic ..252

J-26 Concentrations of nutrient and total available Si nutrient leaf petiole content of female X17-2 x T5 transgenic papaya plants grown in Krome soil after 25 Si applic ....253

-1 -1 J-27 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf petiole silicon content of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) ..254

-1 -1 J-28 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf petiole silicon content of X17-2 x T5 transgenic female papaya (Carica papaya L.) ....255

-1 -1 J-29 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf lamina silicon content on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) .256

-1 -1 J-30 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf lamina silicon content of X17-2 x T5 transgenic female papaya (Carica papaya L.) .....257

J-31 Correlation among totalz and availabley soil-, leaf lamina-, and petiole Si content of bisexual and female X17-2 x T5 transgenic papaya plants grown in Krome soil ...... 258

-1 -1 J-32 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) fruit number per plant ..259

16 -1 -1 J-33 Effect of 0, 500, and 1,000 kg ha year K2SiO3 on X17-2 x T5 transgenic bisexual papaya fruit number plant-1, fruit yield plant-1 and fruit yield treatment-1ha-1 ...... 260

J-34 Correlation among available siliconz content in plant leaf lamina and petiole, and fruit weight (g plant-1) of bisexual X17-2 x T5 transgenic papaya plants ...... 261

-1 -1 K-1 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit...... 263

-1 -1 K-2 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on length of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit ...... 264

-1 -1 K-3 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on diameter of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit...... 265

-1 -1 K-4 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on fruit peel puncture resistance and whole fruit firmness measured with intact peel...... 266

-1 -1 K-5 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on fruit flesh firmness and resistance to shear force of X17-2 x T5 bisexual papaya ...... 267

-1 -1 K-6 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on fruit peel and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) ...... 268

-1 -1 K-7 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on fruit pulp fresh and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) ....269

-1 -1 K-8 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on seed fresh and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) ....270

-1 -1 K-9 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on peel and pulp thickness of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit...... 271

-1 -1 K-10 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on peel and pulp coloration of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit .....272

K-11 Linear regressions of peel and pulp color changes as affected by 0, 500, and 1,000 kg -1 -1 ha year K2SiO3 soil drench applications on X17-2 x T5 bisexual papaya fruit ...... 273

-1 -1 K-12 Effect of 0, 500, and 1,000 kg ha year of K2SiO3 soil drench applications on pH, TA, TSS of X17-2 x T5 transgenic bisexual papaya fruit ...... 274

-1 -1 K-13 Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on peel, pulp, and seed siliconz content of X17-2 x T5 transgenic bisexual papaya fruit ...... 275

17 LIST OF FIGURES

Figure page

2-1 Description of the biogeochemical cycle of Si showing the plant, soil, and water interactions that affect Si availability in the soil solution (from Savant et al., 1996)...... 68

18 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy

EFFECT OF SOIL APPLIED POTASSIUM SILICATE ON PAPAYA (Carica papaya L.) PLANT GROWTH, DEVELOPMENT, YIELDS, PHYSIOLOGY AND, POSTHARVEST FRUIT QUALITY

By

Octavio A. Menocal Barberena

December 2014

Chair: Jonathan H. Crane Major: Horticultural Sciences

The effect of potassium silicate (K2SiO3) applications on the growth and development, gas exchange, silicon (Si) uptake, yields, and postharvest fruit quality of X17-2 x T5 papaya

(Carica papaya L.) plants under south Florida field conditions was investigated. Treatments

-1 -1 were 25 bi-weekly soil drench applications of K2SiO3 at 0, 500, and 1,000 kg ha year .

Potassium silicate applications at three rates had no effect on plant growth among treatments. In general K2SiO3 application rates had no effect on stomatal conductance (gs) but, as K2SiO3 application rates increased transpiration (E) generally decreased and net CO2 assimilation (A) increased. Leaf Si content and SPAD values increased with K2SiO3 application rate. Potassium silicate had no effect on fruit yield. Four experiments under greenhouse and plastic-house conditions investigated the effect of soil and foliarly applied K2SiO3 on ‘Red Lady’ papaya plant growth, gas exchange, and Si uptake. One experiment investigated the effect of foliarly applied

K2SiO3 on plant growth of well-watered and drought stressed plants. Soil drench treatments were

-1 -1 no Si application, 60, 120, and 240 g Si plant application ; foliar K2SiO3 treatments were no silicon application, 2.5, 5, and 10 g Si plant-1application-1. Soil drenched and foliarly applied

K2SiO3 treatments had no consistent effect on plant height, stem diameters, and plant tissue fresh

19 and dry weights. In general, soil drenched K2SiO3 treatments had no effect on gs and E but A increased with K2SiO3 application rate. In general, K2SiO3 application rate had no effect on plant tissue Si content. Silicon content was generally highest to lowest in root, leaf lamina, petiole and trunk. Papaya growth was similar among foliar K2SiO3 application rates; trunk diameters of drought stressed plants increased with foliar K2SiO3 application rates. Plant tissue fresh and dry weights were not affected by K2SiO3 application rates. SPAD values increased as K2SiO3 application rates increased but there was no difference among well-watered and drought-stressed plants. Potassium silicate applications had no effect on mean fruit weight, and pulp pH and an inconsistent effect postharvest peel and pulp firmness, pulp and peel color and titratable acidity, and peel, pulp and seed Si content.

20 CHAPTER 1 INTRODUCTION

Silicon (Si) is the second most abundant element (28-31%) in the earth’s crust after oxygen (49%) [Epstein, 1994, 1999; Ma, 2004; Epstein and Bloom, 2005]. Silicon mostly combines with oxygen to form silicate minerals, which are assimilated by plant roots as

-1 monosilicic acid (H4SiO4) and its concentration in higher plants may vary from <1 to 100 g kg dry matter depending on the growth environment and on the type of plant (Ma and Takahashi,

2002).

Plant uptake of Si may be active and/or passive (Jones and Handreck, 1967; Raven, 1983,

Marschner, 1995; Epstein, 1999; Raven, 2001) and Si is mostly stored as hydrated amorphous silica (SiO2.nH2O) commonly termed plant opal, phytolithic opal, or phytoliths (Jones and

Handreck, 1967; Dress et al., 1989; Epstein, 1994). Some plants mostly exclude Si from uptake and these plants are termed rejective with respect to Si uptake. Silicon accumulates in the transpiration termini, cell lumens, cell walls, intercellular spaces, and the vascular system of stems, leaves, petioles, and other plant tissues (Raven, 1983, Epstein, 2000; Mitani and Ma,

2005; Mitani et al., 2005; Ma and Yamaji, 2006; Epstein, 2009). Silicon may also accumulate in external layers below and above the cuticle of leaves, roots and inflorescence bracts of some cereals crops (Epstein, 1999)

Silica (SiO2) minerals are among the most important constituents of the soil and their main function is to provide a primary substrate for plant growth (Faure, 1991). Though Si has not been determined to be an essential element, it has been demonstrated that it can influence growth and development in plants (Ma and Takahashi, 2002). The uptake mechanisms of Si may differ among plant species with monocotyledons (e.g., Gramineae and Cyperaceae) accumulating higher Si concentrations than that of dicotyledonous plant species (Epstein, 1999). Higher plants

21 may be classified in terms of their Si content as high-, intermediate-, and low- or non- accumulators, which depends on the inherent plant ability to absorb Si, the plant growth environment, and the Si uptake mechanism (Takahashi et al., 1990; Ma et al., 2001b).

The essentiality of Si as a plant nutrient has been controversial because most plants can complete their reproductive cycle when grown in nutrient solutions lacking Si (Marschner, 1995;

Epstein, 2000). The mechanisms of Si uptake and storage by many mono- and dicotyledonous species differ based on their ability to absorb Si through the root system (Hodson et al., 2005).

However, numerous investigations have documented improved rice (Oryza sativa L.), wheat

(Triticum aestivum L.), maize (Zea mays L.), sugarcane (Saccharum officinarum L.), and sorghum [Sorghum bicolor L.) Moench] plant growth and development, plant resistance to abiotic and biotic stresses, improved plant structural strength and P uptake, decreased physiological effects of aluminum (Al), iron (Fe) and manganese (Mn) soil toxicity, and increased crop productivity (Ayres, 1966; Fox et al., 1967; Yoshida et al., 1969; Tamimi and

Voss, 1970; du Preez, 1970; Gascho and Andreis, 1974; Elawad et al., 1982; Snyder et al., 1986;

Medina-Gonzales et al., 1988; Datnoff et al., 1992; Savant et al., 1999; Meyer and Keeping,

2000; Epstein and Bloom, 2005; Sudhakar et al., 2006; Hanafy-Ahmed et al., 2008; Tahir et al.,

2011).

In addition, Si applications to sugarcane, rice, and maize have been well documented to improve insect and disease resistance (Clements, 1965; Fox et al., 1967; 1969; Subbarao and

Perraju, 1976; Dean and Todd, 1979; Alvarez and Datnoff, 2001; Raid and Comstock, 2006).

For example, Si applications improved sugar cane resistance to sugarcane brown rust [Puccinia melanocephala (H. Syd. and P. Syd.)] (Dean and Todd, 1979; Raid and Comstock, 2006) and played a significant role in the defense mechanism of sugarcane against the African stalk borer

22 (Eldana saccharina Walker) [Lepidoptera: Pyralidae] by forming a mechanical barrier and making leaves and stem more difficult to chew (Keeping and Meyer, 2002).

In dicots the severity of diseases caused by two fungal pathogens [Sphaerotheca fuliginea (Schltdl.) Pollacci and Erysiphe cichoracearum (DC) Merat] on cucumber (Cucumis sativus L), muskmelon (Cucumis melo L.), and zucchini squash (Cucurbita pepo L.) was reduced significantly after Si applications (Menzies, 1992). In one investigation, soil applied Si (K2SiO3) combined with mulching provided an effective control of fusarium wilt [Fusarium oxysporum f.sp. cubense (E.F. Sm.) W.C. Snyder & H.N. Hansen] in banana plant (Musa x paradisiaca L.)

[Henriet et al., 2006]. However, Si amendments to soil have also increased resistance of banana to fusarium wilt by increasing the concentrations of hydrogen peroxide (H2O2), pigments

(cholorophyll a, chlorophyll b, total chlorophyll, and carotenoids), total soluble phenolics (TPS), and lignin-thioglycolic acid (LTGA) derivatives; and greater activities of the enzymes phenylalanine ammonialyases (PALs), peroxidases (PPOs), polyphenoloxidases (POXs), chitinases (CHIs), and β-1,3-glucanases (GLUs); and Si concentration in roots (Fortunato et al.,

2012).

The benefit of Si in plant disease resistance has been attributed to: 1) increased mechanical resistance of leaf epidermal tissues to fungal penetration, 2) formation of polymerized Si complexes in plant cell walls that resist fungal cell-wall penetrating enzymes, and 3) increased plant phenolic and phytoalexin compounds that enhance the activity of chitinases, peroxidases, and polyphenol oxidases in response to pathogen infection (Takahashi,

1996; Datnoff et al., 2001; Ma, 2004). Silicon applications have been reported to result in formation of polysilicate compounds that enhanced catalase (CAT), superoxide dismutase

23 (SOD), ascorbate peroxidase (APX), and soluble peroxidases of rice, improving drought stress tolerance (Epstein, 1999; Ma and Takahashi, 2002; Gong et al., 2005).

Modern agriculture has the challenge to produce more food in an environmentally sustainable manner to feed an ever increasing human population. This includes reducing chemical inputs such as pesticides and inorganic nutrients. The use of Si in production of agronomic crops such as rice and wheat has been demonstrated to be beneficial with respect to plant disease and insect tolerance and enhanced plant yield and crop quality (Epstein, 1999,

2000; Ma, 2004; Mitani and Ma, 2005; Mitani et al., 2005; Ma and Yamaji, 2006; Epstein,

2009). However, relatively few investigations have demonstrated the benefit of Si for dicotyledonous plants. Some exceptions include strawberry (Fragaria x Ananassa Duchesne), cucumber, and tomatoes (Solanum lycopersicum L.) [Jones and Handreck, 1967; Ma and

Takahashi, 2002; Laing et al., 2006].

Papaya (Carica papaya L.) is a highly appreciated fruit that is consumed fresh and processed into fruit salads, juices, jellies, pastes, marmalades, jams, candies, and dried snacks

(Crane, 2005). Papaya contains about 9.8% carbohydrate, 0.8% fiber, 0.6% protein, 0.6% ash,

0.14% fat, 0.34% Niacin and it has 16% more vitamin C than oranges [Citrus sinensis (L.)

Osbeck] and provides about 50% more Vitamin A and E than a mango fruit (Mangifera indica

L.) [Chen and Lewin, 1969; Lewin and Reimann, 1969; Lewin, 1995; Vinci et al., 1995;

Gebhardt and Thomas, 2002; Crane, 2005; Wall, 2006]. Papaya has become a commercially important fresh fruit crop, particularly in the USA and Europe (Evans et al., 2012; Yadava et al.,

1990).

The largest papaya producer and the third largest exporter in the world is Brazil which harvested 1.8 x 106 millions of tons of papaya from 34,213 ha (Texeira da Silva et al., 2007;

24 FAOSTAT, 2012). India is reported to have 60,000 ha of papaya with a national average productivity of 27.5 t ha-1 (Eswaran and Manivannan, 2007). Worldwide, papaya consumption is supplied by Mexico at 14%, Nigeria at 11%, India and Indonesia at 10%, and Venezuela, China,

Peru, Congo, and Ethiopia all which contribute less than 3% of the papaya supply (Benassi,

2006).

In USA, papaya is grown commercially in Hawaii, Florida, and Puerto Rico due to their warm climates (Gonçalves de Oliveira and Pierre-Vitória, 2011). In 2012, Hawaii was reported to have 840 ha, followed by Puerto Rico at 180 ha and Florida 200 ha (Townsend and Andrews,

1940; Harkness, 1960; Goenaga et al., 2001; NASS-Hawaii, 2011; FAOSTAT, 2011; J.H. Crane,

2013 - personal communication). However, with the development of transgenic papaya resistant to the papaya ringspot virus potential papaya production in the U.S. could more than double.

There have been very few investigations on the effect of Si applications on papaya growth and development, and none on biotic and abiotic stress tolerance. Under Hawaiian conditions, applications of limestone, phosphate, and slag containing Si were investigated over a

10-month period (Adlan, 1969). The native Kapaa gravelly silty clay soil used was highly deficient in phosphorus, contained high concentrations of aluminum, and was highly acid (pH

4.2-5.0). The improvement in plant growth, development and yields were attributable mainly to improved plant P nutrition and increased soil pH and plant Calcium (Ca) nutrition (Adlan, 1969).

Only during the last 2 to 4 months was there a trend for increased Si uptake, plant growth, and crop yields with increasing Si application rate. Weekly foliar applications of an un-identified ortho-silicate mix to papaya under Colombian growing conditions was reported to improve plant height, stem diameter, and fruit production compared to non-treated controls over a 10-month

25 period (Hernández, 2008). However, the source of Si was not well-defined and there was no statistical analysis of the data.

Previous research on the effect of Si applications to papaya suggests Si may improve plant growth and development. However, the investigation in Hawaii may have been confounded by the highly deficient phosphorus and high aluminum content of the soil and the investigation in

Colombia used a unidentified source of Si and was not statistically analyzed. The purpose and objectives of this investigation was to investigage the effect of soil- and foliar- applied Si on papaya plant growth and development, gas exchange, crop production and postharvest fruit quality under south Florida conditions.

Assumptions 1. Soil-applied Si will effect on plant growth and development, crop yield, fruit quality, gas exchange, and postharvest shelf-life.

2. Foliar-applied Si has will effect on plant growth and development and gas exchange.

3. Papaya plants take up Si passively and it is deposited mostly in leaf petioles rather than leaf lamina.

4. Soil applied Si has no effect on papaya fruit quality in terms of pulp soluble sugar content and acidity or peel and pulp texture and postharvest shelf life. Objectives General

Previous research on the effect of Si applications to papaya suggests Si may improve plant growth and development. The objectives were to determine the effect of soil applied Si on papaya growth and development, gas exchange, nutrient uptake, and postharvest fruit quality.

Specific

1. To determine the effect of Si applications on papaya growth, development, and phenology.

2. To determine the effect Si on papaya gas exchange (e.g., carbon assimilation, transpiration, stomatal conductance).

3. To determine the effect of Si applications on postharvest fruit quality and shelf life.

26 CHAPTER 2 LITERATURE REVIEW

General Description

Papaya (Carica papaya L.) is an herbaceous and monopodial, large lactiferous plant belonging to the order Brassicales and the Caricaceae. The family has six genera and the genus

Carica has only one specie papaya (Van Droogenbroeck et al., 2002; Lorenzi et al., 2006).

Previously up to 10 species were included in the Carica genus including C. cauliflora, C. microcarpa, C. crassipetala, C. goudotiana, C. pubescens, C. sphaerocarpa, C. x heilbornii, C. pulchra, C. stipulata, and C. glandulosa some of which have now been placed in the

Vasconcella genus, (Manshardt and Zee, 1994: Van Droogenbroeck et al., 2002).

Papaya plants may reach two to ten m in height and the leaves are usually large and palmate-lobed with an average length of 125 cm, attached in an alternate or spiraled form along the straight trunk. The leaf blade is usually palmate and ends in five or seven lobes. Leaf lifespan normally ranges from 75 to 240 days (2.5 to 8 months) and up to four new leaves emerge per week (Nakasone and Paull, 1998; Campostrini and Yamanishi, 2001).

Papaya flowers are fragrant and have petals that range from cream-white to yellow orange color. They emerge from the leaf axils and there are three basic types: female, male, and bisexual (Marler et al., 1994; Nakasone and Paull, 1998). Papaya fruit are borne in the leaf axils and hang below the leaf petioles. The fruit may be small to large (50 - 255 g to 6.8 – 10 kg), elongated, spherical, ovoid, or pear-shaped, and this variability is characteristic of the different papaya genotypes (Storey, 1987; Nakasone and Paull, 1998; Paull and Duarte, 2011). At present, the bisexual pear-shaped (e.g., Solo-types) and elongated types (e.g., Formosa-types) are commercially predominant (Marler and de la Cruz, 2001). The fruit possess seeds within fleshy

27 arils and the pulp is smooth and may be yellow to orange-red when ripe depending upon the variety (Sankat and Maharaj, 1997; Nakasone and Paull, 1998).

Papaya plants perform best in hot tropical regions with optimum temperatures between

21oC and 33°C (Yadava et al., 1990; Crane, 2005; Fuggate et al., 2010; Rivera-Pastrana et al.,

2010). Plant growth basically ceases during cool temperatures (i.e., less than 15°C) and unprotected plants do not survive temperatures below 0°C. Prolonged dry periods also reduce crop output (Almeida et al., 2003). Papaya plants have an indeterminate growth habit and grow vegetatively and reproductively simultaneously with the current crop relying on current carbon assimilation to develop (Cull, 1986; Cunha and Haag, 1980). Papaya is native to Central

America (Van Droogenbroeck et al., 2002; Badillo, 1993).

Papaya plants were first mentioned by Oviedo (1535) in his book, “Historia General y

Natural de las Indias”, in which he informed the King of Spain of the discovery of papayas growing between southern Mexico and northern Nicaragua in Central America (Chan and Paull,

2008, Morton, 1987). Papaya seeds were taken by Spanish explorers during the 1500s to Panama and then to Santo Domingo and other Caribbean islands (Sauer, 1966). Subsequently, seeds were taken to South America and Europe from where papaya was spread to Africa, the Philippines,

Malaysia, Oceania, and India by 1598 (Schery, 1952; De Candolle cited by Lassoudiére, 1968).

Papaya was first reported in Hawaii in 1800, in Florida in 1626, and in Puerto Rico in 1598

(Morton, 1987; Storey, 1987; Nakasone, 1986; Nakasone and Paull, 1998). Today papaya is grown throughout the tropical and warm subtropical areas of the world (Chan & Paull, 2008;

Yadava et al., 1990; FAO, 2011 - Statistical Database on Papaya).

Papaya was first known as olocoton, named by indigenous people in Nicaragua; subsequently, it was nicknamed tree melon by the Spanish explorers and nowadays is known as

28 papaya in Mexico and Central America (Ferrão, 1992; Gonçalves de Oliveira and Pierre-Vitória,

2011). In other Spanish-speaking countries papaya is known as melon zapote, papayo, payaya, papayero, fruta mamona, fruta bomba (Cuba), lechosa (Venezuela), and maman (Argentina). In

Portuguese speaking countries, papaya is called mamão or mamoeiro; kapaya, kepaya or lapaya in The Philippines; dangandangan in Indonesia; gedan castela or Spanish musa in Bali; betik in

Malaysia; malakaw, malakor, loko, lawkaw, ma kuai thet or teng ton in Thailand, and du du in

Vietnam. In Africa, Australia and Jamaica it is called paw paw, while in French-speaking countries it is referred to as papaya, papayer or figuier des iles. In the U.S., the term paw paw or papaw refers to Asimina triloba (L.) Michel Félix Dunal, which is in the family Annonaceae

(Storey, 1985; Crane, 2005; Texeira da Silva et al., 2007).

In the U.S., papaya is cultivated in Hawaii (567 ha), Puerto Rico (41 ha) and Florida (121 ha) (USDA-NASS, 2011, 2012a, 2012b; Rieger, 2012; J.H. Crane, 2013 - personal communication). In general, the major commercial cultivation of papaya is concentrated around the Ecuador line, where the tropical and subtropical regions merge (Galán-Saúco and Farré-

Massip, 2006). Interestingly, papaya has been successfully cultivated in the southern part of the former Soviet Union (Kapanadze and Khasaya, 1988). In the Canary Islands, almost 100% of the papaya cultivation is in greenhouses due to the advantages of the controlled climatic conditions; high annual yields greater than 60 t ha-1 have been obtained (Galán-Saúco and Rodríguez-Pastor,

2007). In the U.S. papaya is produced in the islands of Hawaii where average yields range from

20 to 50 t ha-1 (Yee et al., 1970; NASS-USDA, 2009); in Puerto Rico, yields range from 44 to

135 t ha-1 (Goenaga et al., 2001) and, in Florida, yields are estimated from 82 to 192 t ha-1

(Manshardt, 1999; Migliaccio et al., 2010). In Puerto Rico, papaya annual consumption per capita is estimated at 0.75 kg person-1 (Goenaga et al., 2001) while in Hawaii it is estimated at

29 6.8 kg person-1 (Chia et al., 1989). In U.S. during 2002-2012, papaya per capita annual consumption has increased from 0.36 to 0.53 kg person-1 and, in Florida estimated per capita consumption is 0.33 kg person-1 (Evans et al., 2012; US Food Market Estimator, 2012).

Papaya may be grown on many types of well-drained soils (Morton, 1987; Nakasone and

Paull, 1998) and fruit production is enhanced when grown on inherently fertile soils (Marler et al., 2002). Numerous investigations have documented the nutritional requirement of papaya and the optimum leaf petiole nutrient content (Awada and Ikeda, 1957; Awada and Long, 1969;

Awada and Suehisa, 1970; Awada and Long, 1971a; 1971b; Awada et al., 1975; Awada, 1977;

Awada and Long; 1977; 1978; 1980; Awada et al., 1986). However, only two investigations have been reported dealing with the effects of Si applications on papaya growth, production, and fruit quality (Adlan, 1969; Hernández, 2008).

Papaya plants were shown to accumulate soil applied Si under Hawaiian environmental conditions (Adlan, 1969). Plants were grown in the highly weathered Kapaa gravelly silty clay, which had an acid pH (4.2 to 5.0), was deficient in available phosphorus, and contained high levels of bauxite [Al(OH)3]. Soils were treated with three rates each of limestone (to modify soil pH and calcium content) and calcium silicate (electric furnace slag) and triple-superphosphate.

As soil pH, calcium content, and phosphorus content increased, whole plant and petiole Si content increased. However, the main effect on plant growth and crop yields was attributed to increased soil phosphorus and calcium content and increased soil pH (5 to 7). However, there was a trend for papaya growth and production to increase with increased calcium silicate

(Ca2SiO4) rate after 5 to 6 months.

Factors Affecting Papaya Production

Papaya production and fruit quality is highly affected by adverse environmental conditions such as infertile soils, poor soil drainage and flooding, excessively high or low

30 ambient temperatures, drought, and windy conditions (Campostrini et al., 2010; Nunes et al,

2010;). Papaya grown on infertile soils may suffer from nutrient deficiencies (Epstein, 1994,

1999, 2005) and papaya is negatively affected by soils containing heavy metals (e.g., Al, mercury (Hg), cadmium (Cd) and saline and or sodic soils (Vandemark, 1999; Cheikh et al.,

2000).

Papaya growth and development are affected by soil pH, soil compaction, soil aeration and water holding capacity, and soil temperatures (Fawe et al., 2001; Korndörfer and Lepsch,

2001; Campostrini and Glen, 2007). Marler (1998) reported that ‘Waimanalo’ papaya grew well within a pH range of 4 to 9 although others have reported nutrient deficiencies when papayas were grown at low or high pH (Samson, 1986; Chia et al., 1989; Manshardt and Zee, 1994;

Marler et al., 1994; Nakasone and Paull, 1998; Chen et al., 2000a; Li, 2001; Wang et al., 2009).

In general, papaya survives and grows well within the high humidity, warm areas located between the 32° North and South latitudes with well distributed rainfall up to 150 mm per month

(Litz, 1984). Papaya grows best in well-drained and well aerated soils high in organic matter content and with a pH range of 5.5 to 6.7 (Litz, 1984; Morton 1987). Fruit production improves significantly if rains and/or irrigation provide at least 100 mm of water per month (Nishina et al.,

2000; Chan and Paull, 2008). In an investigation in south Florida, substantial papaya yields were reported with water application rates of about 135 mm per month (Migliaccio et al., 2010).

Papaya growth, development, and gas exchange were significantly improved with increased light exposure and plant gas exchange responded rapidly to changes in light intensity and soil moisture content (Marler et al., 1993; Clemente and Marler, 1996; Marler and Mickelbart, 1998).

Samson (1986) observed that papaya fruit developed much more quickly when plants were exposed to full sunlight compared to shaded conditions.

31 Environmental Conditions

Drought

Papaya plants are intolerant of drought, developing external symptoms of leaf yellowing and abscission of older leaves, flower abscission, and poor fruit set (Marler and Discekici, 1997;

Marler and Mickelbart, 1998). Papaya stomatal conduction (gs) and carbon assimilation (A) are reduced in environments with relative humidity below 60% (Marler et al., 1994). Root growth is also reduced and dark respiration increased by drought stress (Marler et al., 2001).

Flooding

Papaya plants are intolerant of hypoxic and anaerobic soil conditions (Samson, 1986; Marler et al., 1994). Typical symptoms of flooding stress are similar to drought stress and include chlorosis of the leaves followed by leaf abscission and eventual plant death three to four days later (Samson, 1986). Papaya plants that do survive short-term flooding make only a slow recovery and never reach their pre-flood potential (Chan and Paull, 2008). Flooded containerized papaya plants had a 71% reduction in stomatal conduction after 1 day of flooding (Marler et al.,

2001).

Temperature

The optimum ambient temperature range for papaya plant growth and development is 21 to 33oC (Nakasone and Paull, 1998; Chan and Paull, 2008). Papaya plants are sensitive to low temperatures (<11oC) which reduce plant growth, fruit development, and fruit quality (Allan,

2002; Chan and Paull, 2008), and papaya plants are intolerant of temperatures below -0.6°C

(Crane, 2005). Papaya plant growth and production are severely affected, and fruit development and quality (e.g., low sugar content) decreased when exposed to low temperatures (Chan and

Paull, 2008). Papaya fruit may develop a deformation called ‘carpeloidy’ when exposed to temperatures below 15oC (Nishina et al., 2000). Likewise, excessively high ambient

32 temperatures (i.e., >32°C-35°C) may reduce flowering and fruit set and also result in carpeloid fruit (Nishina et al., 2000). However, high temperatures do not necessarily impede papaya growth so long as water and nutrient supply remain adequate (Campostrini et al., 2010).

Wind

Papaya plants are a very susceptible to strong winds and tropical storms and an increase in wind speed greater than about 64 km h-1 may destroy the leafy crown, uproot plants, and blow down a plantation (Crane, 2005; Chan and Paull, 2008). Even low speed winds (e.g., ~3.45 m s-1 daytime and 0.13 m s-1 nighttime) increased transpiration and stomatal conductance and the water requirement for young papaya plants (i.e., need for irrigation) [Nakasone, 1986; Storey,

1987; Clemente and Marler, 1996; Marler and Mickelbart, 1998]. Plant height and individual leaf area were also reduced.

Insect Pests and Diseases Affecting Papaya Production

Insect pests

Papaya plants are attacked by numerous insect pests including various mite species (e.g., two-spotted mite, Tetranychus urticae Koch), Lepidoptera (Homolapalpia dalera Dyar), papaya mealybug (Paracoccus marginatus Williams and Granara de Willink), and the papaya fruit fly

(Toxotrypana curvicauda Gerstaecker) [Morton, 1987; Peña and Johnson, 2006]. In Florida, the two-spotted spider mite and papaya fruit fly are major pests (Nishina et al., 2000; Crane, 2005;

Peña and Johnson, 2006; Mossler and Crane, 2008, 2009). Chemical insecticides are commonly used to control mites, scales, and mealybugs, however, the ability of these pest populations to develop resistance to insecticides is a major concern among papaya producers (Pedigo and Rice,

2008). However, control of the two-spotted mite with the release and establishment of the predator swirskii mite (Amblyseius swirskii Athias-Henriot) and the use of commercially

33 available Beauveria bassiana [Beauveria bassiana (Bals.-Criv.) Vuill.] to control the papaya mealybug has been successful (J.H. Crane, 2013 - personal communication).

Diseases

Papaya is susceptible to several diseases caused by fungi and viruses. In the U.S., the major fungal pathogens include phytophthora trunk and root rot (Phytophthora palmivora

Butler), anthracnose (Colletotrichum gloeosporioides Penz.), powdery mildew [Sphaerotheca fuliginea (Schltdl.) Pollacci], and papaya black spot (Cercospora papayae Hansf.) [Adatia and

Besford, 1986; Epstein, 1999; Ma, 2004; Anderson et al., 2005; Mossler and Crane, 2008, 2009].

Worldwide the major disease constraint to papaya production is the Potyvirus papaya ringspot virus (PRV) [Persley and Ploetz, 2003]. Other viruses that are present in some production areas include Potyvirus papaya leaf distortion mosaic and the Tosporvirus tomato spotted wilt mosaic viruses. Some phytoplasmas such a papaya dieback and the mycoplasma causing bunchy top may also limit papaya production (Persley and Ploetz, 2003; Fitch, 2005; Mossler and Crane,

2008, 2009).

Plant Nutrients

Papaya may be grown in most well-drained soils and do best in fertile soils in areas with well distributed rainfall. In soils of low fertility, papaya need to be fertilized, and in areas with dry periods, irrigation is needed to maximize yields. Infertile soils occur often in the tropics due to excessive leaching and demineralization of the soil profile. Pre- and post-plant fertilizers are recommended for optimum papaya production. Pre-plant fertilization includes calcium fertilizers

(e.g., hydrated lime, dolomite) to adjust soil pH and phosphate applications in phosphorus deficient soils (Paull and Duarte, 2011). Commercially, fertilizers may be applied either onto soil surface under the plant canopy or through irrigation lines (called fertigation). Commonly granular soil applied fertilizers include nitrogen (N), phosphorus (P), potassium (K), calcium

34 (Ca), and magnesium (Mg), and foliarly applied fertilizers include magnesium, manganese (Mn), zinc (Zn), iron (Fe), and boron (B) [Crane, 2005; Barker and Pilbeam, 2007; Paull and Duarte,

2011]. Fertilizers applied through the irrigation (fertigation) are usually restricted to nitrogen, potassium, and chelated iron materials.

Papaya generally requires large amounts of fertilizer in order to optimize yields and fruit quality (Rajbhar et al., 2010). Healthy plants are at reduced risk of biotic and abiotic stresses

(Hardisson et al., 2001). Commercial nutrient applications may be based on experience, soil and petiole analysis, and visual observations of leaf color and plant behavior (Awada et al., 1986;

Chia et al., 1989; Nakasone and Paull, 1998; Chen et al., 1999; Nishina et al., 2000). Papaya grows well in a wide range of soil pH including acid soils with a pH range from 5.5 to 6.5

(Nishina et al., 2000), neutral soils (pH 7.0) [Marler et al., 1994] and properly fertilized high pH soils (7.3-8.5) [J.H. Crane, 2014 - personal communication].

Papaya growth and development may be divided into an initial growth phase and the flowering and fruit development phase. Generally, the demand for nutrients increases with the flowering and fruit phase. For example, in Brazil the average amount of N, P, K, Ca, Mg, and S

(sulfur) applied per year to mature plants is 104, 10, 108, 37, 16, and 12 kg ha-1, respectively, and the micronutrients applied are B, Cu (copper), Fe, Mn, Mo (molibdenum) , and Zn at 102,

30, 338, 211, 0.25, and 106 g ha-1, respectively (Cunha and Haag, 1980; Oliveira, 2002).

In Hawaii, 200 g of superphosphate (0-45-0) is applied per plant before transplanting, along with microelements (Awada and Long, 1980; Nishina et al., 2000). After planting, 113.5 g of NPK fertilizer (16-16-16) is applied at an increasing rate every 14 days until bloom and fruit development; thereafter the rate ranges between 454 to 908 g every other month (Crane, 2005).

In a study of plant nutrient use performed with two Hawaiian papaya cultivars, it was reported

35 that ‘Malama-Ki’ removed N, P, K, Ca, and Mg in the amounts of 0.15, 0.02, 0.19, 0.37, and

0.02 kg plant-1year-1, respectively, whereas ‘Waimanalo’ removed 0.12, 0.02, 0.17, 0.05, and

0.02 kg plant-1year-1, respectively (Awada and Suehisa, 1970). Results of a papaya soil nutrient removal investigation in India indicated that N, P, K, Ca, and Mg were removed at rates of 310,

105, 530, 332, and 185 kg ha-1, respectively (Veerannah and Selvaraj, 1984). Kumar et al.

(2008, 2010) recommended a balanced fertilization with NPK in the amount of 300, 300, and

300 kg ha-1year-1 to optimize papaya latex production. In Florida, frequent applications of small amounts of complete fertilizers (i.e., N, P, K, Mg plus minor elements) are recommended for growing healthy papaya that produces good quality fruit (Crane, 2005; Migliaccio et al., 2010).

The suggested recommendations for N begin during the juvenile period with applications of 0.11 kg plant-1month-1, which then increases up to about 0.45 to 0.90 kg plant-1month-1 when plants are bearing fruit.

Nitrogen is an essential element that increases vegetative growth and crop production and improves fruit quality (Costa and Costa, 2003). Nitrogen is reported to enhance the green color, size, and shape of papaya leaves (Awada and Long, 1971a). Symptoms of N deficiency occur first in mature leaves where a progressive change in color from green to light green occurs; severely deficient leaves turn yellow and abscise (Mengel and Kirkby. 1987; Marschner, 1995;

Epstein and Bloom. 2005). Nitrogen deficient young leaves have thinner petioles and the laminas are not well developed (Marinho et al., 2001). On the other hand, when N is in excess, plants may have excessive vegetative growth, possess increased internode length (causing fruits to be widely separated along the trunk), and result in reduced fruit set and fruit quality, and plant ability to withstand strong winds (Awada, 1977; Cibes and Gaztambide, 1978). Nitrogen fertilization increased petiole concentrations of N, Fe, Mn, Cu, and Zn and decreased petiole P,

36 K, Ca, and B concentrations (Awada and Long, 1980). The optimum N concentration of petiole ranges from 1.15 to 1.33% (mean 1.27%) [Appendix A] (Awada and Long, 1971b; Awada,

1977).

Phosphorous is an essential element for root development and root activity and has been linked to increased element uptake (Mengel and Kirkby. 1987; Marschner, 1995; Epstein and

Bloom. 2005). Phosphorus applications have been shown to increase petiole weight and K uptake and improve fruit set (Cibes and Gaztambide, 1978); in contrast, excessive P rates decreased N, Ca, and Mg uptake. Symptoms of P deficiency begin with the oldest leaves, which show a mottled yellow color along the margin of the mature leaf laminas; eventually leaves may appear dark green with some reddish and purple spots (Costa and Costa, 2003). The center of each purple spot may become necrotic with a brownish color. Other symptoms include leaves with pointed lobes and short, slender petioles. When P deficiency is severe, the new leaves are small, the lamina of leaves curl upward from the edges, and leaves eventually turn completely yellow. In contrast excess P causes leaf scorching and leaf abscission (Awada and Long, 1978).

Phosphorus fertilization increased petiole concentrations of N, P, Fe, Mn, and Zn, and decreased

Ca, K, S, and Cu concentrations (Awada et al., 1975; Cibes and Gaztambide, 1978). Phosphorus also increased trunk growth rate and circumference. Petiole P concentrations were determined to be highly associated with maximum yield of marketable fruit (Awada and Long, 1978). The optimum leaf petiole P concentration ranges from 0.16 to 0.20% (mean 0.18%) [Appendix A]

(Awada and Long, 1969, 1978).

Potassium is an essential element that has been shown to increase papaya fruit size and total soluble solids content (TSS) [Gaillard, 1972; Texeira da Silva et al., 2007]. Potassium applications have been shown to increase papaya trunk girth at the bearing stage, but dry petiole

37 weight remained unchanged (Oliveira and Caldas, 2004). Ferreira-Coelho et al. (2007) recommended a N:K ratio close to 1:1 to optimize yields. Symptoms of leaf K deficiency begin in the older leaves, which turn yellow from the central vein to the edges and may develop some marginal necrosis (Mengel and Kirkby. 1987; Marschner, 1995; Epstein and Bloom. 2005). In addition, necrotic leaf spots develop, petioles become more slender, and leaf abscission increases

(Thomas et al., 1995; Costa and Costa, 2003). When K deficiency becomes severe, the number of leaves and fruit are reduced dramatically and trunk diameter decreases (Awada and Long,

1977). In contrast, excess K caused leaf scorching and desiccation and finally leaves abscised

(Cibes and Gastambide, 1978). Potassium fertilization increased K and Mn petiole concentration, but decreased N, Na, Ca, and Mg concentrations (Awada and Long, 1971a; 1980). The optimum

K petiole concentration for bearing plants ranges from 3.53 to 3.69% (mean 3.61%) [Appendix

A] (Awada and Long, 1971b, 1980).

Calcium is an essential nutrient that is necessary for root development and root activity in papaya seedlings and also increases new root dry weight (Gaillard, 1972; Bohn et al., 1979;

Texeira da Silva et al., 2007). Calcium amendments increased root length of papaya growing in a tropic volcanic acid subsoil up to 250 and 310% by using CaSO4 and Ca(OH)2, respectively

(Marler and de la Cruz, 2001). Calcium uptake has been shown to increase P, K, and Mg leaf content (Cibes and Gaztambide, 1978). Calcium deficiency first appears in meristematic regions and young actively photosynthetic leaves (Epstein and Bloom, 2005). Symptoms of Ca deficiency include chlorosis of imature leaves, which develop necrotic spots over the leaf lamina.

When Ca deficiency is severe, fewer leaf lamina lobes develope with most of them having a curled appearance. Eventually leaves appeared twisted and petioles were weak and leaves abscised. Calcium deficiency increased fruit pulp softening and reduced postharvest shelf life

38 (Cibes and Gaztambide, 1978; Mengel and Kirkby. 1987; Marschner, 1995; Costa and Costa,

2003; Epstein and Bloom. 2005). The optimum range for petiole Ca content was 0.8 to 1.33%

(Awada and Long, 1971).

Magnesium is essential for the process of the photosynthesis and is a constituent of the chlorophyll molecule (Hochmuth et al., 2004; Merhaut, 2007). Deficiencies of Mg appear first in mature leaves, which take on an intense yellow color, whereas the vein borders and internal veins of the leaf lamina remain green (Thomas et al., 1995; Epstein and Bloom. 2005). Leaves may also develop numerous small, necrotic spots that coalesce to form large straw-colored areas.

When Mg deficiency becomes severe, the symptoms are similar to those described above for mature leaves (Cibes and Gaztambide, 1978). Leaf petiole Mg concentration is increased by P fertilization, but decreased with increased K and/or Ca uptake, due to the competition with Mg for uptake (Awada, 1977). The optimum range for petiole Mg content has been reported to be

0.19 to 0.8% (Awada, 1977; Hochmuth et al., 2004).

Sulfur is an essential element for papaya growth and development and affects yields and fruit quality (Haneklaus et al., 2006). The protyolitic enzyme papain contains S and has been shown to increase plant starch and protein accumulation (Costa and Costa, 2003). Sulfur deficiency appears first in young leaves which change in color from light green to yellow.

However, when S deficiency becomes severe, mature leaves turn completely yellow (Cibes and

Gaztambide, 1978), additionally, plants become spindly and they grow poorly (Epstein and

Bloom. 2005).

Micronutrients are required in lesser amounts than macronutrients and eight micronutrients are of importance to papaya including iron (Fe), manganese (Mn), boron (B), copper (Cu), molybdenum (Mo), zinc (Zn), and chlorine (Cl) (Mengel and Kirkby, 1987).

39 Recently nickel (Ni) was found to also be essential for papaya (Brown et al., 1987). Other microelements like cobalt (Co), lithium (Li), arsenic (As), vanadium (V), and selenium (Se) have also been reported to be important for some plants, but not papaya, because their deficiency may cause some physiological impairment (Bohn et al., 1979; Clarkson and Hanson, 1980; Asher,

1991; Epstein and Bloom. 2005 ).

Iron is an essential microelement that is a constituent of enzymatic macromolecule complexes that affect leaf carbon assimilation and photorespiration (Oliveira, 2002). Iron deficiency appears as a general chlorosis of younger leaves that first may show a mild interveinal chlorosis, which may be more pronounced at the apical part of the leaf lobes (Nautiyal et al.,

1986; Epstein and Bloom. 2005). As Fe deficiency becomes severe, younger leaves become completely yellow and then turn white; the apical portion of the plant stem may die (Thomas et al., 1995).

Manganese deficiency occurs first in young leaves and appears as a mild chlorosis with a mottling along the veins of leaf lamina (Mengel and Kirkby, 1987; Marschner, 1995; Epstein and

Bloom, 2005). When Mn deficiency becomes severe, leaves change color from green to yellow

(Cibes and Gaztambide, 1978; Thomas et al., 1995; Costa and Costa, 2003). With severe Mn deficiency, necrotic areas may form and leaves become malformed and stunted (Epstein and

Bloom, 2005). In contrast, Mn toxicity is characterized by brown spots in older leaves surrounded by chlorotic areas, loss of apical dominance, and there is a proliferation of auxiliary shoots (Mengel and Kirkby, 1987). Manganese has not been shown to have a dramatic effect on papaya growth but may interfere with normal nutrient absorption (Agarwala et al., 1986). The optimum range for petiole Mn content has been reported to be 23 to 63 mg kg-1 (Awada et al.,

1975; Awada and Long, 1978).

40 Zinc is an essential element involved in the N metabolism of plants, protein synthesis, leaf expansion, and in some enzyme systems in the cytoplasm and the chloroplasts (Mengel and

Kirkby, 1987; Marschner, 1995; Epstein and Bloom, 2005). Zinc deficiency first occurs in young leaves and results in poor leaf development. Symptoms of Zn deficiency include a generalized interveinal chlorosis in the middle of the lamina and a reduction in leaf size (Nautiyal et al.,

1986). Leaves may be crinkled with mottled spots that enlarge very rapidly. In some cases the veins on the adaxial leaf surface become thicker. When Zn deficiency becomes severe, the youngest leaves remain small and the internodes are reduced forming a rosette of chlorotic leaves that turn yellow with necrotic areas along the borders of the leaf lamina; the trunk may appear stunted (Costa and Costa, 2003; Epstein and Bloom, 2005). In contrast, Zn toxicity results in leaf lamina area reduction followed by chlorosis and a reduction in root growth (Mengel and Kirkby,

1987); plants may be stunted and misshapen (Epstein and Bloom, 2005).

Boron is an essential microelement that improves papaya growth, yield, and fruit quality.

Boron deficiencies occur in young and middle-aged leaves of the terminal bud where young leaves turn light-green, and may be misshapen and stunted (Nautiyal et al., 1986). Boron deficiency may cause an accumulation of N, P, K, Ca, and Mg (Cibes and Gaztambide, 1978;

Marschner, 1995) and eventually leaves may abscise (Thomas et al., 1995). In B deficient plants elongation growth is not normal flower abortion increases, fruit set decreases, and the plant may die back (Cibes and Gaztambide, 1978; Oliveira, 2002). Boron deficiency may result in deformed papaya fruit (Islam, 2008). In contrast, B toxicity causes leaf tip yellowing followed by progressive necrosis, and leaves take a scorched appearance and drop prematurely, causing a reduction in plant growth (Nautiyal et al., 1986; Mengel and Kirkby. 1987).

41 Silicic Acid (Silicate)

General biogeological description and cycle

Silicon is the second most common element found on earth (26 to 31% by weight) and is present in higher plants in amounts equivalent to Ca, Mg, and P (Mengel and Kirkby, 1987;

Asher, 1991; Marschner, 1995; Epstein, 1999; Chen et al., 2000a; Gascho, 2001; Epstein and

Bloom, 2005). Silicon is a metalloid chemical element with an atomic number of 14 and a molecular mass 28.09 g mol-1. Silicon is not considered an essential plant element, but it has been shown to result in beneficial effects such as increased stem strength in several agronomic plants including wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), and rice (Oryza sativa L.) [Okuda and Takahashi, 1961; Mengel and Kirkby, 1987; Kim et al., 2002; Ma and

Takahashi, 2002; Gong et al., 2003, Liang et al., 2003; Ma et al., 2003; Ma, 2004; Mitani and

Ma, 2005; Epstein and Bloom, 2005; Gong et al., 2005; Gong et al., 2008). Silicon has been shown to enhance disease resistance in rice, cucumber (Cucumis sativus L), and strawberry

(Fragaria x Ananassa Duchesne). Silicon is absorbed as silicic acid (H4SiO4) and uptake may be passive, active, or both (Takahashi et al., 1990; Epstein, 1999).

The biologically available forms of Si may be described by the biogeochemical cycle in which silicic acid is the unique precursor in the absorption and deposition of Si in biota (Figure

1) [Exley and Birchall, 1992; Exley, 1998]. The biogeochemical cycle of Si results in an abundance of the element, which may be available in different solid, liquid, or gaseous forms

(Exley, 1998). Living organisms, especially plants, are one of the major factors affecting the Si biogeochemical cycle because they influence the weathering of Si rock (Raven, 1983; Lucas,

2001; Raven, 2001). Other factors that influence the cycle include temperature, pH, ionic composition of natural solvents, and hydrological parameters like water flow (Exley, 1998).

42 The most prevalent form of Si is quartz (SiO2), which is stable and weathers slowly.

Quartz is therefore not a good source of silicic acid in the soil solution (Williams, 1986). In contrast, feldspars (KAlSi3O8) weather more rapidly and result in silicic acid-bound clays and free silicic acid (Brady and Walther, 1989). The major silicic acid source is provided by the oxidation of silicate rock by CO2 (Lucas, 2001). However, organic matter is also a good source of silicic acid (Sangster and Hodson, 1986). Soil solution Si concentrations normally range from

0.1 to 0.6 mM and the Si is mostly absorbed by higher plants as orthosilicic acid or monosilicic acid [Si(OH)4] (Barber and Shone, 1966; Epstein, 1994). Usually, monosilicic acid is accumulated in plant tissues as a polymer of hydrated amorphous silica gel (SiO2•nH2O) called phytoliths and opaline silica (Parry et al, 1984; Piperno et al., 1999; Ma, 2004).

Plant uptake of Si starts with silicic acid in the soil solution which is either passively or actively absorbed by plant roots along with organic and inorganic constituents like Al, Fe, Mn oxides, and hydroxides (Figure 1). Living organisms are capable of absorbing, translocating, accumulating, processing, and depositing opaline silica into all parts of the plant (e.g., roots, shoots, and leaves) [Jones and Handreck, 1967; Iler 1979; Piperno, 2006; Cornelis et al., 2010].

During plant tissue degradation and decomposition, the opaline silica is returned to the biogeochemical cycle. As the weathering processes continues, Si particles in the soil solution are washed into rivers, lakes, and ultimately oceans from where planktonic diatoms recycle them into silicic acid (Raven, 2003). Silicic acid and complex hydroxides improve soil properties such as water holding and buffering capacity, as well as the cation exchange capacity (CEC)

[Berthelsen et al., 2001].

The benefits of silicon

The essentiality of mineral elements for higher plants is based on several criteria. First, an element is considered essential if, (a) its deficiency makes it impossible for the plant to

43 complete its vegetative or reproductive life cycle, (b) the impairment to its life cycle can only be prevented and corrected by absorption and use the element, and (c) the element is directly involved in plant nutrition largely independent of its possible effect in correcting some unfavorable microbiological and chemical conditions of soil, environmental condition, and other cultural factors (Arnon and Stout, 1939). An additional, criteria is that an element is essential if it complies with either or both of two criteria: (a) the element is part of a molecule that is a component intrinsic to the structure or metabolism of a plant and/or (b) when the plant is severely depleted of the element, plant growth, development and reproduction is abnormal compared to plants not depleted (Epstein and Bloom, 2005).

Although Si is not strictly an essential plant nutrient it is considered ‘quasi-essential’ for some plants because of the various abnormalities (i.e., reduced growth and production) caused in plants that are deficient in Si. This includes plants in the Graminaceae such as rice, sugarcane

(Saccharum officinarum L.), wheat, barley, maize (Zea mays L.), and sorghum [Sorghum bicolor

(L.) Moench)], tomato (Solanum lycopersicum L.) and cucumber, and specific plants in the

Cyperaceae, Urticaceae, Commelinaceae, Equisetaceae and diatoms (Epstein, 1994, 1999, 2000,

2001, 2005, Epstein and Bloom, 2005; Mitani and Ma, 2005; Epstein, 2009). However, the general consensus is that Si is not an essential element but does have beneficial effects on growth, development, and disease resistance mechanisms of some plants. There are numerous reports of the direct beneficial effects of Si on plant growth and crop yield (Epstein, 1974,

Takahashi et al., 1990; Epstein, 1994; Birchall, 1995; Epstein, 1999; Korndörfer and Lepsch,

2001; Ma et al., 2001a; Neumann and Nieden, 2001; Raven, 2003; Richmond and Sussman,

2003; Ma, 2004; Snyder et al., 2004, 2007; Epstein, 2009). For example, deposition of silicic acid in plant petiole tissues has been shown to improve light interception by keeping leaves erect,

44 thereby stimulating canopy carbon assimilation and increasing plant growth (Jones and

Handreck, 1967; Ma and Takahashi, 2002). Recently, Si was reported to promote cell elongation through increased cell wall extensibility, thereby enhancing root elongation (Hattori et al., 2003).

Applications of silicate compounds have been shown to improve soil physical and chemical properties, reduce mineral toxicity, enhance plant water uptake, increase the availability of some mineral nutrients, and enhance plant disease defense mechanisms (Epstein,

1974; Mengel and Kirkby, 1987; Takahashi et al., 1990; Birchall, 1995; Epstein, 1999; Neumann and Nieden, 2001; Raven, 2003; Richmond and Sussman, 2003; Ma, 2004; Snyder et al., 2007;

Epstein, 2009).

Silicon Uptake, Transport, Distribution and Accumulation in Plant Organs

Silicon uptake is influenced by a number of soil and climatic factors including soil pH and temperature, soluble Si content, organic matter content, redox potential, concentration of metallic ions, presence of phyllo-silicates, soil particle surface area and surface coatings, overall soil solution dynamics, soil hydrology, reactive Fe and Al sesqui-oxides, geo-morphology, precipitation (rainfall), interaction with soil micro-organisms, and plant species (Beckwith and

Reeve, 1963, 1964; Jones and Handreck, 1967; Wilding and Drees, 1971; Drees et al., 1989;

Savant et al., 1999; Ma et al., 2001b; 2006; 2007a, 2007b). Silicon may be absorbed passively from the soil solution by roots as monosilicic acid (H4SiO4) along with water through evapotranspiration and deposited as ‘silica gel’ (also referred to as phytoliths, amorphous silica, opal, opaline silica, phytolithic opal, and opal phytoliths) into roots, shoots, stems, and leaves

(Yoshida, 1975; Epstein, 1994; Smith, 1998; Piperno et al., 1999; Ma et al., 2001b; Piperno et al., 2006). During active uptake the dissolved monosilicic acid passes through the root cortex to the endodermis where it moves into the xylem sap and through the xylem into stems and leaves

(Sangter and Hodson, 1986; Takahashi et al., 1990).

45 In the plant nutrient literature Si may be referred to as soluble silica, monosilicic acid, silicon dioxide, silica or silicate (Jones and Handreck, 1965). The chemistry of Si in solid and dissolved forms in the soil has been extensively reviewed (McKeague and Cline, 1963a, 1963b,

1963c; Iler, 1979; Piperno et al., 1998; Lindsay, 2001; Matichenkov and Bocharnikova, 2001).

Silica in the soil solution is generally in the monosilicic acid form (H4SiO4) and is readily absorbed by diffusion and mass flow into the roots of numerous plant species (Chen et al.,

2000a; Raven, 2003; Matichenkov and Kosobrukhov, 2004; Henriet et al, 2008; Motomura et al.,

2008). Although, there are many other Si forms in soil, most of them occur in an unavailable polymerized form. Silicon may be a constituent of clay particles and there are two general silicate clay groups, expanding 1:1 (kaolinite) and 2:1 (montmorillonite) silicate clays (Brady and Weil, 2009).

Higher plants are classified as Si accumulators and non-accumulators and accumulators may uptake Si passively and/or actively. Non-accumulators are commonly termed rejective and the term was coined to describe those plants that did not take up Si or took up very small amounts of Si (Ma and Takahashi, 2002; Richmond and Sussman, 2003; Rodrigues and Datnoff,

2005). Examples of plants with active uptake include rice and barely; plants with passive uptake include cucumber and banana (Musa x paradisiaca L.), and plants which are termed rejective include tomato and pineapple [Ananas comosus (L.) Merr.] (Jones and Handreck, 1967; Van der

Vorm, 1980; Takahashi et al., 1990, 1991; Epstein, 1994; Savant et al., 1997b;; Ma et al., 2001a;

Raven, 2001; Aziz et al., 2002; Ma and Takahashi, 2002; Richmond and Sussman, 2003; Mitani and Ma, 2005; Mitani et al., 2005; Rodrigues and Datnoff, 2005; Ma et al., 2006; Ma and

Yamaji, 2006; Henriet et al., 2008).

46 In general, active accumulator plants take up Si through the root cells past the casparian strips to the sites of xylem loading where it eventually moves to and accumulates in plant stems and leaf epidermal cells (Elawad and Green, 1979; Raven, 2001; Ma and Yamaji, 2006). Here the Si may be stored as biogenic opal (SiO2•nH2O) within phytolith particles (Ma and Takahashi,

2002; Ma et al., 2004; Taiz and Zeiger, 2006; Henriet et al., 2008) or as a gel under the cuticle of the plant cells, forming a double layer of cuticle (Deren, 2001). Once deposited in plant tissues,

Si is generally not redistributed (Yoshida et al., 1962a). Recently, the isolation of rice mutants defective in active Si uptake indicates the existence of Si transporters in the root cells of some higher plants (Tamai et al., 2002; Lux et al., 2003; Ma and Yamaji, 2006; Van Soest, 2006;

Shakoor, 2014). Plants that possess leaf tissue concentrations of Si above 10 g kg-1 dry matter content are considered active uptakers (Henriet et al., 2008).

In contrast, passive accumulators of Si such as banana, cucumber, and some species in the Graminae, take up Si with transpiration in which it is deposited in the cell walls and/or apoplast of roots, stems, and leaves (Jones and Handreck, 1967; Cornelis et al., 2010). Plants with leaf tissue Si concentrations between 5 to 10 g kg-1 dry matter content are considered passive accumulators (Henriet et al., 2008). Plants considered rejective typically possess some

Si in cortical cell walls and have Si concentrations below 5 g kg-1 dry matter content (Richmond and Sussman, 2003; Ma and Yamaji, 2006).

Some investigators classify active and passive accumulators and rejective plants based on a percent Si on a dry weight basis (Elawad and Green, 1979; Epstein, 1994, 1999; Rodrigues et al., 2001; Ma and Takaashi, 2002; Ma, 2004; Mitiani and Ma, 2005). Plants that possess 1 to

10% or more Si on a dry weight basis are considered active uptakers. Those with 0.1 to 10% Si

47 dry weight are passive uptakers and those with less than 0.1% on a dry weight basis are considered rejective.

In the Gramineae and Cyperaceae families, Si may be actively and passively accumulated

(Jones and Handreck, 1965; Yoshida, 1975; Savant et al., 1997a; Ma and Takahashi, 2002;

Mitani and Ma, 2005). In some plants of the Cucurbitaceae [e.g., cucumber and muskmelon

(Cucumis melo L.)], Urticaceae [e.g., red cecropia (Cecropia glaziovii Loefl.), shield-leaved pumpwood (Cecropia peltata L.), and common or stinging nettle (Urtica dioica L.)], Poaceae

[e.g., wheat, barley, maize, and sorghum], Arecaceae [e.g., date palm (Phoenix dactylifera L.), and scrub palmetto (Sabal etonia Swingle ex Nash)], and Commelinaceae [e.g., bluejacket

(Tradescantia ohiensis Raf.)] Si is passively absorbed in moderate amounts (Jones and

Handreck, 1965; Yoshida, 1975; Savant et al., 1997a; Aziz et al., 2002; Conley, 2002; Ma and

Takahashi, 2002; Hodson et al., 2005; Mitani and Ma, 2005). In some dicotyledonous plants (e.g. tomato, Solanaceae), Si is generally not absorbed (rejective) and thus they are low in Si content

(Conley 2002; Richmond and Sussman, 2003; Ma and Yamaji, 2006; Wu et al., 2006).

Plants differ in the quantities of Si absorbed and stored in the root, stem, petiole, and leaf tissues (Ma et al., 2001b). Silicon is stored in the leaves and other plant tissues primarily as amorphous silicates (e.g., biogenic opal or phytolithic opal) [Epstein, 1994]. Once deposited in this form, Si is immobile and is not redistributed within the plant (Ma et al., 1989). Hydrated, amorphous Si is deposited in cell lumens, cell walls, and intercellular spaces or the intercellular matrix (Epstein, 1994; Prychid et al., 2003). Silicon also accumulates in external layers below the wax cuticle of leaves, playing a role as a structural component that increases cell rigidity

(Kim et al., 2002; Liang et al., 2007). Silicon is present in roots, leaves, shoots, culms, and the inflorescence bracts of cereals, especially in rice, wheat, oat (Avena sativa L.), and barley

48 (Epstein, 1999). Silicon deposits may be found in the epidermis, strengthening vascular tissues or the vascular bundles, and in plant storage organs such as cell walls, cell lumens, intercellular spaces in root, seed or shoot tissues, or in a cuticular layer, or in specialized cells called idioblasts (silica cells), trichomes, and in the stomatal complex (Sangster et al., 2001; Prychid et al., 2003). The function of the Si may be structural, physiological or protective (Lewin and

Reimann, 1969, Sangster and Hodson, 1986; Epstein 1994, 1999).

Some plants low in Si content have been shown to be more susceptible to fungal diseases, insect feeding, as well as other biotic and abiotic stresses that adversely affect crop production

(Epstein, 1994; Birchall, 1995; Exley, 1998). Soils low in Si may also have reduced bioavailability of essential nutrients such as P, Fe, Zn, Mn, B, and Cu. Rice, barley, wheat, cucumber, and strawberry plants low in Si have been shown to have increased plant disease susceptibility compared to plants with higher Si content (Bowen et al., 1992; Bélanger et al.,

1995; Datnoff et al., 1997; Rafi et al. 1997; Savant et al. 1997b; Epstein, 1999; Meyer and

Keeping, 2000; Ma, 2004; Fauteux et al., 2005; Massey and Hartley, 2006; Palmer et al., 2006;

Brecht et al., 2007; Guével et al., 2007; Cai et al., 2009; Kaluwa et al., 2010). The mechanisms by which Si increases disease and insect pest tolerance are not fully understood. However, it has been shown that Si enhances the thickness of leaf lamina and regulates stomata opening, thereby creating a physical barrier that impedes and/or delays pathogen infection (Datnoff et al., 2001).

Likewise, Si has been shown to reduce the susceptibility of plants to borers, sucking, leaf mining, and chewing insect pests by increasing leaf lamina thickness, reducing digestibility, and damaging insect mouth parts as they feed on plant tissues (Epstein, 2000; Massey and Hartley,

2006; Kaluwa et al., 2010).

49 Silica particles have been found in mature hairs of the lamina of canary grass (Phalaris canariensis L., Poaceae), while in oat, it can be found as small rods in the leaf lamina (Kaufman et al., 1970; Mann et al., 1983). In rice, individual silica bodies were found in the stem, which may protect plants against grazers and parasites (Datnoff et al., 1997; Savant et al., 1997a) and Si may be involved in plant structures that release chemical compounds to repel, deter, and delay the entrance of microorganisms (Bekker et al., 2007). Although plants with supplies of soluble Si produce stronger and tougher cell walls, making them more heat and drought tolerant, there are some discrepancies concerning the role Si plays in the protection of higher plants against biotic stresses (Epstein, 1999).

One investigation comparing the nutritional characteristics of plants under the same growth conditions reported that Si and Ca plant content showed the most variability among nearly 500 species evaluated (Takahashi et al., 1990). This helped to identify those plants that accumulate Si from the Bryophyta to Angiospermae. In another study, the variability among 400 barley cultivars reported the Si concentration in the grain ranged from 1.24 to 3.80 mg g-1 (Ma et al., 2003). In kinetic studies carried out in rice, cucumber, and tomato growing under similar conditions, Takahashi et al. (1990), reported Si concentrations in the leaf lamina of 7.3%, 2.3%, and 0.2%, respectively.

In field-grown sugarcane, the Si concentration of leaf lamina ranged from 6.4 to 10.2 mg g-1, whereas greenhouse grown rice had Si concentrations from 4.1 to 6.0% (Deren, 2001).

Silicon concentration in banana leaves ranged from 0.7 to 3.8% dry matter (Jauhari et al., 1974).

In oat, amorphous silica (SiO2) was found in the range of 82 to 86% dry matter of the uppermost mature leaf lamina, along with various amounts of sodium (Na), K, Ca, and Fe (Jones and

Handreck, 1967).

50 Quantifying silicate in soil and water

Worldwide there is huge variation in the Si content of the soil, water, and plants; additionally, most soils have different amounts of Si in the form of aluminosilicate clay, the primary sources of silica mineral and quartz (Henriet et al., 2008). In general, Si has a low capacity to move down in the soil profile because it has a high binding capacity and high affinity for O2 (Khalid et al., 1978; Khalid and Silva, 1980; Snyder, 2001). Quartz is a major source of

Si in many soils and the rate of dissolution of this mineral is very slow and does not contribute significantly to increasing the availability of Si in the soil solution (McKeague and Cline,

1963a). However, other forms of Si such as SiO2 and crystalline Si forms like feldspars and clay minerals such as kaolinite, vermiculite, smectite, and amorphous silicate are constituents of most soils (Matichenkov and Snyder, 1996). The effectiveness of any type of silicate material will depend on its reactivity in soil solution rather than the amount of Si content (Berthelsen and

Korndörfer, 2005).

Silicon concentration in soil depends on the type of soil, weathering status of the immediate geology, and the climate conditions (Exley, 1998; Epstein, 2009). The solubility of Si is affected by many factors, including the type and structure of the soil (particle size), soil pH, temperature, organic complexes, aluminum concentration, iron and phosphate ion content, cation exchange capacity (CEC), dissolution reactions, and soil moisture content (Beckwith and Reeve,

1963; Jones and Handreck, 1963; McKeague and Cline, 1963a, 1963b, 1963c; Beckwith and

Reeve, 1964). Sandy soils have the highest Si content in the form of opal, which is unavailable to plants. Opal needs to be weathered and solubilized in soil in order to be absorbed by plant roots (Jones and Handreck, 1963). Loamy soils have silicic acid in the soil solution and soils with a low pH reduce the silicic acid availability (Jones and Handreck, 1965). Iron and aluminum oxides may bind silicic acid and reduce soil solution concentrations and availability

51 (Jones and Handreck, 1967). In general, most tropical soils are low in silicic acid due to natural desilication occurring through the soil weathering processes (Berthelsen et al., 1999). However, the Si concentration may range from 50 to 400 g Si kg-1 of soil (Snyder et al., 2007). Most of the monosilicic acid can be found in the upper 20 cm soil layer in a range from 0.1 to 1.6 kg of Si per hectare (Matichenkov and Ammosova, 1996; Matichenkov et al., 1997, 2000).

In fresh water, there is also great variation in silicic acid concentration in the form of orthosilicic acid (Birchall and Exley, 1992). The orthosilicic acid content of fresh water has been reported as 151, 200, 126, 196, 389, and 65 μmol dm-3 in North America, South America,

Europe, Asia, Africa, and Australia, respectively (Exley, 1998).

The evaluation and determination of Si in soils has been difficult, and many different approaches have been used (Schwartz, 1942; Jones and Handreck, 1967; Katz, 1968; Fox et al.,

1969; Nonaka and Takahashi, 1990; Elliot and Snyder, 1991; Rayment and Higginson, 1992;

Jones and Dreher, 1996; Kato and Owa, 1997; Savant et al., 1997a; Ma and Takahashi, 2002;

Matichenkov and Bocharnikova, 2001; Pereira et al., 2003; Berthelsen and Korndörfer, 2005;

Buck et al., 2011). A review of different methods for measuring total Si content in soils can be found in Snyder (2001). Previous methods proposed include gravimetric, colorimetric, absorption-emission spectrometry, and a cation exchange resin analysis. However, all of these methods have problems and are currently not accepted as precise enough. Siliconanalysis of soils by autoclave-induced digestion (AID) and acetic acid extraction as proposed by Elliot and

Snyder (1991) are currently the most commonly used methods.

Quantifying silicate in plants

A number of methods have been used to determine Si content in plant tissues (Jones and

Handreck, 1967; Sangster and Hodson, 1986). However, the gravimetric, colorimetric, X-ray, and kinetic methods require the use of special equipment to centrifuge, digest, and ash large

52 amounts of plant tissue as well as being time consuming (Foulger, 1927; King, 1928; Volk and

Weintraub, 1958; Takahashi et al., 1990; John and Dreher, 1996; Bell and Simmons, 1997;

Barbosa-Filho et al., 2001; Snyder, 2001; Haysom and Ostatek-Boczynski, 2006; Guntzer et al.,

2010). Furthermore, these methods do not estimate plant-available Si (Linday, 2001). Other methods utilize different acid extracting solutions along with chelating reagents to enhance tissue extraction or require an auto-clave digestion prior to colorimetric determination (Elliot and

Snyder, 1991). A method with a high correlation between the amount of Si supplied by the source and the amount of the element absorbed by the plant is the leaching column method proposed by Snyder et al. (2005); another method with a high correlation between source and plant Si is the wet oxidation procedure proposed by Haysom and Ostatek-Boczynski (2006).

However, the Elliot and Snyder (1991) method takes less time and provides an estimate of total and available Si in soil and plant tissues (Snyder, 2001; Buck et al., 2011).

Potential Plant Growth and Physiological Effects of Silicic Acid

Plant growth and physiological effects

Silicon uptake may influence plant growth and therefore the root system morphology

(e.g., primary structural and tertiary feeder roots) and absorption characteristics influence plant

Si content (Jones and Handreck, 1965). The concentration of silicic acid varies in plant tissues and ranges from 0.1 to 10% v/v or more on a dry weight basis (Takahashi et al., 1990; Epstein,

1994). Agronomic plants such as sorghum, maize, and sugarcane accumulate and store most of their Si in the roots (Jones and Handreck, 1967). In banana, higher levels of Si accumulated in the leaf lamina than roots in plants treated with Ca2SiO3 and Na2SiO3, whereas higher levels of

Si accumulated in roots of plants treated with K2SiO3 (Asmar et al., 2013). However, commonly

Si is deposited in the intercellular spaces in roots tissues or in an extracellular layer (Sangster and

Hodson, 1986). Interestingly, the results of some investigations shows that young plants store

53 less Si in the roots than mature plants (Ma and Takahashi, 2002; Gong et al., 2006; Henriet et al.,

2006).

Silicon accumulation in plant tissue organs is influenced by the age of the plant and root uptake and transpiration rates (Sangster et al., 2001). Silicon concentration in most monocots increases in shoots and leaves as they mature due to continued systematic accumulation (Jones and Handreck, 1967; Richmond and Sussman, 2003; Ma and Yamaji, 2006). Similarly, Si has been shown to accumulate in cucumber and papaya roots, shoots, and leaves as the plants mature

(Adlan, 1969; Ma and Takahashi, 2002).

Growth and yields

Silicon applied as monosilicic acid (H4SiO4) greatly increased rice growth and yield (by

15 to 33%) compared to plants not receiving H4SiO4 (Okuda and Takahashi, 1961a; Takahashi et al., 1990). Soil applications of Ca2SiO4 to rice increased plant erectness and height and increased yields by 30% (Yoshida, 1975). Several other studies confirmed that rice yield increased from 10 to 48% due to silicate applications (Savant et al., 1997a; Ma and Takahashi, 2002). In sugarcane, silicate applications increased cane yields from 10 to 50% and sugar content from 17 to 22%

(Savant et al., 1999). Other investigations have reported significantly increased plant yields of wheat and barley after Si applications (Takahashi et al., 1990).

Maize plants growing under water stress increased total dry matter by 26 to 45%, shoot dry matter by 30 to 53%, and root dry matter by 3 to 7% when Na2SiO3 was applied at 1µM or 2

µM in the nutrient solution (Kaya et al., 2006; Zargar and Agnihotri, 2013). Sorghum and pearl millet [Pennisetum glaucum (L.) R.Br.] grain yields increased from 325 to 3,600 kg ha-1 and from 1,980 to 3,460 kg ha-1, respectively, when soils were amended with calcium/potassium

-1 silicate (Clark et al., 1990). Application of K2SiO3 (200 mL L ) to sorghum plants subsequently exposed to drought stress had an increased leaf area index, specific leaf weight (SLW),

54 chlorophyll content (SPAD), leaf dry weight (LDW), and shoot, root, and total dry weight compared to non-Si-treated drought-stressed plants (Ahmed et al., 2011). Non-Si-treated plants had decreased net CO2 assimilation rate, relative growth rate (RGR), leaf area ratio (LAR), and water use efficiency (WUE) compared to Si-treated plants.

Potassium silicate applied to wheat under normal field conditions increased average yield of straw by 36 to 47% and grain yield by 12 to 36% (Tahir et al., 2011). In barley, Na2SiO3 applications increased plant dry weight of panicles by 30%, stems plus leaves by 13%, and grain

-1 by up to 64% (Ma and Takahashi, 2002). Similarly, Na2SiO3 applications of 116 kg ha in jute

(Corchorus capsularis L.) increased plant height (9%) and green matter (15%) content (Khan and Roy (1964). In banana [(Musa x paradisiaca (L) Colla. cv. ‘Grande Naine’], applications of

2 Na2SiO3·5H2O increased psuedostem height by 30 cm and leaf area by 15 to 873 cm (Henriet et al., 2006).

In dicotyledons such as tobacco (Nicotiana tabacum L.) Si increased stem rigidity, and leaf erectness and thickness (Neumann et al., 1997). In tomatoes growing in a nutrient solution

-1 containing silica (SiO2; 100 mg Si kg ) applied at the flowering stage there was a significant increase in shoot and root length, shoot and root weight, and fruit number and weight (Ma and

Takahashi, 2002). Silicon applications to cucumber varieties ‘Suyo’ and ‘Kurumeochiai H.’) increased dry weight of shoots and roots and fruit fresh weights (Miyake and Takahashi, 1983a;

Adatia and Besford, 1986). In addition, leaf thickness and dry matter per unit of leaf area was increased. In another cucumber investigation comparing two Si sources (Ca2SiO4 and K2SiO3) at two different rates (700 and 1,400 kg ha-1, respectively), the greatest yield was 155 t ha-1 and

-1 the available soil Si content was 248 mg 100g using the highest rate of K2SiO3 (Miyake and

Takahashi, 1983b).

55 -1 -1 Soil drench applications of Na2SiO3·9H2O at 50, 100, 200, 400, and 800 µg g plant significantly increased cowpea [Vigna unguiculata (L.) Walp. var. ‘Pusa Komal’] shoot and root length and leaf area (by 18.9%, 1.7%, and 52%, respectively) [Mali and Aery, 2009]. In cotton

(Gossypium hirsutum L.) grown in solution culture with or without added Al, addition of sodium silicate pentahydrated (Na2SiO3•5H2O) significantly improved root growth (by 69 to 87%) in the non-Al-amended solution and to a lesser extent (15 to 17%) in the Al-amended solution (Li,

1989). Shoot dry matter of cotton plants increased 3-fold after 20 µM Si applications of

(SiO2•nH2O) to the hydroponic nutrient solution (Aziz et al., 2002).

-1 In strawberry, potassium silicate applications at 50 mg L SiO2 significantly increased the mean number of fruit per plant and individual fruit weight (Miyake and Takahashi, 1986).

After soil applied silicate (K2SiO3; Ca2SiO4, or Na2SiO3•5H2O) applications, Si concentrations increased 14% in the exocarp of avocado fruit (Persea americana Mill.) but not in the mesocarp

(Kaluwa et al., 2010). In a 7-month solution culture experiment application of K2SiO3 to

‘Hamlin’ and ‘Valencia’ orange trees [Citrus sinensis (L.) Osbeck] resulted in increased plant growth (Wutscher, 1989). Application of K2SiO3 to the soil significantly increased total

‘Valencia’ orange tree height and branch length (by 136.2% and 148.1%, respectively), compared to non-silicate treated trees (Matichenkov et al., 2001).

Investigations on the effect of silicate applications on papaya growth, development, and crop yields are limited. In a 10-month investigation with ‘Puna’ Solo papaya growing under field conditions in Hawaii, the interaction among phosphate, limestone, and silicate application rates was varied (Adlan, 1969). The Kapaa gravelly silty clay soil in which the papaya plants were grown was characterized as highly weathered, with less than 35% base saturation, a moderate

CEC (~29 meq/100g soil), low pH 4.2-5.0, high bauxite (aluminum oxide compounds) and iron

56 oxide contents, and low Si content. More than 90% of the P was fixed by the native aluminum and iron sesquioxides (Adlan, 1969). The experiment was a 3x3x3 factorial. Main plots were three rates of lime (crushed coral rock) to raise the soil pH to about 5, 6 or 7, three rates of soil- applied silicate (electric furnace slag), and three rates of triple-superphosphate. In general, the effects of increasing phosphate application rates on plant growth (i.e., trunk diameter and plant height) and crop yield were highly significant; increasing soil pH also had a significant effect.

Interestingly, only as the plants matured was there a trend for plant growth to increase with increased Si application rates. There was a trend for increased crop yield with increasing Si application rates; however, postharvest fruit quality as evaluated by pulp pH, titratable acidity

(TA), °Brix (TSS), and °Brix/acid ratio did not differ among treatments. Plant (i.e., leaf petiole and lamina) and soil P content increased with increased soil pH and phosphate application rates.

Phosphorus, Si, and Ca plant content and whole-plant dry weight increased with increased rates of P, Si, and Ca. Extractable soil Si increased with Si application rates. Interestingly, Si soil content increased from soil pH 5 to 6 but decreased from pH 6 to 7. At all soil pH levels there was a trend for extractable soil Si content to decrease with time.

-1 Foliar applications of potassium silicate (2.7 and 5.4 L ha ), K2SiO3 plus a commercial nutrient mix, or non-K2O3Si treatment each week for 40 weeks to ‘Tainung II’ papayas grown under tropical conditions resulted in a trend of increased plant height and trunk diameter and crop yield with increasing K2SiO3 rate (Hernández, 2008). However, Si content of the plant was not determined and no statistical data analysis was conducted, making comparisons among treatments tentative at best. Mean pulp soluble solid content was lowest for plants treated with

K2SiO3 plus a commercial nutrient mix and a flavor preference test indicated that most respondents preferred K2SiO3-treated fruit over the non-treated control.

57 Silicon Effect on Plant Tolerance to Environmental Stress

Application of silicates either directly to crops or incorporated into the soil has been reported to alleviate many biotic (e.g., fungal and bacteria diseases, insect pest attacks) and abiotic stresses (e.g., drought, soil salinity, heavy metal toxicity, wind, and temperature)

[Bonman et al., 1989; Epstein, 1994, 1999; Voogt and Sonneveld, 2001; Aziz et al., 2002; Ma and Takahashi, 2002]. Other reported beneficial effects of Si in higher plants includes increased photosynthetic rates, increased insect and disease resistance, improved plant nutrient balance, and enhanced drought and frost tolerance (Cherif et al., 1994; Ma, 2004; Currie and Perry, 2007).

These effects have been attributed to 1) Si deposited on plant tissue surfaces acting as a physical barrier to the penetration of microorganisms and/or insect mouth parts, 2) Si reducing leaf cell susceptibility to enzymatic degradation by fungal pathogens, and 3) Si acting as a signal to induce the production of phytoalexins, enhance chitinase activity, and induce the activation of anti-fungal compounds (e.g., peroxidases and polyphenoloxidases) (Datnoff et al., 2002). Other research investigations have demonstrated the potential for Si to alleviate physical stresses such as radiation, extreme temperatures, wind, drought, and water logging, and low and high light exposure (Ma et al., 2001a; Ma and Takahashi, 2002). The photosynthetic and transpiration rates, and stomatal conductance of two sorghum cultivars ‘Gadambalia’ and ‘Tabat’ were higher with a

-1 -1 +Si/dry soil drench application (100 mg K2SiO3 L plant ) than in the -Si/dry treatment

(control), which suggests that Si is involved in the regulation of photosynthesis, transpiration, and stomatal conductance (Hattori et al., 2005).

Drought stress

Several functions have been attributed to Si deposits on plant surfaces, especially for arid or semiarid conditions in which water availability is limited. These functions include the influence of Si on leaf gas exchange and leaf water content (Baker et al., 2007). Soil Si

58 -1 application (100 mg kg , SiO2) has been shown to reduce drought stress by decreasing transpiration rate by 30% in rice (Ma et al., 2001b; Ma, 2004). This was attributed to deposition of Si in the epidermal leaf layer, which reduced water loss through the leaf cuticle (Ma, 2004).

Others attributed the effect of Si to stomatal control (Kim et al., 2002; Yoshida et al., 1962b).

Silicon is also known to increase drought tolerance in ‘Brachiaria’ grasses by maintaining plant water balance, photosynthetic activity, erectness of leaves, and structure of xylem vessels under high transpiration rates (Melo et al., 2003). Pre-plant Si applications significantly increased non-drought-stressed wheat plant height and resulted in similar plant heights among Si+drought-stressed plants and non-Si-treated plants (Gong et al., 2003). In addition, leaf area of Si+drought-stressed plants was similar to non-drought-stressed plants.

Water potential of Si+drought-stressed wheat plants was significantly lower than drought- stressed plants and leaf water content of Si+drought-stressed plants and non-drought-stressed plants was similar. Oxidative damage has been reported to occur in photosynthetic pigments, lipids and proteins, as well as some enzymatic activities during drought stress of wheat (Gong et al., 2005). However, Si applications significantly improved superoxide dismutase (SOD) activity and decreased hydrogen peroxide (H2O2) content of wheat plants grown under controlled greenhouse conditions (Gong et al., 2008).

A higher endodermal silicification was found in the roots of drought tolerant upland rice than in the roots of lowland rice (Lux et al., 1999). In sorghum, Si significantly improved water transport and root growth under drought conditions (Lux et al., 2003; Hattori et al., 2005). This was attributed to the maintenance of the carbon assimilation rate and stomatal conductance and enhanced root growth of Si-treated plants, which decreased the shoot to root ratio. The Si-treated sorghum plants extracted more water from the dry soil than non-Si-treated plants (Hattori et al.,

59 2005). In another sorghum investigation, it was reported that Si soil drench applications enhanced leaf water potential under drought stress conditions because of the formation of a silica-cuticle double layer in the leaf epidermis (Lux et al., 2002). In a grass study, Trenholm et al. (2004) indicated that Si deposition in epidermal cells of St. Augustine grass [Stenotaphrum secundatum (Walt.) Kuntze] formed a barrier that reduced water loss through the cuticle of the leaf lamina.

Flood stress

The direct effect of soil saturation and flooding on soils is that they become hypoxic within hours (Amthor, 1989), however, prolonged soil flooding results in anoxia with profound effects on the plant respiratory metabolism and physiology (Dat et al., 2004). During oxygen stress, roots alter their respiratory metabolism with a drastic reduction in the function of the mitochondrial electron transport, oxidative phosphorylation, and the tricarboxylic acid cycles

(Epstein and Bloom, 2005). In contrast, glycolysis increases with fermentation of pyruvate leading to lactate (in lactic acid fermentation) [Epstein and Bloom, 2005]. Lack of oxygen causes accumulation of the ethylene precursor ACC (1-aminocyclopropane-1-carboxilic acid) and when flooding recedes there is release of the stress-induced ethylene (CH2=CH2), which results in root death and disintegration (Drew et al., 2000; Blanke and Cooke, 2004). However, a reduction of leaf gas exchange is the most common plant response to flooding, even in those plants that are considered tolerant (Marler et al., 1994).

In addition to a negative effect on gas exchange, low soil oxygen conditions increase oxidative damage to root cells due to a reduction in cellular antioxidant enzymatic activity.

Silicon deposition in oxygen-stressed roots of buckwheat (Fagopyrum esculentum Moench) promoted the formation of polysilicate compounds that enhanced catalase (CAT), superoxide dismutase (SOD), ascorbate peroxidase (APX), and soluble peroxidases in root and leaf cells

60 (Stanisavljevic et al., 2011). Similar effects were reported in rice, wheat, barley, and cotton

(Epstein, 1999; Ma and Takahashi, 2002; Gong et al., 2005; Liang et al., 2007; Gong et al., 2008;

Balakhnina et al., 2012).

Wind stress

The reaction of crop plants to a given windy condition depends on the wind speed, the length of exposure, and inherent plant properties (e.g., plant stem, branche, and leaf rigidity, current nutritional status and stage of plant growth) (Epstein, 1994; Chakraborty et al., 2000).

Short-term exposure to relatively strong winds generally results in acute visible foliar injury such as leaf tattering and defoliation, broken stems, and uprooting (Chan and Paull, 2008). Long-term chronic exposure to strong winds may cause physiological alterations that result in chlorosis, premature senescence, lodging, growth and yield reductions, and finally plant death (Storey,

1987). Chronic effects of windy conditions have been reported in rice, potatoes (Solanum tuberosum L.), wheat, soybean [Glycine max (L.) Merr.], beans (Phaseolus vulgaris L.), cotton, and papaya (Storey, 1987; Rosenzweig and Parry, 1994; Crane, 2005; Chan and Paull, 2008).

In general, the benefit of Si applications to wind-stress tolerance for agronomic crops has been attributed to increasing the rigidity of plant stems and leaves (i.e., strengthening cell walls) thus reducing mechanical damage (Epstein, 1994). In several rice investigations, yield losses due to wind were attributed to physical plant damage, reduced gas exchange, desiccation, increased leaf senescence, and plant lodging and sterility (Ma et al., 2001a; Fuhrer, 2009). The beneficial effects of Si applications on rice were attributed to Si deposition in cell walls and the apoplast that strengthened the plant stem, leaf lamina, culm wall, and the size of the vascular bundles (Ma et al., 2001; Ma and Takahashi, 2002; Epstein and Bloom, 2005). However, no one has investigated the effect of Si on the wind tolerance of papaya plants.

61 Cold stress

Freezing temperatures may cause irreversible damage to plant cells due to the mechanical forces generated by formation of intracellular ice crystals that burst the cell membrane and extracellular ice crystal formation that lead to cellular dehydration and increased intracellular solute concentrations (Steponkus, 1984). Plant tolerance to freezing injury varies greatly among species and genotypes. However, the major target of chilling injury from low but non-freezing temperature exposure is the cell membrane, and the primary damage induced is cellular dehydration (Levitt, 1980). Freezing and chilling increase the level of reactive oxygen species

(ROS) in plants, increasing lipid peroxidation, and ROS are the major cause for membrane damage related to chilling injury and freezing injury (Senaratna et al., 1988; McKersie et al.,

1993). Plants have evolved several antioxidative enzymatic and non-enzymatic responses to prevent or alleviate membrane damage caused by ROS, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) [Liang et al., 2003].

It has been reported several times that Si confers resistance or enhances tolerance to chilling or freezing stress of rice, sugarcane, barley, and several dicots (Epstein, 1994, 1999,

2000, 2001, Aziz et al., 2002; Ma and Takahashi, 2002; Ma, 2004; Epstein and Bloom, 2005;

Epstein, 2009; Balakhnina and Borkowska, 2013). Reports from investigactions with rice, maize, cucumber, sunflower (Helianthus annuus L.), and wax gourd (Benincasa hispida Thunb.) indicate that plants grown hydroponically at 0 oC to -4oC and treated with sodium metasilicate

(Na2SiO3•9H2O) were more tolerant (e.g., show greater water and nutrient uptake) to subsequent cold temperature exposure than plants grown under warm conditions without Si and subsequently exposed to cold temperatures (Liang et al., 2006). Zhu et al. (2006) reported wheat leaf photosynthesis and water use efficiency were significantly inhibited under freezing conditions but were enhanced by pre-cold Si applications to the nutrient solution. This was

62 attributed to lower soluble sugar content in the wheat plants grown without Si prior to being exposed to freezing temperatures.

Salinity stress

In rice, Si application at 0.89 mM reduced Na+ translocation from roots to shoots and increased dry matter production when plants were grown under salt stress conditions (Matoh et al., 1986). Similarly, several reports indicate that Si amendments alleviate the negative effects of saline soil conditions (Liang et al., 2007) and increase salt tolerance of rice (Yeo et al., 1999), wheat (Ahmad et al., 1992), barley (Liang et al., 2003), maize (Wang et al., 2004), and cucumber

(Zhu et al., 2004). In tomatoes, reduction of salt translocation from roots to shoots was attributed to deposition of amorphous silica and opal phytoliths in the leaf lamina (Epstein, 1999; Piperno et al., 1999; Romero-Aranda et al., 2001).

Increased salt tolerance of barley and cucumber was attributed to Si-promoted antioxidant enzymatic activity that diminished transpiration and salt accumulation (Liang et al., 2003). In another report, salt-stressed leaves of cucumber had higher activities of SOD, guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) when plants were treated with Si compared to non-Si-treated plants

(Zhu et al., 2004). This suggestes that Si induces protection of cell membranes from oxidative damage (Zhu et al., 2004).

Silicon Effect on Plant Tolerance to Biotic Stress

Silicon’s role in insect pest tolerance

Increased insect pest tolerance and resistance in higher plants treated with Si has been attributed to physical and biochemical mechanisms (Teetes, 2009). Silicon applications were reported to delay the penetration of first instar larvae of the rice yellow stem borer (Scirpophaga incertulas Walker) in rice and to retard the biological development of or reduce the reproduction

63 rates of the green bug (Schizaphis graminum Rondani) in maize and sorghum (Ma and

Takahashi, 2002). Resistance of wheat to hessian fly (Phytophaga destructor Say) increased with increasing Si concentration in leaf lamina (Laing et al., 2006). Silicon applications have been reported to allow reduction in the number of pesticide applications in sugarcane production

(Alvarez and Datnoff, 2001; Alvarez et al., 2004).

Silicon incorporation into epidermal leaf tissues of several crops (e.g., rice, sorghum, wheat, barley and sugarcane) has been shown to reduce sucking insect and lamina feeding of some insects (Yoshida et al., 1969; Epstein, 1994, 1999, 2000, 2001; Aziz et al., 2002; Ma and

Takahashi, 2002; Ma, 2004; Epstein, 2005; Epstein and Bloom, 2005; Epstein, 2009). Various studies have demonstrated that Si reduced insect larval boring and feeding ability, apparently by toughening or hardening of the plant tissues (Elawad et al., 1982; Anderson and Sosa, 2001;

Matichenkov and Calver, 2002; Kvedaras et al., 2005). In another study, increased Si content in rice plants resulted in mandibular teeth loss of stem borer (Chilo suppressalis Walker) larvae

(Savant et al., 1997a).

Silicon applications have also been reported to increase the resistance of sugarcane to the sugarcane borer (Eldana saccharina Walker) [Keeping and Meyer, 2002, 2003]. Insects like the brown planthopper (Nilaparvata lugens Stål), green leafhopper (Cicadella viridis L.), stem borer, whitebacked planthopper (Sogatella furcifera Horváth), and some non-insect pests like rice mites

(Steneotarsonemus spinki Smiley) and spider mites (Tetranychus urticae C.L. Koch.) were suppressed by Si application in the soil solution (Savant et al., 1997a; Ma and Takahashi, 2002;

Ma, 2004). Foliar application of Si has resulted in reduced populations of greenbug (Schizaphis graminum Rond., Homoptera: Aphididae) in sorghum (Carvalho et al., 1999). Several investigations on Si application have documented increased insect pest resistance of tomato,

64 cucumber, and beans (Laing et al., 2006), citrus (Matichenkov et al., 1999, 2001) and turf

(grassland plants – Poaceae, Cyperaceae, and Juncaceae) [Kordörfer and Lepsch, 2001].

Silicon’s role in disease resistance

Plant diseases, like biotic stresses, are major limitations in crop production because they potentially reduce yields (Huber and Haneklaus, 2007). The role of Si in plant disease resistance has been attributed to: 1) increased mechanical resistance of leaf epidermal tissues to fungal penetration, 2) formation of polymerized Si complexes in plant cell walls that resist fungal cell- wall penetrating enzymes, and 3) increased plant phenolic and phytoalexin compounds that enhance the activity of chitinases, peroxidases and polyphenol oxidases as a response to pathogen infection (Takahashi, 1996; Datnoff et al., 2001; Ma, 2004).

Silicon absorption has been reported to enhance rice plant resistance to some fungal pathogens including blast (Pyricularia grisea Sacc.), sheath blight [Rhizoctonia grisea (J.A.

Stev.) Matz], brown spot (Cochliobolus miyabeanus - imperfect fungi, Moniliales), and stem rot

[Magnaporthe salvinii (Catt.) R.A. Krause & R.K. Webster] (Epstein, 1994; Savant et al., 1997a;

Aziz et al., 2002; Kim et al., 2002). It has also been reported that Si reduced blast and brown spot sporulation, lesion size and expansion rate, and spore number per lesion in rice (Datnoff et al.,

2001; Seebold et al., 2001; Rodrigues et al., 2003).

Foliar application of sSi on cucumber, muskmelon, zucchini (Cucurbita pepo L.) and grape (Vitis vinifera L.) controlled powdery mildew (Oidium spp.) [Guével et al., 2007]. Plant absorbed Si deposited on leaf surfaces has been shown to reduce fungal attack by reducing cell wall penetration (Samuels et al., 1991). Application of potassium silicate at 17 mM reduced the severity of powdery mildew on cucumber, muskmelon, and zucchini squash when it was applied seven days prior to plant inoculation with Sphaerotheca fuliginea (Schlecht ex Fr.) Poll.

[Menzies et al., 1992]. In a similar study, application of potassium silicate at 17 mM to grape

65 plants reduced the number of mildew colonies that developed on leaves inoculated with

Uncinula necator (Schwein) Burrill [Bowen et al., 1992].

Datnoff et al. (1997) reported that brown spot and neck blast disease resistance of rice increased in response to Si fertilization under Florida muck soil conditions. Datnoff et al. (1991) reported that adding Si fertilizer (calcium silicate slag) to Everglades Histosols reduced the amount of rice neck blast [Magnaporte grisea (T.T. Hebert) M.E. Barr] by 73 to 86% and reduced the amount of brown spot by 58 to 75%. Silicon fertilization decreased neck blast, sheath blight, and leaf scald fungal disease susceptibility of rice grown on the highly-weathered and Si deficient upland mineral soil conditions of West Africa; rice yields on these soils increased 48% in response to sodium metasilicate fertilization (Winslow, 1992). A similar pattern was reported on rice grown on the highly weathered savannah soils in Colombia (Datnoff et al., 1997).

Effect of Silicate Applications on Postharvest Physiology

Silicon applications have been demonstrated to delay pathogen penetration into plant tissue and thus improve postharvest disease resistance in ‘Hass’ avocado subjected to post- harvest dips and pre-harvest treatments (Bosse et al., 2011; Kaluwa et al., 2011). Silicon has also been reported to play a role in improving postharvest disease resistance of jujube [Ziziphus zizyphus (L.) H.Karst], Chinese cantaloupe var. ‘Hami melon’ and muskmelon var. ‘Reticulatus’ subjected to post-harvest treatments [Fauteux et al., 2005; Tian et al., 2005, 2007]. Postharvest calcium silicate applications to ‘Hass’ avocado decreased fruit losses due to anthracnose

[Colletotrichum gloeosporioides (Stoneman) Spauld. & H. Schrenk] (Anderson et al., 2004,

2005). Similarly, postharvest sodium silicate applications reduced fungal decay in ‘Hami’ melons (var. inodorus Jacq.) caused by leaf spot [Alternaria alternata (Fr.) Keissl.], corky dry

66 rot [Fusarium semitectum (Berk. & Ravenel) Matsush], and pink mold rot [Trichothecium roseum (Pers.) Link.] (Bi et al., 2006).

Postharvest silicon oxide and sodium silicate dips were related to increased peroxidase and phenylalanine ammonia lyase (PAL) activities and reduced muskmelon pink mold rot of

‘Yujingxing’ cantaloupe (Guo et al., 2007). Tian et al. (2005) reported that postharvest Si treatment of jujube fruit significantly increased PAL, polyphenoloxidase (PPO), and peroxidase

(POD) activities. Postharvest silicate applications have also been reported to reduce postharvest disease losses in pear (Prunus communis L.), muskmelon, and cherry [Prunus campanulata (L)

Maxim] (Yang et al., 2009).

Papaya is highly susceptible to postharvest disorders, diseases, and mechanical injuries primarily because of the partially to fully ripe stages at which fruit is harvested (Chitarra and

Chitarra, 1990; Ventura et al., 2003; Protain et al., 2004). Most postharvest research on papaya has used Solo- type fruit grown in Hawaii (Jones and Kubota, 1940; Orr et al., 1953; Yee et al.,

1970; Akamine and Goo, 1977). Adlan (1969) reported no association was found between Si application rates and phytophthora blight [Phytophthora palmivora (E.J. Butler)] of ‘Puna’ Solo papaya fruit grown under Hawaiian soil conditions; a soil pH of six was the main factor responsible for increased disease incidence. Anecdotal evidence was reported that less fruit disease (not identified) developed on ‘Tainung II’ papaya after 40 weekly foliar potassium silicate applications under field conditions in Colombia (Hernández, 2008). To our knowledge, the effect of Si applications on papaya fruit firmness and postharvest quality has not been investigated.

67

Figure 2-1. Description of the biogeochemical cycle of silicon showing the plant, soil, and water interactions that affect silicon availability in the soil solution (redrawn from Savant et al., 1996).

68 CHAPTER 3 EFFECT OF SOIL DRENCH AND FOLIARLY APPLIED POTASSIUM SILICATE RATE ON PAPAYA LEAF GAS EXCHANGE AND GROWTH AND DEVELOPMENT UNDER WELL-WATERED AND DROUGHT STRESSED GREENHOUSE AND PLASTIC-HOUSE CONDITIONS

Overview

Papaya (Carica papaya L.) is a tropical herbaceous plant that grows best under warm to hot climatic conditions and its popularity has increased worldwide during the past 30 years

(FAO, 2012). Papaya is an important fruit crop of tropical and subtropical regions that comes into bearing within a year, is relatively easy to cultivate, and is a good source of vitamins and minerals (Morton, 1987; Chan and Paull, 2008). Papaya plantings have the potential to produce

16 to 166 MT ha-1 (Migliaccio et al., 2010; FAO, 2012). To support this production, papaya has a high nutritional demand for macro- and microelements and optimum soil moisture.

The physiological effect drought conditions on papaya gas exchange and water conductance varies with time of day, ambient light conditions, plant size, and plant water status

(Marler et al., 1994; Marler and Mickelbart, 1998; Clemente and Marler, 1996; Mahouachi et al.,

2006, 2007; Jeyakumar et al., 2007). In general, drought stress results in a rapid reduction in carbon assimilation, stomatal conductance, apparent quantum yield and water use efficiency.

However, drought stress does not appear to reduce the ability of papaya stems to conduct water

(water conductivity) and maintain near normal water status (Marler et al., 1994). Papaya plants tolerate moderate water deficits by osmotic adjustment of the root tissues, stomatal sensitivity to vapor pressure deficits, a rapid decrease in stomatal conductance and transpiration, and an increased rate of leaf abscission (El-Sharkawy et al., 1985; Mahouachi et al., 2006; Marler,

1994). This results in similar leaf water potentials among well-watered and drought stressed leaves. Thus papaya appears to tolerate mild to moderate drought stress by dehydration

69 postponement (Marler, 1994). To our knowledge no one has investigated the effect of silicon on drought tolerance of papaya plants.

Silicon is the second most abundant mineral element in the soil and may be absorbed actively and or passively by plants (Epstein, 1994, 1999, 2000, 2001, 2005, 2009; Ma et al.,

2001; Mitani and Ma, 2005). Ground and foliarly applied silicate compounds (e.g., calcium silicate, sodium silicate, potassium silicate) have been reported to enhance plant growth, carbon assimilation, prevent or ameliorate biotic and abiotic stresses, reduce the effect of toxic soil elements (e.g. Al, As, Cd) and improve nutrient balance in several agronomic plants such as rice

(Oryza sativa L.), wheat (Triticum aestivum L.), and sugarcane (Saccharum officinarum L.)

(Jones and Handreck, 1967; Snyder et al., 1986; Epstein, 1994, 1999; Datnoff et al., 1997; Ma et al., 2001; Ma and Takahashi, 2002; Snyder et al., 2007).

Silicon applications have ameliorated the effect of drought stress of barley (Hordeum vulgare L.), wheat, and sorghum [Sorghum bicolor (L.) Moench.] (Gong et al., 2003; Hattori et al., 2005; Ahmed et al., 2011). This has been attributed to the effect of silicate phytoliths on leaf stomatal function (e.g., osmotic adjustment), improved gas exchange characteristics (e.g., improved leaf light exposure), and the physiological effects of silicate to reduce the oxidative damage to plant cell membranes by increased antioxidative enzymes and depressing free radicals such as hydrogen peroxide (Jones and Handreck, 1967; Iler 1979; Parry et al, 1984; Piperno,

1998, 1999; Liang et al., 2003; Ma, 2004; Gong et al., 2005, 2008; Cornelis et al., 2010;

Stanisavljević, 2011).

There have been some investigations on the effect of silicate applications on fruit crops such as strawberry (Fragaria x Ananassa Duchesne), orange [Citrus sinensis (L.) Osbeck], banana (Musa x paradisiaca L.), papaya and a few fruiting vegetables such as cucumber

70 (Cucumis sativus L), tomato (Solanum lycopersicum L.) and beans (Phaseolus vulgaris L.)

(Miyake and Takahashi, 1983a, 1983b; Adatia and Besford, 1986; Wutscher, 1989; Savant et al.,

1999; Matichenkov et al., 2001; Ma and Takahashi, 2002; Gong et al., 2003; Zhu et al., 2004;

Laing et al., 2006; Henriet et al., 2006). A previous investigation on the effect of soil applied silicate on papaya growth and production established that silicate absorption was mostly passive and to a small extent active, and that pre-plant applications of calcium-silicate slag improved plant phosphorus uptake and mature plant growth (e.g., height and trunk diameter) (Adlan,

1969). However, this study was conducted on an acid Latersol soil high in aluminum-iron oxides which fixed almost all the native soil phosphorus. The soil was pre-plant amended with three rates of triple-super-phosphate [Ca(H2PO4)2·H2O] and Si-slag and three rates CaOH to adjust the soil pH to 5, 6 or 7. Plant growth and yields increased with increasing soil pH and calcium and phosphorus application rates. The highest silicate concentrations were found in leaf petioles as opposed to leaf lamina. In another investigation on papaya, weekly foliar silicate applications were reported to increase papaya trunk diameter, plant height and yields but, had no effect on fruit soluble solids content, appeared to reduce fruit flavor, and increased the amount of deformed fruit (Hernández, 2008). However, data was not statistically analyzed, the silicate source was not clearly defined and was mixed with other unspecified ingredients and the silicate concentration and plant nutrient content within plant tissues was not measured.

Although previous investigations have established critical nutrient levels for papaya production and fertilizer recommendations (Awada, 1977; Awada and Long, 1969, 1971, 1978,

1980; Awada et al., 1975) no investigations on the effect of silicate on papaya growth and development and water relations under well-watered conditions and drought has been reported.

The objectives of these studies were to determine the effect of soil drench and foliarly applied

71 potassium silicate (K2SiO3) on young papaya plant growth and development, gas exchange, and nutrient content under well-watered greenhouse and plastic-house conditions.

Materials and Methods

Research Site and Location

A series of five experiments were established in a greenhouse and plastic-house during

2012 and 2013 at the University of Florida’s Tropical Research and Education Center (UF-

TREC), Homestead, FL. (N Lat 25º25’ N, W Long 80º 25’) (Al-Yahyai et al., 2006; Migliaccio et al., 2010; Kiggundu et al., 2011). The objective of two of the experiments (Exp. 1 and Exp. 2) was to investigate the effect of soil applied (drench) K2SiO3 (25% Si) on plant growth and development and gas exchange under well-watered soil conditions under greenhouse and plastic- house conditions. Two additional experiments (Exp. 3 and Exp. 4) investigated the effect of foliar potassium silicate (K2SiO3, 25% Si) applications on plant growth and development and gas exchange under well-watered soil conditions under greenhouse and plastic-house conditions.

One experiment (Exp. 5) investigated the effect of foliar potassium silicate (K2SiO3, 25% Si) applications on plant growth and development under well-watered and drought-stressed conditions under plastic-house conditions.

Plant Selection, Soil Sampling and Processing, and Crop Management

‘Red Lady’ papaya seeds (Lot No. BZ00638 Min. Germ. 75%, NPK Plus, Inc.

Homestead, FL) were planted into trays (LM 21 seedling tray 65/CA, Winfield Solutions, LLC,

Homestead, FL) with individual cells filled with an artificial soil media (PROMIX BX, Premier

Horticulture, Inc., Quakertown, PA) (75%-85% Canadian Sphagnum Peat Moss, 15% Perlite and

Vermiculite, 10% Pine Bark, and 5% Dolomitic and Calcitic limestone as a pH adjuster)

(Appendix B and C). During and after germination, papaya seedlings were manually watered

72 every three days and fertilized biweekly with 20-20-20 (20-20-20 Multi-Purpose WS Plant Food,

Plant Food Inc., Vero Beach, FL) to promote vigorous crop growth.

Papaya seedlings 2-3 inches tall were transplanted into 3.8 liter pots (LM 300, Windfield

Solutions, LLC, Homestead, FL) filled with an artificial growing soil media [FAFARD Growing

Mix 2 (Canadian sphagnum peat moss 70%, perlite and vermiculite), Diamond-R Fertilizer, Co.

Inc. Homestead, FL] and placed into a shade-house (70% full-sun) (Appendix B and C). After transplanting, plants were drench fertilized with 20-20-20 (Southern Agricultural Insecticides,

Inc., Boone, NC) at a rate of 225 g per 18.0 liters of water and alternated with soil drench applications of minor elements (Miracle Grow®, Marysville, OH) at 2.5 g per 3.8 liters of water every ten days. Iron chelate (Sequestrene®, Becker Underwood, BASF Corporation, Ames, IA) was drench applied at a rate of 10.0 g per 18 liters of water at the start of the investigations.

Once papaya seedlings were 10-12 cm tall they were transplanted into 11 liter containers filled with native Krome gravelly sandy soil (Colburn and Goldweber, 1961; Li, 2009), which is classified as a loamy-skeletal carbonatic hyperthermic Lithic Udorthent (Noble et al., 1996).

Two sets of Krome soil samples were collected from the area of the field from which the soil was obtained at the beginning and four soil samples were obtained from the soil in the containers at termination of each study. Samples were collected at 10 and 20 cm depth and analyzed for soil pH, percent organic matter content, and mineral content (total N, P, K, Ca, Mg, Fe, Mn, B, Zn,

Cu, Al, Si, and available NH3-N and NO3-N, P, K, Ca, SO4, B, Zn, Fe, Mg, Mn, Al, Cu, and Si).

Additionally, four soil samples were collected from containers at the middle of each experiment to determine total and available Si.

The native soil was screened and fertilized with Osmocote® (Everris International B.V.,

The Netherlands; 2.5 g container-1) and iron chelate (Sequestrene®, Becker Underwood – BASF

73 Corporation, Ames, IA; 2.5 g container-1) prior to planting the papaya plants in the containers.

Plants were manually watered about every 3 to 4 days to maintain uniform and vigorous crop growth. Soil samples were sieved using 20 mm mesh sieve (W.S. Tyler, Mentor, OH) and dried at ambient temperature for silicon lab analysis. Soil pH was determined in water [1:2 V/V

(soil:water)] (Hanlon et al., 1998), and mineral element concentrations determined by

Inductively Coupled Argon Plasma Spectrophotometry (Perkin Elmer Optima 5300

Spectrometer, Conquer Scientific Lab Equipment, San Diego, CA) after Mehlich III extraction

(Mehlich, 1938; Alva, 1993). Organic matter was determined by the Walkey-Black procedure

(Hanlon et al., 1998; Wright et al., 2008). Silicon analysis of the soil was determined by the

Autoclave-Induced Digestion (AID) method (Elliot and Snyder, 1991). Sulfur analysis was performed by the extraction method developed by Rehm and Caldwell (1968).

Eighty ‘Red Lady’ papaya plants of uniform size and vigor were used in each of the first four investigations: (1) March 16, 2012 to November 30, 2012, plastic-house conditions, Si soil drench; (2) February 18, 2013 to June 25, 2013, greenhouse conditions, Si soil drench; (3)

August 1, 2012 to December 23, 2012, greenhouse conditions, Si foliar and; (4) April 25, 2013 to September 18, 2013, plastic-house conditions, Si foliar. The fifth investigation was established in the plastic-house with 48 plants of uniform size and vigor and was conducted from June 6,

2013 to December 5, 2013.

Temperature data was collected from the FAWN Weather Station located at the Tropical

Research and Education Center, Homestead, Florida. The weather station is located approximately 100 m from the plastic-house and greenhouse. Weed control was performed manually and pests and disease control was performed on an as needed basis.

74 Once plants reached 30 cm to 40 cm in height the experiments began. Potassium silicate

(K2SiO3) treatments were applied as a foliar spray or a soil drench at a two week intervals. There were 20 plants per treatment. The soil drench treatments in Exp. 1 and Exp. 2 were no silicon application (control), 60 g Si plant-1 application-1, 120 g Si plant-1 application-1 (equivalent to 500 kg Si ha-1year-1), and 240 g Si plant-1 application-1 (1000 kg Si ha-1year-1). There were 11 and nine K2SiO3 soil drench applications for Exp. 1 and Exp. 2, respectively. The silicon source was

® AgSil 25% Si (PQ Corporation, Chester, PA). The foliar K2SiO3 treatments were: no silicon application (control), 2.5 g Si plant-1 application-1, 5 g Si plant-1 application-1, and 10 g Si plant-1 application-1. Twelve foliar applications were made in Exp. 3 and Exp. 4. To maintain similar potassium nutrition for control plants, applications of potassium sulfate (K2SO4) [Ultra sop

K2SO4, SQM Europe N.V., Antwerp, Belgium] were applied bi-weekly (30 g diluted in 1 liter of water). Similarly, to maintain similar sulfur nutrition for K2SiO3 treatments elementary sulfur

(Liquid Sulfur Six®, Tracite, Helena Chemical Company, Collierville, TN or Kolla Sulfur® 6

Micronized Flowable, Cromartie Agricultural Chemicals, Inc., Albany, GA) was applied at 2, 4, and 8 mL of sulfur diluted in 11.36 liters of water for the experiments with foliar Si applications, and in 18.9 liters of water for experiments with soil Si drench applications. To insure plants were

-1 -1 well watered, 1 liter H2O plant application was applied in the greenhouse, however, plants in

-1 the plastic-house received the same 1 liter H2O plant daily by using micro-sprinkler irrigation system for 15 minutes twice each day.

In the fifth experiment K2SiO3 was foliarly applied to plants grown in a plastic-house and the experimental period began on August 1, 2013 and terminated on November 1, 2013. The

-1 -1 foliar K2SiO3 treatments were no silicon application (control), 2.5 g Si plant application , 5 g

Si plant-1 application-1, and 10 g Si plant-1 application-1. Plants were divided into two additional

75 treatments, well-watered and drought stressed. There were 12 plants per treatment. The objective of the experiment was to determine the effect of foliarly applied K2SiO3 on young papaya growth and development under well-watered and drought conditions. To monitor plant soil moisture, three tensiometers (Irrometer, Irrometer Company Inc, Riverside, CA) were positioned at 10 cm soil depth of four plants per treatment (12 totals). Soil moisture of well-watered plants was

-1 maintained at or below 7 kPa and plants were well-watered daily (1 liter H2O plant ). Soil moisture of drought-stressed plants was allowed to reach 15 kPa before watering with sufficient water (1 liter) to bring soil moisture tension at or below 7 kPa.

Plant measurements

Plant height and trunk diameter were measured every two weeks. Height was measured from the soil surface to the height of the last emitted leaf with a tape measure (Stanley

PowerLock 8m/26’ Tape Measuring, Northern Tool & Equipment, Burnsville, MN). Trunk diameter was measured 5 cm above the soil surface with an electronic digital caliper (Caliper

Marathon 0-200 mm, Marathon Watch Company LTD, Richmond Hill, Ontario, Canada).

Plant leaf gas exchange measurements

Leaf gas exchange was measured in experiments 1, 2, 3, and 4 (four out five experiments). Leaf gas exchange: transpiration (E), stomatal conductance of water vapor (gs), and net CO2 carbon assimilation (A) were measured biweekly on 12 plants per treatment on the two most recently matured, sun-exposed leaves per plant, one week after silicon applications using a portable CO2 gas exchange analyzer machine (ADC-LCA3, The Analytical Development

Co. Ltd, Hoddesdon, England). The equipment was set up to measure gas exchange at a

-2 -1 photosynthetic photon flux (PPF) of 1000 μmol m s using a halogen lamp, a reference CO2 concentration of 350 μmol mol-1 and an air flow in the leaf cuvette of 200 mL min-1. For

76 statistical analysis, values from the two measured leaves per plant were averaged to provide one value per leaf. Data was recorded between 8 am to 2 pm.

Photosynthetic pigment analysis (leaf greenness) per plant was determined as an indicator of leaf chlorophyll content (Torres-Neto et al., 2002; Kiggundu et al., 2011). Leaf chlorophyll content was determined with a portable chlorophyll SPAD-502 meter (Minolta Camera Co.,

Osaka, Japan) and expressed as SPAD units (Torres-Netto et al., 2002). Three SPAD readings were recorded from the most recently matured fully sun-exposed leaf per plant per treatment per replication (three plants per treatment). For statistical analysis, values from the two measured leaves per plant per treatment and replication were averaged to provide one value per plant. Data was recorded between 8 am to 2 pm.

Soil sampling, processing and nutrient analysis

A set of two soil samples were collected from the field at the beginning and four at termination of the each trial. Soil samples were collected at 10 cm depth, sieved using 20 mm mesh sieve (W.S. Tyler, Mentor, OH) and dried at ambient temperature for lab analysis to determine: soil pH in water [1:2 V/V (soil:water)] (Hanlon et al., 1998) and percent organic matter by the LOI method (Wright et al., 2008). Total soil mineral concentration was determined by Inductively Coupled Argon Plasma Spectrophotometry (Perkin Elmer Optima 5300

Spectrometer, Conquer Scientific Lab Equipment, San Diego, CA). Total nitrogen was determined by the Wolf digestion method (Wolf, 1982a) and total mineral nutrient content of P,

K, Ca, Mg, Fe, Mn, B, Zn, Cu, and Al by the HCl digestion method (Wolf, 1982a). Silicon content was determined the autoclave-induced digestion (AID) method (Elliot and Snyder,

1991).

Plant available nutrient concentration of P, K, Ca, Mg, Fe, Mn, B, Zn, Cu, and Al were determined by Inductively Coupled Argon Plasma Spectrophotometry after Mehlich III

77 extraction method (Mehlich, 1938; Alva, 1993). Available N (NH4-N and NO3-N) were determined by KCl extraction method (Wolf, 1982b). Available sulfur (SO4-S) content was determined by the ammonium acetate extraction method (Rehm and Caldwell, 1968) and available Si by acetic acid extraction method (Elliot and Snyder, 1991).

To control the two-spotted mite (Tetranychus urticae Koch), Admire® (Imidacloprid,

Bayer Crop Science, Morganville, NC) at 10 mL rate diluted in 9.45 liters of water (2.5 gallons of water) was applied twice to the foliage in experiments 1, 3 and 4. To control soil borne pathogens, Ridomyl® Gold SL (Mefenoxam, Syngenta International AG, Basel, Switzerland) at a rate of 71 mL diluted in 18.9 liters of water (5 gallons of water) was drench applied prior to initiation of experiment 3; Abound® (Azoxystrobin, Syngenta International AG, Basel,

Switzerland) and Dithane® M45 (Mancozeb, Dow AgroSciences, Indianapolis, IN) at 4 mL and

18 mL rate, respectively were diluted in 3.78 liters of water (1 gallon of water) and sprayed onto plants three times in experiments 1, 3 and 4 to prevent papaya root rot (Phytophthora palmivora

E.J. Butler) and powdery mildew (Oidium caricae-papayae J.M. Yen).

Analysis of tissue sample for silicon available content

Beginning 30 days (1 month) after foliar and soil Si drench applications to the termination of the experiments, one plant per treatment was sacrificed monthly for fresh and dry weights. Leaf laminas, petioles, trunks, and roots were separated to determine the silicon concentration in each plant tissue. Tissue fresh and dry weights were measured from one plant per treatment per replication (four plants total) (Scale Denver Instrument, Denver Instrument

Company, Denver, CO). Roots were separated from the Krome soil by carefully washing them in tap water prior to sampling.

Plant tissue samples were rinsed with deionized water and then submerged into a

Liquinox soap solution (30 mL Liquinox diluted into 2,500 mL deionized water) and rinsed with

78 deionized water for 1 to 2 minutes, then dipped into a dilute HCl (12 N) solution (30 mL HCL diluted into 2,500 mL deionized water) and rinsed again with deionized water. Tissue samples were dried on a paper towel and placed into paper bags (Paper Grocery Bags 25#, AJM

Packaging Corp., Bloomfield Hills, MI ), and dried in an oven at 70oC for five days (Wisconsin

Oven Modell 600 and 800, Memmert, Wisconsin Oven Corporation, East Troy, WI). Dried tissue samples were milled to pass a 20 mm mesh sieve with stationary mill with rotary knives

(Thomas-Wiley Intermediate Mill, Thomas ScientificTM, Swedesboro, NJ). The milled samples were put into a 118 mL plastic sample bags with puncture proof tabs (Nasco Whirl-Pak®, Fort

Atkinson, WI). Ground papaya tissues samples were sent to the Soil and Water Laboratory of the

University of Florida’s Everglades Research and Education Center (UF-EREC) in Belle Glade,

FL for organic silicon content analysis. The Si concentration was determined by the Autoclave-

Induced Digestion (AID) method (Elliott and Snyder, 1991).

Statistical Analysis

Treatments were arranged in a randomized complete block design and statistical analysis was conducted using SAS 9.1 statistical software (SAS Institute, Cary, NC), and the PROC

GLM, PROC T-TEST, PROC MEAN STDERR, PROC REG for ‘Linear Regression’, and

PROC REPEATED MEASURES procedures. These statistical procedures generated least-square means ± standard error that was tested for significant differences by LSD’ Studentized test, p≤0.05. The parameters for the study were evaluated by sampling dates using a two-way

ANOVA. The experimental unit was whole plants per row for the developmental parameters and for physiological parameters was a single individual plant per row and per treatment.

79 Results and Discussion

Effect of K2SiO3 Soil Drench Applications Under Well-Watered Soil Conditions

Air temperatures were recorded daily by the FAWN Weather Station located at the

Tropical Research and Education Center, Homestead, FL (Appendix D and E). The weather station is located approximately 100 m from the plastic-house and greenhouse. Air temperatures ranged from 23°C to 40oC with a mean of 32oC and 20 to 45oC with a mean of 33oC for the greenhouse and plastic-house, respectively.

Plant height and diameter measurements

There was no significant difference in plant height among K2SiO3 treatments in Exp. 1; plant heights ranged from 111.9 to 177.3 cm (Table I-1). In contrast, plant heights significantly increased with K2SiO3 application rates in Exp. 2 (Table I-2). Plant heights ranged from 28.7 to

29.3 cm at the beginning of the investigation and increased to 88.5 cm to 97.5 cm at termination.

There was no significant effect of K2SiO3 application rates on trunk diameter during the first 2.5 months in Exp. 1 but during the last 2.5 months trunk diameters was reduced with increased

K2SiO3 rates (Table I-3). Trunk diameters ranged from 26.5 mm to 28.1 mm at the beginning of the investigation and 10 months later ranged from 52.4 mm (240 g K2SiO3 rate per plant) to 62.0 mm (0 g K2SiO3 per plant). In general, there was no significant difference in trunk diameters among K2SiO3 treatments in Exp. 2 (Table I-4). Trunk diameters ranged from 9.6 mm to 10.0 cm at the beginning of the investigation and increased to 34.3 to 37.9 mm at termination. In contrast, under Hawaiian field conditions ‘Puna’ Solo papaya plant height and trunk diameter significantly increased with pre-plant Si-slag rate only after five (Adlan, 1969). In contrast, Si applications significantly increased growth of ‘Valencia’ orange and ‘Marsh’ grapefruit (Citrus x paradisi Macfad.) (Matichenkov et al. (2001), banana cv. ‘Grande Naine’) (Henriet, 2006) and tomatoes (Matichenkov and Bocharnikova (2004).

80 Plant fresh and dry weights

There was no significant increase in fresh and dry weight of roots, leaf lamina and petioles, and trunks as K2SiO3 soil drench application rates increased in Exp. 1 and Exp. 2 (Table

I-5, I-6, I-7 and I-8). In contrast, Adlan (1969) reported field grown ‘Puna’ papaya plant stems, leaf lamina and petioles, and root dry weights increased significantly with increased Si-slag application rate under Hawaiian environmental conditions. Fresh and dry weight of strawberry roots and shoots and fresh weight of seedling orange and grapefruit significantly increased with silicon application rates (Matichenkov et al., 2001; Miyake and Takahashi, 1986). In contrast, although banana accumulated Si (passively and actively) growth was unaffected by Si application rate (Henriet, 2006). Growth of rice, barley, green onion (Allium cepa L.), and

Chinese cabbage (Bok-choi) [Brassica rapa sp. Chinensis L.]were reported to increase with silicon application rates (Okuda and Takahashi, 1961a, 1961b).

Plant gas exchange

Soil K2SiO3 applications had no significant effect on stomatal conductance (gs) and transpiration (E) of well-watered ‘Red Lady’ papaya plants in Exp. 1 and Exp. 2 (Table I-9,

-1 -1 I-10, I-11 and I-12). Stomatal conductance ranged from 206.2 to 1,010.4 mmol H2O m s in

-1 -1 Exp. 1 and 298.3 to 1,410.4 mmol H2O m s in Exp. 2 (Table I-9 and I-10). Transpiration

-1 -1 -1 -1 ranged from 4.2 to 12.1 mmol H2O m s in Exp. 1 and 2.7 to 6.1 mmol H2O m s in Exp. 2

(Table I-11 and I-12). In general, as soil K2SiO3 application rate increased carbon assimilation

(A) significantly increased in Exp. 1 and Exp. 2 (Table I-13 and I-14). This suggests soil K2SiO3 applications may improve net CO2 efficiency.

In general, plants treated with soil K2SiO3 applications had significantly higher SPAD values than non-treated plants for Exp. 1 and Exp. 2 (Table I-15 and I-16). SPAD values ranged from 38.7 to 48.7 in Exp. 1 and 34.0 to 59.4 in Exp. 2.

81 Soil and plant tissue nutrient and Si content

The soil pH (8.1 to 8.2), percent organic matter content (7.0 to 7.5%), and total and plant available nutrient content pre-Si soil treatment of the Krome very gravelly sandy loam soil

(loamy-skeletal, carbonatic, hyperthemic lithic Udorthents) was within the ranges reported previously by Noble et al. (1996), and Rao and Li (2003) (Table I-17 and I-18). Krome soil is high in Ca content (230 g kg-1) but very low for all other nutrients (i.e, N, P, K, Mg, Mn, B, Zn and Fe). Total Si content is low and available Si very low (Chen et al., 2000; Li. 2001; Wang et al., 2009).

In general, 11 (Exp. 1) and nine (Exp. 2) K2SiO3 soil drench applications had little effect on soil pH and total and available plant nutrients (Table I-19 and I-20). Total soil Si content increased slightly with K2SiO3 rate however available Si content did not change. This may be due to leaching of the Si from containers during irrigation. Similarly, K2SiO3 soil drench applications had little effect on total and available leaf nutrient content after eleven (Exp. 1) and nine (Exp. 2) Si soil applications (Table I-21 and I-22). The only exception was for Zn in Exp. 2 which increased greatly as Si application rates increased. Why this occurred is not known. As expected available leaf Si content increased with K2SiO3 soil drench application rate in Exp. 1 and Exp. 2.

Total soil Si content did not significantly increase after 11 K2SiO3 soil drench applications but was significantly higher for the 60 g Si plant-1 application-1 than non-Si treated soil (Exp. 1) (Table I-23). In contrast, soil available Si increased significantly with K2SiO3 application rate after 6 and 11 K2SiO3 soil drench applications. Initial soil total and available Si content were higher than after 6 and 11 K2SiO3 soil drench applications. This may be due to Si leaching due to the daily irrigation regime for well-watered plants. In contrast, total soil Si content increased with K2SiO3 rate after 5 and 9 K2SiO3 soil drench applications in Exp. 2 (Table

82 I-24). Similarly, available soil Si content increased significantly with K2SiO3 soil drench application rate. Initial soil total and available Si content were higher than after 5 and 9 K2SiO3 soil drench applications. This may be due to Si leaching under a daily irrigation regime for well- watered plants.

There was no significant effect of K2SiO3 soil drench application rate on root (main and fibrous), leaf lamina and petiole, and trunk tissue Si content in Exp. 1 and Exp. 2 [Table I-25 and I-26]. In Exp. 1 fibrous Si content was greater than main root content for all treatments

(Table I-25).Leaf lamina Si content was higher than leaf petiole and trunk Si content at all

K2SiO3 soil drench application rates The lower soil available Si content for the 0 K2SiO3

(control) treated soil appeared to be sufficient for plant uptake and accumulation of silicon

(Table I-23).

In Exp. 2 fibrous and main root tissues were combined and root Si content was greater than leaf lamina, petiole and trunk Si content for all K2SiO3 soil drench application rates (Table

I-26). Leaf lamina Si content was greater than petiole and trunk Si content for all Si treatments.

In conclusion, nine and 11 K2SiO3 soil drench applications to container-grown ‘Red

Lady’ papaya plants had little effect on total and available soil nutrient content (Table I-17, I-18,

I-19 and I-20). In general, soil Si content increased slightly after K2SiO3 soil drench applications but was nearly the same as non-Si treated soil. This may be due to the daily irrigation leaching soil applied Si. In general, soil applied K2SiO3 had no consistent significant effect on container grown ‘Red Lady’ plant heights and trunk diameters (Table I-1, I-2, I-3 and I-4). Soil applied

K2SiO3 had no significant effect on plant tissue fresh and dry weights. Soil applied K2SiO3 had no significant effect on plant gs and E although A generally increased with K2SiO3 application rate (Table I-9, I-10, I-11, I-12, I-13 and I-14). The significance of SPAD values among

83 treatments varied by sampling date but there was a trend for SPAD values to increase with increased K2SiO3 soil drench application rate (Table I-15 and I-16). Soil applied K2SiO3 had no significant effect on plant tissue Si content (low to very low r2 values) [Table I-25 and I-26]. In general, ‘Red Lady’ root tissue had higher Si concentrations than leaf lamina and petioles and trunk tissues.

Effect of Foliar K2SiO3 Applications Under Well-Watered Soil Conditions

Plant height and diameter measurements

There was no significant difference in ‘Red Lady’ papaya plant height among foliar

K2SiO3 treatments on any sampling date in Exp. 3 and 4; plant heights ranged from 118.9 to

165.3 cm in Exp. 3 and 44.2 to 134.8 cm in Exp. 4 (Table I-27 and I-28). Similarly, foliar applications of K2SiO3 had no significant effect on ‘Red Lady’ plant trunk diameters in Exp. 3 and Exp. 4 (Table I-29 and I-30). Trunk diameters ranged from 27.1 to 49.2 mm in Exp. 3 and

17.8 to 59.8 mm in Exp. 4. Silicon-slag applications had no significant effect on papaya plant height and diameter under field conditions in Hawai (Adlan, 1969). In contrast, Si applications significantly increased growth of ‘Valencia’ orange and ‘Marsh’ grapefruit, banana, and tomatoes (Henriet, 2006; Matichenkov et al., 2001; Matichenkov and Bocharnikova, 2004).

Plant fresh and dry weights

There was no significant increase in fresh and dry weight of roots, leaf lamina and petioles, and trunks as foliar K2SiO3 application rates increased in Exp. 3 and Exp. 4 (Table I-31,

I-32, I-33 and I-34). In contrast, fresh and dry weights of strawberry and citrus (Citrus sp.) increased with solution Si application rates under controlled conditions (Matichenkov et al.,

2001; Miyake and Takahashi, 1986).

84 Plant gas exchange

In general foliarly applied K2SiO3 had no significant effect on stomatal conductance (gs) of well-watered ‘Red Lady’ papaya plants in Exp. 3 and Exp. 4 (Table I-35 and I-36). Stomatal

-1 -1 conductance ranged from 150.0 to 1,211.7 mmol H2O m s in Exp. 3 and 247.5 to 954.2 mmol

-1 -1 H2O m s in Exp. 4 (Table I-35 and I-36). In Exp. 3 foliarly applied K2SiO3 had no significant

-1 -1 effect on E and ranged from 3.2 to 10.1 mmol H2O m s (Table I-37). In contrast, in Exp. 4 E

-1 -1 increased with foliarly applied K2SiO3 rate and ranged from 6.3 to 11.4 mmol H2O m s (Table

I-38). In general, foliarly applied K2SiO3 had no significant effect on net CO2 assimilation (A) in

-1 -1 Exp. 3 and rates ranged from 1.2 to 6.9 μmol CO2 m s (Table I-39). In contrast, as foliarly applied K2SiO3 application rate increased carbon assimilation (A) significantly increased in Exp.

-1 -1 4; rates ranged from 3.5 to 9.5 μmol CO2 m s (Table I-40). This inconsistency among experiments may be due to higher ambient temperatures in the greenhouse compared to the plastic-house. In general, SPAD values significantly increased with foliarly applied K2SiO3 application rate for Exp. 3 and Exp. 4 (Table I-41 and I-42).

Soil and plant tissue nutrient and Si content

The soil pH (8.1 to 8.2), percent organic matter content (7.0 to 7.9%), and total and plant available nutrient content pre-Si soil treatment of the Krome very gravelly sandy loam soil

(loamy-skeletal, carbonatic, hyperthemic lithic Udorthents) was within the ranges reported previously by Noble et al. (1996), and Rao and Li (2003) (Table I-43 and I-44). Krome soil is high in Ca content (230 g kg-1) but very low for all other nutrients (i.e., N, P, K, Mg, Mn, B, Zn and Fe). Total and plant available Si was low (Chen et al., 2000; Li. 2001; Wang et al., 2009).

In general, 13 (Exp. 3) and 16 (Exp. 4) foliar K2SiO3 applications had little effect on soil pH, percent organic matter and total mineral and available plant nutrients (Table I-45, I-46, I-47 and I-48). Total soil Si content did not change which was expected because Si was foliarly

85 applied. However, plant available soil Si content increased substantially as foliar Si rate increased in Exp. 3 but was similar among Si treatments in Exp. 4. This may be due to greater soil leaching from the irrigation regime under greenhouse conditions (Exp. 4) compared to plastic-house conditions (Exp. 3).

Thirteen (Exp. 3) and 16 (Exp. 4) foliar K2SiO3 applications had little effect on total soil

Si content (Table I-45 and I-46). In contrast, soil available Si content increased with foliar

K2SiO3 application rate after 13 (Exp. 3) and 16 (Exp. 4) applications (Table I-47 and I-48). Soil total and available Si content were slightly greater for Krome soil prior to trial initiation than after 13 and 16 foliar Si applications (Table I-49 and I-50). This may be due to the frequent irrigation of well-watered plants in Exp. 3 and Exp. 4.

-1 The only exception was for NH4-N which was moderately greater for the 0 and 5 g plant

-1 foliar K2SiO3 application rate compared to the 2.5 g and 10.0 g plant foliar K2SiO3 application rates (Exp. 3) (Table I-47 and I-48). Why this occurred is not known since all treatment received the same N fertilization. Unexpectedly available soil Si content increased greatly with foliar

K2SiO3 application rate in Exp. 3 but only slightly in Exp. 4. Why this occurred is not clear.

There was no significant effect of K2SiO3 foliar application rate on root (main and fibrous), leaf lamina and petiole, and trunk tissue Si content in Exp. 3 and Exp. 4. Fibrous root Si content was higher than main root, leaf lamina and petiole and trunk Si concentrations after 13 foliar K2SiO3 applications (Exp. 3) [Table I-51]. Silicon content of leaf lamina was higher than the leaf petiole and trunk tissues (Table I-51). In Exp. 4, fibrous and main root tissues were combined and the silicon content of leaf lamina and roots were similar but higher than leaf petioles and trunks

(Table I-52).

86 In conclusion, 13 and 16 foliar K2SiO3 applications to container-grown ‘Red Lady’ papaya plants had no significant effect on plant growth, fresh and dry plant weights, gs and E, and an inconsistent effect on A and SPAD values (Table I-27 to I-42). In general, 13 (Exp. 3) and 16 (Exp. 4) foliar K2SiO3 applications had little to no effect on soil pH, percent organic matter and total mineral and available plant nutrients (Table I-45, I-46, I-47 and I-48). Total soil Si content did not change which was expected because Si was foliarly applied. However, total soil Si and plant available Si content did not change with foliar K2SiO3 applications in Exp.

3 but unexpectedly available soil Si content increased greatly in Exp. 4. This may be due to greater soil leaching from the irrigation regime under greenhouse conditions (Exp. 4) compared to plastic-house conditions (Exp. 3).

Effect of Foliarly Applied K2SiO3 on Container-Grown Well-Watered and Drought Stressed Papaya Plants

Air and soil temperatures were recorded daily by the FAWN Weather Station located at the Tropical Research and Education Center, Homestead, FL (Appendix D and E). The weather station is located approximately 100 m from the plastic-house and greenhouse. Air temperatures ranged from 23 to 40oC with a mean of 32oC plastic-house study.

Plant height and diameter measurements

There was no significant effect of foliar K2SiO3 rate on ‘Red Lady’ the plant height of well-watered and drought-stressed plants and generally no significant difference among well- watered and drought-stressed plants on any sampling date (Table I-53). However, there was a moderate trend for plant height of drought-stressed plants to increase with foliar K2SiO3 rate on most sampling dates. Very low r2 values indicate other factors influenced plant height.

There was no significant effect of increasing foliar K2SiO3 rates on well-watered ‘Red

Lady’ trunk diameters (Table I-54). In contrast, for drought-stressed plants as foliar K2SiO3 rates

87 increased plant diameter significantly increased. There was no significant difference in trunk diameters among well-watered and drought-stressed plants for any foliar K2SiO3 rate on any sampling date. The increased trunk growth with Si application rate may be due to the ability of papaya plants to quickly adjust gs, E, and A in response to drying soil conditions (Clement and

Marler, 1996; Marler and Mickelbart, 1998). Foliarly applied Si significantly improved cucumber growth under non-saline and saline media conditions and creeping bentgrass (Agrostis palustris Huds. A.) under high and low nutrient regimes (Yildirim et al., 2008; Schmidt et al.,

1999). In contrast, foliar Si applications to wheat did not significantly affect plant growth

(Guével et al., 2007).

Plant fresh and dry weights

Increasing foliarly applied K2SiO3 rates had no significant effect on well-watered or drought-stressed plant root, leaf lamina and petiole, and trunk fresh and dry weights (Table I-55 and I-56). However, there was a trend for fresh weights to increase with K2SiO3 rates. There was no significant difference in plant part fresh and dry weights among well-watered and drought- stressed plants for any foliar K2SiO3 rate. Foliar Si applications to cucumber resulted in significantly greater shoot and root dry weight under non-saline and saline media conditions

(Yildirim et al., 2008). In contrast, foliarly applied Si had no significant effect on fresh and dry weight of wheat (Guével et al., 2007).

SPAD values

On each sampling date, as foliarly applied K2SiO3 rates increased SPAD values for well- watered and drought-stressed plants significantly increased (Table I-57). However, there was no difference in SPAD values among well-watered and drought-stressed plants on any sampling date. The increase in SPAD values may be attributed to increased chlorophyll content of Si treated plants and antioxidant activity (Schmidt et al., 1999; Yildirim et al., 2008). As foliar Si

88 rate increased, leaf chlorophyll content of cucumber and sunflower under non-saline and saline soil conditions increased (Noreen and Ashraf, 2008; Yildirim et al., 2008). Foliar Si applications to corn and soybean temporarily increased A but not gs and E and increased leaf area and shoot dry weights compared to non-Si treated plants (Khan et al., 2003). Similarly, foliar applications of Si stimulated leaf antioxidant activity, increased chlorophyll content and improved A of creeping bentgrass (Schmidt et al., 1999). This suggests foliarly applied Si to young papaya plants may improve photosynthetic capacity of drought-stressed plants.

Soil and plant tissue nutrient and Si content

The soil pH (8.1), percent organic matter content (7.1%), and total and plant available nutrient content pre-Si soil treatment of the Krome very gravelly sandy soil (loamy-skeletal, carbonatic, hyperthemic lithic Udorthents) was within the ranges reported previously by Noble et al. (1996), and Rao and Li (2003) (Table I-58). Krome soil is high in Ca content (233 g kg-1) but very low for all other nutrients (i.e., N, P, K, Mg, Mn, B, Zn and Fe). Total and plant available Si was low (Chen et al., 2000; Li. 2001; Wang et al., 2009).

In general, foliar K2SiO3 application rate had little effect on soil pH, percent organic matter and total and available plant nutrients (Table I-58 and I-59). Total soil Si content increased slightly and plant available Si content did not change. This was expected because Si was foliarly applied. However, total and available soil Si content increased significantly after four and nine foliar K2SiO3 applications (Table I-62). Why available soil Si content increased greatly after nine foliar Si applications is not clear unless Si moved from the leaves through the roots to the soil or the soil was contaminated with Si during foliar applications.

Increasing foliar K2SiO3 application rate had no significant effect on Si content of roots, leaf and petioles and trunks under well-watered or drought-stressed conditions (Table I-63).

There was no significant difference in root, trunk and leaf petiole and lamina Si content among

89 well-watered and drought-stressed plants. Though not significant, petiole and trunk Si content tend to be higher for well-watered as compared to drought-stressed plants at all K2SiO3 application rates. In general, Si plant tissue content was highest in leaf lamina, followed by roots, leaf petioles and trunks regardless of soil moisture content.

Conclusions

In conclusion, foliar K2SiO3 application rate had little effect on ‘Red Lady’ papaya plant height and trunk diameters of well-watered plants but a significant effect on trunk diameter of drought-stressed plants (Table I-53 and I-54). Similarly, foliar Si application rate had little effect on well-watered and drought-stressed plant fresh and dry weights (Table I-55 and I-56). As foliar

K2SiO3 application rate increased SPAD values significantly increased for well-watered and drought-stressed plants (Table I-57).

In general, foliar K2SiO3 application rate had little effect on soil pH, percent organic matter and total and available plant nutrients (Table I-58 and I-59). Total soil Si content increased slightly and plant available Si content did not change. This was expected because Si was foliarly applied. However, total and available soil Si content increased significantly after 5 and 9 foliar K2SiO3 applications (Table I-60 and I-61). There was no significant effect of foliar

Si application rate on root, trunk and leaf lamina and petiole content of well-watered and drought-stressed plants and no difference in tissue Si content among well-watered and drought- stressed plants (Table I-63). Foliar K2SiO3 applications appear to enhance or help maintain drought-stressed ‘Red Lady’ papaya plant growth and chlorophyll content (SPAD values) compared to well-watered plants.

90 CHAPTER 4 EFFECT OF SILICATE APPLICATION RATES ON PAPAYA GAS EXCHANGE, GROWTH AND YIELDS UNDER FIELD CONDITIONS IN SOUTH FLORIDA

Overview

Papaya (Carica papaya L.) is a member of the Caricaceae, a small dicotyledonous family consisting of six genera of herbaceous and shrubby plants, best known for its nutritive fruit value, milky latex containing papain and its use in the medical pharmaceutical industry

(Manshardt and Drew, 1998). World-wide papaya production is about 11.3 million MT year-1 with nearly, 60.3% produced in Latin America and the Caribbean, 30% in Asia and the Pacific, and 9.7% in Africa, during the past ten years (Texeira da Silva et al., 2007; FAO, 2012). Papaya consumption in non-tropical areas of the world has increased to 29.5% of the total world production (FAO, 2012).

Silicon applications to monocotyledonous plants e.g., barley (Hordeum vulgare L.), rice

(Oryza sativa L.), sugarcane (Saccharum officinarum L.), and wheat (Triticum aestivum L.) improved stem strength by 11 to 17.6%, reduced seed-shattering by 10 to 21%, improved drought tolerance by decreasing transpiration 15 to 30%, and increased crop yields by 17 to 30%

(Ayres, 1966; Fox et al., 1967, 1969; Plucknett, 1969; Gascho and Andreis, 1974; Epstein, 1994,

1999, 2000, 2001, 2005; Alvarez and Datnoff, 2001; Korndörfer and Lepsch, 2001; Ma and

Takahashi, 2002; Ma, 2004; Alvarez et al., 2004; Snyder et al., 2004; Sudhakar et al., 2006;

Tahir et al., 2011). Matichenkov et al. (2001) reported a trend for increased young ‘Valencia’ orange [Citrus sinensis (L.) Osbeck] tree plant height and branch length with increased application rate of soil applied Ca-Mg silica slag. Increased Si application rates to solution cultured cucumber plants (Cucumis sativus L.) increased mature stem rigidity, leaf fresh and dry weight, leaf RuBPcarboxylase activity, and resistance to powdery mildew [Sphaerotheca fuliginea (Schltdl.) Pollacci] (Adatia and Besford, 1986; Epstein, 1999; Ma, 2004). Solution

91 cultured strawberry (Fragaria x Ananassa Duchesne) plant growth and yields significantly improved by 25.4% with increased SiO2 application rate (Miyake and Takahashi, 1986; Ma and

Takahashi, 2002). In contrast, banana (Musa x paradisiaca L.) shoot and root growth did not significantly increase with increasing H4SiO4 application rates in solution culture, however, passive and active Si uptake increased with increased Si application rate (Henriet et al., 2006).

The effect of silicon applications on gas exchange of fruit crops has not been investigated.

In Hawaii, applications of electric furnace slag (silicon dioxide plus other metal oxides and 46% CaO) incorporated into the soil at the rate of 0, 833 and 1,166 kg Si ha-1 prior to planting papaya were investigated (Adlan, 1969). The acid pH Kapaa gravelly silty clay soil used in the study was characterized by a low pH (~4) and high aluminum-iron oxide content and very low available phosphorus content. The soil was amended with three rates of limestone (CaOH) and furnace slag three months prior to planting in order to raise the soil pH to about 5, 6 or 7. At planting three rates of triple superphosphate were applied (0, 560 or 1,120 kg ha-1) (Adlan,

1969). In general, the main effects on plant growth and yield were due to increased soil pH and phosphate content (i.e., plant calcium and phosphorus content). Only after 210 days (7 months) was there a trend for increasing soil and plant silicate content to increase plant growth and fruit yields. This may have been due to the lack of solublization of the furnace slag since plants were not irrigated and plants only received water through rainfall. In addition, no attempt was made to ameliorate or differentiate the effect of the slag contaminants (i.e., plant nutrients, heavy metals, minor elements) in the treatments on papaya growth and yields.

Weekly foliar applications of an ortho-silicate mix to field-grown papaya in Colombia resulted in greater plant height, stem diameter, and fruit production compared to non-treated controls over a 10 month period (Hernández, 2008). There was no effect on fruit soluble solids

92 but the authors reported reduced disease incidence. However, the mix contained unknown amounts of Si, N, K, and minor elements and soil and plant Si was not measured prior to, during, or at the conclusion of the experiment.

Various investigations on papaya have determined the critical leaf mineral element levels for optimum plant growth and yields (Awada, 1977; Awada and Long, 1969, 1971, 1978, 1979;

1980; 1986; Awada et al. 1975). However, none have investigated the effect of Si on gas exchange, and plant growth and development and crop yields of papaya under well-watered conditions. The objective of this experiment was to determine the effect of bi-weekly soil drench

-1 -1 of 0, 500, and 1,000 kg K2SiO3 (16% Si) ha year (Appendix G) on transgenic papaya plant growth and development, gas exchange, nutrient uptake and yield under well-watered field conditions.

Materials and Methods

Research Site and Location

A 0.13 ha transgenic X17-2 x T5 papaya planting was established at the University of

Florida’s Tropical Research and Education Center (UF-TREC), Homestead, FL. (Lat. 25º25’N;

Long. 80º 25’W) on September 10, 2012. The Florida Agricultural Weather Network weather station located at UF-TREC was used to monitor weather conditions (Migliaccio et al., 2010;

FAWN data: http://www.fawn.ifas.ufl.edu).

Plant Selection and Crop Management

To eliminate the potential detrimental effect of papaya ringspot virus (PRV) on plant performance, the PRV resistant X17-2 x T5 (Accession 2562) transgenic papaya line was used

(Davis and Ying, 2004; Davis et al., 2003, 2004). Seeds were planted on 8, 18 and 26 June 2012 into trays (LM 21 seedling tray 65/CA, Winfield Solutions, LLC, Homestead, FL) with individual cells filled with an artificial soil media (FARFAR Promix BX, Premier Horticulture,

93 Inc., Quakertown, PA) which contained 75%-85% Canadian sphagnum peat moss, 15% perlite and vermiculite, 10% pine bark, and 5% dolomitic and calcitic limestone as a pH adjuster

(Appendix B and C). Papaya seedlings were manually watered every three days to ensure uniform and vigorous crop growth and fertilized biweekly with 20-20-20 (20-20-20 Multi-

Purpose WS Plant Food, Plant Food Inc., Vero Beach, FL).

An area of 0.33 ha was molboard plowed and disked (leveled) twice, then, 24 beds 1 m wide by 15 cm tall by 15.2 m long were constructed, covered with black plastic mulch (IP VIF

1.25 m x 500 m, Winfield Solutions, LLC, Homestead, FL) under which four drip lines

(EURODRIP, 0.48 L h-1, 20.3 cm, Lovett Irrigation, Homestead, FL) were laid, two for irrigation and two for fertigation. Once papaya seedlings reached 15-20 cm tall, they were planted in the field, on September 10, 2012.

The study plot consisted of 24 rows of raised beds with seven papaya plants per row.

Plants were spaced 2.1 m in-row and 3.6 m between-rows (1,279 plants per hectare). Plants were fertigated (irrigation plus fertilizer) daily for 45 minutes with 4-0-8 [4% N (0.49% NH4-N and

3.51% NO3-N), 0% phosphorus (P2O5) and 8% potassium (K2O)] (4-0-8 liquid fertilizer, Helena

Chemical Co., Fort Pierce, FL). The rate of 4-0-8 increased as plants aged: from planting to 90 days (3 months), 0.28 kg day-1; from 120 to 240 days (4 to 8 months), 0.56 kg day-1, and from

270 days (9 months) onward 1.12 kg day-1. Secondary (Mg) and minor plant nutrients i.e., Mn,

Zn, B, and Mo were foliarly applied at 146 mL KeyPlex-350 ha-1 (KeyPlex Co., Winter Park,

FL) on an as needed basis (Crane, 2005; Migliaccio et al., 2010). Chelated iron (Sequestrene®-

138 6% iron (EDDHA form, Becker Underwood – BASF Corporation, Ames, IA) was applied monthly through the fertigation system and the rate increased as plants aged: from planting to 90 days (3 months), 0.03 kg day-1 (0.91 kg month-1); from 120 to 210 days (4 to 7 months), 0.5 kg

94 day-1 (1.36 kg month-1), and from 240 days (8 months) onward 0.6 kg day-1 (1.82 kg month-1).

The irrigation was managed by automated switching tensiometers (Irrometer Company Inc.,

Riverside, CA) set to initiate an irrigation event at 7 kPa and timed to apply enough water to bring the soil to field capacity (Migliaccio et al., 2010). In-row weed control was performed manually and between-row managed by tractor with a rototiller.

® The silicon solution was prepared with AgSil (K2SiO3, 16% Si; PQ Corporation,

Chester, PA) by adding 1,600 and 3,200 g in 121 L of water (32 gallons), respectively, and then injected through the fertigation system biweekly from January 15 to December 17, 2013 (25 applications total). Treatments included: no silicon application (control), 500 and 1,000 kg Si

-1 -1 ® ha year . To balance the potassium nutrition of the AgSil , potassium sulfate (K2SO4) [Ultra- sop K2SO4, SQM Europe N.V., Antwerp, Belgium] was drenched to the control at 2,020 g per

0.13 hectare diluted in 121 L of water. To balance the sulfate applied with the potassium sulfate applications of elementary sulfur (Liquid Sulfur Six®, Tracite, Helena Chemical Co., Collierville,

TN or Kolla Sulfur® 6 Micronized Flowable, Cromartie Agricultural Chemicals, Inc., Albany,

GA) was applied to the silicon treatments at 350 and 700 mL per 0.13 hectare, diluted in 121 L of water, respectively, from January 14 to December 17, 2013. Nitrogen (Urea 46%, Brokerage

International Ag Labs, Fairmont, MN) was applied through the drip irrigation system

(fertigation) to the experimental plot from November 1 to December 17, 2013 at 1,135 g per 0.13 hectare diluted in 75 L of water.

Insect pests and diseases were monitored weekly by scouting. Insect pests were controlled through a biological control program. To control eastern lubber grasshopper (Romalea microptera Beauvois) three applications of Nolo Bait (Nosema locustae Canning) (BICONET,

Brentwood, TN) mixed with canola cooking oil were applied by placing the mix in petri dishes

95 in-rows and around the field study plot. Two-spotted spider mites (Tetranychus urticae Koch) were controlled by two releases of the spider mite predator (Stethorus punctillum Weise)

(Rincon-Vitova Insectaries, Inc., Ventura, CA) and a predatory mite (Amblyseius swirskii Athias-

Henriot) [Koppert Biological Systems, Inc., Howell, MI]. To control papaya mealybugs

(Paracoccus marginatus Williams and Granara de Willink, Pseudococcidae, Heymons), Impede®

(potassium salts of fatty acids, Dow AgroSciences, Indianapolis IN) and Mycotrol® (Beauvaeria bassiana Strain) (GHA, Laverlam International Corp., Butt, MT) were sprayed on an as needed basis. To control the papaya fruit fly (Toxotrypana curvicauda Gerstaecker), styrophoam balls were painted green, inserted on to a 30 cm stiff wire then brushed with Tangle-Trap Adhesive

(BioQuip Products, Co., Rancho Dominguez, CA) and then inserted in the papaya plant trunk just below the fruit column. To control anthracnose (Colletotrichum gloeosporioides Penz.) foliar fungicides [Manzate® (Northwest Crop Protection, LLC., Bonners Ferry, ID) and Dithane®

M-45 (Dow AgroSciences, Indianapolis, IN)] were applied on an as needed basis. Powdery mildew (Oidium caricae-papayae J.M. Yen) was controlled with foliar sulfur applications

(Liquid Sulfur Six®, Tracite, Helena Chemical Co., Collierville, TN) on an as needed basis.

Plant measurements

The sex of each plant was determined upon flowering (about 120 days after planting) on

Dec. 16 and 24, 2012, and January 18, 2013. Bisexual and female papaya plant height and trunk diameter were measured monthly. Height was measured from the soil surface to the height of the last emitted leaf by using a tape measure (Stanley PowerLock 8m/26’ Tape Measuring, Northern

Tool & Equipment, Burnsville, MN). Trunk diameter was measured 10 cm above the soil surface by using an electronic digital caliper (Caliper Marathon 0-200 mm, Marathon Watch Company

LTD, Richmond Hill, Ontario, Canada).

96 Leaf area of bisexual and female papaya plants was determined on a subset of treated plants (one plant per treatment per row, eight plants per treatment) at the commencement of treatments (January 14 to April 20, 2013) and about 6 months later (June 1 to August 24, 2013).

One to two young terminal leaves were tagged per plant and leaf lamina length and width recorded biweekly until mature. The specific leaf area (SLA = leaf area/dry leaf weight) was calculated as per Beadle’s methodology (Beadle, 1985).

The effect of K2SiO3 application rate on mature leaf abscission was measured during three periods (January to June, June to August, and August to November, 2013) by tagging ten leaves per bisexual and female plant (acropetally i.e., starting with the leaf closest to the ground and tagging additional leaves toward the apex) per row for a total of eight bisexual and female plants per treatment. The number of leaves abscising was monitored biweekly.

Plant leaf gas exchange measurements

Leaf gas exchange was measured on bisexual and female papaya plants from January 14 to September 3, 2013. Leaf gas exchange: transpiration (E), stomatal conductance of water vapor

(gs), and net CO2 carbon assimilation (A) were measured biweekly on eight plants per treatment per gender (bisexual and female, respectively) on the two most recently matured, sun-exposed leaves per plant one week after silicon applications using a portable CO2 gas exchange analyzer machine (ADC-LCA3, The Analytical Development Co. Ltd, Hoddesdon, England). The equipment was set up to measure gas exchange at a photosynthetic photon flux (PPF) of 1000

-2 -1 -1 μmol m s using a halogen lamp, a reference CO2 concentration of 350 μmol mol and an air flow in the leaf cuvette of 200 mL min-1. For statistical analysis, values from the two measured leaves per plant were averaged to provide one value per plant. Data was recorded between 8 am to 2 pm.

97 Photosynthetic pigment analysis (leaf greenness) was determined for bisexual and female papaya plants as an indicator of leaf chlorophyll content (Torres-Neto et al., 2002; Kiggundu et al., 2011). Leaf chlorophyll content was determined with a portable chlorophyll SPAD-502 meter (Minolta Camera Co., Osaka, Japan) and expressed as SPAD units (Torres-Netto et al.,

2002). Three SPAD readings were recorded from the most recently matured fully sun-exposed leaf for one plant per treatment per row, eight plants per treatment. Values from the three SPAD values per leaf were averaged for statistical analysis.

Soil sampling, processing and nutrient analysis

A set of six soil samples were collected from the field at the beginning and termination of the investigation. Soil samples were collected at 10 cm depth, sieved using 20 mm mesh sieve and dried at ambient temperature for lab analysis of soil pH in water [1:2 V/V (soil:water)]

(Hanlon et al., 1998), and organic matter by the LOI method (Wright et al., 2008). Total N was determined by Wolf digestion method (Wolf, 1982a) and total P, K, Ca, Mg, Fe, Mn, B, Zn, Cu, and Al were extracted with HCl digestion method (Wolf, 1982a) and determined using

Inductively Coupled Argon Plasma Spectrophotometry (Perkin Elmer Optima 5300

Spectrometer, Conquer Scientific Lab Equipment, San Diego, CA). Silicates in soil were measured by autoclave-induced digestion (AID) method (Elliot and Snyder, 1991).

Soil available nutrient concentrations of P, K, Ca, Mg, Fe, Mn, B, Zn, Cu, and Al were determined by Inductively Coupled Argon Plasma Spectrophotometry after Mehlich III extraction method (Mehlich, 1938; Alva, 1993). Available N (NH4-N and NO3-N) were determined by KCl extraction method (Wolf, 1998a). However, available sulfur (SO4-S) was determined by ammonium acetate extraction method (Rehm and Caldwell, 1968) and available

Si by acetic acid extraction method (Elliot and Snyder, 1991).

98 Analysis of tissue sample for silicon available content

Beginning 120 days after transplanting (January 14, 2013) to the end of the field experiment (December 31, 2013) leaves from bisexual and female papaya plants were sampled monthly (one most recently matured leaf per plant per treatment per row; eight leaves per treatment, respectively), separated into petiole and leaf lamina and their fresh and dry weight recorded (Scale Denver Instrument, Denver Instrument Company, Denver, CO). Plant tissue samples were rinsed with dionized water and then submerged into a Liquinox soap solution (30 mL Liquinox diluted into 2,500 mL dionized water) and rinsed with dionized water for 1 to 2 minutes, then dipped into a dilute HCl (12 N) solution (30 mL HCL diluted into 2,500 mL dionized water) and rinsed again with dionized water. Tissue samples were dried on a paper towel and placed into paper bags (Paper Grocery Bags 25#, AJM Packaging Corp., Bloomfield

Hills, MI ), and dried in an oven at 70oC for five days (Wisconsin Oven Modell 600 and 800,

Memmert, Wisconsin Oven Corporation, East Troy, WI). Dried tissue samples were milled to pass a 20 mm mesh sieve with stationary mill with rotory knives (Thomas-Wiley Intermediate

Mill, Thomas ScientificTM, Swedesboro, NJ). The milled samples were put into a 118 mL (4 oz.) plastic sample bags with puncture proof tabs (Nasco Whirl-Pak®, Fort Atkinson, WI). Ground papaya petiole and leaf lamina tissue samples were sent to the Soil and Water Laboratory of the

University of Florida’s Everglades Research and Education Center (UF-EREC) in Belle Glade,

FL for Si analysis. The Si concentration was determined by using acetic acid extraction method after Autoclave-Induced Disgestion (Elliot and Snyder, 1991). Plant petiole and lamina P, K, Ca,

Mg, Fe, Mn, B, Zn, Cu, and Al nutrient concentrations were determined by Inductively Coupled

Argon Plasma Spectrophotometry after extracted with Mehlich III extraction method (Mehlich,

1938; Alva, 1993). Available N (NH4-N) was determined by KCl extraction method (Wolf,

1982b).

99 Fruit yield

Fruit yields were determined after 17 and 22 potassium silicate applications on August 27 and October 7, 2013 (150 and 276 days after treatment, respectively) by placing a flag between the highest set fruit on the trunk and the lowest flower and then counting all the set fruit on the seven plants per row and per treatment. The average fresh weight of 18 mature fruit per treatment was used to calculate the mean weight of fruit per treatment and production per hectare

(Appendix H).

Statistical Analysis

Treatments were arranged in a randomized complete block design with a factorial 3 x 2 arrangement (3 silicon treatments with 2 genders; 8 rows per treatment and seven plants per row). The statistical analysis was conducted using SAS 9.1 statistical software (SAS Institute,

Cary, NC), and the PROC GLM, PROC MEAN STDERR, PROC REG for ‘Linear Regression’, and PROC REPEATED MEASURES procedures. These statistical procedures generated least- square means ± standard error that was tested for significant differences by LSD’ Studentized test, p≤0.05. The parameters for the study were evaluated by sampling dates using a two-way

ANOVA. The experimental unit was whole plants per row for the developmental parameters and for physiological parameters was a single individual plant per row and per treatment.

Results and Discussion

Ambient Air and Soil Temperatures and Rainfall

The environmental conditions from January 1, 2012 to January 1, 2014 were recorded by the Florida Automated Weather Network station (2012-2014) located 300 m away from the experimental planting at the TREC-UF are shown in Appendix D, E and F. Mean monthly air temperature was 24°C, with the minimum of 0°C on one brief occasion and a maximum of 39°C

(Apendix D and E). Mean soil temperature was 25.5°C, with a minimum of 19°C and a

100 maximum of 30.5°C. The average rainfall was 20.7 cm per month (FAWN, 2014) [Appendix D and F].

Plant Growth Measurements

At about 120 days (4 months) in the field plants began to flower and 67% of the plants were bisexual and 33% female. There was no significant effect of plant sex on plant height and trunk diameter among K2SiO3 treatments over an eleven month period, therefore the data was combined. Biweekly soil applications of K2SiO3 at three rates had no significant effect on plant height and trunk diameter (Table J-1 and J-2). Similarly, silicon slag soil applications had no significant effect on papaya plant height and diameter under Hawaiian conditions (Adlan, 1969).

Likewise, Si applications did not significantly affect plant growth of other fruit crops such as

‘Valencia’ orange and ‘Marsh’ grapefruit (Citrus x paradisi Macfad.) [Matichenkov et al., 2001], banana (Musa x paradisi L. cv. ‘Grande Naine’) [Henriet et al., 2006], and tomatoes (Solanum lycopersicum L.) [Matichenkov and Bocharnikova, 2004]. As expected as papaya plants matured there was an increase in plant height and trunk diameter such that after 3.5 months in the field plant height ranged from 58 cm to 61 cm and after 16 months in the field ranged from 193 to 196 cm in height (Table J-1). Trunk diameters were ranged from about 48 cm to 126 cm after 3.5 months in the field and 125 cm to 126 cm after 16 months (Table J-2).

In general, leaf area of bisexual and female lamina did not significantly increase with

K2SiO3 rate (Table J-3, J-4, J-5, and J-6). However only for bisexual plant leaf lamina during the

14 January to 20 April 2013 period was there a consistent significant increase in leaf area with

2 increased K2SiO3 rate (Table J-3). However, low r values for bisexual plant lamina (14 January to 20 April 2013 period) indicate other factors influenced the increase in leaf area. Ultimate leaf areas were slightly greater at maturity during the spring period for bisexual plants (600 to 867 cm2) [Table J-3] and female plants (649 to 846 cm2) [Table 4-4] as compared to the summer for

101 bisexual (626 to 711 cm2) [Table J-4 and J-5] and female plants (699 to 793 cm2) [Table J-4 and

J-6]. In contrast, Henriet et al. (2006) reported mature banana leaf lamina area increased with

. Na2SiO3 5H2O rate under hydroponic controlled conditions. Similarly, leaf area of several bamboo species [Phyllostachys pubescens (Carrière) Mazel ex J. Honz; Pyllostachys bambusoides (Siebold & Zucc.) and Sasa veitchii (Carrière) Rehder] increased with Si application rates (Motomura et al., 2004; 2008).

Plant sex type had no significant effect on the amount of leaf abscission at any sampling date and therefore data was combined (Table J-7, J-8, and J-9). Potassium silicate application rate had no significant effect on the number of abscised leaves at any sampling date. Leaf abscission was greatest during late April and mid-May (Table J-7), mid-July and mid-August

(Table J-8), and mid-September to late October (Table J-9) for all treatments.

Potassium silicate applications had no significant effect on bisexual and female plant leaf petiole and lamina fresh weights (Table J-10, J-11, J-12 and J-13). Bisexual plant petiole fresh weights ranged from 25 to 135 g whereas female plant fresh petiole weights ranged from 25 to

115 g (Table J-10). Dry weight of bisexual plant petioles ranged from 13 to 35 g whereas female plant dry petiole weight ranged from 12 to 29 g (Table J-12). Leaf lamina fresh weights of bisexual plants ranged from 29 to 148 g whereas female lamina fresh weights ranged from 30 to

112 g (Table J-11). Dry weight of bisexual and female plant leaf lamina ranged from 16 to 41 g and 15 to 34 g, respectively (Table J-13). Similarly, the effect of increased Si-slag application rates on papaya leaf petiole and lamina dry weights of papaya grown under Hawaiian conditions were inconsistent (Adlan, 1969). In contrast, Henriet et al. (2006) reported increased fresh and dry banana leaf weight with increased solution culture silicon rates; it was not specified if this was for the leaf petiole and lamina tissue or lamina alone. Miyake and Takahashi (1986) reported

102 increased strawberry leaf fresh and dry weight of new leaves after plants were supplied with silicon in solution culture. Matichenkov et al. (2001) reported increased ‘Valencia’ orange and

‘Marsh’ grapefruit fresh and dry leaf weight with increased Si-slag rates. Similar results were reported for rice, barley, green onion (Allium cepa L.), and Chinese cabbage (Bok-choi)

[Brassica rapa sp. Chinensis L.] plants supplied with silicon (Okuda and Takahasih, 1961a;

1961b). However, no increase in leaf fresh and dry weights occurred in tomato and radish

(Okuda and Takahashi, 1965).

Plant Gas Exchange

In general K2SiO3 applications had no consistent significant effect on stomatal conductance (gs) of bisexual and female plants (Table J-14 and J-15). Stomatal conductance was lower (0.2 to 1.0 mol m-1s-1) during the winter-early spring months (i.e., January to May) compared to summer months (i.e., June to September) when values ranged from 1.0 to 1.3 mol m-1s-1.

In contrast, transpiration (E) rates generally decreased with increasing K2SiO3 rates for bisexual and female papaya plants (Table J-16 and J-17). Transpiration rates were generally

-1 -1 lower during winter-spring (4.5 to 10.3 mmol H2O m s ) than summer (7.4 to 10.2 mmol H2O m-1s-1). Similarly, Migliaccio et al. (2010) reported lower E values during late winter-early spring than during summer and early fall. Stomatal conductance values were within the range reported by Migliaccio et al. (2010) and Jeyakumar et al. (2007) for well-watered papaya plants.

In general net CO2 assimilation (A) significantly increased as K2SiO3 rate increased and

-1 -1 were higher during summer (6.4 to 10.7 µmol CO2 m s ) than during winter-spring period (4.2

-1 -1 to 9.7 µmol CO2 m s ) [Table J-18 and J-19]. In general, Migliaccio et al. (2010) reported

-1 -1 moderately to substantially higher A values (12.1 to 24.3 µmol CO2 m s ) for transgenic bisexual papaya plants grown in the same soil conditions as the current investigation (no silicon

103 applications). Similarly, higher A values were reported for four papaya cultivars grown in sandy

-1 -1 -1 -1 loam (20.8 to 25.8 µmol CO2 m s ) and clay soil (12.7 to 16.8 µmol CO2 m s ) in Brazil

(Campostrini and Yamanishi, 2001). Marler and Mickelbart (1998) and Jeyakumar et al. (2007) reported higher A values for well-watered container-grown papaya plants. The lower A rates may be due to differences among genotypes.

No significant differences were found among bisexual and female plant leaf temperatures and sub-stomatal conductance and among treatments (data not shown). Bisexual plant leaf temperatures ranged from 29oC to 34oC and female plant leaf temperatures ranged from 28oC to

34oC. Average air temperatures during the 2012-2013 at the trial location was consistent with the optimum temperature for growing papaya (21oC to 33oC) reported by Marler et al. (1994) and

Campostrini and Glenn (2007).

SPAD values among bisexual and female papaya plant leaves differed (Table J-20 and

J-21). In general, SPAD values significantly increased with K2SiO3 rate for both sex types.

Interestingly, there were similar dates (e.g., March 9, 23; May 4, and June 1) among bisexual and female plants when no significant differences were found among SPAD values due to K2SiO3 applications. For bisexual plants SPAD values ranged from 37.0 to 47.2 whereas for female plants SPAD values ranged from 36.4 to 43.4. These values are within the range reported for

Solo and Formosa type papaya plants grown under commercial conditions in Brazil (Torres-

Netto et al., 2002). The increase in SPAD values and generally higher A rates for plants supplied with K2SiO3 suggests K2SiO3 had a positive effect on plant photosynthetic capacity.

Soil, Plant Petiole, and Lamina Tissue Nutrient Content

Soil nutrients

The soil pH (8.1), percent organic matter content (6.5%), and total and plant available nutrient content pre-treatment of the Krome very gravelly sandy loam soil (loamy-skeletal,

104 carbonatic, hyperthemic lithic Udorthents) was within the limits reported previously by Noble et al. (1996), and Rao and Li (2003) [Table J-22[. Krome soil is high in Ca content but generally low for all other nutrients (e.g., N, P, K, Mg, Mn, and Fe). Total Si content is low and available

Si very low (Chen et al., 2000; Li. 2001; Wang et al., 2009),

Potassium silicate (K2SiO3) applications had no effect on soil pH (about 8.0) [Table J-22 and J-23). Although, papaya grows well on many soil types, pH in the range of 6 to 7 is preferred

(Chia, 1989). Previously, Ikeda and Si (1976) reported that papaya seedlings can grow well in a pH range from 4.5 to 7.5 and Nakasone and Paull (1998) reported that soils with a pH range from

5 to 7 are favorable for commercial papaya production. However, Manshardt and Zee (1994) reported that the center of origin for papaya is characterized by calcareous soils with high pH.

Awada et al. (1975), Samson, (1986), and Marler et al. (1994) indicated that the optimum pH for papaya commercial production ranged from 5.5 to 7. Additionally, Marler (1998) reported that papaya seedlings grown under complete nutrient solution were not affected by pH within a range of 4 to 9. Adlan (1969) confirmed that papaya grew well in soil with pH from 5 to 7 if essential plant nutrients were not limiting. He concluded that Si-slag applications had no effect on soil pH of a Kapaa gravelly silty clay soil. Savant et al. (1999) reported that the solubility of monosilicic acid (H4SiO4) increased at or above pH 9. Supporting this finding, Beckwith and Reeve (1964) and Drees et al. (1989) reported that sesquioxides, especially Al oxides, are largely responsible for much of the capacity of soils to absorb soluble Si, with the maximum capacity between pH 8 and 10.

There was no consistent effect of K2SiO3 applications on soil organic matter content over a twelve month period; %OM ranged from 6.4 to 7.3% (Table J-22 and J-23). Sadzawka and

Aomine (1977) reported that humus protected soil silicon from dissolution and at the same time

105 prevented silicon soil fixation. In contrast, chemical sorption of metallic cations such as Fe, Mn and Zn to SiO2 may form insoluble soil particle coatings and reduce soil available Si.

Total soil N increased slightly from 1.4 (pre-plant) to 1.9 to 2.1 g kg-1, probably due to frequent fertigation of N during the 12 months of the experiment (Table J-22 and J-23). In contrast, plant available NH4-N increased about 93% and NO3-N decreased 26% regardless of treatment during this period. In general, total soil P did not change due to K2SiO3 applications but available P decreased about 40% (i.e., 0.1 to 0.04 g kg-1) [Table J-22, J-23, J-24 and J-25].

This is in contrast to the findings of Adlan (1969) where soil P content increased with Si application rate. Similarly, total soil K did not change (0.8 g kg-1) but available K increased about 30% regardless of treatment. The decrease in available P and increase in K was probably due to the fertigation of soluble K but no additional applications of P were made during the experimental period.

In general, total soil nutrient content of Mg, Fe, Mn, Cu, B, and Zn decreased slightly from pre-planting to twelve months later (Table J-22 and J-23). However, there was no change in soil available Mg, Mn, and Cu content. In contrast, there was a substantial increase in soil available Fe, B and Zn. Pre-plant soil Ca content was much higher (232 g kg-1) compared to

-1 after 25 K2SiO3 applications (about 31.5 g kg ) regardless of K2SiO3 application rate (Table J-22 and J-23). However, pre-plant soil available Ca content (21 g kg-1) was about 38% higher than

-1 values (12.4 to 15.0 g kg ) after K2SiO3 applications (Table J-22 and J-24). Pre-plant total soil

Al was about 87% higher than total soil Al after 25 K2SiO3 applications; however, there was no change in soil available Al. The variation in soil nutrient content after K2SiO3 applications of papaya plant grown in a Krome very gravelly sandy soil may be due the soil applications of N,

106 K, Fe, and S, foliar applications of minor nutrients and plant uptake during this time (Cunha and

Haag, 1980; Watson, 1997).

Total soil Si ranged from 32.0 g kg-1 pre-planting to 27.4 to 35.1 g kg-1 after 25 application of K2SiO3 (Table J-22 and J-23). In contrast, plant available soil Si increased 81 to

91% from 0.03 g kg-1 pre-planting to 0.16 g kg-1 (non-treated control) to 0.25 g kg-1 (500 kg

-1 -1 -1 -1 -1 K2SiO3 ha year ) to 0.35 g kg (1,000 kg K2SiO3 ha year ) after 25 K2SiO3 applications (Table

J-22 and J-24). Similarly, Adlan (1969) reported soil extractable Si content increased with increased slag-Si application rate for a Kapaa gravelly silty clay soil under Hawaiian growing conditions. However, there was no differentiation among total and plant available soil Si content.

Plant leaf petiole nutrients

In general, leaf petiole N, Ca, Mg, Mn and Fe contents were similar for bisexual and female X17-2 x T5 papaya plants (Table J-25 and J-26). Bisexual and female leaf petiole P and

Si content increased significantly with K2SiO3 application rate. Similarly, ‘Puna’ Solo papaya leaf petiole P and Si content increased with Si-slag application rate under Hawaiian growing conditions (Adlan, 1969). In contrast, leaf petiole K and Zn content was higher for X17-2 x T5 bisexual plants compared to female plants but, there were no consistent significant differences among K2SiO3 treatments. There were no consistent significant differences in bisexual and female leaf petiole Mg content (Table J-25 and J-26). Bisexual plant Mn leaf petiole content significantly decreased with K2SiO3 rate whereas there was no significant difference in Mn leaf petiole content for female plants (Table J-25 and J-26).

Plant leaf petiole and lamina silicon

There was no significant effect of K2SiO3 application rate on leaf petiole and lamina Si contents of bisexual and female plants; overall leaf lamina Si content was substantially greater than leaf petiole content (Table J-27, J-28, J-29 and J-30). There was no trend for leaf petiole and

107 lamina Si content to increase with the number of K2SiO3 applications (25 applications total). This may have been due to the sampling of the most recently matured leaves at each sampling date as opposed to sampling the most oldest mature leaves. The r2 values for petioles and lamina Si content and K2SiO3 application rate were generally low to moderately low and highly variable among sampling dates. Values ranged from 0.001 to 0.798 for petiole silicon content and 0.01 to

0.87 for leaf lamina silicon content, respectively, indicating other factors than K2SiO3 application rates influenced Si uptake.

In general, bisexual plant leaf petiole Si content increased from January through March then decreased from April through June then increased again from July through November whereas female plant leaf petiole Si content was highest during January then dramatically decreased during February but remained stable from February through November (Table J-27 and J-28). In contrast, there was no trend in bisexual and female leaf lamina Si content from

January through November (Table J-29 and J-30). Leaf petiole Si content of bisexual and female plants during November was below plant available soil Si drench (Table J-24, J-27 and J-28). In contrast, leaf lamina Si content of bisexual and female plants had positive correlation (R=0.61 and R=0.76) between Si content within plant leaf lamina and soil available silicon content

(values of 3.5 (non-Si treatment) to 8.5 times higher than soil available Si content) [Table J-24,

J-29 and J-30]. This contrasts with previous findings in which papaya leaf petiole and lamina Si content were similar except during spring (March) at the highest soil slag-Si application rate; leaf petiole Si content exceeded leaf lamina Si content (Adlan, 1969). This difference among investigations may be due to differences in soil chemistry, genotypic differences, and how silicon was applied (i.e., Si-slag incorporated into the soil versus fertigated liquid Si). In the previous investigation, Si-slag and limestone were incorporated into the soil prior to the

108 investigation and triple superphosphate was incorporated at planting; plants were not irrigated.

The native Kapaa gravelly silt clay was characterized as bauxitic (i.e., very high in aluminum minerals) with a low pH (4.2-5.0), highly drained and highly leached of Si and composed mostly of amorphous iron and aluminum oxides. In contrast, the Krome very gravelly loam soil in the current investigation is characterized by its high calcium carbonate (limestone) content (CaCO3 fragments make up to about 70% of the soil and dominate the cation exchange capacity), high pH (7.3-8.5) and is highly drained. Potassium silicate was applied bi-weekly in liquid form through a drip system.

There was no correlation among total soil Si content and petiole and leaf lamina Si content of bisexual and female plants and no correlation was found among available soil Si content and female plant leaf lamina content (Table J-31). In contrast, there were positive correlations among soil available Si content for bisexual leaf lamina and petiole (R=0.60 and

0.70, respectively) and female leaf petiole content (R=0.54) [Table J-32]. Adlan (1969) reported a similar correlation among Si treatment rate and papaya leaf petiole Si content under Hawaiian conditions.

Fruit number and fruit weight per plant

Potassium silicate applications (17 before the first harvest and 22 before the second harvest) had no significant effect on fruit number, fruit weight and fruit yield per hectare (Table

J-32 and J-33). In general, no correlation was found among total or plant available soil Si content and fruit weight per plant at either harvest (data not shown). The only exception was among available soil Si content and fruit weight per plant during the first harvest (R=0.76). This agrees with previous findings where there was a trend for papaya crop yields (i.e., fruit number and yield) to increase with Si-slag application rates under Hawaiian conditions (Adlan, 1969).

No correlation was found among total leaf lamina or leaf petiole Si content and fruit number per

109 plant for the first and second harvest (data not shown). The correlation among available leaf lamina and petiole Si content and fruit weight were low to very low (Table J-34).

Conclusions

Soil applied K2SiO3 had no significant effect on transgenic bisexual and female papaya plant growth. Plant height and trunk diameter were similar among K2SiO3 treatments over a 12 month period (Table J-1 and J-2). This was similar to the effect of soil incorporated Si-slag on papaya growth under Hawaiian conditions (Adlan, 1969). In general, bisexual and female plant leaf lamina area did not increase with K2SiO3 rate (Table J-3, J-4, J-5 and J-6). Potassium silicate applications had no significant effect on the number of abscised leaves during spring, summer and fall (Table J-7, J-8, and J-9). Fresh and dry leaf petiole and lamina dry weights were not significantly affected by K2SiO3 treatments (Table J-10, J-11, J-12 and J-13).

Potassium silicate had no consistent significant effect on gs whereas E rate decreased as

K2SiO3 rate increased (Table J-14, J-15, J-16 and J-17). In general, A significantly increased with K2SiO3 rate (Table J-18 and J-19). In general, gs values in the present investigation were similar to those previously reported for papaya (Clemente and Marler, 1996; Jeyakumar et al.,

2007; and Migliaccio et al., 2010). However, whereas E rates were similar to those reported by

Migliaccio et al. (201) under identical environmental conditions they were slightly higher than those reported by Jeyakumar et al. (2007) under South India soil (clay-loam) and climatic conditions. Interestingly A rates in the present study were 25% to 50% lower than those reported by Campostrini and Yaminshi (2001), Clemente and Marler (1996) and Migliaccio et al. (2010) but similar to those of Jeyakumar et al. (2007). In general, SPAD values increased significantly with K2SiO3 application rate (Table J-20 and J-21). This along with an increase in A with

K2SiO3 application rate suggests K2SiO3 may affect chlorophyll content and/or photosynthetic capacity of papaya (Al-Aghabary et al., 2004).

110 Plant available Si content of the Krome very gravelly soil increased 81 to 91% after 25 applications of K2SiO3. In contrast, K2SiO3 applications had no effect on soil pH and percent organic matter content (Table J-22 and J-23). However, plant available NH4-N, P and K increased; all probably due to frequent N-P-K fertigation applications (Table J-22 and J-24).

Plant available Fe, Zn and B increased whereas there was no change in available Mg, Mn, and

Cu. Plant available Ca content decreased slightly.

As K2SiO3 application rate increased P nutrient and Si leaf lamina and petiole element content significantly increased (Table J-25 and J-26). However , 25 K2SiO3 applications had no effect on leaf petiole and lamina Si content (J-27, J-28, J-29 and J-30). In addition, there was no correlation among soil available Si content and female and bisexual plant petiole Si content

[Table J-31]. In general, 25 K2SiO3 applications had no effect on leaf petiole N, Ca, Mg, Mn, and

Fe content (Table J-25 and J-26). Potassium silicate applications had no consistent effect on Mn and Zn leaf petiole content. Papaya bisexual and female fruit number per plant had no significant differences after 11 (first harvest) and 20 K2SiO3 applications (second harvest) except for the bisexual fruit number per plant after 20 K2SiO3 applications (second harvest) [Table J-32].

Potassium silicate applications had no significant effect on fruit number, fruit weight and fruit yield after 11 and 22 K2SiO3 applications (first and second harvest) [Table J-33 and J-34].

Similar findings for soil incorporated Si-slag applications to ‘Puna’ papaya were reported under

Hawaiian conditions.

In conclusion, soil applied potassium silicate (K2SiO3) had little to no effect on plant growth, leaf gas exchange, and Si tissue content of X17-2 x T5 papaya. In general, A and SPAD values increased, whereas E decreased with increased K2SiO3 rate Perhaps the effect of K2SiO3 on soil chemistry and/or plant metabolism may require a longer time period to show a consistent

111 effect than investigated here. Future investigation of the effect higher rates of soil applied

K2SiO3 or foliar applications on papaya plant growth, development and crop yields and pest resistance may be warranted.

112 CHAPTER 5 EFFECT OF POTASSIUM SILICATE SOIL APPLICATIONS ON POSTHARVEST QUALITY OF X17-2 x T5 PAPAYA FRUIT

Overview

Papaya (Carica papaya L.) is a member of the Caricaceae, a small dicotyledonous family consisting of six genera of herbaceous and shrubby plants. Papaya is best known for the nutritive value of its fruit, it’s milky latex, which is a source of the proteolytic enzyme papain, and its use in the pharmaceutical industry (Manshardt and Drew, 1998). Most papayas in the commercial export trade are hybrid hermaphrodite types (e.g., ‘Solo’ types from Hawaii and Brazil, and

‘Maradol’ types from Mexico and Belize). In general, these hybrids exhibit a consistent postharvest behavior in contrast to open pollinated seedlings (Nakasone, 1986; Martin et al.,

1987). The principal papayas grown in Florida are ‘Red Lady’, ‘Tainung No. 1’ and ‘Exp 15’.

However, ‘Solo’ types grown in Hawaii and Brazil, and ‘Maradol’ types grown in Mexico and

Brazil are also common in the U.S. market (Crane, 2005).

Papaya is classified as a climacteric fruit with the associated characteristic respiratory and ethylene production pattern, and the fruit are generally picked when the peel exhibits a color change from green to yellow at the blossom end (Nakasone and Paull, 1998; Kader et al., 2002).

In general, papayas are harvested at 5% to 10% color break (i.e., sections of the peel are yellow- green to yellow) to allow time for handling and shipping to their retail destination. In Hawaii, papaya fruit with at least 3% color break reportedly can be expected to meet the state’s grade requirement of 11.5% total soluble solids (TSS) content (Akamine and Goo, 1971). After several days of ripening at room temperature, fruit become almost fully yellow and slightly soft to the touch. When stored at 22°C (72°F), papaya fruit exhibited a climacteric respiratory peak about six days after harvest (Paull and Chen, 1983). As the fruit ripen, the flesh firmness decreases from approximately 240 N to 50 N (An and Paull, 1990). However, peel color, which is used

113 commercially to determine papaya harvest maturity, is not adequate to judge suitability of the fruit for minimal processing such as fresh-cut (Proulx et al., 2005).

Papaya fruit picked at an immature stage (i.e., dark green) will not ripen properly off the plant even though the peel may turn yellow (Wills and Widjanarko, 1995). Green papayas should not be eaten raw because of the proteolytic latex they contain, however green fruit are frequently boiled and eaten as a vegetable, or cooked and served with a myriad of other foods (Morton,

1987; Wills et al., 1998). However, for optimum fresh fruit quality and marketability, the overall peel ground color, size of the fruit, % TSS, internal pulp color, and absence of any external peel damage such as lenticel spots, scars, wounds, and stem rot, are all critically important (Nazeeb and Broughton, 1978). Papaya fruit quality encompasses a combination of peel appearance including freedom from mechanical scarring and decay, semi-firm pulp texture, appealing flavor, and sweetness (Miranda et al., 2003).

Papaya is a popular fruit with high visual appeal, desirable flavor, and sweetness, but its relatively short shelf life can limit its profitability (Chitarra and Chitarra, 1990; Kader et al.,

2002; Chan and Paull, 2008). Mature green to one-half yellow papaya fruit can be stored at 13°C

(55°F) for about three weeks (Sankat and Maharaj, 1997; Kader et al., 2002). Paull et al. (1997) reported that papaya have a shelf life of four to six days under ambient tropical conditions where temperatures ranged from 25°C to 28°C (77-82°F), or up to three weeks at lower temperatures from 10°C to 12°C (50-54°F).

Much postharvest research with ‘Solo’ type papayas has characterized the optimum postharvest handling for this type of papaya (Jones and Kubota, 1940; Orr et al., 1953; Yee et al.,

1970; Akamine and Goo, 1971). Cámara et al. (1993) studied the ripening stages of ‘Solo’ papaya in the Canary Islands, Spain under different controlled storage conditions and concluded

114 that postharvest fruit quality was best evaluated by eight physico-chemical parameters including fruit water content, pulp pH, % TSS, oBrix, acidity, neutral detergent fiber, proteins, and mineral concentrations.

As a climacteric fruit, papaya suffers from high postharvest losses when harvesting treatments and handling techniques are inadequate or inappropriate (Medlicott, 1990). These include extreme and fluctuating temperatures and mechanical injury, which result in fruit with poor appearance, flavor, and nutritional value (Proulx et al., 2005). Optimum storage conditions for Solo-type papayas have been established to be 13°C and 98% relative humidity (RH); storing papayas below 10°C results in chilling injury (Kader et al., 2002, Proulx et al., 2005). Symptoms of chilling injury include pitting, blotchy coloration of the peel and flesh, uneven ripening, skin scald, hard core, water soaking of tissues, and increased susceptibility to decay (Proulx et al.,

2005). Interestingly, papaya susceptibility to chilling injury varies among cultivars; in addition, fruit at the mature-green stage are more sensitive to chilling damage than ripening fruit (Kader,

-1 -1 1997). The respiration rate of unripe papaya fruit is low, ranging from 5 to 8 mg CO2 kg h at temperatures ranging from 7ºC to 13°C (Kader, 2002). Along with it’s climacteric respiratory ethylene production patterns, papaya ripening is associated with biochemical changes including increased soluble pectins, hemicelluloses, and several enzymes associated with cell wall degradation and anthocyanin and fatty acid biosynthesis (Paull and Chen, 1983; Bron and

Jacomino, 2006). During the ripening period, changes in skin color, firmness and flavor improve fruit quality for fresh consumption (Kader et al., 2002). However, changes in fruit color indicate not only the ripeness stage, but also the edibility, and improve simultaneously the visual appearance and sensory quality, thus increasing fruit marketability (Francis 1980; Chitarra and

Chitarra, 1990; McGuire, 1992; Paull et al., 1997).

115 Papaya fruit soften during ripening and this is the major quality attribute used to measure shelf life (Bron and Jacomino, 2006). The main cellular change during ripening that is responsible for pulp softening is the partial breakdown of the fruit cell walls, which become hydrous due to the hydrolysis of intercellular pectins (Tilgner, 1971; Jellinek, 1985; Brummell,

2006). Cell membrane integrity and cell wall constituents (e.g., calcium content) affect the rate of fruit peel and pulp softening (Campostrini et al., 2005). Fruit texture is also an important factor in determining fruit quality, and fruit pulp that is too hard, chewy or tough is not marketable (Stone and Sidel, 2004; Meilgaard et al., 2006; Sims, 2010).

Throughout the papaya production and marketing channels efforts are made to maintain optimum fruit firmness and peel color because papaya quality is assessed by consumers using fruit appearance and firmness, rather than flavor and odor intensity. Therefore, firmness is an important attribute of papaya, used as a harvest indicator for growers and researchers, as well as a quality indicator by inspectors, buyers, retailers, and consumers (Kader, 1997; Paull et al.,

1997; Miranda et al., 2003; Proulx et al., 2005; Bron and Jacomino, 2006).

Fruit quality assessments usually involve measuring flesh firmness using a penetrometer, which uses a probe with either a flat or convex tip that is driven into the flesh, and the maximum force is recorded (Magness and Taylor, 1925; Voisey, 1977; Blanpied et al., 1978; Brown and

Bourne, 1988; Mitcham et al., 1998; Kohyama et al., 2009). A penetrometer measures fruit firmness by measuring the force-deformation response from gradual compression resistance up to fruit tissue failure or reaching of the bioyield point (Clayton et al., 1998). Penetrometer testing, sometimes called “puncture” testing, has been used by many researchers to evaluate fruit firmness and pulp texture after peel removal in several crops like cherry [Prunus campanulata

(L) Maxim] (Mitcham et al., 1997), cucumber (Cucumis sativus L.) [Suojala-Ahlfors, 2005;

116 Kohyama et al., 2009], pear (Pirus communis L.) [Slaughter and Thompson, 2007], avocado

(Persea americana Mill.) [Tesfay et al., 2011], and papaya (Bron and Jacomino, 2006).

Papaya fruit harvested at different stages of maturity or ripeness and stored at 23°C and

80 to 90% RH were assessed for firmness during postharvest ripening using a digital penetrometer (Bron and Jacomino, 2006). As papaya fruit harvest maturity advanced, pulp firmness declined. After two days of storage, papaya fruit that had been harvested at stage 0

(totally green) or stage 2 to 3 (25 to 50% yellow color) had lost 39% and 60% of initial firmness respectively. Nevertheless, no significant differences were determined due to high variation in fruit firmness (CV=25%) [Bron and Jacomino, 2006]. In a study using finger pressure to assess fruit firmness, pulp firmness of papayas harvested at color break was considered not acceptable for marketing after two to three days storage at 20oC, but in contrast, fruit stored at 15oC were acceptable for as long as seven days (Proulx et al., 2005).

Fruit firmness is an important quality attribute of papaya because of its effect on postharvest storage or shelf life and for marketing purposes (Clayton et al., 1998). There are numerous devices used for measuring fruit firmness, some of which may have commercial application for the papaya industry. These include the Instron Universal Testing Instrument

(Norwood, MA), and the Texture Technologies Texture Analyzer (Hamilton, MA), the

Momentum Transfer Generator (MTG) developed at Washington State University (WSU), the

FirmTech 1 from Michigan State University (MSU), the Low Mass Impactor (LMI) developed by the University of California at Davis, the UC Firmness Tester (also marketed as the

AMETEK penetrometer), the Impactor Deceleration developed by Sinclair Systems International

(Fresno, CA), the Acoustic Transmission Decelerator developed by the Aweta-Autoline

Company (Fresno, CA), and the Durometer (Rex Gauge Co., Buffalo Grove, IL). However, the

117 Instron Universal Testing Instrument is the most widely accepted device used because of its reliability and accuracy (Mitcham et al., 1997; Clayton et al., 1998; Mitcham et al., 1998;

Slaughter and Thompson, 2007).

The above devices measure fruit firmness using the force-deformation response from gradual compression. There are two classifications, non-destructive and destructive. The MTG,

LMI, FirmTech 1, Impactor Deceleration, and Acoustic Transmission Deceleration were developed for commercial applications. These are non-destructive fruit firmness sensors that interface with computers. Their disadvantage is that they cannot be used in the field. The

Durometer and UC Firmness Tester/Ametek Penetrometer may be used in the field however the

Penetrometer is a destructive testing device. The Instron and the Texture Analyzer are the most commonly instruments used in research to measure fruit texture, and are sensitive and reputable research instruments that eliminate much operator error and allows not only maximum force values determination, but can also provide a pulp texture profile when using attachments that measure shear and extrusion forces in addition to force-deformation (Mitcham et al., 1996).

The shear-blade method refers to the action of applying force to cut plant tissue (e.g., peel and pulp) into two separate pieces and it is useful for measuring the textural properties of fleshy fruit and vegetable tissues. This type of attachment for the Instron and Texture Analyzer basically consists of a thin blade that fits a triangular opening in a slotted base so that, as the blade moves through the fruit sample and into the slot, the tissue is first compressed and then cut into two pieces and the maximum force for cutting the tissue is recorded (Waldron, 2004).

Additionally, in the simple compression-extrusion test, force is applied through a plunger to compress the food sample in the test compartment until it is crushed and flows through the gap between the plunger and the test compartment. However, this method is considered to be a shear

118 device method rather than a compression device, and it is more popularly used for processed products than for fresh fruits and vegetables (Lu and Abbott, 2004). Mitcham et al. (1996) indicated that the shear and extrusion methods can be used for determining the texture of soft fruits such as papaya, pear, avocado, tomato (Solanum lycopersicum L.), cherry, grape (Vitis vinifera L.), strawberry (Fragaria x ananassa Duchesne), and mango (Mangifera indica L.).

Fauteux et al. (2005) reported that silicon (Si) forms a cuticle-Si double layer in plant tissues (e.g., leaf lamina, fruit peel). Postharvest dip applications of K2SiO4, Nontox-Silica

(NTS), Ca2SiO4, and Na2SiO3 to avocado fruit increased Si concentration in the exocarp rather than the mesocarp with increased Si rates (Kaluwa et al., 2010, 2011). However this seemed to increase fruit firmness due to higher Si deposition in the exocarp which may produce fruit with a higher ability to withstand long-term storage. Thus, it seems possible that supplemental Si applied to plants will be deposited in the fruit tissues during development and result in textural differences.

Silicon application to fruits and vegetables has been reported to improve fruit quality by maintaining fruit firmness, lowering respiration rate (reduces CO2 production), reducing ethylene evolution, increasing the stress-relieving ability of the fruit, producing fruit with a higher ability to withstand long term storage, and prolonging shelf life; increasing TSS and vitamin content, fruit peel thickness, sugar content, and decreasing the severity and incidence of postharvest decay diseases in several crops [e.g., avocado, watermelon [Citrullus lanatus var. lanatus

(Thunb.) Matsum. & Nakai], tomatoes, strawberry, jujube (Ziziphus jujube Mill.), sugarcane

(Saccharum officinarum L.) [Takahashi et al., 1990; Ma and Takahashi, 2002; Matichenkov and

Bocharnikova, 2004; Tian et al., 2005; Bekker et al., 2007; Snyder et al., 2007; Kaluwa et al.,

119 2010; Bosse et al., 2011; Kaluwa et al., 2011; Toresano et al., 2012]. Despite of all these benefits, increases in quality of fruit and vegetable products remain debatable.

Increase in fruit weight has also been reported for Si-treated cucumbers and tomatoes

(Voogt and Sonneveld, 2001; Ma and Takahashi, 2002). Specifically, Toresano et al. (2012) reported significant differences occurred in watermelon pulp firmness for the Si (H4SiO4) treatment compared to the non-Si control. However, sporadic reports indicated that these texture analyzers have not been used to measure textural attributes of fruit that had received large amounts of Si.

There have been a number of investigations into the effect of Si applications on the postharvest quality of agronomic crops such as rice and corn (Korndörfer and Lepsch, 2001; Ma and Takahashi, 2002). In general, preharvest Si applications improved rice grain strength and corn kernel (Zea mays L.) color. Microbial biocontrol combined with Na2SiO3 proved to have positive effect on controlling postharvest diseases caused by Penicillim expansum Link. in sweet cherry cv. ‘Hongdeng’, Monilinia fructicola, (G. Winters) Honey in peach [Prunus persica (L.)

Barsch], and Alternaria alternata (Fr.) Keissl. in jujube fruits (Tian et al., 2005; Tian et al.,

2007). Potassium silicate applied to lemon fruit [Citrus lemon (L.) Burm. f.], reduced postharvest disease caused by Penicillium digitatum (Pers.) Sacc. (Abraham et al., 2008).

Silicon may act as a physical barrier to infection by microbial plant pathogens as it is stored in the exocarp of the fruit, forming a cuticle-Si double layer (Fauteux et al. 2005). It is thought that Si deposited in the fruit cell walls acts as a physical barrier enhancing the resistance mechanism against the attack of pathogens that can cause fruit decay (Bosse et al., 2011). Silicon has been found to enhance host resistance by strengthening the cell wall, stimulating defense reaction mechanisms, increasing the production of defense proteins, and enhancing

120 polyphenoloxidase, peroxidase, and chitinase activities (Dann and Muir, 2002), making fungal penetration and colonization within plant fruit tissue difficult (Fawe et al., 2001; Kaluwa et al.,

2010). Nevertheless, despite these advances in Si research, the mechanism involved in Si- mediated reduction of plant diseases remains unclear.

In contrast to the research on Si and plant disease, there are no reports on the effect of preharvest Si applications on the postharvest quality of most fruits and vegetables. There have been numerous postharvest investigations on papaya in order to understand the postharvest factors that influence papaya fruit quality. However, few of them have involved the effect of preharvest Si applications. One such study involved the effect of soil-applied phosphate, limestone, and slag-silicate on Solo papaya plant growth, disease resistance, and postharvest quality under Hawaiian climatic and soil conditions (Adlan, 1969). The highly weathered native soil was severely deficient in phosphorus and had a low pH. The soil was amended with limestone to achieve three levels of pH (5, 6, and 7) and treated with three rates of slag-silicate

(0, 833, and 1,166 kg ha-1) and triple-super phosphate (0, 560, and 1,120 kg ha-1). Plant growth increased significantly with increased soil pH, limestone rate and phosphate rate and there was a trend for increased plant growth with Si rate. However, there were no significant differences among treatments in fruit pulp TSS and titratable acidity (TA). Fruit texture and Si content were not measured and plants were more affected by increased soil pH and phosphorus rates than Si treatments (Adlan, 1969).

In Colombia, foliar applications of potassium-silicate at 0, 2.7 L ha-1, 2.7 L ha-1 plus

-1 micronutrients, and 5.4 L ha (29.1% K2SiO3) were evaluated with regard to ‘Tainung 2’ papaya growth and fruit quality (Hernández, 2008). As the rate of K2SiO3 was increased, yield increased

121 by 13.2%. However, TSS and flavor evaluation values were not significantly different among treated and non-treated fruit. Plant and fruit Si contents and fruit texture were not measured.

The objective of the study reported here was to test the effect of soil drench potassium silicate (K2SiO3; AgSil 16) application rates on yield and postharvest fruit quality, including firmness, sensory attributes (color, TA, TSS), and fruit weight (peel, pulp, and seed).

Specifically, the intent was to test the hypothesis that differences in textural characteristics of papaya fruit occur due to Si soil drench applications during fruit development.

Materials and Methods

Twenty-four rows with seven plants per row of transgenic X17-2 x T5 papaya were planted on September 10, 2012 at the Tropical Research and Education Center, Homestead, FL

(Lat. 25º25’N; Long. 80º 25’W). Plants were spaced 2.1 m in-row and rows were 4.5 m apart.

No pre-plant fertilizer was applied during land preparation. After plants were established in the field (30 cm to 4 cm tall; January 14, 2013) three potassium silicate (K2SiO3; AgSil 16, Malvern,

PA) treatments were applied biweekly through fertigation (irrigation plus fertilizer; Appendix

G). Treatments were no Si application (control), 500 and 1,000 kg Si ha-1year-1. Plants were fertigated daily for 45 minutes with 4-0-8 [4% N (0.49% NH4-N and 3.51% NO3-N), 0% phosphorus (P2O5) and 8% potassium (K2O). Minor elements were foliarly applied on an as needed basis. Chelated iron was applied monthly through the fertigation system.

Fruit Selection

Fruit were harvested twice for postharvest evaluations, on August 22 and October 29, 2013, after

16 and 21 K2SiO3 applications, respectively. The fruit were harvested at 30 to 75% color-break and sorted into two groups: those of 50% or less color break and those greater than 50% color break. Two to three fruit were harvested per row for a total of eighteen fruit per treatment.

Immediately after harvest, the fruit were placed in cooler above ice and transported to the

122 postharvest laboratory at the Horticultural Sciences Department in Gainesville, FL within 12 hours. Upon arrival at the laboratory, fruit with 50% or less color were stored at 20°C and 80-

90% relative humidity (RH) and those with greater than 50% color break were stored at 12°C

(80-90% RH) to standardize the stage of fruit ripeness stage among the Si treatments. The fruit with greater than 50% color break (i.e., riper) were evaluated over the next 3 days (Paull, 1995;

Bron and Jacomino, 2006). Fruit with 50% or less color were allowed to ripen until the yellow color area was greater than 50% (up to 75%) prior to evaluation.

Postharvest Fruit Evaluation

Measurements of fruit weight, length, and diameter, peel and pulp firmness, peel and pulp color, peel, pulp and seed fresh and dry weight, peel and pulp thickness, and pulp total soluble solids (TSS), pH and titratable acidity (TA) were assessed when fruit had reached greater than 50% color break.

Total fruit weight was measured using an electronic scale (Ohaus Explorer® Pro, max. weight 4100 g, OHAUS Co., Parsippany, NJ). Fruit length and diameter were measured using a fruit sizing device graded with a ruler and reported in mm.

Peel puncture resistance and pulp firmness were measured using the Texture Analyzer

(Model TA.HD Plus, Texture Technologies Co., Hamilton, MA). For the peel puncture (peel intact) and flesh firmness (peel removed) measurements, the Texture Analyzer was set up with a

500 kg load cell, an 8 mm diameter convex tip probe, with 5 mm sec-1 pretest speed and then, set up to 5 mm sec-1 test speed, and 20 mm travel distance into the papaya fruit. For the pulp shear measurements, the Texture Analyzer was set up to measure a 19 mm thick slice through the equatorial region of the papaya with a second, 19 mm cut to exclude outer peel and inner surface, a 500 kg load cell, and using a Warner Bratzler single blade shear cell, 5 mm sec-1 pretest speed, and then, set up to 5 mm sec-1 test speed, and 33 mm travel distance through the pulp sample. For

123 whole fruit compression measurements, the Texture Analyzer was used with a wide flat probe.

The whole fruit compression test conditions used a 75 mm diameter compression platen with the

500 kg load cell; 2 mm sec-1 pretest speed, and then, set up to 2 mm sec-1 test speed, and 5 mm travel distance. All data was reported in Newtons [N = m (kg s-2)-1].

Peel puncture resistance and pulp firmness were also manually measured using a fruit pressure tester (Handheld Digital Penetrometer Model FT 30, Wagner Instruments, Greenwich,

CT), with an 8 mm diameter Magness-Taylor type convex tip probe applied after removing a small section of the papaya fruit epidermis on two sides of each fruit at the equator on the cheeks using a manual fruit peeler (Wagner Instruments, Greenwich, CT). The data reported by the handheld penetrometer was also in Newtons.

Peel, pulp, and seed fresh and dry weight were measured in grams using an electronic scale (Ohaus Explorer® Pro, max. weight 4100 g, OHAUS Co., Parsippany, NJ). Samples were placed in an aluminum pan (Fisher Scientific UK Ltd., Loughborough, UK).

Peel thickness and pulp thickness were measured in mm using an electronic digital caliper (Caliper Marathon, 0-200 mm, Marathon Watch Company LTD, Richmond Hill, Ontario,

Canada). Peel and pulp color were measured using a Chroma Meter (Model CR-410; Konica

Minolta Inc., Japan) operating with a C illuminant and 11-mm diameter aperture according to

McGuire (1992). Fruit color characteristics were measured in CIE L*a*b* values where L* = lightness; a* = green/red hue component; b* = yellow/blue hue component; C* = [(a*2 + b*2)1/2]

= chroma and; Ho (from arctangent b*/a*) = hue angle (0o = red-purple, 90o = yellow, 180o = bluish-green, 270o = blue) [Francis, 1980; McGuire, 1992].

Papaya pulp was collected after texture measurements and homogenized with a commercial Waring blender. To obtain juice samples, a 20-g sample of each homogenate was

124 centrifuged at 17600 x gn at for 20 min at 4°C in a refrigerated vacuum centrifuge (J2-21,

Beckman Coulter, Palo Alto, CA). The supernatant was filtered through cheesecloth and recovered as the juice fraction for analyses. Juice pH and TA were measured using an automated titrator (905 Titrino, Metrohm, Riverview, FL) with an autosampler (814 USB Sample Processor,

Metrohm) on 6.0 mL of the fruit juice fraction mixed with 50 mL of DI water. The diluted juice samples were titrated with 0.1 N sodium hydroxide (Fisher Scientific UK Ltd., Loughborough,

UK), and the acidity was expressed as percentage of citric acid. The sample pH was measured at beginning of the titration and the end point of the titration was pH 8.2 to reproduce historical results performed with the AOAC method 22.058 reported by AOAC International (1995). Juice soluble solids contents were determined with a digital refractometer (model AR200; Reichert

Depew, NY), and expressed as per cent TSS.

Analysis of Tissue Samples for Available Silicon Content

Peel, pulp, and seed samples were dried in an oven (Wisconsin Oven Modell 600 and

800, Memmert, Wisconsin Oven Corp., East Troy, WI) at 70°C for 14 days and then milled up to

20 mm mesh sieve in an intermediate mill with stationary and rotary knives (Thomas-Wiley

Intermediate Mill, Thomas ScientificTM, Swedesboro, NJ). Then, milled tissue samples were put into 118-mL (4-oz.) plastic sample bags with puncture proof tabs (Nasco Whirl-Pak®, Fort

Atkinson, WI). Ground papaya fruit peel, pulp, and seed tissue samples were sent to the Soil and

Water Laboratory of the University of Florida’s Everglades Research and Education Center (UF-

EREC) in Belle Glade, FL for Si analysis. The Si concentration was determined by using the acetic acid extraction method after Autoclave-Induced Digestion (AID) as described by Elliot and Snyder (1991).

125 Statistical Analysis

Treatments were arranged in a randomized complete block design (CBD) with six papaya rows per treatment and seven plants per row. The Si treatments (K2SiO3) were: no silicon application (control), 500 kg Si ha-1year-1, and 1,000 kg Si ha-1year-1. The were two harvest: on

August 22 and October 29, 2013. The statistical analysis was conducted using SAS 9.1 statistical software (SAS Institute, Cary, NC), and the PROC GLM, PROC MEAN STDERR, PROC REG for ‘Linear Regression’ and SAS PROC GLM and PROC T-test for the analysis procedures.

These statistical procedures generated least-square means ± standard error that were tested for significant differences by LSD’ Studentized test, p≤0.05. The parameters for the study were evaluated by sampling dates using a two-way ANOVA. The experimental unit was a single individual fruit per treatment replication.

Results and Discussion

Potassium silicate applications had no consistent effect on X17-2 x T5 mean fruit weight for the August and October harvests (Table K-1), made after 16 and 21 K2SiO3 applications, respectively. Fruit weight ranged from 1,245 to 1,342 g, a range of less than 8%. There was no significant effect of K2SiO3 application rates on fruit length and diameter (Table K-2 and K-3).

Fruit lengths ranged from 202 to 249 mm and fruit diameters ranged from 106 to 118 mm.

Similarly, soil- and foliar-applied Si also had no significant effect on Solo-type papaya fruit weight under Hawaiian and Colombian conditions, respectively (Adlan, 1969; Hernández, 2008).

However, similar results were reported for tomato (Woolley, 1957; Miyake and Takahashi, 1978;

Matichenkov and Bocharnikova, 2004) and cucumber (Matichenkov and Bocharnikova, 2004).

However, foliar-applied oligomeric silicic acid plus boric acid (OSAB = Agroforce®) [KON-

DES AGRO BV, ALG Trading Co., J.B. Vleuten, The Netherlands] significantly increased papaya fruit weight in a Colombian study (Hernández, 208; Realpe and Laane, 2008).

126 Potassium silicate applications had no consistent effect on fruit peel puncture resistanc as evaluated by the Texture Analyzer and Wagner penetrometer methods (Table K-4). In general, there were significantly lower peel firmness values as K2SiO3 application rate increased when measured by the Texture Analyzer and Wagner penetrometer methods in August-harvested fruit.

In contrast, there was significantly greater peel puncture resistance as measured by the Wagner

-1 -1 penetrometer at the 500 kg ha year K2SiO3 application rate but not at all for Texture Analyzer peel puncture resistance in October-harvested fruit. Peel puncture resistance values were less by the Texture Analyzer method compared to the Wagner penetrometer method. Values from the

Texture Analyzer method ranged from 23 to 32 N whereas values for the Wagner penetrometer method ranged from 27.3 to 47.4 N.

Potassium silicate applications had no consistent effect on fruit peel resistance for the

August-harvested fruit, but whole fruit peel resistance was significantly greater for fruit harvested in October from Si-treated plants (Table 5-5). Potassium silicate applications had a consistent effect on fruit flesh texture as evaluated by the puncture and shear blade methods

(Table 5-5). In general, there were significantly greater flesh firmness and shear force values as

K2SiO3 application rate increased (both harvests). Flesh texture values were less by the puncture method than the shear blade method. Fruit firmness as measured by the whole fruit compression resistance method ranged from 40 to 54 N. Values from the puncture method ranged from 9 to

26 N whereas values for the shear blade method ranged from 5 to 6.5 N.

As a result, it can be speculated that variations in fruit peel puncture resistance and pulp texture may depend upon the maturity and ripeness stage of the fruit harvested which it is supported due to lower r2. However, Bron and Jacomino (2006) reported no significant differences in non-Si treated ‘Golden’ papaya fruit peel strength and pulp firmness at full

127 ripeness when harvested at green to >50% color break stage and allowed to ripen. Similarly, fruit firmness decreased based upon fruit harvest maturity and ripeness for mango fruit [Dea,

2009], muskmelon (Cucumis melo L.) [Harty, 2009], and peach (Kao, 2011).

There were no effect of K2SiO3 applications on peel and pulp fresh and dry weights of fruit harvested in August or October (Table K-6 and K-7). Papaya peel fresh weights ranged from 248 g to 353 g and dry weights from 31 to 40 g (Table K-6). Pulp fresh weights ranged from 815 to 988 g per fruit and dry weights from 43 to 66 g (Table K-7). There was no significant increase for fresh and dry seed weights to increase with increasing K2SiO3 application rate (Table K-8). Seed fresh weights ranged from 51 to 91 g and dry weights from 8 to 12 g.

Potassium silicate rate had no significant effect on mean peel thickness but fruit pulp thickness increased with increased K2SiO3 application rates (Table K-9). Papaya peel thickness ranged from 2 to 5 mm and pulp thickness ranged from 25 to 30 mm. Ma and Takahashi (2002) and

Matichenkov and Bocharnikova (2004) reported increased tomato pulp fresh and dry weights with increased Si application rates. Strawberry and cucumber fruit fresh weights increased with increasing Si and Zn application rates (Miyake and Takahashi 1978; Miyake and Takahashi,

1986; Ma and Takahashi, 2002). Although there was no consistent effect of K2SiO3 application rate on X17-2 x T5 papaya fresh and dry seed weight with increasing Si application rate, Okuda and Takahashi (1961), Dakora and Nelwamondo (2003), and Tahir et al., (2006) reported that rice (Oryza sativa L.), cowpea (Vigna unguiculata L. Walp.), and wheat (Triticum aestivum L.) seed fresh and dry weight significantly increased with increasing Si application rate.

In general, K2SiO3 applications had a consistent overall effect on fruit peel color attributes of August- and October-harvested fruit (Table K-10). There was a consistent tendency for peel a*, b* and C* values to increase with increased K2SiO3 application rate. Papaya peel L*

128 o and H (Hue angle) showed no consistent significant differences among K2SiO3 application rates

(Table K-10). Peel color L* ranged from 48 to 55 values, a* from 35 to 51, b* from 30 to 48, C* from 31 to 49, and Ho from 81 to 88. However, from the values of a* (positive numbers increasing red component) and b* (positive numbers increasing yellow component) there was an indication that, as K2SiO3 application rate increased, the fruit peel color retained more green and yellow (McGuire, 1992). At the same time, Chroma (C*) values significantly increased with

K2SiO3 application rate indicating the saturation (intensity) of the peel red-yellow/orange color

2 increased with K2SiO3 application rate. However, the low and inconsistent r values indicated that these changes in peel color were affected by factors other than K2SiO3 applications (Table

K-11). In contrast, potassium silicate applications had no significant effect on pulp color (Table

K-10 and K-11). In contrast, K2SiO3 applications had no significant effect on pulp color (Table

K-10 and K-11). This may have been due to the fact that fruit were evaluated at the same degree of ripeness. Possible effects of K2SiO3 applications on the rate at which the color changes occurred during ripening on or off the plant were not evaluated. Pulp color L* ranged from 45 to

55 values, a* from 24 to 26, b* from 37 to 39, Chroma C* from 45 to 47, and Ho (Hue angle) from 55 to 57.

Potassium silicate application had no significant effect on pulp pH, titratable acidy (TA) and total soluble solids (TSS) of fruit harvested in August or October (Table K-12). Hernandez

(2008) also reported no significant effect of foliar-applied SiO2 on TSS. In contrast, Realpe and

Laane (2008) reported that foliar-applied oligomeric silicic acid plus boric acid significantly increased papaya TSS. Similarly, Adlan (1969) reported no effect of soil applied silicate slag on pulp pH, TA and TSS values of ‘Puna Solo’. Papaya fruit pH ranged from 5.3 to 5.4, TA from

129 1.0 to 1.3, and TSS from 10.3 to 11.4. Pulp pH and TSS values were similar for ‘Puna Solo’ and

X17-2 x T5.

There was no significant effect of K2SiO3 application rates on peel, pulp, and seed Si content of fruit harvested in August and October (Table K-13). Papaya peel Si content values were generally greater than pulp and seed values of fruit harvested in August, but peel and pulp were lower for fruit harvested in October compared to seed Si content. Peel Si content ranged from 23 to 109 mg kg-1, pulp Si content ranged from 15 to 68 mg kg-1 and seed Si content ranged from 53 to 75 mg kg-1.

Conclusions

Soil applied K2SiO3 had no consistent significant effect on papaya fruit quality. Mean fruit weight was similar among K2SiO3 treatments and there were no K2SiO3 treatment effects on fruit length and diameter.. There was no significant decrease in fruit peel puncture resistance when measured by the texture analyzer or by the handheld penetrometer. Potassium silicate had no effect on pulp texture and no effect on pulp fresh and dry weight. Seed fresh and dry weights and pulp thickness did not increase significantly with K2SiO3 application rate Overall, the effect of K2SiO3 treatments on peel color were inconsistent although Chroma C* significantly increased and H° decreased with increasing K2SiO3 application rate. Peel and seed Si content significantly increased with K2SiO3 application rates. After 16 and 21 K2SiO3 applications, there was a significant but inconsistent effect on fruit length, but fruit diameter increased significantly with

K2SiO3 application.

Soil-applied K2SiO3 application rate had little to no significant effect on papaya fruit quality, and trends, where they existed, were inconsistent among fruit harvested in August and

October. Similar findings were reported by Adlan (1969), Hernández (2008) and Realpe and

130 Laane (2008) under Hawaiian and Colombian conditions, respectively. The only parameters affected with any consistency were the peel color factors a*, b*, H° and C* (Table K-10).

131 CHAPTER 6 SUMMARY AND CONCLUSIONS

Silicon (Si) is the second most abundant mineral element (28-31%) in the earth’s crust after oxygen (49%) (Epstein, 1994; 1999; Ma, 2004; Epstein and Bloom, 2005). Silicon mostly combines with oxygen to form silicate minerals which are assimilated by plant roots as

-1 monosilicic acid (H4SiO4) and its concentration in higher plants ranges from 0 to 100 g kg dry matter depending on plant type and the growth environment (Ma and Takahashi, 2002).

Papaya (Carica papaya L.) is grown commercially throughout the tropical and warm- subtropical world and is ranked fourth in tropical fruit production after banana (Musa x paradisiaca L.), mango (Mangifera indica L.) and pineapple [Ananas comosus L.) Merr.] (Evans et al., 2012; FAO, 2012) and in the U.S. is grown in Hawaii, Florida, and Puerto Rico (NASS-

USDA, 2009). The per capita consumption of papaya in the U.S. has increased and market demand is high for this fresh fruit (Evans et al., 2012; US Food Market Estimator, 2012).

The effect of Si on plant growth, development, physiology and yields have been well- documented for a number of agronomic crops including rice (Oryza sativa L.), maize (Zea mays

L.), sorghum [Sorghum bicolor (L.) Moench], and sugarcane (Saccharum officinarum L.)

[Okuda and Takahashi, 1961; Ayres, 1966; Fox et al., 1967; Yoshida et al., 1969; Tamini and

Voss, 1970; du Preez, 1970; Gasho and Andreis, 1974; Elawad et al., 1982; Snyder et al., 1986;

Medina-Gonzales et al., 1988; Clark et al., 1990; Datnoff et al., 1992; Savant et al., 1997a, 1999;

Meyer and Keeping, 2000; Kim et al., 2002; Ma and Takahashi, 2002; Gong et al., 2003, 2005,

2008; Liang et al., 2003, 2006; Ma et al., 2003; Gao et al., 2004; Ma, 2004; Wang et al., 2004;

Mitani and Ma, 2005; Kaya et al., 2006; Sudhakar et al., 2006; Hanafy-Ahmed et al., 2008; Tahir et al., 2011; Zargar and Agnihotri, 2013]. However, there have been relatively few investigations on the effect of Si on dicots such as tomato (Solanum lycopersicum L.), strawberry

132 (Fragaria x Ananassa Duchesne), tobacco (Nicotiana tabacum L.), cucumber (Cucumis sativus

L.) and banana (Musa x paradisiaca L.)[(Neumann et al., 1997; Takahashi et al., 1990; Miyake and Takahashi, 1983a; Miyake and Takahashi, 1986; Adatia and Besford, 1986; Jauhari et al.,

1974; Henriet et al., 2006]. The author is aware of only two investigations on the effect of Si on papaya. The effect of pre-plant incorporation of three rates of Si-slag, superphosphate, and limestone to Kapaa gravelly silty clay soil on ‘Puna’ papaya growth and development and yields was investigated under Hawaiian conditions (Adlan, 1969). As superphosphate and limestone application rate increased growth and yield and plant P and Ca content significantly increased.

Plant Si content significantly increased with Si-slag rate and as plants matured there was a trend for growth and yield to increase with Si application rate. However, there was no significant effect of Si application rate on papaya fruit quality. In another investigation, foliar Si applications to ‘Tainung II’ papaya under tropical conditions were reported to increase plant growth and crop yield. However, this investigation may have been compromised by unknown constituents in the Si formula and Si content of the plants was not verified.

With this in mind, two investigations on the effect of soil applied and two investigations with foliarly applied Si on ‘Red Lady’ papaya plant growth and development and gas exchange was conducted on well-watered plants under greenhouse and plastic house conditions. The treatments were soil applied or foliarly applied potassium silicate (K2SiO3, 25% Si) at 0

(control), 60, 120, 240 g plant-1application-1, and 0 (control), 2.5, 5, and 10 g plant-1 application-1, respectively. There were a total of 11 and 9 soil K2SiO3 applications and 13 and 16 foliar applications. A fifth experiment investigated the effect of 9 foliarly applied K2SiO3 on well- watered and drought-stressed ‘Red Lady’ plants under plastic house conditions. An 11 month field investigation into the effect of bi-weekly K2SiO3 (16% Si) applications through a drip

133 system on the growth, development and gas exchange of the transgenic line X17-2 x T5 papaya was conducted under south Florida conditions. There were a total of 25 bi-weekly K2SiO3 applications. Fruit harvested from the field investigation was used to determine the effect of

K2SiO3 applications on fruit weight and diameter, pulp, seed, and peel Si content, peel and pulp color, and peel and pulp firmness.

Under controlled greenhouse and plastic-house conditions soil applied Si had no consistent significant effect on ‘Red Lady’ papaya plant height and trunk diameters and no significant effect on plant fresh and dry weights. Silicon application rate had no significant effect on gs and E but A significantly increased with Si application rate. There was a trend for SPAD values to increase with Si application rate. In general, the highest to lowest Si tissue concentrations were in the root, lamina, petiole and trunks. Similarly, foliarly applied Si had no significant effect on plant height, trunk diameter, and fresh and dry weight of ‘Red Lady’ papaya. Silicon application rate had no significant effect on gs and an inconsistent effect on E and A. There was no significant effect of increasing Si applications on plant tissue content. The

Si tissue concentration was highest in the roots and leaf lamina followed by the leaf petiole and trunk.

In general, there was no significant increase in plant height and trunk diameter with foliar

Si application rate for well-watered and drought-stressed ‘Red Lady’ plants grown under plastic house conditions. Foliar Si application rate had no significant effect on fresh and dry weight of well-watered or drought-stressed plants. As Si application rate increased SPAD values for well- watered and drought-stressed plants increased but there was no significant difference among well-watered and drought-stressed plant SPAD values. Foliar Si application rate had no significant effect on plant tissue Si content of well-watered or drought-stressed plants. The tissue

134 concentration of Si was greatest for leaf lamina, followed by the roots with leaf petioles and trunks with similar concentrations.

After 25 soil applications of K2SiO3 (16% Si) at three rates to X17-2 x T5 papaya there was no significant effect on plant height and trunk diameter. In general leaf area of bisexual and female lamina did not significantly increase with increasing K2SiO3 rate and Si applications had no significant effect on leaf absiccion. Potassium silicate applications had no significant effect on leaf lamina and petiole fresh weight and an inconsistent effect on dry weights. There was no difference in fresh and dry leaf lamina and petioles weights among female and bisexual plants.

Potassium silicate had an inconsistent effect on gs but as K2SiO3 rate increased E significantly decreased. In general, as K2SiO3 rate increased A and SPAD values significantly increased.

Total soil Si content was similar for pre-treated soil and Si treated soil. However, soil available Si increased with K2SiO3 rate.

Potassium silicate applications had no significant effect on fruit number, fruit weight and fruit yield. Potassium silicate applications had no consistent effect on mean total, peel, and pulp fruit weight after 16 and 21 applications. Similarly, papaya fruit length and diameter were unaffected by Si applications Potassium silicate applications had no consistent effect on peel and pulp firmness, pulp pH, titratable acidity, and total soluble solid content. Silicon content of peel, pulp, and seed did not increased with K2SiO3 application rate. Fruit peel color attributes a*, b*, and C* increased with K2SiO3 application rate whereas the effect on L* values was inconsistent.

In conclusion, soil and foliarly applied Si had inconsistent effects on ‘Red Lady’ and

X17-2 x T5 papaya plant growth, development and gas exchange. Similarly, the effect of Si on papaya fruit yields and postharvest fruit quality was inconsistent. Additional investigations into

135 the effect of foliarly applied Si on papaya plant growth and stress drought-stress tolerance may be justified.

136

APPENDIX A CRITICAL PETIOLE RANGES FOR NITROGEN (N), PHOSPHORUS (P), AND POTASSIUM (K) LEVELS IN PAPAYA

Critical petiole ranges for nitrogen (N), phosphorus (P), and potassium (K) levels in papaya (Carica papaya L.) plants growing under Hawaiian soil conditions. Hawaii Agricultural Experiment Station. Honolulu, HI.

Nutrient element Petiole critical range, % Average concentration range, %

Nitrogen 1.15 - 1.33 1.27

Phosphorus 0.16 - 0.20 0.18

Potassium 3.53 - 3.69 3.61 Source: Awada, 1977; Awada and Long, 1971b & 1978.

137

APPENDIX B CONCENTRATIONS OF CONSTITUENTS AND TOTAL MINERAL ELEMENTSz IN THREE COMMERCIAL ARTIFICIAL SOIL MEDIA

Concentrations of constituents and total mineral elementsz in three commercial artificial soil media. January 2012. Tropical Research and Education Center, University of Florida (UF- TREC), Homestead, FL. FAFARD MIX Constituent / Element FAFARD MIX Peat Moss Super fine pHy 6.4 6.2 8 OMx (%) 61.9 51.2 6.6 Total Nw (g kg-1) 3.2 5.8 1.3 P (g kg-1) 1.4 1 2.1 K (g kg-1) 3.8 9.6 0.9 Ca (g kg-1) 16.9 13.1 212 Mg (g kg-1) 16 23.4 3.1 Fe (g kg-1) 11.7 21.2 20.1 Al (g kg-1) 7.6 15.2 36.8 Mn (g kg-1) 0.2 0.3 1.1 Cu (mg kg-1) 18 29 143 B (mg kg-1) 7 9 12 Zn (mg kg-1) 30 58 48 Siv (g kg-1) 34 72 29.3 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

138

APPENDIX C CONCENTRATIONS OF CONSTITUENTS AND SOIL PLANT AVAILABLE NUTRIENT ELEMENTSz IN THREE COMMERCIAL ARTIFICIAL SOIL MEDIA

Concentrations of constituents and soil plant available nutrient elementsz in three commercial artificial soil media. January 2012. Tropical Research and Education Center, University of Florida (UF-TREC), Homestead, FL. FAFARD MIX Constituent / Element FAFARD MIX Peat Moss Super fine y -1 NH4-N (mg kg ) 22.4 15.4 18

x -1 NO3-N (mg kg ) 13.7 11.2 19.5

P (g kg-1) 0.2 0.1 0.1 K (g kg-1) 1.3 1.5 0.2 Ca (g kg-1) 10.2 8.8 17.5

Mg (g kg-1) 3.8 4.9 0.3 Fe (g kg-1) 0.5 0.4 0.04 Al (g kg-1) 0.4 0.05 0.4

w -1 SO4-S (g kg ) 6.8 5.1 0.8 Mn (g kg-1) 0.05 0.04 0.05 Cu (mg kg-1) 2 2 37 B (mg kg-1) 0 0 1

Zn (mg kg-1) 6 9 11 Siv (g kg-1) 0.1 0.1 0.003 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991.

139

APPENDIX D MONTHLY MINIMUM, MAXIMUM AND AVERAGE AIR AND SOIL TEMPERATURES (OC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION

140

Monthly minimum, maximum and average air and soil temperatures (oC), and precipitation (mm) from the Florida Automated Weather Network (FAWN) station located at UF-TREC, Homestead, FL. Data are from September 1, 2012 to January 1, 2014.

o o Air temperature, C Soil temperature, C Precipitation Date Minimum Maximum Average Minimum Maximum Average (mm) September 1, 2012 22 33 27 25 33 28 9.88 October 1, 2012 10 32 25 19 32 26 4.95 November 1, 2012 10 29 20 18 27 22 0.33 December 1, 2012 5 30 20 15 27 22 0.21 January 1, 2013 12 28 21 18 26 23 0.16 February 1, 2013 6 30 20 14 28 23 1.32 March 1, 2013 4 31 18 15 29 22 0.29 April 1, 2013 15 31 24 20 31 26 4.28 May 1, 2013 14 34 25 22 33 27 7.01 June 1, 2013 21 32 27 25 36 29 6.88 July 1, 2013 22 33 27 25 33 29 10.55 August 1, 2013 21 34 27 26 31 36 2.21 September 1, 2013 21 34 27 25 33 28 5.60 October 1, 2013 17 33 25 23 32 28 2.01 November 1, 2013 12 31 24 19 30 25 5.02 December 1, 2013 14 29 23 20 27 23 2.25 January 1, 2014 0 29 25 16 25 20 2.99

141

APPENDIX E MONTHLY MINIMUM, MAXIMUM AND AVERAGE AIR TEMPERATURES (oC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION

142

50 Minimum Maximum Average 40

C

o 30

20

Air temperature, Airtemperature,

10

0

April 1, 2013May 1, 2013June 1, 2013July 1, 2013 March 1, 2013 August 1, 2013 October 1, 2012 January 1,February 2013 1, 2013 October 1, 2013 January 1, 2014 September 1, 2012 NovemberDecember 1, 2012 1, 2012 September 1, 2013 NovemberDecember 1, 2013 1, 2013 Time

Monthly minimum, maximum and average air temperatures (oC) from the Florida Automated Weather Network (FAWN) station located at UF-TREC, Homestead, FL. Data are from September 1, 2012 to January 1, 2014.

143

APPENDIX F MONTHLY MINIMUM, MAXIMUM AND AVERAGE SOIL TEMPERATURES (oC), AND PRECIPITATION (mm) FROM THE FLORIDA AUTOMATED WEATHER NETWORK (FAWN) STATION

144

50 Minimum Maximum Average 40

C

o

30

20

Soil temperature,

10

0

April 1, 2013May 1, 2013June 1, 2013July 1, 2013 March 1, 2013 August 1, 2013 October 1, 2012 January 1,February 2013 1, 2013 October 1, 2013 January 1, 2014 September 1, 2012 NovemberDecember 1, 2012 1, 2012 September 1, 2013 NovemberDecember 1, 2013 1, 2013 Time

Monthly minimum, maximum and average soil temperatures (oC) from the Florida Automated Weather Network (FAWN) station located at UF-TREC, Homestead, FL. Data are from September 1, 2012 to January 1, 2014.

145

APPENDIX G SCHEDULE OF POTASSIUM SILICATE SOIL DRENCH APPLICATIONS ON X-17-2 x T5 TRANSGENIC BISEXUAL AND FEMALE PAPAYA PLANTS GROWN UNDER WILL- WATERED FIELD CONDITIONS

Schedule of potassium silicate (K2SiO3, 16%) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plants grown under well-watered field conditions from Jan. 15 to Dec. 17, 2013 at UF-TREC, Homestead, FL. Number of applications Application dates 1 January 15 2 January 29 3 February 12 4 February 26 5 March 12 6 March 26 7 April 9 8 April 23 9 May 7 10 May 21 11 June 4 12 June 18 13 July 2 14 July 16 15 July 30 16 August 13 17 August 27 18 September 10 19 September 24 20 October 8 21 October 22 22 November 5 23 November 19 24 December 3 25 December 17

146

APPENDIX H AVERAGE FRUIT FRESH WEIGHT OF POTASSIUM SILICATE SOIL DRENCH APPLICATIONS ON X17-2 x T5 TRANSGENIC PAPAYA PLANTS GROWN IN A KROME VERY GRAVELLY SANDY SOIL UNDER WELL-WATERED FIELD CONDITIONS

Average (n = 18) fruit fresh weight (g) for three potassium silicate (K2SiO3, 16% Si) soil drench application treatments on X17-2 x T5 transgenic papaya plants grown in a Krome very gravelly sandy soil under well-watered field conditions in a 2013 experiment at UF-TREC.

First harvest (August 22, 2013)

Fruit Silicon treatments

number 0 kg Si ha-1year-1 500 kg Si ha-1year-1 1,000 kg Si ha-1year-1

1 1,519.88 1,158.92 1,490.55 2 1,549.23 1,783.06 1,446.18 3 1,251.62 1,320.48 1,145.62 4 1,288.30 1,301.61 1,358.72 5 1,326.82 1,007.55 1,511.43 6 1,441.25 1,758.95 1,418.61 7 1,230.60 1,010.47 1,355.43 8 1,237.07 1,284.79 1,124.52 9 1,278.26 1,275.38 1,157.91 10 1,334.93 1,515.48 1,419.99 11 1,315.39 1,978.29 1,044.77 12 1,136.81 1,314.32 1,326.23 13 999.18 1,479.73 1,388.21 14 1,144.93 1,024.02 1,015.64 15 1,476.33 1,228.24 1,008.25 16 1,686.54 991.28 1,086.50 17 1,012.89 1,028.51 1,097.72 18 905.93 1,301.12 1,004.47 Average 1,285.33 1,320.12 1,244.49

147

Appendix H--continued.

Second harvest (October 29, 2013)

Fruit Silicon treatments

number 0 kg Si ha-1year-1 500 kg Si ha-1year-1 1,000 kg Si ha-1year-1 1 1,108.14 1,365.42 1,196.90 2 1,120.22 1,624.95 1,322.73 3 1,317.88 1,095.64 1,344.44 4 1,312.66 1,025.29 1,494.67 5 1,522.28 1,147.41 1,227.49 6 902.07 1,015.74 1,570.44 7 839.21 1,187.45 1,183.37 8 1,145.46 1,130.25 1,237.56 9 1,226.09 1,351.02 1,633.35 10 1,070.42 1,392.96 1,360.39 11 886.18 1,333.63 1,262.49 12 1,175.03 986.95 1,096.41 13 1,061.84 1,369.51 1,208.14 14 1,003.05 1,537.13 1,619.39 15 1,177.55 1,653.23 1,064.29 16 1,048.31 1,604.34 905.54 17 964.40 1,790.27 1,619.39 18 1,059.20 1,545.39 1,332.16 Average 1,107.78 1,342.03 1,315.51

148

APPENDIX I ADDITIONAL TABLES FOR CHAPTER 3

149

-1 Table I-1. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant height under well-watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean height ± SE (cm) K2SiO3 rate (g plant-1) July 19 July 31 August 13 August 23 September 7 September 21

0 111.9 ± 6.2 a 117.1 ± 7.0 a 126.5 ± 7.0 a 136.3 ± 7.2 a 146.9 ± 6.9 a 156.1 ± 8.1 a

60 105.1 ± 6.6 a 109.4 ± 6.8 a 119.5 ± 7.1 a 125.9 ± 6.7 a 138.8 ± 7.2 a 144.7 ± 5.2 a

120 106.3 ± 9.0 a 111.5 ± 4.7 a 121.2 ± 4.1 a 128.4 ± 4.0 a 138.8 ± 3.8 a 144.9 ± 4.1 a

240 101.9 ± 7.1 a 107.8 ± 6.7 a 115.0 ± 6.6 a 122.9 ± 7.4 a 134.8 ± 9.6 a 140.7 ± 10.9 a

Mean height ± SE (cm) K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30

0 163.4 ± 7.9 a 170.4 ± 7.8 a 171.3 ± 8.1 a 170.6 ± 8.5 a 177.3 ± 10.1 a

60 150.7 ± 6.5 a 157.7 ± 6.2 a 156.6 ± 7.2 a 156.3 ± 8.7 a 160.8 ± 5.2 a

120 155.7 ± 4.3 a 162.5 ± 3.8 a 161.8 ± 4.1 a 160.9 ± 5.7 a 165.5 ± 5.3 a

240 149.8 ± 12.3 a 157.8 ± 13.0 a 156.4 ± 13.2 a 157.1 ± 13.9 a 161.8 ± 11.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

150

-1 Table I-2. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant height under well-watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL. Mean plant height ± SE (cm) K2SiO3 rate (g plant-1) February 25 March 8 March 22 April 5 April 19

0 29.3 ± 1.1 a 30.8 ± 1.3 a 41.8 ± 0.9 a 53.3 ± 0.7 b 61.7 ± 1.8 c

60 28.7 ± 1.5 a 31.5 ± 1.2 a 44.3 ± 1.5 a 57.4 ± 1.9 a 69.8 ± 2.5 ab

120 27.9 ± 1.6 a 31.0 ± 1.7 a 42.5 ± 1.5 a 54.5 ± 0.9 ab 66.3 ± 1.6 bc

240 29.0 ± 0.7 a 32.3 ± 0.3 a 44.2 ± 1.1 a 57.9 ± 1.1 a 71.8 ± 0.8 a

Mean plant height ± SE (cm) K2SiO3 rate (g plant-1) May 3 May 17 May 31 June 14

0 64.1 ± 0.5 b 69.8 ± 0.6 c 78.6 ± 3.8 b 88.5 ± 1.2 b

60 71.0 ± 3.2 a 76.6 ± 3.5 ab 92.3 ± 2.4 a 94.0 ± 2.6 a

120 68.1 ± 0.7 ab 71.3 ± 1.3 bc 85.2 ± 1.1 ab 97.5 ± 1.5 ab

240 72.4 ± 0.4 a 77.4 ± 1.0 a 91.2 ± 1.0 a 91.8 ± 3.4 ab Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

151

-1 Table I-3. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter under well-watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) July 19 July 31 August 13 August 23 September 7 September 21

0 28.1 ± 0.5 a 30.7 ± 0.9 a 36.2 ± 1.2 a 39.3 ± 0.4 a 46.8 ± 1.5 a 51.8 ± 1.9 a

60 27.0 ± 0.4 a 29.1 ± 0.6 a 34.7 ± 0.9 a 39.5 ± 1.3 a 43.7 ± 1.4 a 47.1 ± 1.0 b

120 26.9 ± 0.7 a 29.5 ± 0.9 a 35.7 ± 0.8 a 37.9 ± 1.2 a 45.4 ± 0.7 a 48.5 ± 0.6 ab

240 26.5 ± 0.1 a 28.5 ± 1.1 a 34.1 ± 0.9 a 37.7 ± 0.9 a 45.1 ± 1.4 a 48.2 ± 1.5 ab

Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30

0 56.4 ± 2.2 a 58.5 ± 2.1 a 57.3 ± 1.3 a 60.4 ± 3.3 a 62.0 ± 4.9 a

60 49.9 ± 1.3 b 53.8 ± 1.9 a 52.7 ± 1.5 b 53.2 ± 1.4 b 53.3 ± 1.7 ab

120 52.2 ± 0.8 ab 56.0 ± 0.6 a 55.0 ± 0.7 ab 57.3 ± 1.2 ab 57.8 ± 2.0 ab

240 50.6 ± 1.9 ab 54.0 ± 2.1 a 52.3 ± 1.7 b 53.0 ± 1.9 b 52.4 ± 1.1 b Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

152

-1 Table I-4. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter under well-watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL. Plant trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) February 25 March 8 March 22 April 5 April 19

0 9.6 ± 0.1 a 11.4 ± 0.2 a 16.2 ± 0.4 a 21.7 ± 0.7 a 22.2 ± 0.5 a

60 9.9 ± 0.3 a 11.7 ± 0.4 a 16.8 ± 0.5 a 22.0 ± 0.6 a 23.3 ± 0.6 a

120 9.7 ± 0.6 a 11.9 ± 0.8 a 16.6 ± 0.6 a 22.6 ± 0.9 a 22.7 ± 0.6 a

240 10.0 ± 0.5 a 12.1 ± 0.6 a 16.9 ± 0.8 a 22.4 ± 0.7 a 23.8 ± 0.5 a

Plant trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) May 3 May 17 May 31 June 14

0 25.8 ± 0.8 a 29.8 ± 1.8 a 31.4 ± 0.5 a 34.3 ± 1.2 b

60 26.6 ± 0.9 a 29.0 ± 1.2 a 33.2 ± 1.3 a 34.3 ± 0.8 b

120 26.1 ± 0.7 a 28.2 ± 1.0 a 32.1 ± 1.1 a 37.9 ± 0.7 a

240 27.4 ± 0.9 a 29.9 ± 1.2 a 34.1 ± 1.4 a 37.5 ± 1.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

153

-1 Table I-5. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight under well-watered plastic-house conditions from August 1 to December 23, 2012 at UF-TREC, Homestead, FL. Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) August 1 August 23 September 23 0 329.6 ± 44.6 453.7 ± 63.0 1,398.7 ± 108.4 60 721.7 ± 275.8 1,157.6 ± 476.1 2,673.2 ± 921.2 120 913.3 ± 344.5 1,477.9 ± 499.4 3,478.9 ± 694.3 240 288.6 ± 85.6 375.9 ± 139.6 2,492.1 ± 58.3 Linear Y = 656.5 – 24.9x Y = 1,036.7 – 45.4x Y = 2,127.7 + 102.1x regression r2 0.02 0.02 0.04

Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) October 23 November 23 December 23 0 1,601.5 ± 117.0 1,076.5 ± 67.1 1,475.3 ± 115.9 60 3,624.9 ± 1,425.7 3,271.8 ± 1,403.0 3,967.5 ± 1,774.3 120 5,032.9 ± 1,110.4 3,750.3 ± 914.1 5,813.7 ± 1,051.8 240 2,905.9 ± 155.8 1,856.5 ± 128.3 3,486.2 ± 262.9 Linear Y = 2,918.2 + 99.5x Y = 2,470.3 + 4.9x Y = 3,103.7 + 169.9x regression r2 0.02 0.00004 0.03 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

154

-1 Table I-6. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight under well-watered greenhouse conditions from February 18 to June 25, 2013 at UF-TREC, Homestead, FL. Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) February 18 February 25 March 25 0 45.0 ± 13.2 171.9 ± 34.8 215.7 ± 64.8 60 72.4 ± 33.4 166.8 ± 37.3 100.7 ± 34.4 120 72.7 ± 22.5 242.0 ± 72.4 218.7 ± 69.0 240 75.4 ± 36.7 277.2 ± 70.9 270.4 ± 62.8 Linear Y = 64.3 + 3.4x Y = 202.8 + 7.3x Y = 180.4 + 6.9x regression r2 0.03 0.04 0.04

Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) April 25 May 25 June 25 0 290.2 ± 77.3 205.1 ± 42.5 270.0 ± 73.2 60 363.0 ± 90.2 288.2 ± 68.5 432.6 ± 124.6 120 518.4 ± 68.5 222.9 ± 50.6 281.9 ± 76.7 240 370.4 ± 101.4 308.9 ± 107.9 338.3 ± 83.8 Linear Y = 315.6 + 4.3x Y = 248.4 + 9.3x Y = 317.2 + 3.3x regression r2 0.01 0.04 0.003 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

155

-1 Table I-7. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight under well-watered plastic-house conditions from August 1 to December 23, 2012 at UF-TREC, Homestead, FL. Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) August 1 August 23 September 23 0 71.9 ± 7.6 99.3 ± 11.4 273.8 ± 31.0 60 88.5 ± 21.3 139.5 ± 40.6 425.7 ± 156.9 120 99.0 ± 27.1 162.8 ± 39.1 525.8 ± 123.4 240 64.7 ± 7.3 74.8 ± 14.9 345.5 ± 11.7 Linear Y = 87.9 – 1.8x Y = 139.8 – 5.5x Y = 379.5 + 3.5x regression r2 0.02 0.05 0.002

Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) October 23 November 23 December 23 0 432.9 ± 55.7 235.9 ± 29.2 282.7 ± 37.2 60 582.3 ± 184.9 526.5 ± 236.8 683.6 ± 304.4 120 705.9 ± 188.5 605.8 ± 181.0 837.2 ± 210.8 240 369.8 ± 28.5 294.9 ± 9.6 456.8 ± 35.4 Linear Y = 582.9 – 16.1x Y = 437.4 – 5.8x Y = 542.0 + 6.2x regression r2 0.02 0.002 0.002 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

156

-1 Table I-8. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight under well-watered greenhouse conditions from February 18 to June 25, 2013 at UF-TREC, Homestead, FL. Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) February 18 February 25 March 25 0 24.1 ± 3.2 27.4 ± 4.7 28.8 ± 6.8 60 26.2 ± 5.0 45.2 ± 18.8 15.8 ± 15.8 120 37.6 ± 11.0 40.5 ± 8.4 26.1 ± 6.7 240 39.1 ± 7.3 40.2 ± 15.3 37.6 ± 6.7 Linear Y = 30.2 + 0.7x Y = 38.9 + 1.4x Y = 28.4 + 0.5x regression r2 0.04 0.03 0.02

Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) April 25 May 25 June 25 0 43.3 ± 9.2 28.9 ± 4.1 45.1 ± 9.2 60 56.8 ± 11.1 39.2 ± 6.9 77.5 ± 18.3 120 49.9 ± 8.3 31.4 ± 5.6 55.2 ± 10.9 240 58.8 ± 11.3 41.4 ± 12.6 83.8 ± 31.0 Linear Y = 46.9 + 1.3x Y = 35.3 + 1.0x Y = 55.5 + 1.9x regression r2 0.04 0.04 0.04 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

157

-1 Table I-9. Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) under well- watered plastic-house conditions from July 23 to December 7, 2012 at UF-TREC, FL. -2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) July 23 August 4 August 16 0 612.1 ± 0.06 a 630.2 ± 0.02 a 770.0 ± 0.07 a 60 727.1 ± 0.09 a 704.2 ± 0.03 a 845.0 ± 0.07 a 120 686.7 ± 0.08 a 693.8 ± 0.02 a 927.9 ± 0.09 a 240 669.6 ± 0.09 a 702.5 ± 0.01 a 1,010.4 ± 0.10 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) August 30 September 13 September 27 0 843.8 ± 0.07 a 861.7 ± 0.10 a 550.8 ± 0.07 a 60 810.4 ± 0.07 a 853.3 ± 0.10 a 710.0 ± 0.08 a 120 795.0 ± 0.06 a 723.3 ± 0.09 a 678.3 ± 0.07 a 240 762.1 ± 0.05 a 715.0 ± 0.06 a 612.1 ± 0.09 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) October 12 October 26 November 9 0 337.5 ± 0.01 a 206.2 ± 0.02 a 348.1 ± 0.03 a 60 351.3 ± 0.004 a 212.5 ± 0.03 a 268.8 ± 0.04 a 120 350.0 ± 0.01 a 303.3 ± 0.04 a 307.5 ± 0.04 a 240 351.7 ± 0.004 a 244.6 ± 0.04 a 348.8 ± 0.05 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mol H2O m s ) -1 (g plant ) November 23 December 7 0 270.6 ± 0.03 a 346.2 ± 0.02 a 60 303.1 ± 0.03 a 348.8 ± 0.02 a 120 275.0 ± 0.03 a 328.8 ± 0.02 a 240 490.0 ± 0.24 a 325.0 ± 0.02 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

158

-1 Table I-10. Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) under well- watered greenhouse conditions from Feb. 22 to June 14, 2013 at UF-TREC, FL. -2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) February 22 March 2 March 16 0 1,410.4 ± 0.03 b 983.3 ± 0.14 a 722.2 ± 0.12 a 60 1,408.3 ± 0.05 b 1,392.5 ± 0.12 a 1,088.3 ± 0.11 a 120 1,387.5 ± 0.04 a 784.2 ± 0.05 a 761.7 ± 0.12 a 240 1,285.0 ± 0.03 a 1,091.7 ± 0.12 a 1,145.0 ± 0.14 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) March 30 April 13 April 27 0 317.5 ± 0.03 a 692.9 ± 0.04 a 815.4 ± 0.14 b 60 307.5 ± 0.02 a 801.7 ± 0.07 a 1,106.7 ± 0.06 a 120 298.3 ± 0.02 a 825.8 ± 0.04 a 1,205.8 ± 0.04 a 240 303.3 ± 0.02 a 890.8 ± 0.07 a 1,165.8 ± 0.07 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) May 14 May 28 June 14 0 843.8 ± 0.07 a 1,321.9 ± 0.04 a 897.5 ± 0.13 a 60 847.9 ± 0.07 a 1,314.4 ± 0.06 a 1,308.8 ± 0.07 a 120 739.2 ± 0.04 a 1,327.5 ± 0.05 a 1,251.3 ± 0.05 a 240 787.1 ± 0.05 a 1,252.5 ± 0.03 a 1,280.0 ± 0.18 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

159

-1 Table I-11. Effect of 0, 60, 120, and 240 g plant of 11 K2SiO3 soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) under well-watered plastic-house conditions from July 25 to Dec. 7, 2012 at UF-TREC, Homestead, FL. -2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) July 25 August 4 August 16 0 10.9 ± 0.4 a 11.1 ± 0.5 a 7.9 ± 0.5 a 60 11.2 ± 0.4 a 12.1 ± 0.2 a 8.3 ± 0.4 a 120 11.2 ± 0.4 a 11.5 ± 0.5 a 8.6 ± 0.5 a 240 11.0 ± 0.4 a 11.2 ± 0.3 a 8.7 ± 0.5 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) August 30 September 13 September 27 0 8.6 ± 0.5 a 8.6 ± 0.3 a 8.0 ± 0.3 a 60 8.5 ± 0.4 a 8.8 ± 0.4 a 8.8 ± 0.2 a 120 9.3 ± 0.3 a 8.4 ± 0.2 a 8.7 ± 0.2 a 240 8.8 ± 0.4 a 8.5 ± 0.3 a 8.6 ± 0.3 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) October 12 October 26 November 9 0 6.5 ± 0.1 a 4.4 ± 0.2 a 5.9 ± 0.1 a 60 6.5 ± 0.1 a 4.3 ± 0.2 a 5.7 ± 0.4 a 120 6.2 ± 0.1 a 5.1 ± 0.4 a 5.7 ± 0.4 a 240 6.3 ± 0.2 a 4.6 ± 0.3 a 6.3 ± 0.5 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) November 23 December 7 0 4.2 ± 0.2 a 4.9 ± 0.1 a 60 4.4 ± 0.3 a 4.9 ± 0.1 a 120 4.3 ± 0.3 a 4.8 ± 0.3 a 240 4.3 ± 0.2 a 4.8 ± 0.2 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

160

-1 Table I-12. Effect of 0, 60, 120, and 240 g plant of 9 K2SiO3 soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) under well-watered greenhouse conditions from Feb. 22 to June 14, 2013 at UF-TREC, Homestead, FL. -2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) February 22 March 2 March 16 0 2.7 ± 0.2 a 2.7 ± 0.10 a 2.5 ± 0.1 a 60 2.7 ± 0.1 a 2.7 ± 0.10 a 2.7 ± 0.1 a 120 2.9 ± 0.1 a 2.8 ± 0.10 a 2.7 ± 0.1 a 240 2.7 ± 0.1 a 2.9 ± 0.04 a 3.1 ± 0.1 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) March 30 April 13 April 27 0 4.0 ± 0.1 a 4.2 ± 0.1 b 5.6 ± 0.3 a 60 4.2 ± 0.1 a 5.6 ± 0.2 a 6.1 ± 0.1 a 120 4.0 ± 0.1 a 4.8 ± 0.2 b 5.7 ± 0.3 a 240 4.2 ± 0.1 a 4.6 ± 0.2 b 5.6 ± 0.1 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) May 14 May 28 June 14 0 2.7 ± 0.1 b 3.5 ± 0.3 a 4.0 ± 0.3 a 60 3.1 ± 0.5 b 4.0 ± 0.3 a 4.8 ± 0.7 a 120 4.9 ± 0.4 a 4.1 ± 0.3 a 4.7 ± 0.4 a 240 4.9 ± 0.3 a 4.8 ± 0.2 a 4.6 ± 0.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

161

-1 Table I-13. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) under well-watered plastic-house conditions from July 25 to November 7, 2012 at UF-TREC, Homestead, FL.

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) July 25 August 4 August 16 August 30 September 13 September 27 0 7.8 ± 0.7 a 2.1 ± 0.2 b 5.0 ± 0.5 b 6.4 ± 0.4 c 7.9 ± 0.5 a 7.1 ± 0.4 a 60 8.9 ± 0.8 a 3.1 ± 0.3 ab 7.1 ± 0.4 a 7.8 ± 0.3 b 9.5 ± 0.6 a 8.5 ± 0.4 a 120 9.1 ± 0.7 a 3.0 ± 0.2 ab 6.1 ± 0.5 ab 8.9 ± 0.6 ab 9.3 ± 0.4 a 8.4 ± 0.3 a 240 9.0 ± 0.9 a 3.9 ± 0.2 a 6.1 ± 0.4 ab 9.2 ± 0.5 a 8.7 ± 0.6 a 8.2 ± 0.4 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) October 12 October 26 November 9 November 23 December 7 0 4.8 ± 0.3 b 3.6 ± 0.2 a 4.9 ± 0.4 b 5.4 ± 0.6 a 2.4 ± 0.1 c 60 6.5 ± 0.3 a 4.6 ± 0.5 a 6.0 ± 0.5 ab 7.2 ± 0.5 a 3.4 ± 0.3 b 120 6.7 ± 0.3 a 5.0 ± 0.6 a 6.8 ± 0.9 ab 7.0 ± 0.7 a 3.6 ± 0.2 b 240 7.3 ± 0.4 a 5.0 ± 0.5 a 7.2 ± 0.8 a 6.5 ± 0.4 a 4.7 ± 0.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

162

-1 Table I-14. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) under well-watered greenhouse conditions from February 22 to June 14, 2013 at UF-TREC, Homestead, FL.

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) February 22 March 2 March 16 March 30 April 13 0 2.9 ± 0.2 a 2.7 ± 0.2 b 3.2 ± 0.3 b 2.0 ± 0.3 a 2.4 ± 0.1 c 60 2.8 ± 0.4 a 3.2 ± 0.2 ab 3.9 ± 0.4 ab 2.4 ± 0.3 a 3.6 ± 0.2 b 120 3.3 ± 0.3 a 3.6 ± 0.2 a 4.3 ± 0.2 ab 3.0 ± 0.3 a 3.7 ± 0.2 b 240 3.1 ± 0.2 a 3.9 ± 0.2 a 4.5 ± 0.3 a 2.6 ± 0.3 a 4.1 ± 0.2 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) April 27 May 14 May 28 June 14 0 2.4 ± 0.1 c 5.6 ± 0.4 ab 5.1 ± 0.7 b 3.7 ± 0.3 c 60 3.7 ± 0.2 b 4.9 ± 0.4 b 5.7 ± 0.8 ab 5.3 ± 0.2 ab 120 3.5 ± 0.2 b 5.3 ± 0.4 b 5.2 ± 0.9 b 5.3 ± 0.4 bc 240 4.2 ± 0.2 a 6.9 ± 0.3 a 6.0 ± 0.2 a 7.5 ± 0.8 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

163

-1 Table I-15. Effect of 0, 60, 120, and 240 g plant of 11 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values under well-watered plastic-house conditions from July 27 to November 30, 2012 at UF-TREC, Homestead, FL. Mean SPAD ± SE K2SiO3 rate (g plant-1) July 27 August 3 August 10 August 23 September 7 September 21 0 39.8 ± 0.6 a 41.2 ± 0.2 a 44.1 ± 0.6 a 43.8 ± 1.1 a 46.8 ± 1.7 ab 43.1 ± 0.8 a 60 39.9 ± 0.5 a 41.3 ± 1.0 a 43.4 ± 0.4 a 41.5 ± 0.2 a 44.7 ± 1.0 b 41.6 ± 1.1 a 120 40.5 ± 0.4 a 40.4 ± 0.3 a 43.2 ± 0.4 a 41.8 ± 0.6 a 44.9 ± 0.7 ab 41.9 ± 1.0 a 240 40.4 ± 0.6 a 41.3 ± 0.4 a 44.3 ± 0.6 a 43.3 ± 1.6 a 48.2 ± 0.8 a 43.3 ± 1.1 a

Mean SPAD ± SE K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30 0 43.3 ± 1.3 a 38.7 ± 0.7 b 39.0 ± 0.2 b 38.8 ± 0.5 b 39.9 ± 1.2 c 60 42.3 ± 1.7 a 39.9 ± 0.4 ab 40.1 ± 0.6 ab 42.5 ± 0.9 a 44.5 ± 1.9 b 120 41.4 ± 1.7 a 40.3 ± 0.5 a 40.8 ± 0.7 ab 42.9 ± 0.6 a 45.2 ± 1.5 ab 240 43.8 ± 0.1 a 39.2 ± 0.1 ab 41.4 ± 0.8 a 43.3 ± 0.6 a 48.7 ± 0.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

164

-1 Table I-16. Effect of 0, 60, 120, and 240 g plant of 9 potassium silicate (K2SiO3, 25% Si) soil drench applications (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values under well-watered greenhouse conditions from February 22 to June 21, 2013 at UF-TREC, Homestead, FL. Mean SPAD ± SE K2SiO3 rate (g plant-1) February 22 March 1 March 15 March 29 April 12 0 41.8 ± 1.1 b 55.7 ± 0.6 b 52.8 ± 1.3 b 48.5 ± 1.2 a 40.8 ± 0.9 b 60 44.6 ± 0.9 a 59.4 ± 1.6 a 56.8 ± 0.6 a 45.0 ± 1.1 b 44.8 ± 1.1 a 120 46.0 ± 0.6 a 57.9 ± 0.7 ab 57.4 ± 1.2 a 48.8 ± 1.0 a 43.8 ± 0.9 a 240 44.9 ± 0.6 a 57.5 ± 1.0 ab 55.9 ± 0.3 a 49.2 ± 1.0 a 44.9 ± 0.8 a

Mean SPAD ± SE K2SiO3 rate (g plant-1) April 26 May 10 May 24 June 7 June 21 0 40.1 ± 0.7 a 34.0 ± 3.2 a 40.4 ± 0.2 a 47.9 ± 0.9 b 46.0 ± 1.8 b 60 41.6 ± 1.0 a 35.3 ± 2.5 a 45.2 ± 0.4 a 50.6 ± 0.6 a 51.8 ± 0.6 a 120 41.3 ± 1.2 a 37.5 ± 2.8 a 45.7 ± 1.1 a 53.0 ± 1.0 a 51.5 ± 0.2 a 240 40.9 ± 0.3 a 35.7 ± 2.7 a 46.1 ± 0.7 a 52.5 ± 0.7 a 51.2 ± 0.6 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

165

Table I-17. Concentration of constituent and total mineral elementsz of Krome soil (n = 2) prior to soil drench K2SiO3 applications to ‘Red Lady’ papaya (C. papaya L.) plants under well-watered plastic-house (Exp. 1) and greenhouse (Exp. 2) conditions at UF-TREC. Soil drench Constituent / Element Plastic-house Greenhouse pHy 8.2 8.1

OMx (%) 7.9 7

Nw (g kg-1) 1.3 1.5 P (g kg-1) 1.7 1.8

K (g kg-1) 0.9 0.9

Ca (g kg-1) 230 231

Mg (g kg-1) 3 3

Fe (g kg-1) 19.8 20.6

Al (g kg-1) 33.9 34

Mn (g kg-1) 0.4 0.5

Cu (g kg-1) 0.3 0.2

B (mg kg-1) 12.5 7

Zn (mg kg-1) 64.5 52

Siv (g kg-1) 35.1 29.3 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

166

Table I-18. Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to soil drench K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered plastic-house (Exp. 1) and greenhouse (Exp. 2) conditions at UF-TREC. Soil drench Constituent / Element Plastic-house Greenhouse

y -1 NH4-N (mg kg ) 3.2 3.1

x -1 NO3-N (mg kg ) 10 12

P (g kg-1) 88 70

K (g kg-1) 130 143

Ca (g kg-1) 16.1 20.6

Mg (g kg-1) 0.1 0.2

Fe (g kg-1) 0.1 0.02

Al (g kg-1) 0.4 0.3

w -1 SO4-S (g kg ) 1.7 1.2

Mn (g kg-1) 0.1 0.1

Cu (g kg-1) 0.1 0.1

B (mg kg-1) 0.3 0.5

Zn (mg kg-1) 19 17

Siv (mg kg-1) 27 28 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

167

Table I-19. Soil pH and organic matter (OM) and concentration of total mineral elementsz and silicon of Krome soil (n = 2) collected after 11 soil drench potassium silicate (K2SiO3, 25% Si) applications (Exp. 1) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 60 g Si plant-1 120 g Si plant-1 240 g Si plant-1 pHy 8 7.8 8 8.1 OMx (%) 8.1 7.6 8.4 7.1 Nw (g kg-1) 1.2 1.2 1.1 1.5 P (g kg-1) 1.9 1.8 2.1 1.9 K (g kg-1) 0.9 0.9 0.9 0.9 Ca (g kg-1) 205 211 197 219 Mg (g kg-1) 2.2 2.3 2.3 3.2 Fe (g kg-1) 14.4 17.4 19.7 22 Al (g kg-1) 31.9 34.1 33.7 29 Mn (g kg-1) 0.7 0.7 0.7 0.4 Cu (g kg-1) 0.1 0.04 0.05 0.04 B (mg kg-1) 11 11 12 12 Zn (mg kg-1) 24 28 27 25.2 Siv (g kg-1) 27 30.5 29.1 29.4 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

168

Table I-20. Soil pH and organic matter (OM) and concentration of total mineral elementsz and silicon of Krome soil (n = 2) collected after 9 soil drench potassium silicate (K2SiO3, 25% Si) applications (Exp. 2) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 60 g Si plant-1 120 g Si plant-1 240 g Si plant-1 pHy 8.1 7.9 8 8 OMx (%) 7.4 7.0 7 6.8 Nw (g kg-1) 1.6 1.4 1.1 1.8 P (g kg-1) 1.7 1.8 2.1 2.5 K (g kg-1) 0.9 0.9 1.1 1 Ca (g kg-1) 286 227.5 236 190 Mg (g kg-1) 1.8 2.3 1.7 2.1 Fe (g kg-1) 12.4 13.4 13.9 15.1 Al (g kg-1) 32.4 29.3 24.1 22.4 Mn (g kg-1) 0.4 0.5 0.3 0.1 Cu (g kg-1) 0.3 0.4 0.3 0.2 B (mg kg-1) 9.9 10.9 9.1 10 Zn (mg kg-1) 54.5 50.0 49 41 Siv (g kg-1) 27.1 32.4 37.3 41 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a).

169

Table I-21. Concentration of constituent and plant available nutrient elementsz and silicon of Krome very gravelly sandy soil (n = 2) after 11 soil drench potassium silicate (K2SiO3, 25% Si) applications (Exp. 1) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 60 g Si plant-1 120 g Si plant-1 240 g Si plant-1

y -1 NH4-N (mg kg ) 2.3 3.3 3.4 3.3 x -1 NO3-N (mg kg ) 10.4 6.9 6.2 7.5 P (g kg-1) 0.1 0.1 0.1 0.1 K (g kg-1) 0.1 0.1 0.1 0.1 Ca (g kg-1) 14.7 15.9 15 22.7 Mg (g kg-1) 0.1 0.1 0.1 0.2 Fe (g kg-1) 0.1 0.02 0.02 0.02 Al (g kg-1) 0.4 0.4 0.4 0.3 w -1 SO4-S (g kg ) 0.9 1.8 0.9 0.7 Mn (g kg-1) 0.1 0.1 0.1 0.04 Cu (g kg-1) 0.1 0.02 0.02 0.1 B (mg kg-1) 1.3 0.9 1.2 0.4 Zn (mg kg-1) 8 8.1 8 9.2 Siv (mg kg-1) 19 183 235 275 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

170

Table I-22. Concentration of constituent and plant available nutrient elementsz and silicon of Krome very gravelly sandy soil (n = 2) after 9 soil drench potassium silicate (K2SiO3, 25% Si) applications (Exp. 2) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 60 g Si plant-1 120 g Si plant-1 240 g Si plant-1

y -1 NH4-N (mg kg ) 3.1 3.4 3.8 3.7 x -1 NO3-N (mg kg ) 5.9 4.1 5.7 4.4 P (g kg-1) 0.2 0.4 0.5 0.3 K (g kg-1) 0.2 0.3 0.2 0.3 Ca (g kg-1) 19.1 18.2 17 18.4 Mg (g kg-1) 0.2 0.2 0.1 0.2 Fe (g kg-1) 0.2 0.4 0.5 0.3 Al (g kg-1) 0.3 0.3 0.2 0.3 w -1 SO4-S (g kg ) 0.8 1.0 0.9 0.8 Mn (g kg-1) 0.1 0.1 0.2 0.1 Cu (g kg-1) 0.1 0.1 0.2 0.1 B (mg kg-1) 0.2 0.1 0.07 0.02 Zn (mg kg-1) 25 29 28.3 26.3 Siv (mg kg-1) 22 77 113 202 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

171

Table I-23. Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and after 6 and 11 soil drench applications of potassium silicate (K2SiO3, 25% Si) [Exp. 1] to ‘Red Lady’ papaya (Carica papaya L.) plants under well- watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Silicon concentration, g kg-1 K SiO rate 2 3 (g plant-1) 0 application 6 applications 11 applications Total Availablez Total Availablez Total Availablez Non-treated soil 35.1 27.0 - - - - 0 - - 26.3 a 0.04 b 27.4 b 0.05 d 60 - - 30.5 a 0.08 a 30.5 a 0.18 c 120 - - 30.8 a 0.09 a 29.1 ab 0.24 b 240 - - 28.3 a 0.10 a 29.4 ab 0.28 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

172

Table I-24. Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and after 5 and 9 soil drench applications of potassium silicate (K2SiO3, 25% Si) [Exp. 2] to ‘Red Lady’ papaya (Carica papaya L.) plants under well- watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL. Silicon concentration, g kg-1 K SiO rate 2 3 (g plant-1) 0 application 5 applications 9 applications Total Availablez Total Availablez Total Availablez Non-treated soil 29.3 28.0 - - - - 0 - - 29.7 b 0.04 c 27.1 c 0.02 c 60 - - 29.0 b 0.05 bc 32.4 bc 0.08 bc 120 - - 30.4 ab 0.08 ab 37.3 ab 0.11 ab 240 - - 32.0 a 0.10 a 41.0 a 0.20 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

173

-1 -1 Table I-25. Effect of 11 soild drench potassium silicate (K2SiO3, 25% Si) applications at a 0, 60, 120, and 240 g plant application (Exp. 1) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue silicon content (n = 4) under well-watered plastic-house conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL.

z -1 K2SiO3 rate Mean plant tissue silicon concentration ± SE (mg kg ) (g plant-1) Main roots Fibrous roots Leaf lamina Petiole Trunk

0 1,211.0 ± 256.0 3,468.3 ± 1,018.7 842.7 ± 408.6 184.0 ± 53.4 184.5 ± 81.8

60 1,923.0 ± 1,144.3 2,937.7 ± 1,061.5 1,477.7 ± 636.6 544.8 ± 258.6 194.8 ± 82.9 120 1,179.5 ± 226.2 3,297.7 ± 1,019.9 1,725.0 ± 902.3 213.0 ± 92.2 192.5 ± 103.8 240 1,574.8 ± 375.7 4,747.8 ± 1,098.8 2,137.3 ± 736.3 288.3 ± 14.9 191.8 ± 109.8 Linear Y = 1,433. 9 + 10.2x Y = 2,788.0 + 220.0x Y = 944.2 + 160.4x Y = 331.1 – 6.3x Y = 189.0 + 0.5x regression r2 0.0004 0.06 0.07 0.002 0.00004 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

174

-1 -1 Table I-26. Effect of 9 soil drench potassium silicate (K2SiO3, 25% Si) applications at a 0, 60, 120, and 240 g plant application (Exp. 2) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue silicon content (n = 4) under well-watered greenhouse conditions from February 25 to June 14, 2013 at UF-TREC, Homestead, FL.

z -1 K2SiO3 rate Mean plant tissue silicon concentration ± SE (mg kg ) (g plant-1) Root Leaf lamina Petiole Trunk

0 2,612.7 ± 181.2 622.5 ± 64.3 175.5 ± 21.6 288.5 ± 46.9

60 4,204.8 ± 537.1 1,146.8 ± 88.2 303.6 ± 38.2 279.0 ± 46.6

120 4,031.9 ± 464.7 1,228.7 ± 76.4 487.5 ± 80.5 367.7 ± 45.2

240 3,272.3 ± 259.2 1,378.6 ± 91.1 390.7 ± 53.0 416.3 ± 54.0 Linear Y = 3,482.0 + 12.9x Y = 774.9 + 85.1x Y = 239.1 + 26.7x Y = 262.3 + 20.2x regression r2 0.0003 0.23 0.07 0.05 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

175

-1 Table I-27. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant height under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean height ± SE (cm) K2SiO3 rate (g plant-1) July 19 July 31 August 13 August 23 September 7 September 21 0 128.9 ± 5.8 a 134.8 ± 6.1 a 138.7 ± 4.9 a 139.0 ± 5.5 a 126.8 ± 11.5 a 128.1 ± 6.5 a 2.5 130.9 ± 2.7 a 135.6 ± 3.0 a 139.9 ± 2.3 a 140.2 ± 2.8 a 133.4 ± 4.7 a 133.5 ± 5.3 a 5 122.6 ± 11.8 a 128.2 ± 12.1 a 131.3 ± 11.5 a 136.7 ± 7.2 a 132.3 ± 15.4 a 129.7 ± 14.1 a 10 118.9 ± 13.2 a 123.1 ± 13.3 a 126.3 ± 13.5 a 127.3 ± 13.4 a 131.4 ± 8.8 a 133.3 ± 7.8 a

Mean height ± SE (cm) K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30 0 138.7 ± 1.3 a 144.3 ± 2.8 a 143.9 ± 2.5 a 147.6 ± 5.5 a 163.3 ± 6.8 a 2.5 144.7 ± 7.7 a 151.3 ± 6.3 a 152.6 ± 7.1 a 158.8 ± 7.5 a 152.8 ± 11.8 a 5 138.5 ± 12.1 a 145.5 ± 12.6 a 147.2 ± 12.4 a 152.1 ± 13.3 a 165.3 ± 8.6 a 10 144.1 ± 6.5 a 151.5 ± 8.7 a 154.8 ± 8.8 a 153.4 ± 9.7 a 149.0 ± 7.8 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

176

-1 Table I-28. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant height under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL. Mean height ± SE (cm) K2SiO3 rate (g plant-1) April 24 May 8 May 22 June 4 June 18 July 2 0 43.9 ± 11.5 a 67.0 ± 2.3 a 79.5 ± 2.8 a 91.8 ± 3.0 ab 92.5 ± 3.6 a 98.6 ± 3.6 a 2.5 44.2 ± 11.8 a 67.5 ± 1.7 a 82.5 ± 1.7 a 96.8 ± 2.7 a 92.2 ± 1.9 a 104.9 ± 2.3 a 5 47.6 ± 13.6 a 72.9 ± 3.8 a 86.0 ± 4.2 a 88.0 ± 1.2 b 95.3 ± 3.5 a 96.6 ± 2.0 a 10 47.4 ± 12.6 a 68.8 ± 3.1 a 83.3 ± 2.0 a 89.4 ± 3.1 ab 93.9 ± 2.8 a 98.2 ± 4.2 a

Mean height ± SE (cm) K2SiO3 rate (g plant-1) July 16 July 30 August 13 August 27 September 10 September 24 0 103.0 ± 5.0 a 106.9 ± 5.9 a 119.3 ± 6.5 a 123.4 ± 14.4 a 128.5 ± 21.9 a 130.0 ± 22.6 a 2.5 106.1 ± 1.7 a 108.8 ± 1.4 a 124.7 ± 1.2 a 123.6 ± 1.9 a 125.5 ± 4.6 a 120.3 ± 3.5 a 5 108.6 ± 2.2 a 112.1 ± 1.1 a 131.6 ± 0.7 a 125.9 ± 3.0 a 130.5 ± 8.0 a 129.3 ± 6.6 a 10 106.2 ± 4.8 a 109.5 ± 4.8 a 130.3 ± 5.4 a 131.5 ± 6.1 a 134.8 ± 3.3 a 133.3 ± 4.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

177

-1 Table I-29. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) July 19 July 31 August 13 August 23 September 7 September 21 0 29.0 ± 0.6 a 30.5 ± 0.7 a 30.4 ± 0.5 a 29.9 ± 0.5 a 33.1 ± 0.7 a 36.2 ± 1.3 a 2.5 28.0 ± 0.5 a 29.5 ± 0.6 a 29.6 ± 0.6 a 29.1 ± 0.6 a 35.6 ± 1.2 a 36.7 ± 0.9 a 5 27.9 ± 1.1 a 29.2 ± 0.5 a 29.0 ± 0.5 a 28.6 ± 0.7 a 31.2 ± 2.0 a 33.1 ± 2.1 a 10 27.1 ± 1.1 a 28.7 ± 1.1 a 28.5 ± 1.2 a 28.2 ± 1.1 a 32.73± 1.8 a 34.6 ± 2.1 a

Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30 0 40.2 ± 1.4 a 41.9 ± 1.5 a 41.4 ± 1.2 a 43.2 ± 2.5 a 49.2 ± 2.9 a 2.5 38.2 ± 1.3 a 41.3 ± 1.1 a 40.2 ± 1.1 a 43.1 ± 2.1 a 46.7 ± 5.0 a 5 35.4 ± 2.4 a 38.6 ± 2.7 a 38.2 ± 2.5 a 39.5 ± 1.5 a 48.7 ± 4.4 a 10 36.5 ± 2.1 a 40.2 ± 2.5 a 38.0 ± 1.5 a 41.7 ± 3.5 a 48.6 ± 2.2 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

178

-1 Table I-30. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL. Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) April 24 May 8 May 22 June 4 June 18 July 2 0 18.3 ± 1.8 a 26.6 ± 1.1 a 35.0 ± 2.9 a 39.9 ± 1.2 a 41.1 ± 1.1 ab 46.4 ± 1.2 a 2.5 17.8 ± 1.5 a 25.9 ± 1.0 a 32.2 ± 1.0 a 37.8 ± 1.1 a 43.0 ± 1.3 a 45.3 ± 0.9 a 5 19.6 ± 2.4 a 28.4 ± 1.9 a 35.0 ± 1.7 a 41.2 ± 1.8 a 38.9 ± 1.0 b 47.9 ± 1.5 a 10 19.0 ± 1.6 a 26.9 ± 0.8 a 34.5 ± 0.8 a 40.5 ± 1.0 a 41.7 ± 1.5 ab 46.9 ± 0.8 a

Mean trunk diameter ± SE (mm) K2SiO3 rate (g plant-1) July 16 July 30 August 13 August 27 September 10 September 24 0 47.1 ± 1.0 a 46.9 ± 0.4 c 48.6 ± 0.9 b 53.0 ± 0.9 a 54.2 ± 0.8 a 58.4 ± 1.1 a 2.5 46.4 ± 0.2 a 48.3 ± 0.9 bc 49.9 ± 1.4 ab 51.0 ± 0.7 a 53.9 ± 1.3 a 57.5 ± 1.5 a 5 49.4 ± 1.5 a 51.9 ± 0.7 a 53.6 ± 1.4 a 54.8 ± 2.5 a 54.4 ± 2.7 a 57.1 ± 3.5 a 10 48.6 ± 1.1 a 50.5 ± 1.2 ab 52.6 ± 2.2 ab 56.0 ± 2.3 a 56.4 ± 2.2 a 59.8 ± 3.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

179

-1 Table I-31. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight under well-watered greenhouse conditions from August 1 to December 23, 2012 at UF-TREC, Homestead, FL. Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) August 1 August 23 September 23 0 348.4 ± 118.8 400.5 ± 138.1 827.1 ± 333.3 2.5 347.0 ± 114.1 402.6 ± 130.4 933.1 ± 447.1 5 365.7 ± 116.6 429.4 ± 135.9 933.6 ± 367.1 10 412.3 ± 128.4 457.6 ± 131.8 1,036.8 ± 415.7 Linear Y = 332.1 + 9.7x Y = 390.3 + 8.6x Y = 837.1 + 25.5x regression r2 0.01 0.01 0.01

Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) October 23 November 23 December 23 0 1,369.0 ± 489.2 1,447.9 ± 605.4 903.4 ± 41.6 2.5 1,666.1 ± 482.4 2,074.0 ± 798.3 2,824.7 ± 1,220.0 5 1,600.9 ± 561.2 1,990.0 ± 762.6 3,629.3 ± 940.8 10 1,439.7 ± 559.4 1,787.6 ± 753.7 1,622.9 ± 144.2 Linear Y = 1,540.0 – 5.6x Y = 1,761.8 + 16.8x Y = 2,195.9 + 13.1x regression r2 0.0002 0.001 0.0004 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

180

-1 Table I-32. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight under well-watered plastic-house conditions from April 25 to September 18, 2013 at UF-TREC, Homestead, FL. Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) April 25 May 18 June 18 0 159.0 ± 57.4 203.0 ± 72.5 340.2 ± 131.3 2.5 212.2 ± 74.6 254.6 ± 90.0 391.2 ± 142.0 5 242.7 ± 97.2 261.2 ± 91.5 409.2 ± 138.8 10 240.3 ± 102.2 299.6 ± 103.2 511.7 ± 196.9 Linear Y = 177.9 + 9.5x Y = 210.9 + 11.6x Y = 327.4 + 22.9x regression r2 0.03 0.04 0.05

Mean plant tissue fresh weight ± SE (g) K2SiO3 rate (g plant-1) July 18 August 18 September 18 0 487.0 ± 188.1 642.6 ± 202.9 764.7 ± 249.4 2.5 575.8 ± 212.0 687.5 ± 223.9 741.5 ± 283.5 5 634.0 ± 281.6 820.6 ± 294.7 792.6 ± 287.7 10 612.4 ± 229.9 746.5 ± 238.5 933.2 ± 322.8 Linear Y = 523.3 + 14.4x Y = 671.1 + 14.2x Y = 708.4 + 26.6x regression r2 0.01 0.01 0.02 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

181

-1 Table I-33. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight under well-watered greenhouse conditions from August 1 to December 23, 2012 at UF-TREC, Homestead, FL. Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) August 1 August 23 September 23 0 61.0 ± 17.2 62.9 ± 22.8 135.3 ± 54.1 2.5 71.2 ± 16.2 70.6 ± 24.3 161.7 ± 74.0 5 78.4 ± 17.6 76.1 ± 23.5 173.0 ± 76.5 10 92.1 ± 19.5 84.3 ± 28.2 179.6 ± 75.9 Linear Y = 60.2 + 4.1x Y = 63.0 + 2.8x Y = 142.7 + 5.3x regression r2 0.10 0.02 0.01

Mean plant tissue dry weight ± SE (g) K2SiO3 rate -1 (g plant ) October 23 November 23 December 23 0 340.9 ± 119.8 255.5 ± 123.1 192.4 ± 23.2 2.5 395.6 ± 118.8 313.0 ± 93.6 431.3 ± 198.9 5 402.1 ± 152.6 304.3 ± 92.7 515.6 ± 154.5 10 342.4 ± 129.3 281.7 ± 96.6 251.9 ± 8.6 Linear Y = 379.9 – 2.6x Y = 285.6 + 0.8x Y = 358.8 – 2.9x regression r2 0.001 0.0001 0.001 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

182

-1 Table I-34. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant tissue dry weight under well-watered plastic-house conditions from April 25 to September 18, 2013 at UF-TREC, Homestead, FL. Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) April 25 May 18 June 18 0 24.8 ± 5.3 67.7 ± 24.1 64.4 ± 19.4 2.5 35.5 ± 10.3 86.4 ± 29.6 96.1 ± 30.5 5 30.8 ± 7.2 79.2 ± 27.9 69.4 ± 20.7 10 33.1 ± 8.2 81.5 ± 25.4 82.3 ± 23.6 Linear Y = 28.8 + 0.6x Y = 74.9 + 1.0x Y = 75.2 + 0.8x regression r2 0.01 0.003 0.002

Mean plant tissue dry weight ± SE (g) K2SiO3 rate (g plant-1) July 18 August 18 September 18 0 98.2 ± 38.2 115.0 ± 28.3 116.6 ± 35.0 2.5 104.4 ± 34.9 123.9 ± 30.7 152.1 ± 49.7 5 108.8 ± 35.4 109.3 ± 25.0 124.0 ± 45.5 10 113.1 ± 47.0 132.7 ± 37.0 115.8 ± 40.4 Linear Y = 98.9 + 1.9x Y = 112.7 + 2.0x Y = 135.4 – 2.2x regression r2 0.01 0.01 0.01 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

183

-1 Table I-35. Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) under well-watered greenhouse conditions from July 23 to Dec.8, 2012 at UF-TREC, Homestead, FL. -2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) July 23 August 3 August 16 0 676.7 ± 0.09 a 951.7 ± 0.04 a 1,211.7 ± 0.03 a 2.5 554.2 ± 0.06 a 1,053.3 ± 0.07 a 1,151.7 ± 0.03 a 5 481.7 ± 0.08 a 983.3 ± 0.03 a 1,185.0 ± 0.04 a 10 378.3 ± 0.04 a 1,045.8 ± 0.07 a 1,121.7 ± 0.02 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) August 30 September 14 September 28 0 178.3 ± 0.01 a 558.3 ± 0.05 a 357.5 ± 0.02 b 2.5 262.5 ± 0.06 a 491.7 ± 0.05 a 402.5 ± 0.01 ab 5 166.7 ± 0.01 a 541.7 ± 0.10 a 421.7 ± 0.01 a 10 150.0 ± 0.10 a 516.7 ± 0.05 a 420.8 ± 0.01 ab

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) October 13 October 27 November 10 0 181.7 ± 0.02 a 134.2 ± 0.01 a 146.2 ± 0.02 a 2.5 207.5 ± 0.02 a 160.8 ± 0.02 a 140.0 ± 0.01 a 5 192.5 ± 0.02 a 105.0 ± 0.01 a 141.3 ± 0.01 a 10 196.7 ± 0.02 a 153.3 ± 0.02 a 136.3 ± 0.01 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) November 24 December 8 0 161.2 ± 0.01 a 362.5 ± 0.04 a 2.5 150.0 ± 0.01 a 375.0 ± 0.05 a 5 143.8 ± 0.02 a 285.0 ± 0.04 a 10 147.5 ± 0.01 a 302.5 ± 0.03 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

184

-1 Table I-36. Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) stomatal conductance (gs) under well-watered plastic-house conditions from April 26 to September 20, 2013 at UF-TREC, FL. -2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 (g plant ) April 26 May 18 June 1 0 543.3 ± 0.04 a 500.0 ± 0.09 a 540.0 ± 0.03 b 2.5 730.8 ± 0.05 a 831.7 ± 0.09 ab 772.5 ± 0.07 ab 5 664.2 ± 0.06 a 785.0 ± 0.08 ab 917.5 ± 0.06 a 10 735.8 ± 0.11 a 728.3 ± 0.10 b 890.8 ± 0.07 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 -1 (kg ha year ) June 15 June 29 July 13 0 804.2 ± 0.04 a 852.5 ± 0.07 a 563.3 ± 0.05 a 2.5 954.2 ± 0.16 a 802.5 ± 0.08 a 721.7 ± 0.08 a 5 778.3 ± 0.03 a 712.5 ± 0.07 a 848.3 ± 0.10 a 10 750.8 ± 0.04 a 699.2 ± 0.07 a 677.5 ± 0.08 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 -1 (kg ha year ) July 27 August 9 August 23 0 372.5 ± 0.01 a 255.0 ± 0.02 a 401.2 ± 0.03 a 2.5 359.2 ± 0.01 a 271.7 ± 0.02 a 320.0 ± 0.03 a 5 355.0 ± 0.01 a 305.8 ± 0.04 a 401.3 ± 0.05 a 10 357.5 ± 0.01 a 247.5 ± 0.04 a 360.0 ± 0.05 a

-2 -1 K2SiO3 rate Stomatal conductance (gs) ± SE (mmol H2O m s ) -1 -1 (kg ha year ) September 6 September 20 0 345.0 ± 0.02 a 308.8 ± 0.02 a 2.5 412.5 ± 0.03 a 320.0 ± 0.04 a 5 360.0 ± 0.11 a 418.8 ± 0.04 a 10 372.5 ± 0.12 a 385.0 ± 0.03 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

185

-1 Table I-37. Effect of 0, 2.5, 5, and 10 g plant of 13 K2SiO3 foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) under well-watered greenhouse conditions from July 23 to Dec. 28, 2012 at UF-TREC, Homestead, FL. -2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) July 23 August 3 August 16 0 10.2 ± 0.3 a 10.1 ± 0.3 a 9.2 ± 0.3 a 2.5 10.1 ± 0.2 a 10.1 ± 0.3 a 9.6 ± 0.3 a 5 9.1 ± 0.5 a 10.1 ± 0.2 a 9.6 ± 0.2 a 10 8.8 ± 0.5 a 9.7 ± 0.2 a 9.0 ± 0.2 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) August 30 September 14 September 28 0 4.4 ± 0.2 a 6.5 ± 0.2 a 6.9 ± 0.3 a 2.5 4.6 ± 0.2 a 7.5 ± 0.5 a 6.7 ± 0.2 a 5 4.6 ± 0.2 a 6.8 ± 0.4 a 7.0 ± 0.2 a 10 4.7 ± 0.1 a 7.8 ± 0.4 a 6.7 ± 0.1 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) October 13 October 27 November 10 0 4.3 ± 0.3 a 3.9 ± 0.3 a 4.4 ± 0.3 a 2.5 4.0 ± 0.2 a 4.3 ± 0.3 a 4.3 ± 0.1 a 5 4.2 ± 0.3 a 3.9 ± 0.4 a 4.3 ± 0.3 a 10 4.2 ± 0.3 a 3.2 ± 0.2 a 4.1 ± 0.3 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) November 24 December 8 0 3.7 ± 0.1 ab 7.6 ± 0.4 a 2.5 3.7 ± 0.1 ab 7.8 ± 0.7 a 5 3.5 ± 0.1 b 7.0 ± 0.3 a 10 4.2 ± 0.2 a 7.6 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

186

-1 Table I-38. Effect of 0, 2.5, 5, and 10 g plant of 16 K2SiO3 foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) plant transpiration (E) under well-watered plastic- house conditions from April 26 to September 20, 2013 at UF-TREC, Homestead, FL. -2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) April 26 May 18 June 1 0 10.3 ± 0.2 b 9.0 ± 0.8 b 9.4 ± 0.4 a 2.5 10.9 ± 0.3 ab 11.1 ± 0.9 a 9.9 ± 0.2 a 5 11.2 ± 0.3 a 11.4 ± 0.4 a 9.9 ± 0.4 a 10 11.3 ± 0.4 ab 11.2 ± 0.2 a 9.8 ± 0.2 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) June 15 June 29 July 13 0 7.6 ± 0.3 b 8.2 ± 0.3 a 8.3 ± 0.3 a 2.5 8.1 ± 0.3 ab 8.9 ± 0.3 a 8.7 ± 0.2 a 5 9.2 ± 0.1 a 8.0 ± 0.4 a 8.4 ± 0.2 a 10 8.9 ± 0.2 a 8.0 ± 0.2 a 8.4 ± 0.2 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) July 27 August 9 August 23 0 7.8 ± 0.3 b 9.8 ± 0.2 a 7.9 ± 0.2 c 2.5 8.7 ± 0.3 ab 9.3 ± 0.2 a 9.9 ± 0.2 b 5 9.7 ± 0.2 a 9.7 ± 0.3 a 10.0 ± 0.3 ab 10 9.0 ± 0.3 a 9.5 ± 0.3 a 10.7 ± 0.2 a

-2 -1 K2SiO3 rate Transpiration (E) ± SE (mmol H2O m s ) -1 (g plant ) September 6 September 20 0 6.7 ± 0.2 c 6.3 ± 0.3 b 2.5 9.4 ± 0.4 a 7.7 ± 0.2 ab 5 8.4 ± 0.3 b 8.1 ± 0.6 a 10 8.7 ± 0.4 a 7.8 ± 0.8 ab Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

187

-1 Table I-39. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) values under well-watered greenhouse conditions from July 23 to December 8, 2012 at UF-TREC, Homestead, FL.

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) July 23 August 3 August 16 August 30 September 14 September 28 0 4.0 ± 0.5 a 2.2 ± 0.4 a 1.5 ± 0.1 a 2.0 ± 0.4 b 3.6 ± 0.6 a 4.8 ± 0.7 a 2.5 3.5 ± 0.4 a 3.4 ± 0.5 a 1.4 ± 0.1 a 2.4 ± 0.3 ab 6.1 ± 0.7 a 4.1 ± 0.4 a 5 3.2 ± 0.2 a 2.6 ± 0.4 a 1.2 ± 0.2 a 2.6 ± 0.3 ab 5.4 ± 0.6 a 3.4 ± 0.4 a 10 3.3 ± 0.4 a 2.4 ± 0.3 a 1.4 ± 0.2 a 3.2 ± 0.4 a 5.9 ± 1.0 a 4.6 ± 0.7 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) October 13 October 27 November 10 November 24 December 8 0 3.3 ± 0.4 a 3.4 ± 0.5 a 4.3 ± 0.6 a 2.7 ± 0.2 a 4.6 ± 1.8 a 2.5 3.7 ± 0.4 a 3.8 ± 0.5 a 4.4 ± 0.2 a 2.1 ± 0.2 a 7.7 ± 1.4 a 5 3.7 ± 0.4 a 2.5 ± 0.4 a 4.1 ± 0.3 a 3.0 ± 0.7 a 6.5 ± 1.4 a 10 3.7 ± 0.3 a 3.8 ± 0.7 a 3.9 ± 0.5 a 4.0 ± 0.7 a 6.9 ± 1.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

188

-1 Table I-40. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) net CO2 assimilation (A) values under well-watered plastic-house conditions from April 26 to September 20, 2013 at UF-TREC, Homestead, FL.

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) April 26 May 18 June 1 June 15 June 29 July 13 0 7.7 ± 0.4 a 3.5 ± 0.3 b 4.4 ± 0.4 b 5.8 ± 0.3 c 7.2 ± 0.5 ab 7.1 ± 0.4 b 2.5 9.4 ± 0.7 a 6.0 ± 0.7 ab 7.1 ± 0.4 a 8.0 ± 0.4 b 9.5 ± 0.4 a 8.3 ± 0.3 ab 5 9.1 ± 0.7 a 4.3 ± 0.2 a 6.5 ± 0.4 a 8.7 ± 0.4 ab 9.1 ± 0.3 a 8.5 ± 0.2 a 10 9.6 ± 0.8 a 6.8 ± 0.6 a 6.9 ± 0.4 a 9.7 ± 0.3 a 9.3 ± 0.5 a 8.5 ± 0.3 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate (g plant-1) July 27 August 9 August 23 September 6 September 20 0 4.9 ± 0.3 b 3.7 ± 0.2 c 5.0 ± 0.4 b 5.6 ± 0.6 a 4.5 ± 0.1 c 2.5 6.5 ± 0.2 a 5.4 ± 0.4 b 6.1 ± 0.5 ab 7.2 ± 0.5 a 5.1 ± 0.3 b 5 6.9 ± 0.3 a 5.8 ± 0.4 ab 6.9 ± 0.7 ab 7.2 ± 0.7 a 4.8 ± 0.2 bc 10 7.5 ± 0.4 a 6.4 ± 0.2 a 7.5 ± 0.7 a 6.7 ± 0.3 a 5.6 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

189

-1 Table I-41. Effect of 0, 2.5, 5, and 10 g plant of 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) on ‘Red Lady’ papaya (Carica papaya L.) plant SPAD values under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean SPAD ± SE K2SiO3 rate (g plant-1) July 19 July 31 August 13 August 23 September 7 September 21 0 40.8 ± 0.6 ab 39.5 ± 0.6 b 40.4 ± 0.6 a 39.0 ± 0.8 a 37.7 ± 0.6 b 42.5 ± 0.5 b 2.5 42.0 ± 0.5 a 41.7 ± 0.8 a 39.6 ± 0.3 a 38.8 ± 0.4 a 41.8 ± 0.3 a 44.1 ± 0.9 ab 5 39.7 ± 1.0 b 41.0 ± 0.6 ab 39.1 ± 0.4 a 39.1 ± 0.1 a 41.8 ± 0.6 a 43.8 ± 1.3 b 10 40.0 ± 0.7 ab 40.8 ± 0.8 ab 38.7 ± 1.6 a 38.4 ± 0.5 a 42.7 ± 1.2 a 46.7 ± 0.7 a

Mean SPAD ± SE K2SiO3 rate (g plant-1) October 5 October 19 November 2 November 16 November 30 0 38.5 ± 0.5 b 38.3 ± 0.4 b 36.6 ± 1.5 b 39.1 ± 0.5 b 39.2 ± 1.2 b 2.5 44.8 ± 0.6 a 43.2 ± 0.8 a 44.1 ± 1.3 a 43.9 ± 0.4 a 45.2 ± 1.9 a 5 43.8 ± 0.5 a 42.9 ± 2.8 a 43.6 ± 1.3 a 43.9 ± 2.2 a 44.8 ± 1.5 a 10 44.4 ± 0.7 a 42.6 ± 0.3 a 43.3 ± 0.9 a 42.9 ± 1.1 a 44.3 ± 0.4 ab Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

190

-1 Table I-42. Effect of 0, 2.5, 5, and 10 g plant of 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) on ‘Red Lady’ papaya (Carica papaya L.) SPAD under well-watered plastic-house conditions from April 28 to September 29, 2013 at UF-TREC, Homestead, FL. Mean SPAD ± SE K2SiO3 rate (g plant-1) April 28 May 12 May 26 June 9 June 23 July 7 0 40.6 ± 0.6 a 40.1 ± 0.3 a 40.5 ± 0.6 a 42.0 ± 0.8 a 44.0 ± 0.8 a 38.8 ± 0.7 b 2.5 40.8 ± 0.3 a 41.3 ± 0.2 a 42.7 ± 0.7 ab 43.9 ± 0.8 a 44.7 ± 1.7 a 41.2 ± 0.3 a 5 41.2 ± 0.3 a 42.0 ± 0.2 a 44.2 ± 1.4 a 45.6 ± 2.2 a 45.0 ± 1.1 a 41.4 ± 0.9 a 10 40.2 ± 0.6 a 42.0 ± 0.4 a 44.6 ± 0.4 a 46.1 ± 1.2 a 42.5 ± 1.2 a 43.0 ± 0.7 a

Mean SPAD ± SE K2SiO3 rate (g plant-1) July 21 August 4 August 18 September 1 September 15 September 29 0 39.8 ± 0.6 b 41.4 ± 1.4 a 39.9 ± 0.2 c 39.4 ± 0.5 b 39.9 ± 2.0 a 38.9 ± 2.3 a 2.5 42.7 ± 0.4 a 41.0 ± 1.3 a 41.9 ± 0.4 ab 41.7 ± 0.5 a 41.2 ± 0.6 a 42.9 ± 0.8 a 5 42.9 ± 0.5 a 42.8 ± 0.8 a 41.4 ± 0.2 b 42.4 ± 0.8 a 43.4 ± 0.9 a 41.9 ± 1.3 a 10 43.5 ± 0.7 a 40.5 ± 1.4 a 41.9 ± 0.4 a 42.0 ± 0.5 a 42.7 ± 1.4 a 41.7 ± 1.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

191

Table I-43. Concentration of constituent and total mineral elementsz of Krome soil (n = 2) prior to K2SiO3 foliar applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse (Exp. 3) and plastic-house (Exp. 4) conditions at UF-TREC. Foliar Constituent / Element Greenhouse Plastic-house pHy 8.2 8.1

OMx (%) 7.9 7

Nw (g kg-1) 1.3 1.5 P (g kg-1) 1.7 1.8

K (g kg-1) 0.9 0.9

Ca (g kg-1) 230 231

Mg (g kg-1) 3 3

Fe (g kg-1) 19.8 20.6

Al (g kg-1) 33.9 34

Mn (g kg-1) 0.4 0.5

Cu (g kg-1) 0.3 0.2

B (mg kg-1) 12.5 7

Zn (mg kg-1) 64.5 52

Siv (g kg-1) 35.1 29.3 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

192

Table I-44. Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to K2SiO3 foliar applications of ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse (Exp. 3) and plastic-house (Exp. 4) conditions at UF-TREC. Foliar Constituent / Element Greenhouse Plastic-house

y -1 NH4-N (mg kg ) 3.2 3.1

x -1 NO3-N (mg kg ) 10 12

P (g kg-1) 88 70

K (g kg-1) 130 143

Ca (g kg-1) 16.1 20.6

Mg (g kg-1) 0.1 0.2

Fe (g kg-1) 0.1 0.02

Al (g kg-1) 0.4 0.3

w -1 SO4-S (g kg ) 1.7 1.2

Mn (g kg-1) 0.1 0.1

Cu (g kg-1) 0.1 0.1

B (mg kg-1) 0.3 0.5

Zn (mg kg-1) 19 17

Siv (mg kg-1) 27 28 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

193

Table I-45. Soil pH and organic matter (OM) and concentration of total mineral elementsz and silicon of Krome very gravelly sandy soil (n = 2) collected after 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, FL Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1 pHy 8 7.9 8.2 8.1 OMx (%) 6.8 6.8 6.9 6.8 Nw (g kg-1) 1.2 1.2 1.5 1.6 P (g kg-1) 1.8 1.8 1.9 1.6 K (g kg-1) 0.9 0.8 0.9 0.8 Ca (g kg-1) 216 181 174 159 Mg (g kg-1) 2.4 2.4 2.6 2.5 Fe (g kg-1) 17.2 19.1 18.8 15.6 Al (g kg-1) 33.1 35.2 34.6 29 Mn (g kg-1) 0.5 0.4 0.5 0.4 Cu (g kg-1) 0.2 0.2 0.1 0.2 B (mg kg-1) 10.5 12 16.5 12 Zn (mg kg-1) 33 27 18 22.5 Siv (g kg-1) 17 18 19 19 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

194

Table I-46. Soil pH and organic matter (OM) and concentration of total mineral elementsz and silicon of Krome very gravelly sandy soil (n = 2) collected after 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) to ‘Red Lady’ papaya plants under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1 pHy 8.0 7.8 7.7 7.8 OMx (%) 7.1 7.0 6.5 6.9 Nw (g kg-1) 1.4 1.3 1.2 1.4 P (g kg-1) 1.8 1.9 1.9 1.8 K (g kg-1) 0.8 0.8 0.8 0.7 Ca (g kg-1) 211.7 204.7 208.3 199 Mg (g kg-1) 2.7 2.5 2.2 2.5 Fe (g kg-1) 20.6 21.3 24.0 27.2 Al (g kg-1) 28.9 29.3 28.0 28.2 Mn (g kg-1) 0.5 0.5 0.6 0.5 Cu (g kg-1) 0.1 0.1 0.1 0.1 B (mg kg-1) 13.3 10.3 8.7 12.0 Zn (mg kg-1) 24.8 25.3 25.3 24.8 Siv (g kg-1) 24.5 23.8 24.0 24.5 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

195

Table I-47. Concentration of constituent and plant available nutrient elementsz and silicon of Krome very gravelly sandy soil (n = 2) collected after 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1

y -1 NH4-N (mg kg ) 2.0 3.6 3.5 3.2 x -1 NO3-N (mg kg ) 13.8 6.0 12 7.9 P (g kg-1) 0.1 0.1 0.1 0.1 K (g kg-1) 0.1 0.1 0.2 0.1 Ca (g kg-1) 18.4 19.4 19.2 17.4 Mg (g kg-1) 0.2 0.2 0.2 0.1 Fe (g kg-1) 0.02 0.02 0.02 0.01 Al (g kg-1) 0.3 0.4 0.3 0.36 w -1 SO4-S (g kg ) 1.1 1.0 1.1 1.2 Mn (g kg-1) 0.1 0.04 0.04 0.1 Cu (g kg-1) 0.03 0.1 0.04 0.1 B (mg kg-1) 1.2 0.6 1 0.7 Zn (mg kg-1) 11 14 9.5 12.5 Siv (mg kg-1) 15 76 106 132 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

196

Table I-48. Concentration of constituent and plant available nutrient elementsz and silicon of Krome very gravelly sandy soil (n = 2) collected after 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1

y -1 NH4-N (mg kg ) 3.5 3.1 3.0 3.2 x -1 NO3-N (mg kg ) 8.8 6.0 5.7 5.0 P (g kg-1) 0.1 0.1 0.1 0.1 K (g kg-1) 0.1 0.1 0.2 0.1 Ca (g kg-1) 17.2 18.2 17.8 18.0 Mg (g kg-1) 0.2 0.2 0.2 0.1 Fe (g kg-1) 0.01 0.02 0.02 0.04 Al (g kg-1) 0.3 0.4 0.3 0.3 w -1 SO4-S (g kg ) 1.0 1.3 1.1 1.0 Mn (g kg-1) 0.1 0.1 0.1 0.1 Cu (g kg-1) 0.1 0 0 0.1 B (mg kg-1) 1.2 0.7 1.1 0.9 Zn (mg kg-1) 10.0 9.8 10.3 10.0 Siv (mg kg-1) 20.3 20.3 24.0 25.8 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

197

Table I-49. Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and after 7 and 13 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 3) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL. Mean silicon concentration, g kg-1 K SiO rate 2 3 (g plant-1) 0 applications 7 applications 13 applications Total Availabley Total Availabley Total Availabley Non-treated soil 35.1 0.027 - - - - 0 - - 27.4 a 0.05 b 17.0 a 0.05 a 2.5 - - 30.5 a 0.03 a 17.7 b 0.08 b 5 - - 29.1 a 0.04 a 19.3 a 0.11 b 10 - - 29.4 a 0.03 a 19.2 a 0.13 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

198

Table I-50. Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and after 9 and 16 potassium silicate (K2SiO3, 25% Si) foliar applications (Exp. 4) to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL. Silicon concentration, g kg-1 K SiO rate 2 3 (g plant-1) 0 applications 9 applications 16 applications Total Availabley Total Availabley Total Availabley Non-treated soil 29.3 0.028 - - - - 0 - - 18.9 a 0.03 ab 17.7 a 0.03 ab 2.5 - - 18.1 a 0.02 b 17.6 a 0.03 b 5 - - 18.6 a 0.03 ab 18.0 a 0.04 ab 10 - - 19.8 a 0.03 a 18.3 a 0.04 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

199

-1 -1 Table I-51. Effect of 13 potassium silicate (K2SiO3, 25% Si) foliar applications at a 0, 2.5, 5, and 10 g plant application (Exp. 3) to ‘Red Lady’ papaya (Carica papaya L.) plant tissue silicon content (n = 4) under well-watered greenhouse conditions from July 19 to November 30, 2012 at UF-TREC, Homestead, FL.

Mean plant tissue silicon concentrationz ± SE (mg kg-1) K2SiO3 rate (g plant-1) Main roots Fibrous roots Leaf lamina Petiole Trunk

0 983.3 ± 362.1 3,560.8 ± 772.9 415.5 ± 83.2 147.8 ± 68.4 90.3 ± 23.3

2.5 890.2 ± 134.6 4,162.3 ± 1,359.1 742.8 ± 216.2 116.3 ± 23.1 77.0 ± 35.3 5 1,180.0 ± 203.3 3,317.2 ± 1,170.7 973.5 ± 327.9 142.3 ± 23.1 106.2 ± 16.5 10 1,163.5 ± 255.1 3,314.5 ± 766.7 1,034.2 ± 392.6 151.8 ± 38.0 82.8 ± 27.8 Linear Y = 926.7 + 34.0x Y = 3870.5 – 75.2x Y = 505.2 + 76.4x Y = 130.4 + 2.5x Y = 89.7 – 0.2x regression r2 0.03 0.01 0.09 0.01 0.0004 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

200

-1 -1 Table I-52. Effect of 16 potassium silicate (K2SiO3, 25% Si) foliar applications at a 0, 2.5, 5, and 10 g plant application (Exp. 4) to ‘Red Lady’ papaya (Carica papaya L.) plant tissue silicon content (n = 4) under well-watered plastic-house conditions from April 24 to September 24, 2013 at UF-TREC, Homestead, FL.

Mean plant tissue silicon concentrationz ± SE (mg kg-1) K2SiO3 rate (g plant-1) Roots Leaf lamina Petiole Trunk

0 1,974.5 ± 159.4 887.3 ± 44.5 314.8 ± 65.7 169.0 ± 10.0

2.5 2,691.8 ± 247.6 2,505.8 ± 278.5 286.9 ± 20.0 185.4 ± 11.8

5 2,187.0 ± 221.3 2,412.3 ± 239.5 327.0 ± 13.1 228.5 ± 13.6

10 2,498.8 ± 171.0 2,983.7 ± 319.8 315.4 ± 14.3 219.3 ± 8.4 Linear Y = 2,204.2 + 35.7x Y = 1,354.9 + 224.6x Y = 303.9 + 1.9x Y = 174.5 + 7.0x regression r2 0.01 0.18 0.001 0.10 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

201

-1 -1 Table I-53. Comparison of the effect of 9 foliar applications at 0, 2.5, 5, and 10 g plant application of potassium silicate (K2SiO3, 25% Si) to ‘Red Lady’ papaya (Carica papaya L.) plant height under well-watered and drought stressed conditions in a plastic-house from August 1 to December 5, 2013 at UF-TREC, Homestead, FL (Exp. 5). Mean height ± SE (cm) K SiO rate 2 3 (g plant-1) August 1 August 15 Well-watered Drought p≤value Well-watered Drought p≤value 0 33.7 ± 1.1 a 34.0 ± 1.7 a NS 0.7820 50.8 ± 1.4 a 43.7 ± 1.8 b * 0.0312 2.5 31.2 ± 0.6 b 35.7 ± 0.9 a NS 0.8182 49.8 ± 0.2 a 50.3 ± 0.9 a NS 0.8471 5 32.2 ± 0.7 ab 31.0 ± 2.1 a NS 0.4838 50.3 ± 0.8 a 50.3 ± 0.3 a NS 0.9999 10 34.0 ± 0.5 a 31.3 ± 0.3 a NS 0.3750 48.4 ± 0.6 a 48.7 ± 3.4 ab NS 0.1062

Mean height ± SE (cm) K SiO rate 2 3 (g plant-1) August 29 September 12 Well-watered Drought p≤value Well-watered Drought p≤value 0 82.4 ± 3.0 a 69.7 ± 4.4 b * 0.0196 90.3 ± 3.0 a 79.3 ± 4.5 a * 0.0251 2.5 82.2 ± 1.1 a 87.0 ± 1.0 a NS 0.0838 90.6 ± 1.7 a 93.3 ± 4.4 a NS 0.3628 5 82.1 ± 1.8 a 83.7 ± 0.3 a * 0.0252 88.7 ± 2.3 a 90.7 ± 0.7 a NS 0.3158 10 78.9 ± 1.6 a 79.7 ± 6.9 ab NS 0.9223 86.4 ± 2.1 a 84.3 ± 8.7 a NS 0.1992

202

Table I-53 --continued. Mean height ± SE (cm) K SiO rate 2 3 (g plant-1) September 26 October 10 Well-watered Drought p≤value Well-watered Drought p≤value 0 102.1 ± 2.8 a 89.7 ± 6.2 b * 0.0196 109.4 ± 3.7 a 95.3 ± 5.8 a * 0.0313 2.5 101.1 ± 2.3 a 104.0 ± 3.0 a NS 0.3203 108.6 ± 2.0 a 114.0 ± 5.5 a NS 0.1136 5 101.2 ± 2.4 a 104.0 ± 0.6 a NS 0.2581 106.3 ± 2.4 a 108.7 ± 1.2 a NS 0.1768 10 97.2 ± 2.5 a 96.0 ± 7.2 a NS 0.2627 103.8 ± 0.8 a 101.7 ± 9.5 a NS 0.8399

Mean height ± SE (cm) K SiO rate 2 3 (g plant-1) October 24 November 7 Well-watered Drought p≤value Well-watered Drought p≤value 0 112.3 ± 3.5 a 99.0 ± 5.7 a NS 0.9943 117.9 ± 3.5 a 106.7 ± 5.8 a * 0.0325 2.5 111.2 ± 1.7 a 116.3 ± 5.8 a NS 0.0699 116.3 ± 1.7 a 120.0 ± 5.5 a NS 0.2794 5 109.9 ± 2.6 a 113.2 ± 0.4 a * <0.0001 115.1 ± 2.5 a 119.3 ± 1.2 a NS 0.3606 10 107.6 ± 0.9 a 105.7 ± 7.4 a * 0.0125 112.6 ± 0.9 a 111.3 ± 8.4 a NS 0.8953

203

Table I-53 --continued. Mean height ± SE (cm) K SiO rate 2 3 (g plant-1) November 21 December 5 Well-watered Drought p≤value Well-watered Drought p≤value 0 126.1 ± 3.3 a 111.7 ± 7.3 a * 0.0454 130.3 ± 2.9 a 120.3 ± 9.0 a * 0.0483 2.5 125.7 ± 1.6 a 126.0 ± 5.0 a NS 0.3714 133.2 ± 2.4 a 134.0 ± 5.2 a NS 0.1712 5 123.2 ± 2.7 a 127.3 ± 2.7 a NS 0.8907 129.4 ± 3.4 a 133.5 ± 0.3 a * 0.0053 10 120.6 ± 1.5 a 119.7 ± 9.2 a NS 0.0920 129.7 ± 2.7 a 129.0 ± 7.6 a NS 0.2864 Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

204

-1 -1 Table I-54. Comparison of the effect of 9 foliar applications at 0, 2.5, 5, and 10 g plant application of potassium silicate (K2SiO3, 25% Si) to ‘Red Lady’ papaya (Carica papaya L.) plant trunk diameter under well-watered and drought stressed conditions in a plastic-house from August 1 to December 5, 2013 at UF-TREC, Homestead, FL (Exp. 5). Mean trunk diameter ± SE (cm) K SiO rate 2 3 (g plant-1) August 1 August 15 Well-watered Drought p≤value Well-watered Drought p≤value 0 11.4 ± 0.6 a 11.0 ± 0.7 a NS 0.9176 17.0 ± 0.8 a 12.5 ± 0.2 b NS 0.1330 2.5 10.5 ± 0.4 a 12.0 ± 1.3 a NS 0.1632 16.2 ± 0.5 a 16.9 ± 0.4 a NS 0.8878 5 10.5 ± 0.5 a 11.1 ± 0.5 a NS 0.4783 16.4 ± 0.6 a 17.1 ± 0.6 a NS 0.8786 10 11.1 ± 0.6 a 9.2 ± 1.0 a NS 0.0614 17.1 ± 0.9 a 15.7 ± 1.5 a NS 0.5032

Mean trunk diameter ± SE (cm) K SiO rate 2 3 (g plant-1) August 29 September 12 Well-watered Drought p≤value Well-watered Drought p≤value 0 26.7 ± 1.0 a 21.3 ± 0.5 b NS 0.2381 30.8 ± 0.8 a 25.6 ± 1.3 b NS 0.8078 2.5 25.3 ± 0.7 a 27.7 ± 0.7 a NS 0.4377 28.7 ± 0.9 a 30.6 ± 0.8 ab NS 0.7249 5 25.8 ± 0.7 a 26.5 ± 1.3 a NS 0.9213 29.4 ± 0.6 a 31.7 ± 2.1 a NS 0.0885 10 26.7 ± 1.0 a 26.0 ± 1.3 a NS 0.9152 31.1 ± 1.0 a 31.0 ± 1.6 a NS 0.4875

205

Table I-54 --continued. Mean trunk diameter ± SE (cm) K SiO rate 2 3 (g plant-1) September 26 October 10 Well-watered Drought p≤value Well-watered Drought p≤value 0 33.1 ± 0.8 a 28.8 ± 1.2 b * 0.8968 40.3 ± 1.3 a 34.6 ± 3.8 b NS 0.4275 2.5 32.9 ± 1.0 a 33.2 ± 0.8 a NS 0.6662 39.6 ± 1.7 a 43.2 ± 1.8 ab NS 0.6135 5 32.7 ± 0.9 a 34.5 ± 1.3 a NS 0.2466 39.8 ± 1.4 a 42.1 ± 3.6 ab NS 0.3431 10 34.5 ± 1.1 a 36.1 ± 0.6 a NS 0.4036 41.8 ± 1.3 a 45.3 ± 1.2 a NS 0.6559

Mean trunk diameter ± SE (cm) K SiO rate 2 3 (g plant-1) October 24 November 7 Well-watered Drought p≤value Well-watered Drought p≤value 0 41.4 ± 1.3 a 36.6 ± 3.5 b NS 0.4812 42.5 ± 1.2 a 38.2 ± 3.7 b NS 0.2761 2.5 41.8 ± 1.3 a 45.0 ± 1.4 ab NS 0.6449 44.1 ± 1.1 a 46.3 ± 0.9 a NS 0.3329 5 42.2 ± 1.5 a 44.8 ± 3.9 ab NS 0.2815 45.0 ± 1.3 a 46.9 ± 2.6 a NS 0.2794 10 43.4 ± 1.0 a 47.0 ± 1.1 a NS 0.5644 44.1 ± 1.0 a 47.8 ± 0.9 a NS 0.6525

206

Table I-54 --continued. Mean trunk diameter ± SE (cm) K SiO rate 2 3 (g plant-1) November 21 December 5 Well-watered Drought p≤value Well-watered Drought p≤value 0 47.6 ± 1.1 a 42.3 ± 1.8 b NS 0.4339 48.9 ± 0.8 b 45.8 ± 2.6 b NS 0.1424 2.5 48.3 ± 0.9 a 51.4 ± 2.9 a NS 0.1949 51.6 ± 2.1 b 49.6 ± 3.6 ab NS 0.7430 5 50.0 ± 2.3 a 50.6 ± 1.0 a NS 0.4169 55.5 ± 3.3 a 53.7 ± 1.0 ab NS 0.1258 10 48.8 ± 1.0 a 53.5 ± 2.6 a NS 0.3404 51.4 ± 1.5 b 55.1 ± 2.5 a NS 0.1440 Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

207

-1 -1 Table I-55. Comparison of the effect of 9 foliar applications at 0, 2.5, 5, and 10 g plant application of potassium silicate (K2SiO3, 25% Si) to ‘Red Lady’ papaya (Carica papaya L.) plant tissue fresh weight under well-watered and drought stressed conditions in a plastic-house from August 1 to November 11, 2013 at UF-TREC, Homestead, FL (Exp. 5). Mean plant tissue fresh weight ± SE (g) K SiO rate 2 3 Root Leaf lamina (g plant-1) Well-watered Drought p≤value Well-watered Drought p≤value 0 511.9 ± 100.2 819.5 ± 67.1 NS 0.2089 132.9 ± 16.9 134.0 ± 8.6 NS 0.5573 2.5 729.3 ± 174.0 1,058.4 ± 53.1 NS 0.1357 151.4 ± 25.8 169.4 ± 8.0 NS 0.6290 5 876.0 ± 299.3 1,016.0 ± 54.4 NS 0.1646 183.9 ± 41.9 151.1 ± 24.1 NS 0.8224 10 768.6 ± 263.4 1,217.2 ± 27.9 NS 0.2603 171.3 ± 31.0 190.8 ± 27.9 NS 0.7633 Linear Y = 616.9 + 27.9x Y = 855.4 + 46.0x -- -- Y = 141.1 + 5.0x Y = 137.3 + 6.4x -- -- regression r2 0.05 0.59 -- -- 0.08 0.25 -- --

Mean plant tissue fresh weight ± SE (g) K SiO rate 2 3 Petiole Trunk (g plant-1) Well-watered Drought p≤value Well-watered Drought p≤value 0 107.4 ± 21.0 94.2 ± 4.9 NS 0.2107 561.1 ± 94.0 698.3 ± 40.0 NS 0.6897 2.5 125.2 ± 26.5 155.0 ± 9.0 NS 0.1470 702.8 ± 168.2 894.0 ± 78.6 NS 0.4472 5 163.5 ± 46.1 119.0 ± 21.4 NS 0.2238 782.4 ± 229.5 824.9 ± 121.5 NS 0.3171 10 151.7 ± 34.3 162.2 ± 14.3 NS 0.1987 727.4 ± 194.1 908.6 ± 9.5 NS 0.9145 Linear Y = 114.6 + 6.0x Y = 107.9 + 6.6x -- -- Y = 626.4 + 17.9x Y = 755.4 + 20.3x -- -- regression r2 0.09 0.27 -- -- 0.03 0.16 -- -- Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

208

-1 -1 Table I-56. Comparison of the effect of 9 foliar applications at 0, 2.5, 5, and 10 g plant application of potassium silicate (K2SiO3, 25% Si) to ‘Red Lady’ papaya (Carica papaya L.) plant dry weight under well-watered and drought stressed conditions in a plastic-house from August 1 to November 11, 2013 at UF-TREC, Homestead, FL. Mean plant tissue dry weight ± SE (g) K SiO rate 2 3 Root Leaf lamina (g plant-1) Well-watered Drought p≤value Well-watered Drought p≤value 0 83.6 ± 15.5 136.4 ± 6.7 NS 0.9948 34.0 ± 7.3 25.7 ± 1.1 NS 0.5233 2.5 145.5 ± 49.7 170.5 ± 8.4 NS 0.1555 37.8 ± 8.7 34.7 ± 0.5 NS 0.6968 5 141.1 ± 44.5 173.8 ± 13.7 NS 0.7668 50.3 ± 14.0 30.3 ± 2.3 NS 0.4125 10 173.9 ± 65.6 403.4 ± 1.1 NS 0.7810 44.2 ± 10.8 39.3 ± 5.8 NS 0.9549 Linear Y = 98.2 + 10.1x Y = 79.6 + 37.7x -- -- Y = 36.2 + 1.4x Y = 26.8 + 1.5x -- -- regression r2 0.13 0.89 -- -- 0.06 0.36 -- --

Mean plant tissue dry weight ± SE (g) K SiO rate 2 3 Petiole Trunk (g plant-1) Well-watered Drought p≤value Well-watered Drought p≤value 0 19.8 ± 5.0 15.5 ± 0.5 NS 0.2821 86.6 ± 17.1 107.2 ± 3.2 NS 0.5196 2.5 22.5 ± 6.1 31.1 ± 1.4 NS 0.9448 106.1 ± 27.4 134.0 ± 12.3 NS 0.3036 5 29.7 ± 8.8 22.6 ± 2.3 NS 0.9802 119.1 ± 38.9 120.9 ± 10.3 NS 0.4533 10 27.1 ± 7.3 24.9 ± 2.1 NS 0.6177 134.4 ± 56.2 142.3 ± 1.9 NS 0.0987 Linear Y = 21.1 + 1.0x Y = 21.6 + 0.5x -- -- Y = 88.5 + 6.2x Y = 112.3 + 3.7x -- -- regression r2 0.06 0.05 -- -- 0.09 0.31 -- -- Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

209

-1 -1 Table I-57. Comparison of the effect of 9 foliar applications at 0, 2.5, 5, and 10 g plant application of potassium silicate (K2SiO3, 25% Si) to ‘Red Lady’ papaya (Carica papaya L.) SPAD under well-watered and drought stressed conditions in a plastic- house from August 1 to December 5, 2013 at UF-TREC, Homestead, FL. Mean SPAD ± SE (cm) K SiO rate 2 3 (g plant-1) August 1 August 15 Well-watered Drought p≤value Well-watered Drought p≤value 0 38.9 ± 0.2 b 38.8 ± 0.3 b NS 0.1512 39.3 ± 0.3 b 38.9 ± 0.3 b NS 0.2575 2.5 40.2 ± 0.3 a 40.4 ± 0.6 a NS 0.4168 42.0 ± 0.6 a 42.9 ± 1.4 a NS 0.4380 5 40.1 ± 0.2 a 39.4 ± 0.3 ab NS 0.5310 41.9 ± 0.5 a 40.1 ± 1.0 ab NS 0.7541 10 40.8 ± 0.3 a 40.1 ± 0.4 ab NS 0.8233 42.6 ± 0.4 a 42.1 ± 1.4 ab NS 0.2704

Mean SPAD ± SE (cm) K SiO rate 2 3 (g plant-1) August 29 September 12 Well-watered Drought p≤value Well-watered Drought p≤value 0 40.0 ± 0.5 b 39.0 ± 0.6 c NS 0.0712 38.5 ± 0.8 b 36.7 ± 0.7 b NS 0.5798 2.5 42.9 ± 0.9 a 45.0 ± 1.2 a NS 0.7712 41.4 ± 0.8 a 42.9 ± 0.7 a NS 0.9053 5 43.3 ± 1.0 a 41.3 ± 1.6 bc NS 0.6875 41.1 ± 0.7 a 41.8 ± 1.8 a NS 0.1876 10 44.7 ± 0.6 a 43.7 ± 0.9 ab NS 0.1388 41.4 ± 1.1 a 42.2 ± 0.6 a NS 0.9909

210

Table I-57 --continued. Mean SPAD ± SE (cm) K SiO rate 2 3 (g plant-1) September 26 October 10 Well-watered Drought p≤value Well-watered Drought p≤value 0 39.1 ± 0.8 b 40.6 ± 0.6 b * 0.5069 37.5 ± 1.0 b 38.4 ± 1.1 a NS 0.5855 2.5 42.2 ± 0.5 a 41.5 ± 1.4 ab NS 0.1657 40.1 ± 1.4 ab 39.6 ± 1.5 a NS 0.9143 5 41.6 ± 0.4 a 42.4 ± 0.2 ab NS 0.0884 40.9 ± 0.7 a 38.9 ± 0.4 a NS 0.5528 10 42.0 ± 0.7 a 43.6 ± 0.8 a NS 0.9771 40.3 ± 1.1 ab 38.4 ± 1.7 a NS 0.8581

Mean SPAD ± SE (cm) K SiO rate 2 3 (g plant-1) October 24 November 7 Well-watered Drought p≤value Well-watered Drought p≤value 0 35.7 ± 0.7 b 34.3 ± 2.3 a NS 0.5866 42.6 ± 0.6 b 43.9 ± 2.4 a NS 0.1758 2.5 38.3 ± 1.1 ab 38.4 ± 1.5 a NS 0.1492 46.3 ± 0.9 a 44.9 ± 2.9 a NS 0.3248 5 39.3 ± 1.2 a 34.6 ± 1.4 a NS 0.7492 47.5 ± 1.4 a 46.8 ± 1.8 a NS 0.8840 10 38.1 ± 1.6 ab 38.2 ± 2.7 a NS 0.8519 48.2 ± 1.2 a 49.1 ± 3.2 a NS 0.2038

211

Table I-57 --continued. Mean SPAD ± SE (cm) K SiO rate 2 3 (g plant-1) November 21 December 5 Well-watered Drought p≤value Well-watered Drought p≤value 0 40.2 ± 0.6 c 40.7 ± 0.6 c NS 0.7690 38.3 ± 0.5 c 40.1 ± 1.2 b NS 0.6599 2.5 45.0 ± 1.0 b 42.6 ± 1.4 bc NS 0.8929 41.9 ± 0.6 b 40.3 ± 0.5 b NS 0.4926 5 46.3 ± 1.4 ab 47.7 ± 2.8 ab NS 0.4387 41.2 ± 0.5 b 42.2 ± 0.3 ab NS 0.4804 10 49.5 ± 1.4 a 49.7 ± 1.5 a NS 0.5654 44.1 ± 0.5 a 43.8 ± 1.0 a NS 0.6087 Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

212

Table I-58. Concentration of constituents and total mineral elementsz of Krome soil (n = 2) prior to foliar K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered and drought stressed plastic-house conditions at UF-TREC, Homestead. Constituent / Element Plastic-house pHy 8.1

OMx (%) 7.1

Nw (g kg-1) 1.4 P (g kg-1) 1.8

K (g kg-1) 0.9

Ca (g kg-1) 233

Mg (g kg-1) 3.5

Fe (g kg-1) 22

Al (g kg-1) 33.9

Mn (g kg-1) 0.4

Cu (g kg-1) 0.1

B (mg kg-1) 6

Zn (mg kg-1) 25

Siv (g kg-1) 24.8 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

213

Table I-59. Concentration of plant available nutrient elementsz of Krome soil (n = 2) prior to foliar K2SiO3 applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered and drought stressed plastic-house conditions at UF-TREC, Homestead. Constituent / Element Plastic-house

y -1 NH4-N (mg kg ) 3.2

x -1 NO3-N (mg kg ) 3

P (g kg-1) 94.3

K (g kg-1) 130

Ca (g kg-1) 17.3

Mg (g kg-1) 0.3

Fe (g kg-1) 0.1

Al (g kg-1) 0.5

w -1 SO4-S (g kg ) 1.1

Mn (g kg-1) 0.3

Cu (g kg-1) 0.1

B (mg kg-1) 0

Zn (mg kg-1) 18.5

Siv (mg kg-1) 20.6 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

214

Table I-60. Soil pH and organic matter (OM) and concentration of total mineral elementsz and silicon of Krome soil (n = 2) collected after 9 potassium silicate (K2SiO3, 25% Si) foliar applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well- watered and drought stressed plastic-house conditions from August 1 to December 5, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1 pHy 7.8 7.7 8.0 7.9 OMx (%) 6.6 6.1 6.4 6.7 Nw (g kg-1) 1.2 1.1 1.3 1 P (g kg-1) 1.9 2.0 1.9 1.9 K (g kg-1) 0.9 0.8 0.9 0.7 Ca (g kg-1) 218 213 207 198 Mg (g kg-1) 2.6 2.7 2.2 2.5 Fe (g kg-1) 17.4 17.6 19.2 22.3 Al (g kg-1) 18.2 19.4 20 26 Mn (g kg-1) 0.6 0.4 0.5 0.4 Cu (g kg-1) 0.04 0.04 0.02 0.01 B (mg kg-1) 5.5 6 5 12 Zn (mg kg-1) 20 19 14 21 Siv (g kg-1) 16.3 19 18.3 20.4 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

215

Table I-61. Concentration of constituents and plant available nutrient elementsz and silicon of Krome soil (n = 2) collected after 9 potassium silicate (K2SiO3, 25% Si) foliar applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered and drought stressed plastic-house conditions from August 1 to December 5, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 g Si plant-1 2.5 g Si plant-1 5 g Si plant-1 10 g Si plant-1

y -1 NH4-N (mg kg ) 3.8 2.3 2.5 3.1

x -1 NO3-N (mg kg ) 5.7 5.1 5.4 4.9 P (g kg-1) 0.1 0.1 0.1 0.1 K (g kg-1) 0.2 0.1 0.1 0.1 Ca (g kg-1) 19 15.1 17.6 16.9 Mg (g kg-1) 0.2 0.1 0.2 0.1 Fe (g kg-1) 0.02 0.02 0.02 0.03 Al (g kg-1) 0.4 0.4 0.4 0.4

w -1 SO4-S (g kg ) 1.3 1.1 1.1 1 Mn (g kg-1) 0.1 0.1 0.1 0.04 Cu (g kg-1) 0.02 0.02 0.02 0.02 B (mg kg-1) 0.7 0.6 0.7 0.6 Zn (mg kg-1) 9.5 8 6.3 5.1 Siv (mg kg-1) 23 20 18.4 19.2 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

216

Table I-62. Silicon concentration in Krome very gravelly sandy soil samples (n = 2) collected at 0, and 5 and after 9 potassium silicate (K2SiO3, 25% Si) foliar applications to ‘Red Lady’ papaya (Carica papaya L.) plants under well-watered and drought stressed plastic-house conditions from August 1 to December 7, 2013 at UF-TREC, Homestead, FL. Silicon concentration, g kg-1 K SiO rate 2 3 (g plant-1) 0 applications 5 applications 9 applications Total Availablez Total Availablez Total Availablez Non-treated soil 24.8 0.021 - - - - 0 - - 28.6 b 0.06 b 18.8 b 0.03 b 2.5 - - 32.8 a 0.08 a 19.1 a 0.07 b 5 - - 34.5 a 0.09 a 19.3 a 0.11 a 10 - - 32.7 a 0.07 a 18.6 b 0.10 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

217

-1 -1 Table I-63. Effect of 9 potassium silicate (K2SiO3, 25% Si) foliar applications at a 0, 2.5, 5, and 10 g plant application to ‘Red Lady’ papaya (Carica papaya L.) plant tissue silicon content (n = 3) under well-watered and drought stressed plastic-house conditions from August 1 to December 7, 2013 at UF-TREC, Homestead, FL. Mean plant tissue silicon concentrationz ± SE (mg kg-1) K SiO rate 2 3 (g plant-1) Root Leaf lamina Well-watered Drought p≤value Well-watered Drought p≤value 0 1,740.1 ± 365.8 1,012.9 ± 345.5 NS 0.7300 1,800.4 ± 412.3 771.5 ± 58.2 NS 0.3115 2.5 1,582.4 ± 218.8 1,073.5 ± 260.5 NS 0.9434 3,556.0 ± 503.2 2,619.4 ± 388.0 NS 0.5403 5 2,095.1 ± 475.1 1,173.5 ± 154.7 NS 0.8784 5,449.3 ± 555.7 4,113.1 ± 272.2 NS 0.4103 10 1,862.4 ± 231.0 1,341.8 ± 169.0 NS 0.8350 6,628.2 ± 741.1 3,681.1 ± 876.7 NS 0.4596 Linear Y = 1521.0 - 98.8x Y = 1496.2 + 346.7x -- -- Y = 3526.6-194.8x Y = 1976.7 + 146.3x -- -- regression r2 0.05 0.26 -- -- 0.07 0.05 -- --

Mean plant tissue silicon concentrationz ± SE (mg kg-1) K SiO rate 2 3 (g plant-1) Petiole Trunk Well-watered Drought p≤value Well-watered Drought p≤value 0 190.8 ± 19.9 132.8 ± 14.2 NS 0.8168 126.5 ± 11.7 90.0 ± 25.6 NS 0.4195 2.5 429.4 ± 36.4 820.1 ± 58.3 NS 0.3283 147.8 ± 10.7 124.5 ± 9.4 NS 0.3072 5 915.2 ± 266.4 480.7 ± 65.1 NS 0.5929 208.1 ± 16.9 148.2 ± 10.8 NS 0.5398 10 550.1 ± 111.6 351.8 ± 31.6 NS 0.3279 237.1 ± 16.2 255.4 ± 6.9 NS 0.3844 Linear Y = 161.5 + 102.6x Y = 470.5 - 6.4x -- -- Y = 123.3 + 8.3x Y = 168.9 + 22.9x -- -- regression r2 0.02 0.47 -- -- 0.12 0.16 -- -- Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. Data analyzed by T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. * = Statistical significance within row. NS = No significant within row.

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APPENDIX J ADDITIONAL TABLES FOR CHAPTER 4

219

-1 -1 Table J-1. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant height under well-watered field conditions from December 24, 2012 to November 24, 2013 at UF-TREC, Homestead, FL. Mean plant height ± SE (cm) K2SiO3 rate (kg ha-1year-1) December 24 January 24 February 24 March 24 April 24 May 24 0 59.0 ± 1.0 a 77.5 ± 1.3 a 94.1 ± 1.0 a 105.5 ± 1.4 a 119.8 ± 1.5 a 131.7 ± 1.8 a 500 60.8 ± 1.0 a 79.5 ± 0.9 a 95.3 ± 0.8 a 106.8 ± 0.9 a 120.3 ± 1.3 a 132.7 ± 1.3 a 1000 58.0 ± 0.9 a 76.8 ± 1.2 a 91.6 ± 1.3 a 103.1 ± 1.2 a 119.6 ± 1.5 a 130.3 ± 1.6 a

Mean plant height ± SE (cm) K2SiO3 rate (kg ha-1year-1) June 24 July 24 August 24 September 24 November 24 0 140.6 ± 1.7 a 155.0 ± 1.9 a 165.5 ± 1.8 a 175.5 ± 1.8 a 194.6 ± 2.3 a 500 141.0 ± 1.1 a 157.5 ± 1.2 a 167.1 ± 1.2 a 177.1 ± 1.1 a 195.7 ± 2.0 a 1000 138.4 ± 1.7 a 152.9 ± 2.0 a 162.3 ± 1.7 a 173.1 ± 1.8 a 192.6 ± 1.8 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

220

-1 -1 Table J-2. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant trunk diameter under well-watered field conditions from December 24, 2012 to November 24, 2013 at UF-TREC, Homestead, FL. Mean plant trunk diameter ± SE (mm) K2SiO3 rate (kg ha-1year-1) December 24 January 24 February 24 March 24 April 24 May 24 0 47.5 ± 1.0 a 69.7 ± 1.1 a 86.8 ± 1.2 a 98.2 ± 1.4 a 106.4 ± 1.2 a 111.7 ± 1.2 a 500 47.7 ± 0.9 a 68.8 ± 1.0 a 88.2 ± 1.1 a 99.0 ± 1.3 a 106.4 ± 1.2 a 111.8 ± 1.1 a 1000 47.9 ± 0.8 a 68.4 ± 0.9 a 86.0 ± 1.0 a 96.3 ± 1.2 a 104.5 ± 1.2 a 109.6 ± 1.0 a

Mean plant trunk diameter ± SE (mm) K2SiO3 rate (kg ha-1year-1) June 24 July 24 August 24 September 24 November 24 0 113.5 ± 1.1 a 116.8 ± 1.2 a 120.8 ± 1.4 a 125.2 ± 1.4 a 126.0 ± 1.4 a 500 114.3 ± 1.0 a 116.8 ± 1.0 a 121.6 ± 1.2 a 123.9 ± 1.2 a 126.3 ± 1.3 a 1000 113.2 ± 1.0 a 116.5 ± 1.0 a 122.3 ± 1.2 a 124.1 ± 1.3 a 125.5 ± 1.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

221

-1 -1 Table J-3. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant leaf expansion area under well-watered field conditions from January 14 to April 20, 2013 at UF-TREC, Homestead, FL. Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) January 14 January 26 February 9 February 23

0 260.9 ± 24.0 a 339.3 ± 19.5 a 396.6 ± 22.0 b 414.7 ± 21.2 b

500 298.9 ± 16.6 a 370.3 ± 16.8 a 432.2 ± 51.9 b 472.5 ± 25.0 ab

1000 309.7 ± 28.3 a 405.1 ± 31.9 a 504.6 ± 22.7 a 513.6 ± 27.9 a

Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) March 9 March 23 April 6 April 20

0 538.6 ± 29.6 b 604.4 ± 23.3 c 629.6 ± 26.9 a 660.2 ± 27.2 c

500 636.3 ± 29.9 ab 713.9 ± 25.6 b 774.4 ± 43.1 a 781.8 ± 21.7 b

1000 654.7 ± 40.4 a 788.5 ± 25.1 a 845.2 ± 24.2 a 866.7 ± 35.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

222

-1 -1 Table J-4. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant leaf expansion area under well-watered field conditions from January 14 to April 20, 2013 at UF-TREC, Homestead, FL. Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) January 14 January 26 February 9 February 23 0 231.1 ± 17.4 a 375.8 ± 18.0 a 484.4 ± 39.8 a 499.1 ± 30.4 a 500 254.8 ± 26.5 a 385.1 ± 10.5 a 511.4 ± 25.4 a 552.4 ± 20.6 a 1000 246.6 ± 23.7 a 381.1 ± 11.6 a 467.5 ± 15.5 a 506.2 ± 10.9 a

Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) March 9 March 23 April 6 April 20 0 588.8 ± 38.2 a 691.7 ± 60.2 a 818.6 ± 37.5 a 779.3 ± 42.6 a 500 621.8 ± 38.6 a 730.3 ± 47.7 a 868.7 ± 38.7 a 875.9 ± 33.8 a 1000 563.2 ± 19.2 a 648.6 ± 20.0 a 786.0 ± 31.7 a 846.4 ± 30.8 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

223

-1 -1 Table J-5. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant leaf expansion area under well-watered field conditions from June 1 to August 24, 2013 at UF-TREC, Homestead, FL. Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) June 1 June 15 June 29 July 13 0 219.3 ± 15.7 a 351.3 ± 9.3 a 413.2 ± 14.0 a 612.9 ± 26.1 a 500 220.3 ± 19.2 a 354.0 ± 13.1 a 427.9 ± 19.8 a 631.0 ± 18.9 a 1000 225.0 ± 11.8 a 356.9 ± 5.2 a 410.9 ± 12.2 a 621.4 ± 28.7 a

Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1year-1) July 27 August 10 August 24 0 625.5 ± 29.1 a 684.6 ± 34.2 a 688.5 ± 35.1 a 500 640.2 ± 23.7 a 670.2 ± 40.8 a 674.9 ± 40.4 a 1000 633.3 ± 27.9 a 703.8 ± 16.2 a 710.9 ± 17.6 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

224

-1 -1 Table J-6. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant leaf expansion area under well-watered field conditions from June 1 to August 24, 2013 at UF-TREC, Homestead, FL. Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1 year-1) June 1 June 15 June 29 July 13 0 226.8 ± 11.9 b 301.6 ± 4.7 b 413.6 ± 12.1 b 666.7 ± 19.9 a 500 260.9 ± 12.2 a 314.8 ± 8.3 a 470.6 ± 16.4 a 705.2 ± 20.6 a 1000 288.8 ± 7.1 a 325.3 ± 5.0 a 396.0 ± 10.8 a 678.8 ± 25.0 a

Mean leaf expansion area ± SE (cm2) K2SiO3 rate (kg ha-1year-1) July 27 August 10 August 24 0 719.5 ± 41.6 a 748.8 ± 47.4 a 749.2 ± 45.0 a 500 752.7 ± 31.1 a 766.2 ± 46.4 a 792.7 ± 47.1 a 1000 698.8 ± 12.6 a 739.4 ± 22.0 a 763.8 ± 21.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

225

-1 -1 Table J-7. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant leaf abscission number under well-watered field conditions from January 31 to June 15, 2013 at UF-TREC, Homestead, FL.

Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) January 31* February 15* February 28* March 15 March 31 0 - - - 0.4 ± 0.3 a 0.7 ± 0.3 a 500 - - - 0.4 ± 0.3 a 1.1 ± 0.4 a 1000 - - - 0.4 ± 0.2 a 1.4 ± 0.4 a

Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) April 15 April 30 May 15 May 31 June 15 0 0.2 ± 0.1 a 3.6 ± 0.6 a 4.1 ± 0.7 a 0.8 ± 0.3 a 0.2 ± 0.1 a 500 0.2 ± 0.1 a 2.4 ± 0.5 a 4.6 ± 0.4 a 1.2 ± 0.3 a 0.1 ± 0.1 a 1000 0.2 ± 0.2 a 2.5 ± 0.5 a 4.4 ± 0.5 a 0.9 ± 0.2 a 0.2 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. * No leaf abscission occurred during these three dates.

226

-1 -1 Table J-8. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant leaf abscission number under well-watered field conditions from June 1 to August 31, 2013 at UF-TREC, Homestead, FL. Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) June 1* June 15* June 30* July 15 0 - - - 2.6 ± 0.4 a 500 - - - 1.9 ± 0.3 a 1000 - - - 2.6 ± 0.3 a

Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) July 15 August 15 August 31 0 4.8 ± 0.4 a 2.2 ± 0.5 a 0.4 ± 0.2 a 500 5.4 ± 0.4 a 2.3 ± 0.4 a 0.4 ± 0.1 a 1000 5.0 ± 0.5 a 2.0 ± 0.4 a 0.4 ± 0.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. * No leaf abscission occurred during these three dates.

227

-1 -1 Table J-9. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) plant leaf abscission number under well-watered field conditions from August 1 to November 7, 2013 at UF-TREC, Homestead, FL.

Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) August 1* August 15* August 29* September 12 0 - - - 2.2 ± 0.6 a 500 - - - 1.9 ± 0.5 a 1000 - - - 1.8 ± 0.5 a

Mean number of leaves abscised plant-1date-1 ± SE K2SiO3 rate (kg ha-1 year-1) September 26 October 10 October 24 November 7 0 3.7 ± 0.5 a 2.1 ± 0.4 a 2.0 ± 0.4 a -** 500 2.4 ± 0.5 b 2.8 ± 0.4 a 2.8 ± 0.6 a 0.1 ± 0.1 a 1000 3.5 ± 0.4 ab 2.2 ± 0.5 a 2.4 ± 0.4 a 0.1 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. * No leaf abscission occurred during these three dates; ** Total leaf abscission completed for this treatment.

228

-1 -1 Table J-10. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) petiole fresh weight under well-watered field conditions from Jan. 14 to Dec. 1, 2013 at UF-TREC, FL. Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) January 14 January 28 Bisexual Female Bisexual Female 0 63.0 ± 4.1 38.2 ± 2.9 46.1 ± 7.2 26.4 ± 2.0 500 59.0 ± 4.0 37.0 ± 2.7 25.9 ± 2.6 33.2 ± 5.4 1000 58.8 ± 3.4 36.9 ± 2.9 41.6 ± 3.4 30.2 ± 0.7 Linear Y = 63.0 – 1.2x Y= 38.2 – 0.4x Y = 38.2 – 0.2x Y= 27.8 + 0.9x regression r2 0.02 0.004 0.002 0.02

Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) February 11 February 25 Bisexual Female Bisexual Female 0 36.8 ± 2.6 30.4 ± 1.4 45.4 ± 5.7 25.2 ± 1.2 500 29.1 ± 3.2 28.9 ± 2.8 25.2 ± 2.7 39.5 ± 3.1 1000 45.1 ± 2.9 39.5 ± 1.3 35.1 ± 2.5 28.1 ± 2.0 Linear Y = 28.8 + 3.5x Y= 25.0 + 3.4x Y = 40.5 – 2.3x Y= 30.9 + 0.01x regression r2 0.19 0.36 0.04 0.00004

Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) March 11 March 25 Bisexual Female Bisexual Female 0 46.6 ± 1.3 44.9 ± 0.9 80.4 ± 6.7 76.7 ± 4.7 500 50.2 ± 1.2 51.3 ± 2.2 83.4 ± 5.0 84.8 ± 3.7 1000 49.5 ± 1.9 46.6 ± 1.5 92.9 ± 6.4 85.4 ± 3.5 Linear Y = 47.0 + 0.8x Y= 47.3 + 0.2x Y = 75.6 + 4.3x Y= 76.4 + 2.6x regression r2 0.05 0.001 0.10 0.08

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Table J-10 –continued. Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) April 25 May 25 Bisexual Female Bisexual Female 0 78.1 ± 4.0 72.9 ± 4.1 82.1 ± 4.5 93.7 ± 8.1 500 82.6 ± 4.3 77.0 ± 3.2 109.4 ± 12.1 95.3 ± 3.9 1000 80.4 ± 5.0 77.6 ± 4.0 91.7 ± 4.8 85.9 ± 2.4 Linear Y = 79.2 + 0.5x Y= 72.6 + 1.4x Y = 90.9 + 1.5x Y= 98.3 – 2.9x regression r2 0.003 0.03 0.01 0.06

Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) June 25 August 1 Bisexual Female Bisexual Female 0 89.2 ± 4.9 108.2 ± 6.3 104.8 ± 2.5 107.1 ± 5.5 500 102.2 ± 5.0 100.7 ± 5.5 109.3 ± 4.1 114.6 ± 5.0 1000 103.7 ± 5.6 103.5 ± 6.2 120.5 ± 5.5 97.2 ± 4.3 Linear Y = 88.5 + 4.2x Y= 106.9 – 1.2x Y = 99.2 + 5.3x Y= 115.8 – 4.1x regression r2 0.12 0.01 0.20 0.12

Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) September 1 October 1 Bisexual Female Bisexual Female 0 89.6 ± 4.3 85.0 ± 4.8 111.1 ± 4.7 88.4 ± 5.3 500 95.6 ± 4.5 89.5 ± 4.6 106.6 ± 6.0 96.2 ± 3.6 1000 95.2 ± 4.7 85.1 ± 3.0 113.5 ± 4.2 100.4 ± 2.8 Linear Y = 89.9 + 1.5x Y= 87.2 + 0.3x Y = 107.6 + 1.2x Y= 86.3 + 3.7x regression r2 0.03 0.001 0.01 0.16

230

Table J-10 –continued. Mean petiole fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) November 1 December 1 Bisexual Female Bisexual Female 0 105.0 ± 5.6 107.5 ± 7.4 94.5 ± 6.5 98.3 ± 4.2 500 113.8 ± 4.5 115.1 ± 3.8 102.3 ± 7.4 93.3 ± 2.5 1000 134.6 ± 3.8 109.4 ± 3.1 134.5 ± 9.5 106.8 ± 8.2 Linear Y = 94.6 + 9.9x Y= 110.3 + 0.2x Y = 78.4 + 13.7x Y= 91.5 + 3.4x regression r2 0.05 0.0002 0.40 0.07 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

231

-1 -1 Table J-11. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) lamina fresh weight under well-watered field conditions from Jan. 14 to Dec. 1, 2013 at UF-TREC, FL. Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) January 14 January 28 Bisexual Female Bisexual Female 0 53.9 ± 6.4 43.8 ± 3.8 49.2 ± 6.1 31.6 ± 2.1 500 57.7 ± 5.6 46.2 ± 3.4 28.8 ± 3.7 40.9 ± 5.6 1000 56.5 ± 3.6 50.4 ± 3.4 46.1 ± 3.8 37.3 ± 3.3 Linear Y = 54.5 + 0.7x Y = 41.7 + 2.2x Y = 40.6 + 0.3x Y = 33.4 + 1.4x regression r2 0.003 0.08 0.001 0.02

Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) February 11 February 25 Bisexual Female Bisexual Female 0 37.7 ± 2.9 34.6 ± 0.6 43.1 ± 3.0 29.6 ± 1.8 500 30.4 ± 3.1 34.8 ± 3.4 31.0 ± 3.8 45.9 ± 4.5 1000 46.2 ± 2.9 47.9 ± 2.4 47.1 ± 4.5 35.8 ± 3.2 Linear Y = 29.8 + 3.6x Y = 28.1 + 4.7x Y = 35.0 + 2.3x Y = 34.6 + 1.1x regression r2 0.19 0.44 0.06 0.01

Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) March 11 March 25 Bisexual Female Bisexual Female 0 51.3 ± 2.0 50.4 ± 1.4 83.0 ± 6.1 81.9 ± 3.1 500 64.1 ± 3.2 61.8 ± 3.5 92.8 ± 9.2 97.0 ± 3.6 1000 62.5 ± 4.4 57.9 ± 3.7 100.4 ± 5.0 95.4 ± 5.6 Linear Y = 52.1 + 3.1x Y = 52.4 + 1.8x Y = 79.2 + 5.5x Y = 82.7 + 3.7x regression r2 0.13 0.06 0.14 0.13

232

Table J-11 –continued. Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) April 25 May 25 Bisexual Female Bisexual Female 0 96.6 ± 14.4 89.7 ± 5.2 87.8 ± 6.1 91.4 ± 7.4 500 101.9 ± 7.4 91.2 ± 5.9 100.9 ± 10.2 93.5 ± 3.1 1000 98.8 ± 7.2 87.5 ± 5.4 92.8 ± 3.9 88.1 ± 3.3 Linear Y = 98.2 + 0.4x Y = 91.5 – 0.9x Y = 96.7 – 2.6x Y = 94.1 – 1.3x regression r2 0.0004 0.01 0.02 0.02

Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) June 25 August 1 Bisexual Female Bisexual Female 0 95.0 ± 10.3 112.4 ± 5.7 108.8 ± 3.7 109.3 ± 5.5 500 92.6 ± 4.0 104.3 ± 2.9 112.6 ± 4.7 121.5 ± 5.0 1000 95.8 ± 6.3 110.3 ± 6.6 122.6 ± 5.6 104.3 ± 4.0 Linear Y = 93.4 + 0.5x Y= 109.4 – 0.2x Y = 103.8 + 4.6x Y = 117.8 – 2.6x regression r2 0.001 0.0003 0.18 0.05

Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) September 1 October 1 Bisexual Female Bisexual Female 0 89.7 ± 4.9 88.4 ± 6.3 103.7 ± 7.5 86.6 ± 5.8 500 93.3 ± 3.9 89.0 ± 5.6 102.9 ± 6.3 98.3 ± 4.1 1000 92.6 ± 4.8 84.5 ± 3.4 109.0 ± 5.9 99.2 ± 2.3 Linear Y = 90.0 + 0.8x Y = 90.6 – 1.4x Y = 100.6 + 2.0x Y = 86.2 + 3.7x regression r2 0.01 0.02 0.02 0.13

233

Table J-11 –continued. Mean lamina fresh weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) November 1 December 1 Bisexual Female Bisexual Female 0 110.9 ± 6.6 104.5 ± 6.7 96.8 ± 3.1 108.5 ± 4.5 500 123.3 ± 6.1 112.2 ± 5.9 112.1 ± 5.5 110.0 ± 5.0 1000 148.0 ± 8.1 101.5 ± 1.8 124.1 ± 7.3 108.6 ± 4.5 Linear Y = 98.6 + 12.3x Y = 109.9 – 1.6x Y = 90.8 + 8.7x Y = 109.2 – 0.1x regression r2 0.41 0.02 0.34 0.0001 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

234

-1 -1 Table J-12. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) petiole dry weight under well-watered field conditions from Jan. 14 to Dec. 1, 2013 at UF-TREC, FL. Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) January 14 January 28 Bisexual Female Bisexual Female 0 13.9 ± 0.7 11.9 ± 0.4 22.5 ± 2.1 17.8 ± 1.6 500 13.6 ± 0.6 12.0 ± 0.3 18.4 ± 1.4 20.5 ± 2.9 1000 13.9 ± 0.5 12.1 ± 0.4 27.0 ± 1.7 19.4 ± 1.5 Linear Y = 13.8 + 0.02x Y = 11.8 + 0.1x Y = 18.2 + 1.9x Y = 18.3 + 0.4 regression r2 0.0001 0.01 0.16 0.01

Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) February 11 February 25 Bisexual Female Bisexual Female 0 21.7 ± 1.0 19.3 ± 1.5 22.5 ± 3.3 12.3 ± 1.1 500 22.1 ± 2.1 19.3 ± 2.3 12.9 ± 1.3 21.4 ± 1.8 1000 34.8 ± 1.9 29.0 ± 1.1 22.4 ± 1.3 18.6 ± 1.7 Linear Y = 15.3 + 4.7x Y = 14.4 + 3.5x Y = 17.7 + 0.7x Y = 13.7 + 1.6x regression r2 0.58 0.46 0.01 0.12

Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) March 11 March 25 Bisexual Female Bisexual Female 0 20.3 ± 0.5 20.6 ± 0.7 17.6 ± 0.9 15.4 ± 0.5 500 23.9 ± 0.6 25.3 ± 0.6 16.4 ± 0.7 16.4 ± 0.6 1000 26.3 ± 0.9 26.8 ± 1.4 21.2 ± 1.5 16.1 ± 0.4 Linear Y = 19.1 + 1.9x Y = 19.8 + 1.9x Y = 15.2 + 1.4x Y = 15.5 + 0.2x regression r2 0.60 0.41 0.24 0.02

235

Table J-12 –continued. Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) April 25 May 25 Bisexual Female Bisexual Female 0 18.8 ± 0.9 15.4 ± 0.5 18.4 ± 0.9 18.4 ± 1.1 500 19.0 ± 0.9 15.6 ± 0.6 21.8 ± 1.7 19.6 ± 0.6 1000 17.6 ± 0.9 16.3 ± 0.8 16.8 ± 0.7 19.5 ± 1.2 Linear Y = 19.5 – 0.4x Y = 15.1 + 0.3x Y = 20.9 – 0.8x Y = 18.4 + 0.3x regression r2 0.05 0.04 0.07 0.02

Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) June 25 August 1 Bisexual Female Bisexual Female 0 16.8 ± 2.1 18.6 ± 1.6 18.7 ± 0.5 19.4 ± 0.7 500 20.2 ± 2.1 19.9 ± 2.0 19.9 ± 0.8 21.0 ± 0.7 1000 21.1 ± 1.9 20.7 ± 1.8 21.4 ± 0.8 18.8 ± 0.6 Linear Y = 16.3 + 1.3x Y = 18.2 + 0.6x Y = 17.9 + 0.9x Y = 20.5 – 0.3x regression r2 0.08 0.03 0.26 0.04

Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) September 1 October 1 Bisexual Female Bisexual Female 0 16.1 ± 0.6 14.6 ± 0.6 18.5 ± 0.7 17.2 ± 0.8 500 17.6 ± 0.6 16.9 ± 0.7 19.5 ± 0.7 18.5 ± 0.5 1000 17.0 ± 0.9 15.4 ± 0.5 19.2 ± 0.4 19.1 ± 0.3 Linear Y = 16.4 + 0.2x Y = 15.3 + 0.1x Y = 18.7 + 0.2x Y = 16.9 + 0.6x regression r2 0.02 0.01 0.01 0.17

236

Table J-12 –continued. Mean petiole dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) November 1 December 1 Bisexual Female Bisexual Female 0 19.6 ± 0.7 19.8 ± 0.7 16.9 ± 0.8 17.1 ± 0.6 500 21.3 ± 0.7 21.8 ± 0.9 18.6 ± 1.0 16.7 ± 0.6 1000 25.1 ± 0.4 19.8 ± 0.2 22.8 ± 1.3 18.4 ± 1.2 Linear Y = 17.7 + 1.8x Y = 20.8 – 0.1x Y = 14.8 + 2.0x Y = 16.2 + 0.5x regression r2 0.67 0.01 0.44 0.07 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

237

-1 -1 Table J-13. Effect of 0, 500, and 1,000 kg ha year K2SiO soil drench applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) lamina dry weight under well-watered field conditions from Jan. 14 to Dec. 1, 2013 at UF-TREC, FL. Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) January 14 January 28 Bisexual Female Bisexual Female 0 21.9 ± 1.2 16.4 ± 2.9 21.4 ± 2.4 17.3 ± 2.5 500 21.1 ± 1.7 20.0 ± 2.7 15.8 ± 2.4 22.8 ± 2.6 1000 20.7 ± 1.6 18.9 ± 2.9 26.1 ± 3.1 23.0 ± 2.0 Linear Y = 22.1 – 0.4x Y = 17.0 + 0.6x Y = 16.2 + 2.1x Y = 17.2 + 1.6x regression r2 0.01 0.04 0.10 0.09

Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) February 11 February 25 Bisexual Female Bisexual Female 0 23.3 ± 2.3 20.9 ± 1.7 21.8 ± 1.8 14.9 ± 1.1 500 19.6 ± 1.9 23.1 ± 2.2 17.7 ± 2.0 26.9 ± 3.5 1000 32.4 ± 2.1 31.6 ± 1.6 33.0 ± 3.2 25.8 ± 2.4 Linear Y = 16.9 + 3.5x Y = 16.6 + 3.7x Y = 14.1 + 4.3x Y = 15.5 + 3.0x regression r2 0.32 0.47 0.35 0.19

Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) March 11 March 25 Bisexual Female Bisexual Female 0 25.9 ± 1.7 21.2 ± 0.7 25.4 ± 1.3 22.2 ± 0.5 500 34.4 ± 2.0 28.6 ± 1.2 26.6 ± 1.8 26.9 ± 0.7 1000 36.7 ± 2.6 31.0 ± 2.5 30.0 ± 2.1 25.2 ± 1.5 Linear Y = 24.7 + 3.3x Y = 20.0 + 3.0x Y = 23.6 + 1.6x Y = 23.0 + 0.8x regression r2 0.31 0.38 0.15 0.08

238

Table J-13 –continued. Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) April 25 May 25 Bisexual Female Bisexual Female 0 31.4 ± 2.8 24.4 ± 1.3 25.9 ± 2.0 27.2 ± 2.0 500 30.9 ± 2.1 26.0 ± 1.4 33.1 ± 3.6 28.7 ± 1.3 1000 29.8 ± 2.2 25.3 ± 1.1 27.1 ± 1.4 25.6 ± 0.5 Linear Y = 31.9 – 0.5x Y = 24.7 + 0.2x Y = 28.9 – 0.1x Y = 28.8 – 0.7x regression r2 0.01 0.01 0.02 0.05

Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) June 25 August 1 Bisexual Female Bisexual Female 0 27.6 ± 3.1 28.2 ± 1.4 27.4 ± 0.8 26.9 ± 1.1 500 26.0 ± 1.1 26.8 ± 0.7 28.5 ± 1.1 30.3 ± 1.3 1000 25.6 ± 1.4 28.6 ± 1.6 30.7 ± 1.1 26.0 ± 0.9 Linear Y = 27.8 – 0.6x Y = 27.3 + 0.2x Y = 26.3 + 1.1x Y = 29.0 – 0.6x regression r2 0.02 0.01 0.21 0.04

Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) September 1 October 1 Bisexual Female Bisexual Female 0 26.8 ± 1.3 24.8 ± 1.4 28.9 ± 1.5 26.3 ± 1.7 500 28.6 ± 1.3 26.7 ± 1.6 28.4 ± 1.7 29.6 ± 1.2 1000 28.1 ± 1.3 24.9 ± 0.8 28.9 ± 1.0 27.2 ± 0.7 Linear Y = 27.0 + 0.4x Y = 25.7 – 0.1x Y = 28.6 + 0.1x Y = 27.5 + 0.1x regression r2 0.02 0.001 0.0002 0.001

239

Table J-13 –continued. Mean lamina dry weight ± SE (g) K SiO rate 2 3 (kg ha-1year-1) November 1 December 1 Bisexual Female Bisexual Female 0 30.2 ± 1.3 29.4 ± 1.6 25.6 ± 1.0 27.6 ± 1.0 500 34.3 ± 1.7 33.6 ± 2.0 29.3 ± 1.4 27.5 ± 0.9 1000 40.8 ± 2.0 31.0 ± 0.9 32.3 ± 1.6 29.7 ± 1.4 Linear Y = 26.9 + 3.5x Y = 30.7 + 0.3x Y = 24.1 + 2.1x Y = 26.5 + 0.7x regression r2 0.50 0.01 0.35 0.09 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

240

-1 -1 Table J-14. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) stomatal conductance (gs) under well-watered field conditions from Jan. 14 to September 3, 2013 at UF-TREC, FL. -2 -1 Stomatal conductance (gs) ± SE (mol m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 0.3 ± 0.02 a 0.3 ± 0.01 b 0.3 ± 0.01 b 0.3 ± 0.01 c 500 0.3 ± 0.02 a 0.3 ± 0.01 ab 0.3 ± 0.01 b 0.3 ± 0.01 b 1000 0.3 ± 0.01 a 0.3 ± 0.02 a 0.4 ± 0.01 a 0.4 ± 0.01 a

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 0.3 ± 0.01 b 0.4 ± 0.02 a 0.6 ± 0.02 a 0.7 ± 0.1 a 500 0.4 ± 0.03 a 0.4 ± 0.02 a 0.6 ± 0.03 a 0.7 ± 0.1 a 1000 0.4 ± 0.03 a 0.4 ± 0.03 a 0.6 ± 0.03 a 0.7 ± 0.04 a

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 0.5 ± 0.1 a 0.8 ± 0.1 a 1.3 ± 0.1 a 1.1 ± 0.1 a 500 0.7 ± 0.1 a 0.7 ± 0.1 a 1.1 ± 0.1 a 0.9 ± 0.1 b 1000 0.6 ± 0.1 a 0.7 ± 0.1 a 1.3 ± 0.1 a 1.0 ± 0.04 b

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) July 28 August 18 September 3 0 1.2 ± 0.1 a 1.0 ± 0.1 a 1.1 ± 0.1 a 500 1.1 ± 0.1 a 1.0 ± 0.1 a 1.2 ± 0.1 a 1000 1.2 ± 0.1 a 1.0 ± 0.1 a 1.3 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

241

-1 -1 Table J-15. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) stomatal conductance (gs) under well-watered field conditions from Jan. 14 to September 3, 2013 at UF-TREC, FL. -2 -1 Stomatal conductance (gs) ± SE (mol m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 0.2 ± 0.01 b 0.3 ± 0.01 b 0.3 ± 0.01 b 0.3 ± 0.01 b 500 0.3 ± 0.03 a 0.4 ± 0.02 b 0.3 ± 0.02 b 0.4 ± 0.04 ab 1000 0.3 ± 0.02 a 0.4 ± 0.02 a 0.4 ± 0.01 a 0.5 ± 0.05 a

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 0.2 ± 0.02 a 0.2 ± 0.01 a 0.2 ± 0.01 b 0.3 ± 0.01 a 500 0.2 ± 0.08 a 0.2 ± 0.01 a 0.3 ± 0.01 a 0.3 ± 0.01 a 1000 0.2 ± 0.01 a 0.2 ± 0.02 a 0.3 ± 0.01 a 0.3 ± 0.01 a

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 0.6 ± 0.02 a 1.0 ± 0.10 a 0.9 ± 0.10 a 1.0 ± 0.1 a 500 0.5 ± 0.03 a 1.0 ± 0.10 a 1.1 ± 0.04 a 0.9 ± 0.1 a 1000 0.6 ± 0.02 a 1.0 ± 0.10 a 1.0 ± 0.10 a 1.2 ± 0.1 a

-2 -1 Stomatal conductance ( s) ± SE (mol m s ) K2SiO3 rate g -1 -1 (kg ha year ) July 28 August 18 September 3 0 1.0 ± 0.10 a 0.9 ± 0.10 a 0.9 ± 0.10 a 500 1.0 ± 0.10 a 0.9 ± 0.10 a 1.1 ± 0.04 a 1000 1.0 ± 0.10 a 1.0 ± 0.04 a 1.0 ± 0.10 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

242

-1 -1 Table J-16. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant transpiration (E) under well- watered field conditions from Jan. 14 to Sept. 3, 2013 at UF-TREC, Homestead, FL. -2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 5.9 ± 0.1 a 6.3 ± 0.3 a 5.9 ± 0.1 a 5.8 ± 0.1 c 500 6.0 ± 0.2 a 4.8 ± 0.1 c 5.3 ± 0.1 b 6.2 ± 0.2 b 1000 6.3 ± 0.3 a 5.6 ± 0.1 b 5.8 ± 0.2 a 7.0 ± 0.2 a

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 8.8 ± 0.2 a 8.4 ± 0.4 a 9.6 ± 0.1 a 8.6 ± 0.3 a 500 8.2 ± 0.3 ab 7.3 ± 0.1 ab 8.8 ± 0.2 b 7.6 ± 0.1 b 1000 8.0 ± 0.3 b 7.0 ± 0.5 b 8.3 ± 0.2 c 7.1 ± 0.1 b

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 9.8 ± 0.3 a 9.5 ± 0.6 a 8.8 ± 0.2 a 9.7 ± 0.3 a 500 9.3 ± 0.3 a 8.6 ± 0.4 a 8.9 ± 0.3 a 8.9 ± 0.2 b 1000 9.6 ± 0.2 a 8.6 ± 0.5 a 8.4 ± 0.2 a 9.0 ± 0.2 b

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) July 28 August 18 September 3 0 9.5 ± 0.2 a 10.2 ± 0.2 a 10.1 ± 0.1 a 500 8.4 ± 0.1 b 7.9 ± 0.4 b 8.7 ± 0.2 b 1000 8.9 ± 0.3 b 8.3 ± 0.6 b 9.1 ± 0.5 b Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

243

-1 -1 Table J-17. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant transpiration (E) under well- watered field conditions from Jan. 14 to Sept. 3, 2013 at UF-TREC, Homestead, FL. -2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 5.9 ± 0.1 a 5.8 ± 0.1 a 6.2 ± 0.2 a 5.7 ± 0.3 a 500 4.5 ± 0.1 c 4.5 ± 0.1 c 4.5 ± 0.1 c 5.7 ± 0.4 a 1000 5.5 ± 0.1 b 5.4 ± 0.1 b 5.4 ± 0.1 b 6.1 ± 0.2 a

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 5.8 ± 0.1 a 7.2 ± 0.2 b 7.1 ± 0.1 a 8.8 ± 0.1 a 500 5.6 ± 0.2 a 8.0 ± 0.3 a 6.9 ± 0.1 ab 7.2 ± 0.2 b 1000 5.5 ± 0.1 a 7.6 ± 0.2 ab 6.7 ± 0.1 b 7.3 ± 0.2 b

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 8.2 ± 0.1 a 8.5 ± 0.5 a 9.8 ± 0.6 a 9.1 ± 0.3 a 500 7.0 ± 0.2 b 7.9 ± 0.5 a 10.3 ± 0.5 a 8.2 ± 0.4 a 1000 6.5 ± 0.2 b 7.3 ± 0.4 a 9.5 ± 0.5 a 8.5 ± 0.3 a

-2 -1 Transpiration (E) ± SE (mmol H2O m s ) K2SiO3 rate -1 -1 (kg ha year ) July 28 August 18 September 3 0 9.7 ± 0.3 a 8.8 ± 0.4 a 8.7 ± 0.3 a 500 9.3 ± 0.1 a 7.8 ± 0.2 a 8.4 ± 0.3 b 1000 9.3 ± 0.3 a 7.4 ± 0.3 a 7.7 ± 0.3 b Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

244

-1 -1 Table J-18. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2- T5 transgenic bisexual papaya (Carica papaya L.) net CO2 assimilation under well- watered field conditions from Jan. 14 to Sept. 3, 2013 at UF-TREC, Homestead, FL. -2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 6.3 ± 0.1 b 5.3 ± 0.1 b 5.5 ± 0.2 b 5.7 ± 0.1 b 500 6.2 ± 0.1 b 5.8 ± 0.1 a 5.6 ± 0.2 ab 6.0 ± 0.2 b 1000 6.5 ± 0.1 a 6.1 ± 0.2 a 5.9 ± 0.1 a 6.9 ± 0.3 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 6.8 ± 0.1 a 6.5 ± 0.1 b 7.7 ± 0.1 b 7.5 ± 0.2 b 500 7.0 ± 0.2 a 7.6 ± 0.2 a 8.1 ± 0.3 ab 8.1 ± 0.4 ab 1000 7.0 ± 0.1 a 7.5 ± 0.3 a 8.3 ± 0.1 a 8.5 ± 0.2 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 8.0 ± 0.3 a 8.5 ± 0.1 c 8.7 ± 0.1 b 9.0 ± 0.3 a 500 8.7 ± 0.4 a 9.7 ± 0.1 a 9.6 ± 0.1 a 8.9 ± 0.5 a 1000 8.4 ± 0.3 a 9.2 ± 0.1 b 9.1 ± 0.2 b 9.4 ± 0.2 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) July 28 August 18 September 3 0 9.3 ± 0.3 a 8.7 ± 0.10 b 10.0 ± 0.3 b 500 9.0 ± 0.4 a 9.2 ± 0.10 a 10.4 ± 0.1 ab 1000 9.2 ± 0.2 a 9.0 ± 0.04 ab 10.7 ± 0.3 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

245

-1 -1 Table J-19. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2- T5 transgenic female papaya (Carica papaya L.) net CO2 assimilation under well- watered field conditions from Jan. 14 to Sept. 3, 2013 at UF-TREC, Homestead, FL -2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 0 4.4 ± 0.1 b 4.2 ± 0.1 c 5.3 ± 0.2 c 6.8 ± 0.3 c 500 4.4 ± 0.1 b 4.5 ± 0.1 b 5.8 ± 0.1 b 7.2 ± 0.3 b 1000 5.1 ± 0.1 a 5.3 ± 0.1 a 7.1 ± 0.1 a 9.2 ± 0.4 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) March 9 March 23 April 6 April 20 0 6.2 ± 0.1 b 6.5 ± 0.1 c 8.0 ± 0.1 b 6.5 ± 0.1 c 500 7.0 ± 0.5 b 7.2 ± 0.1 b 8.1 ± 0.1 ab 7.5 ± 0.2 b 1000 8.1 ± 0.2 a 7.9 ± 0.2 a 8.2 ± 0.1 a 8.3 ± 0.2 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) May 4 May 25 June 16 July 7 0 6.6 ± 0.2 c 6.9 ± 0.1 c 7.8 ± 0.04 c 6.4 ± 0.1 b 500 7.3 ± 0.3 b 8.3 ± 0.4 b 9.2 ± 0.1 b 8.0 ± 0.2 a 1000 8.2 ± 0.2 a 9.0 ± 0.1 a 8.7 ± 0.1 a 8.1 ± 0.2 a

-2 -1 Net CO2 assimilation (A) ± SE (μmol CO2 m s ) K2SiO3 rate -1 -1 (kg ha year ) July 28 August 18 September 3 0 6.8 ± 0.1 b 6.7 ± 0.2 b 7.1 ± 0.1 b 500 7.8 ± 0.4 a 8.5 ± 0.2 a 8.4 ± 0.1 a 1000 8.4 ± 0.2 a 8.2 ± 0.1 a 8.6 ± 0.1 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

246

-1 -1 Table J-20. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) plant SPAD values under well- watered field conditions from Jan. 14 to Nov. 1, 2013 at UF-TREC, Homestead, FL. Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 March 9 0 37.1 ± 0.3 c 37.0 ± 0.7 c 38.2 ± 0.8 b 38.1 ± 0.9 b 38.6 ± 0.7 a 500 39.1 ± 0.3 b 39.3 ± 0.2 b 40.2 ± 0.4 a 41.1 ± 0.9a 40.3 ± 0.8 a 1000 41.5 ± 0.4ª 41.4 ± 0.4a 41.0 ± 0.6 a 40.1 ± 0.7ab 38.5 ± 1.4 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) March 23 April 6 April 20 May 4 0 43.0 ± 0.6 a 40.7 ± 0.6 a 40.5 ± 0.9 b 41.7 ± 0.4 a 500 43.5 ± 0.8 a 41.3 ± 0.8 a 42.7 ± 0.8 ab 41.4 ± 0.6 a 1000 42.4 ± 0.7 a 40.4 ± 0.5 a 44.1 ± 0.6 a 41.2 ± 0.5 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) May 18 June 1 June 15 July 1 0 40.2 ± 0.5 b 42.8 ± 0.6 a 40.1 ± 0.7 b 39.5 ± 0.7 b 500 41.7 ± 0.5 b 41.9 ± 0.7 a 42.8 ± 0.7 a 41.2 ± 0.7 ab 1000 43.9 ± 0.6 a 42.7 ± 1.0 a 43.9 ± 1.0 a 43.3 ± 0.8 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) August 1 September 1 October 1 November 1 0 40.3 ± 0.6 b 41.3 ± 0.5 b 43.5 ± 0.6 a 38.5 ± 0.3 b 500 43.4 ± 1.2 a 46.3 ± 0.9 a 40.8 ± 1.1 a 42.3 ± 0.7 a 1000 43.1 ± 0.7 a 47.2 ± 1.0 a 42.5 ± 1.3 a 42.2 ± 0.4 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

247

-1 -1 Table J-21. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic female papaya (Carica papaya L.) plant SPAD values under well- watered field conditions from Jan. 14 to Nov. 1, 2013 at UF-TREC, Homestead, FL Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) January 14 January 26 February 9 February 23 March 9 0 36.4 ± 0.4 c 36.7 ± 0.6 c 36.4 ± 0.9 c 36.4 ± 0.9 b 37.2 ± 1.4 a 500 39.1 ± 0.4 b 39.0 ± 0.3 b 38.8 ± 0.5 b 38.5 ± 0.6 b 39.0 ± 0.6 a 1000 41.6 ± 0.2a 41.7 ± 0.3a 41.4 ± 0.3a 41.6 ± 0.7 a 39.5 ± 1.7 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) March 23 April 6 April 20 May 4 0 39.9 ± 0.7 a 38.9 ± 0.3 a 38.9 ± 0.3 b 39.8 ± 0.6 a 500 39.5 ± 0.6 a 38.5 ± 0.5 a 42.2 ± 0.3 a 39.0 ± 0.3 a 1000 40.1 ± 0.8 a 39.0 ± 0.6 a 41.9 ± 1.1 a 39.8 ± 0.6 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) May 18 June 1 June 15 July 1 0 39.7 ± 0.4 a 38.6 ± 0.4 a 39.3 ± 0.4 b 39.3 ± 0.6 b 500 40.5 ± 0.6 a 38.1 ± 0.4 a 42.5 ± 1.4 a 39.9 ± 0.4 b 1000 40.6 ± 0.8 a 38.1 ± 0.3 a 42.8 ± 1.3 a 42.7 ± 1.0 a

Mean SPAD ± SE K2SiO3 rate -1 -1 (kg ha year ) August 1 September 1 October 1 November 1 0 39.8 ± 0.6 a 39.9 ± 0.4 a 39.1 ± 0.5 b 39.9 ± 0.7 b 500 41.4 ± 1.9 a 41.5 ± 0.9 a 40.3 ± 0.5 ab 42.2 ± 0.5 a 1000 39.0 ± 0.5 a 41.8 ± 1.2 a 41.3 ± 0.7 a 43.4 ± 0.7 a Data analyzed by SAS REPEATED MEASURES. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different.

248

Table J-22. Concentration of constituents and total mineral, and plant available nutrient z elements of Krome soil samples prior to K2SiO3 soil drench applications to X17-2 x T5 transgenic papaya plants under field conditions at UF-TREC, Homestead, FL. Soil nutrient Constituent / Element Total mineralz Plant availabley pHx 8.1 - OMw (%) 6.5 - Nv (g kg-1) 1.4 -

u -1 NH4-N (mg kg ) - 3.4

t -1 NO3-N (mg kg ) - 7.6 P (g kg-1) 1.5 0.1 K (g kg-1) 0.8 0.1 Ca (g kg-1) 238 21 Mg (g kg-1) 3.1 0.2 Fe (g kg-1) 20.4 0.02 Al (g kg-1) 34.3 0.3

s -1 SO4-S (g kg ) - 0.7 Mn (g kg-1) 0.4 0.04 Cu (g kg-1) 0.3 0.1 B (mg kg-1) 13 0.01 Zn (mg kg-1) 70 18 Si (g kg-1) 32r 0.03q z Total mineral: P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y Plant available nutrients by Mehlic 3 extraction method (Alva, 1993). x pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). w Organic matter (OM) by LOI method (Wright et al., 2008). v Total N by Wolf digestion method (Wolf, 1982a). u (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). t (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). s (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). r Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991). q Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

249

Table J-23. Concentration of constituent and total mineral elementsz of Krome very gravelly sandy soil (n = 8) collected after 25 potassium silicate (K2SiO3, 16% Si) soil drench applications to X17-2 x T5 transgenic papaya (Carica papaya L.) plants under well-watered field conditions from January 14 to December 23, 2013 at UF-TREC, Homestead, FL. Constituent / Mineral 0 kg ha-1year-1 500 kg ha-1year-1 1000 kg ha-1year-1 pHy 8 8 8.1 OMx (%) 7.3 7.3 6.4 Nw (g kg-1) 1.9 1.9 2.1 P (g kg-1) 1.4 1.2 1.5 K (g kg-1) 0.8 0.8 0.9 Ca (g kg-1) 32.1 31.7 30.6 Mg (g kg-1) 0.4 0.7 0.7

Fe (g kg-1) 2.3 2.8 3.3 Al (g kg-1) 4.6 4.3 8.7 Mn (g kg-1) 0.2 0.2 0.2 Cu (g kg-1) 0.2 0.1 0.1 B (mg kg-1) 5 4.4 4.3 Zn (mg kg-1) 50 41 42 Siv (g kg-1) 27.4 31.4 35.1 z Total P, K, Ca, Mg, Mn, Fe, Cu, Zn, B, Al by HCl digestion method (Wolf, 1982a). y pH determined in water [1:2 V/V (soil:water)] method (Hanlon et al., 1998). x Organic matter (OM) by LOI method (Wright et al., 2008). w Total N by Wolf digestion method (Wolf, 1982a). v Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991).

250

Table J-24. Concentration of constituent and plant available nutrient elementsz of Krome very gravelly sandy soil samples (n = 8) collected after 25 potassium silicate (K2SiO3, 16% Si) soil drench applications to X17-2 x T5 transgenic papaya (Carica papaya L.) plants under well-watered field conditions from January 14 to December 23, 2013 at UF-TREC, Homestead. Constituent / Mineral 0 kg ha-1year-1 500 kg ha-1year-1 1000 kg ha-1year-1

y -1 NH4-N (mg kg ) 47 49 47

x -1 NO3-N (mg kg ) 2 2 2 P (g kg-1) 0.03 0.04 0.05 K (g kg-1) 0.3 0.2 0.4 Ca (g kg-1) 15 12.4 13.2 Mg (g kg-1) 0.2 0.2 0.2 Fe (g kg-1) 0.04 0.04 0.03

Al (g kg-1) 0.3 0.2 0.2

w -1 SO4-S (g kg ) 0.9 0.9 0.9 Mn (g kg-1) 0.03 0.04 0.04 Cu (g kg-1) 0.1 0.1 0.08 B (mg kg-1) 0.1 0.1 0.1 Zn (mg kg-1) 34 34 30 Siv (g kg-1) 0.16 0.25 0.35 z Available nutrients by Mehlic 3 extraction method (Alva, 1993). y (NH4-N), available NH4 by KCl extraction method (Wolf, 1982b). x (NO3-N), available NO3 by KCl extraction method (Wolf, 1982b). w (SO4-S), available S by ammonium acetate extraction method (Rehm and Caldwell, 1968). v Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

251

Table J-25. Concentration (n = 8) of nutrients and total available silicon nutrient mineral leaf petiole content of bisexual X17-2 x T5 transgenic papaya (Carica papaya L.) plants grown in Krome soil after 25 potassium silicate (K2SiO3, 16% Si) soil drench applications under well-watered field conditions from January 14 to December 23, 2013 at UF-TREC, Homestead, FL.

Mean mineral concentrationy (mg kg-1)

K2SiO3 rate (kg ha-1year-1) Bisexual Petiole

Nx P K Ca Mg Mn Fe Zn Siw

0 7,318 a 1,872 b 15,419 a 21,455 a 4,386 a 130 a 49 a 17 a 179 b

500 7,146 a 2,036 a 17,283 a 20,630 a 3,529 b 123 a 44 a 18 a 253 a

1000 6,672 a 2,106 a 16,107 a 20,801 a 3,834 ab 97 b 31 a 12 a 257 a Data analyzed by SAS PROC GLM. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different z Day after treatment. y Available P, K, Ca, Mg, Mn, Fe, Zn nutrients by Mehlic 3 extraction method (Alva, 1993). x -1 Ammonium N (mg L ) available NH4 by KCl extraction method (Wolf, 1982b). w Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

252

Table J-26. Concentrations (n = 8) of nutrient and total available silicon nutrient mineral leaf petiole content of female X17-2 x T5 transgenic papaya (Carica papaya L.) plants grown in Krome soil after 25 potassium silicate (K2SiO3, 16% Si) soil drench applications under well-watered field conditions from January 14 to December 23, 2013 at UF-TREC, Homestead, FL.

Mean mineral concentrationy (mg kg-1)

K2SiO3 rate (kg ha-1year-1) Female Petiole

Nx P K Ca Mg Mn Fe Zn Siw

0 6,496 a 1,536 b 12,156 a 20,684 a 4,480 b 115 a 49 a 5 b 159 c

500 6,400 a 1,774 a 9,558 ab 21,953 a 5,602 a 108 a 45 a 8 b 225 b

1000 6,025 a 2,029 a 9,179 b 21,291 a 5,374 a 106 a 46 a 15 a 266 a Data analyzed by SAS PROC GLM. Least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different z Day after treatment. y Available P, K, Ca, Mg, Mn, Fe, Zn nutrients by Mehlic 3 extraction method (Alva, 1993). x -1 Ammonium N (mg L ) available NH4 by KCl extraction method (Wolf, 1982b). w Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

253

-1 -1 Table J-27. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf petiole silicon content of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) under well-watered field conditions from January 14 to Nov. 1, 2013 at UF-TREC. z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) January 14 January 28 February 15 0 343.4 ± 36.7 157.5 ± 11.5 209.0 ± 31.7 500 322.0 ± 37.5 258.4 ± 23.8 266.1 ± 16.1 1000 334.9 ± 38.9 245.5 ± 27.6 355.3 ± 37.7

Linear Y = 337.7 – 0.01x Y = 176.5 + 0.1x Y = 203.7 + 0.2x regression r2 0.001 0.24 0.36

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) March 1 April 1 May 1 0 249.0 ± 30.6 158.6 ± 21.4 105.9 ± 7.5 500 417.1 ± 59.7 148.3 ± 19.1 134.1 ± 13.6 1000 533.9 ± 74.3 171.4 ± 34.2 164.0 ± 13.3

Linear Y = 257.6 + 0.3x Y = 153.0 + 0.01x Y = 105.6 + 0.1x regression r2 0.37 0.01 0.37

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) June 1 July 1 August 1 0 114.6 ± 19.2 241.6 ± 53.0 211.6 ± 13.0 500 157.9 ± 15.4 421.5 ± 30.7 302.3 ± 14.1 1000 130.6 ± 20.2 484.1 ± 51.0 311.4 ± 19.3

Linear Y = 126.5 + 0.02x Y = 267.4 + 0.3x Y = 225.2 + 0.1x regression r2 0.02 0.41 0.44

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) September 1 October 1 November 1 0 141.0 ± 22.5 87.0 ± 8.7 97.2 ± 20.3 500 222.9 ± 13.8 229.0 ± 17.5 207.3 ± 29.6 1000 202.1 ± 9.3 260.8 ± 16.1 182.9 ± 29.9

Linear Y = 158.1 + 0.1x Y = 105.4 + 0.2x Y = 119.6 + 0.1x regression r2 0.21 0.70 0.17 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

254

-1 -1 Table J-28. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf petiole silicon content of X17-2 x T5 transgenic female papaya (Carica papaya L.) under well-watered field conditions from January 14 to Nov. 1, 2013 at UF-TREC. z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) January 14 January 28 February 15 0 690.8 ± 22.8 591.1 ± 65.7 142.5 ± 15.9 500 700.6 ± 16.2 690.0 ± 12.8 134.1 ± 7.5 1000 716.9 ± 8.6 766.5 ± 32.1 163.8 ± 11.1 Linear Y = 689.7 + 0.03x Y = 511.5 + 0.2x Y = 136.2 + 0.02x regression r2 0.05 0.13 0.07

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) March 1 April 1 May 1 0 235.3 ± 34.9 149.9 ± 15.6 154.3 ± 12.2 500 360.0 ± 94.9 180.1 ± 13.1 207.6 ± 28.4 1000 398.6 ± 48.0 230.8 ± 27.8 206.1 ± 17.1 Linear Y = 249.6 + 0.2x Y = 146.5 + 0.1x Y = 163.4 + 0.1x regression r2 0.13 0.28 0.13

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) June 1 July 1 August 1 0 93.0 ± 4.4 86.0 ± 9.5 108.6 ± 10.4 500 150.1 ± 13.7 183.8 ± 16.2 146.6 ± 14.5 1000 142.5 ± 10.6 222.1 ± 14.3 168.3 ± 8.8 Linear Y = 103.8 + 0.1x Y = 95.9 + 0.1x Y = 111.4 + 0.1x regression r2 0.29 0.67 0.39

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) September 1 October 1 November 1 0 146.3 ± 9.4 95.3 ± 3.5 43.9 ± 4.3 500 236.5 ± 13.8 208.3 ± 40.8 109.8 ± 13.3 1000 256.6 ± 24.1 202.1 ± 18.3 160.8 ± 6.9 Linear Y = 157.9 + 0.1x Y = 115.1 + 0.1x Y = 46.4 + 0.1x regression r2 0.47 0.26 0.80 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

255

-1 -1 Table J-29. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf lamina silicon content on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) under well-watered field conditions from January 14 to Nov. 1, 2013 at UF-TREC. z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) January 14 January 28 February 15 0 1,872.8 ± 97.3 915.9 ± 70.1 1,089.8 ± 118.1 500 1,891.0 ± 99.6 1,634.3 ± 72.2 1,585.0 ± 135.2 1000 2,066.1 ± 77.2 1,683.6 ± 90.3 2,175.3 ± 207.5 Linear Y = 1,846.6 + 0.2x Y = 1,027.4 + 0.8x Y = 1,073.9 + 1.1x regression r2 0.09 0.59 0.53

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) March 1 April 1 May 1 0 1,444.1 ± 248.5 1,356.0 ± 199.6 906.0 ± 14.8 500 2,496.8 ± 301.3 1,890.0 ± 89.4 1,785.8 ± 112.3 1000 2,759.9 ± 277.4 2,285.6 ± 89.8 2,169.8 ± 190.7 Linear Y = 1,575.7 + 1.3x Y = 1,379.1 + 0.9x Y = 988.6 + 1.3x regression r2 0.34 0.52 0.68

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) June 1 July 1 August 1 0 825.3 ± 62.1 852.5 ± 94.4 906.0 ± 61.8 500 1,927.6 ± 140.6 1,485.1 ± 200.0 2,060.5 ± 148.2 1000 2,970.4 ± 254.0 1,567.8 ± 106.0 2,185.0 ± 101.6 Linear Y = 835.2 + 2.2x Y = 944.2 + 0.7x Y = 1,077.7 + 1.3x regression r2 0.79 0.35 0.66

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) September 1 October 1 November 1 0 617.6 ± 109.4 391.5 ± 57.7 687.8 ± 45.1 500 2,064.1 ± 156.7 1,427.3 ± 194.7 2,297.4 ± 316.0 1000 2,027.8 ± 394.1 1,435.9 ± 159.5 3,004.3 ± 174.2 Linear Y = 864.8 + 1.4x Y = 562.7 + 1.0x Y = 838.2 + 2.3x regression r2 0.37 0.46 0.72 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

256

-1 -1 Table J-30. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on leaf lamina silicon content of X17-2 x T5 transgenic female papaya (Carica papaya L.) under well-watered field conditions from January 14 to Nov. 1, 2013 at UF-TREC. z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) January 14 January 28 February 15 0 2,032.0 ± 121.0 1,414.5 ± 71.0 1,228.3 ± 85.2 500 2,092.9 ± 104.0 1,867.8 ± 51.6 1,401.9 ± 89.7 1000 2,113.0 ± 75.2 1,730.0 ± 54.0 1,646.6 ± 81.2 Linear Y = 2,038.8 + 0.1x Y = 1,513.0 + 0.3x Y = 1,216.4 + 0.4x regression r2 0.02 0.27 0.36

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) March 1 April 1 May 1 0 2,174.5 ± 180.7 1,304.3 ± 118.8 1,584.4 ± 210.5 500 2,026.4 ± 232.8 2,095.3 ± 152.6 1,506.6 ± 166.7 1000 1,831.5 ± 130.9 2,225.0 ± 267.3 1,710.9 ± 335.4 Linear Y = 2,182.3 – 0.3x Y = 1,414.5 + 0.9x Y = 1,537.4 + 0.1x regression r2 0.08 0.34 0.01

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) June 1 July 1 August 1 0 879.5 ± 96.0 2,075.6 ± 448.2 862.0 ± 47.5 500 2,122.6 ± 172.6 2,912.0 ± 416.1 1,884.6 ± 83.6 1000 2,219.4 ± 101.0 3,016.4 ± 398.4 2,466.9 ± 117.1 Linear Y = 1,070.6 + 1.3x Y = 2,197.6 + 0.9x Y = 935.4 + 1.6x regression r2 0.61 0.10 0.87

z -1 K2SiO3 rate Mean silicon concentration ± SE (mg kg ) -1 -1 (kg ha year ) September 1 October 1 November 1 0 436.3 ± 43.5 530.3 ± 72.3 587.9 ± 91.1 500 1,485.8 ± 123.1 1,584.1 ± 119.2 2,292.6 ± 297.6 1000 1,718.1 ± 194.7 1,714.5 ± 232.1 2,698.2 ± 211.6 Linear Y = 572.7 + 1.3x Y = 684.2 + 1.2x Y = 804.4 + 2.1x regression r2 0.61 0.52 0.64 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

257

Table J-31. Correlation (n = 4) among totalz and availabley soil silicon content and leaf lamina and petiole silicon content of bisexual and female X17-2 x T5 transgenic papaya (Carica papaya L.) plants grown in Krome soil after 25 soil drench applications x (371 DAT ) of potassium silicate (K2SiO3, 16% Si) under well-watered field conditions at UF-TREC, Homestead, FL. Linear regression Coefficient of Plant sex Leaf tissue Soil silicon (g kg-1) regression

Total Y = –0.4 + 0.1x r2 = 0.06 Lamina Available Y = –0.4 + 22.0x r2 = 0.37

Bisexual

Total Y = 186.5 + 0.002x r2 = 0.01 Petiole Available Y = 132.0 + 1.2x r2 = 0.50

Total Y = –1.4 + 0.1x r2 = 0.15 Lamina Available Y = –0.3 + 17.1x r2 = 0.30

Female

Total Y = 92.0 + 0.01x r2 = 0.10 Petiole Available Y = 108.7 + 1.5x r2 = 0.49

Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Total Si analysis by autoclave-induced digestion method (Elliot and Snyder, 1991). y Available Si by acetic acid extraction method (Elliot and Snyder, 1991). x Day after treatment.

258

-1 -1 Table J-32. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil applications on X17-2 x T5 transgenic bisexual and female papaya (Carica papaya L.) fruit number per plant after 142 DATz (4.5 months) and 267 DATz (8.5 months) and 11 and 20 soil drench applications respectively, under well-watered field conditions at UF-TREC, Homestead.

Mean fruit number plant-1 ± SE

K2SiO3 rate (kg ha-1year-1) Harvest 1 (142 DATz) Harvest 2 (267 DATz) Bisexual Female Bisexual Female 0 24.1 ± 3.1 5.6 ± 1.6 7.0 ± 0.8 5.1 ± 0.9 500 23.8 ± 3.3 5.5 ± 1.0 8.5 ± 0.8 6.8 ± 1.3

1000 15.6 ± 3.5 6.4 ± 2.2 10.3 ± 0.7 7.4 ± 0.9 Linear regression Y = 29.7 – 4.3x Y = 5.1 + 0.4x Y = 5.3 + 1.6x Y = 4.2 + 1.1x

r2 0.13 0.01 0.30 0.10 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. Data harvest analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within row are not significantly different. z Day after treatment.

259

-1 -1 Table J-33. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit number plant-1, fruit yield plant-1treatment-1, and fruit yield treatment-1ha-1 after 17 and 22 soil drench applications (234 and 308 DATz) under well-watered field conditions at UF-TREC, Homestead, FL.

Mean number fruity ± SE Mean fruit weightx ± SE Mean fruit yield ± SE -1 -1 -1 K2SiO3 rate (Fruit plant ) (kg plant ) (kg ha ) (kg ha-1year-1) Harvest 1 Harvest 2 Harvest 1 Harvest 2 Harvest 1 Harvest 2

0 24.1 ± 3.1 7.0 ± 0.8 30.8 ± 3.9 7.7 ± 0.8 39,375.7 ± 4,972.8 9,838.3 ± 1,069.7

500 23.8 ± 3.3 8.5 ± 0.8 31.0 ± 4.4 11.5 ± 0.9 39,611.4 ± 5,587.1 14,722.2 ± 1,184.7

1000 15.6 ± 3.5 10.3 ± 0.7 19.3 ± 4.4 13.6 ± 0.9 24,704.6 ± 5,608.6 17,361.7 ± 1,206.0

Linear Y = 27.9 – 4.3x Y = 5.3 + 1.6x Y = 36.6 - 4.1x Y = 6.7 + 1.8x Y = 46,829.0 – 5,256.5x Y = 8,518.0 + 2,338.1x regression

r2 0.13 0.30 0.17 0.45 0.17 0.45 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Day after treatment. y Average fruit number of 8 rows, 7 plants each. x Plant distance: 2.1 m x 3.6 m (7’ x 12’); 518 plants/ha = 1,279 plants ha-1.

260

Table J-34. Correlation (n = 4) among available siliconz content in plant leaf lamina and petiole, and fruit weight (g plant-1) of bisexual X17-2 x T5 transgenic papaya (Carica papaya L.) plants grown in Krome soil after 11 and 20 potassium silicate (K2SiO3, 16% Si) soil drench applications (142 and 267 DATx) under well-watered field conditions at UF-TREC, Homestead, FL. Linear regression Coefficient of Harvest Plant tissue (g kg-1) regression

Lamina Y = 0.6 + 0.2x r2 = 0.37 First Petiole Y = 0.3 + 2.5x r2 = 0.42

Lamina Y = 0.9 + 0.04x r2 = 0.05 Second Petiole Y = 0.3 + 2.8x r2 = 0.37 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991). y Day after treatment.

261

APPENDIX K ADDITIONAL TABLES FOR CHAPTER 5

262

-1 -1 Table K-1. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions from January 14 to November 1, 2013 at UF-TREC, Homestead, FL. Harvest K SiO rate 2 3 Mean fruit weight ± SE (g) Linear regression r2 Date (kg ha-1year-1)

0 1,285.3 ± 47.8

August 500 1,320.1 ± 68.0 Y = 1,303.7 – 0.04x 0.01 22

1000 1,244.5 ± 43.2

0 1,107.8 ± 39.9

October 500 1,342.0 ± 58.0 Y = 1,151.2 + 0.21x 0.14 29

1000 1,315.5 ± 48.7

Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

263

-1 -1 Table K-2. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on length of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions from January 14 to November 1, 2013 at UF-TREC, Homestead, FL. Harvest K SiO rate 2 3 Mean fruit length ± SE (mm) Linear regression r2 Date (kg ha-1year-1)

0 249.3 ± 5.3

August 500 235.0 ± 5.3 Y = 247.6 – 0.02x 0.12 22

1000 230.8 ± 3.9

0 201.9 ± 3.5

October 500 222.3 ± 4.4 Y = 205.4 + 0.02x 0.22 29

1000 222.3 ± 3.0

Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

264

-1 -1 Table K-3. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on diameter of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions from January 14 to November 1, 2013 at UF-TREC, Homestead, FL. Harvest K SiO rate 2 3 Mean fruit diameter ± SE (mm) Linear regression r2 Date (kg ha-1year-1)

0 106.3 ± 1.3

August 500 116.1 ± 2.3 Y = 107.6 + 0.01x 0.30 22

1000 118.0 ± 1.4

0 107.8 ± 1.2

October 500 115.8 ± 2.3 Y = 109.3 + 0.01x 0.10 29

1000 114.4 ± 1.9

Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

265

-1 -1 Table K-4. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on fruit peel puncture resistance and whole fruit firmness measured with intact peel of X17-2 x T5 transgenic bisexual papaya grown under well-watered field conditions at UF-TREC.

Peel puncture resistance (texture Analyzer puncture method).

Harvest K SiO rate Mean puncture resistance 2 3 Linear regression r2 date (kg ha-1year-1) ± SE (Newton) 0 31.2 ± 3.3 August 500 25.7 ± 1.9 Y = 30.7 – 0.01x 0.11 22 1 1000 23.0 ± 1.0 0 32.2 ± 2.8 October 500 31.7 ± 3.1 Y2 = 33.3 – 0.01x 0.09 29 1000 24.2 ± 1.2

Whole fruit firmness (Texture Analyzer compression method).

Harvest K2SiO3 rate Mean fruit firmness ± SE Linear regression r2 date (kg ha-1year-1) (Newton) 0 42.8 ± 3.0 August 500 46.8 ± 3.1 Y1 = 44.6 – 0.003x 0.01 22 1000 39.9 ± 2.6 0 39.6 ± 2.9 October 500 53.6 ± 2.9 Y2 = 43.9 + 0.002x 0.01 29 1000 42.0 ± 2.2

Penetrometer resistance (Wagner penetrometer puncture method).

Harvest K SiO rate Mean puncture resistance 2 3 Linear regression r2 date (kg ha-1year-1) ± SE (Newton) 0 47.4 ± 2.4 August 500 41.4 ± 2.4 Y1 = 45.6 – 0.001x 0.003 22 1000 46.3 ± 1.7 0 27.7 ± 3.0 October 500 36.1 ± 1.9 Y2 = 30.6 – 0.001x 0.0004 29 1000 27.3 ± 0.8 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

266

-1 -1 Table K-5. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on fruit flesh firmness and resistance to shear force of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) grown under well- watered field conditions at UF-TREC for Aug. 22 and Oct. 29, 2013 harvests. HortScience Postharvest Laboratory, UF.

Flesh firmness (Texture Analyzer puncture method).

Harvest K SiO rate Mean fruit firmnessy ± SE 2 3 Linear regression r2 Date (kg ha-1year-1) (Newton) 0 8.9 ± 0.9

August 22 500 9.6 ± 0.7 Y1 = 8.7 + 0.002x 0.06 1000 11.3 ± 1.3 0 17.0 ± 3.7

October 29 500 25.7 ± 1.9 Y2 = 20.1 – 0.001x 0.001 1000 16.3 ± 2.1

Shear resistance (Texture Analyzer shear blade method).

Harvest K SiO rate Mean fruit firmnessx ± SE 2 3 Linear regression r2 Date (kg ha-1year-1) (Newton) 0 5.0 ± 0.3

August 22 500 5.3 ± 0.3 Y1 = 4.9 + 0.001x 0.10 1000 6.4 ± 0.5 0 5.8 ± 0.4

October 29 500 6.5 ± 0.3 Y2 = 5.9 + 0.0003x 0.01 1000 6.1 ± 0.4 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

267

-1 -1 Table K-6. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on fruit peel and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) grown under well-watered field conditions at UF- TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF, Gainesville, FL.

Peel fresh weight.

Harvest K SiO rate 2 3 Mean peel fresh weight ± SE (g) Linear regression r2 Date (kg ha-1year-1) 0 352.9 ± 16.5

August 22 500 281.3 ± 15.9 Y1 = 335.8 – 0.04x 0.06 1000 312.3 ± 11.1 0 247.8 ± 10.9

October 29 500 320.3 ± 18.9 Y2 = 262.0 + 0.06x 0.10 1000 307.4 ± 21.1

Peel dry weight.

Harvest K SiO rate 2 3 Mean peel dry weight ± SE (g) Linear regression r2 Date (kg ha-1year-1) 0 38.9 ± 1.4

August 22 500 30.9 ± 1.6 Y1 = 36.9 + 0.001x 0.002 1000 39.6 ± 1.3 0 31.1 ± 1.4

October 29 500 37.1 ± 2.6 Y2 = 32.0 + 0.01x 0.07 1000 37.6 ± 2.5 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

268

-1 -1 Table K-7. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on fruit pulp fresh and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) grown under well-watered field conditions at UF-TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF, Gainesville, FL.

Pulp fresh weight.

Harvest K SiO rate 2 3 Mean pulp fresh weight ± SE (g) Linear regression r2 Date (kg ha-1year-1) 0 799.3 ± 29.1

August 22 500 948.9 ± 45.9 Y1 = 846.6 + 0.02x 0.002 1000 814.7 ± 28.9 0 773.7 ± 30.8

October 29 500 987.8 ± 35.6 Y2 = 821.3 + 0.14x 0.12 1000 916.6 ± 36.0

Pulp dry weight.

Harvest K SiO rate 2 3 Mean pulp dry weight ± SE (g) Linear regression r2 Date (kg ha-1year-1) 0 42.9 ± 2.9

August 22 500 52.4 ± 3.0 Y1 = 45.0 + 0.01x 0.05 1000 49.5 ± 1.8 0 49.4 ± 2.2

October 29 500 65.5 ± 3.5 Y2 = 53.4 + 0.01x 0.06 1000 57.5 ± 2.4 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

269

-1 -1 Table K-8. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on seed fresh and dry weight of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions at UF-TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF, Gainesville, FL.

Seed fresh weight.

Harvest K SiO rate 2 3 Mean seed fresh weight ± SE (g) Linear regression r2 date (kg ha-1year-1) 0 64.4 ± 3.7

August 22 500 86.5 ± 5.9 Y1 = 67.4 + 0.03x 0.17 1000 90.8 ± 6.8 0 51.0 ± 2.6

October 29 500 63.0 ± 2.7 Y2 = 53.3 + 0.01x 0.10 1000 61.3 ± 3.5

Seed dry weight.

Harvest K SiO rate 2 3 Mean seed dry weight ± SE (g) Linear regression r2 date (kg ha-1year-1) 0 9.6 ± 0.5

August 22 500 11.2 ± 0.8 Y1 = 9.8 + 0.002x 0.10 1000 12.0 ± 0.7 0 7.8 ± 0.4

October 29 500 9.1 ± 0.3 Y2 = 8.0 + 0.002x 0.16 1000 9.4 ± 0.3 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

270

-1 -1 Table K-9. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on peel and pulp thickness of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions at UF-TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF, Gainesville, FL.

Peel thickness.

Harvest K SiO rate 2 3 Mean peel thickness ± SE (mm) Linear regression r2 date (kg ha-1year-1) 0 4.6 ± 0.2

August 22 500 5.4 ± 0.2 Y1 = 4.9 + 0.0001x 0.001 1000 4.7 ± 0.1 0 2.1 ± 0.1

October 29 500 3.3 ± 0.2 Y2 = 2.3 + 0.001x 0.33 1000 3.1 ± 0.1

Pulp thickness.

Harvest K SiO rate 2 3 Mean pulp thickness ± SE (mm) Linear regression r2 date (kg ha-1year-1) 0 26.6 ± 0.6

August 22 500 29.0 ± 0.6 Y1 = 26.8 + 0.004x 0.28 1000 30.2 ± 0.6 0 25.2 ± 0.1

October 29 500 29.0 ± 0.2 Y2 = 25.7 + 0.004x 0.41 1000 29.4 ± 0.1 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

271

-1 -1 Table K-10. Effect of 0, 500, and 1,000 kg ha year potassium silicate (K2SiO3, 16% Si) soil drench applications on peel and pulp coloration of X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions at UF-TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF. Gainesville, FL.

Peel coloration

z K SiO rate Colorimetric factors Date 2 3 (kg ha-1year-1) L* a* b* C* Hue angle (Ho) 0 56.5 ± 0.8 a 38.6 ± 1.7 b 44.3 ± 1.1 b 44.9 ± 1.1 b 88.0 ± 1.3 a August 500 55.2 ± 0.5 a 44.6 ± 2.5 ab 46.1 ± 0.8 ab 46.8 ± 0.9 ab 83.0 ± 1.4 b 22 1000 55.0 ± 0.8 a 50.9 ± 2.6 a 48.3 ± 1.0 a 49.3 ± 1.1 a 81.0 ± 1.3 b 0 49.9 ± 0.5 b 35.2 ± 3.5 b 30.4 ± 0.8 b 31.1 ± 0.9 b 84.5 ± 1.5 ab October 500 47.9 ± 0.7 c 38.0 ± 1.9 b 31.7 ± 1.1 b 32.1 ± 1.1 b 86.9 ± 1.8 a 29 1000 51.9 ± 0.6 a 47.3 ± 3.7 a 40.3 ± 1.2 a 41.2 ± 1.3 a 80.6 ± 1.3 b

Pulp coloration

z K SiO rate Colorimetric factors Date 2 3 (kg ha-1year-1) L* a* b* C* Hue angle (Ho) 0 55.0 ± 0.4 a 25.1 ± 0.4 a 38.9 ± 0.5 a 46.4 ± 0.4 ab 57.2 ± 0.6 a August 500 48.7 ± 0.8 b 24.4 ± 0.4 a 37.7 ± 0.8 a 44.9 ± 0.8 b 56.7 ± 0.4 a 22 1000 49.5 ± 0.7 b 25.3 ± 0.4 a 39.4 ± 0.6 a 46.9 ± 0.6 a 57.2 ± 0.5 a 0 45.5 ± 0.4 a 26.1 ± 0.4 a 37.4 ± 0.5 a 45.7 ± 0.5 a 55.1 ± 0.4 a October 500 45.2 ± 0.7 a 25.4 ± 0.5 a 37.0 ± 1.0 a 45.0 ± 1.0 a 55.4 ± 0.6 a 29 1000 46.4 ± 0.6 a 25.1 ± 0.4 a 37.9 ± 0.7 a 45.5 ± 0.7 a 56.4 ± 0.4 a Data analyzed by SAS T-test based on least-square mean separation by LSD’s studentized test, p≤0.05. Means with a common letter within a factor are not significantly different. z Means of 18 fruit treatment-1 using a Minolta chroma meter CR-410 measuring in CIELAB. L* = Lightness; a* = bluish-green/red- purple hue component; b* = yellow/blue hue component; C* = [(a*2 + b*2)1/2] = chroma; Ho (from arctangent b*/a*) = Hue angle (0o = red-purple, 90o = yellow, 180o = bluish-green, 270o = blue) [McGuire, 1992].

272

-1 -1 Table K-11. Linear regressions of peel and pulp color changes as affected by 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on X17-2 x T5 transgenic bisexual papaya (Carica papaya L.) fruit grown under well-watered field conditions at UF-TREC for August 22 and October 29, 2013 harvests. HortScience Postharvest Laboratory, UF, Gainesville, FL.

Peel coloration

z K SiO rate Colorimetric factors Date 2 3 (kg ha-1year-1) L* a* b* C* Hue angle (Ho) 0 August Y = 56.3 – 0.002x Y = 38.6 + 0.01x; Y = 44.2 + 0.004x; Y = 44.8 + 0.004x; Y = 87.5 – 0.01x; 500 1 1 1 1 1 22 r2 = 0.04 r2 = 0.22 r2 = 0.14 r2 = 0.15 r2 = 0.21 1000 0 October Y = 48.9 + 0.002x; Y = 34.1 + 0.01x; Y = 29.2 + 0.01x; Y = 29.8 + 0.01x; Y = 86.0 – 0.004x; 500 2 2 2 2 2 29 r2 = 0.07 r2 = 0.13 r2 = 0.44 r2 = 0.41 r2 = 0.06 1000

Pulp coloration

z K SiO rate Colorimetric factors Date 2 3 (kg ha-1year-1) L* a* b* C* Hue angle (Ho) 0 August Y = 53.8 – 0.01x; Y = 24.8 + 0.0002x; Y = 38.4 + 0.001x; Y = 45.8 + 0.001x; Y = 57.1 + 0.00002x 1 1 1 1 1 22 500 r2 = 0.34 r2 = 0.003 r2 = 0.01 r2 = 0.01 r2 = 0.0001 1000 0 October Y = 45.3 + 0.001x; Y = 26.1 – 0.001x; Y = 37.2 + 0.001x; Y = 45.5 - 0.0001x; Y = 54.9 + 0.001x; 500 2 2 2 2 2 29 r2 = 0.02 r2 = 0.07 r2 = 0.01 r2 = 0.0003 r2 = 0.07 1000 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Color characteristics measured in CIELAB values. L* = Lightness; a* = bluish-green/red-purple hue component; b* = yellow/blue hue component; C* = [(a*2 + b*2)1/2] = chroma; Ho (from arctangent b*/a*) = Hue angle (0o = red-purple, 90o = yellow, 180o = bluish- green, 270o = blue) [McGuire, 1992].

273

-1 -1 Table K-12. Effect of 0, 500, and 1,000 kg ha year of K2SiO3 soil drench applications on pH, TA, TSS of X17-2 x T5 transgenic bisexual papaya fruit grown under well-watered field conditions at UF-TREC and measured for Aug. 22 and Oct. 29, 2013 harvests.

Fruit pH

Harvest K SiO rate 2 3 Mean pH values ± SE Linear regression r2 date (kg ha-1year-1) 0 5.3 ± 0.1 August 500 5.3 ± 0.1 Y = 5.3 - 0.000002x 0.0001 22 1 1000 5.3 ± 0.1 0 5.3 ± 0.02 October 500 5.4 ± 0.01 Y = 5.3 - 0.0001x 0.29 29 2 1000 5.4 ± 0.01

Titratable acidity (TA)

Harvest K SiO rate Mean TA values ± SE 2 3 Linear regression r2 date (kg ha-1year-1) (% Citric acid) 0 1.1 ± 0.10 August 500 1.2 ± 0.03 Y1 = 1.1 + 0.0002x 0.14 22 1000 1.3 ± 0.04 0 1.0 ± 0.003 October 500 1.0 ± 0.003 Y2 = 1.0 – 0.00001x 0.12 29 1000 1.0 ± 0.002

Total soluble solids (TSS)

Harvest K2SiO3 rate Mean TSS values ± SE Linear regression r2 date (kg ha-1year-1) (oBrix). 0 10.3 ± 0.2 August 500 11.2 ± 0.2 Y1 = 10.6 + 0.001x 0.08 22 1000 10.8 ± 0.1 0 11.4 ± 0.2 October 500 11.3 ± 0.1 Y = 11.4 – 0.0001x 0.004 29 2 1000 11.3 ± 0.1 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05.

274

-1 -1 Table K-13. Effect of 0, 500, and 1,000 kg ha year K2SiO3 soil drench applications on peel, pulp, and seed siliconz content of X17-2 x T5 transgenic bisexual papaya fruit grown under well-watered field conditions for Aug. 22 and Oct. 29, 2013 harvests at UF.

Peel silicon content

Harvest K SiO rate Mean peel Si values ± SE 2 3 Linear regression r2 date (kg ha-1year-1) (mg kg-1) 0 86.7 ± 8.5 August 500 104.4 ± 14.2 Y1 = 88.8 + 0.02x 0.04 22 1000 109.3 ± 11.2 0 22.7 ± 5.0 October 500 38.4 ± 4.2 Y2 = 15.9 + 0.07x 0.60 29 1000 94.9 ± 6.5

Pulp silicon content

Harvest K SiO rate Mean pulp Si values ± SE 2 3 Linear regression r2 date (kg ha-1year-1) (mg kg-1) 0 14.5 ± 1.7 August 500 67.5 ± 5.4 Y1 = 25.6 + 0.04x 0.34 22 1000 54.1 ± 3.8 0 31.8 ± 3.7 October 500 33.5 ± 3.5 Y2 = 31.0 + 0.01x 0.05 29 1000 40.0 ± 3.1

Seed silicon content

Harvest K2SiO3 rate Mean seed Si values ± SE Linear regression r2 date (kg ha-1year-1) (mg kg-1) 0 52.8 ± 4.6 August 500 53.0 ± 8.3 Y1 = 49.2 + 0.02x 0.08 22 1000 75.2 ± 8.2 0 67.6 ± 2.5 October 500 60.6 ± 2.7 Y = 65.0 + 0.001x 0.003 29 2 1000 69.0 ± 2.5 Data analyzed by SAS PROC REG procedures based on least-square mean separation by LSD’s studentized test, p≤0.05. z Available Si by acetic acid extraction method (Elliot and Snyder, 1991).

275

LIST OF REFERENCES

Abraham, A.O., M.D. Laing, J.P. Bower, and C. Clark. 2008. Preharvest or postharvest silicon treatment for the control of postharvest Penicillium digitatum of citrus fruit. pp:20. In: M. Laing, M. Keeping and O. Kvedaras (eds.). Silicon in Agriculture Conference: 4th. International Conference, October 26-31, 2008. Abstract # l. Wild Coast, Port Edward, KwaZulu-Natal, South Africa. 109 p.

Adatia, M.H. and R.T. Besford. 1986. The effects of silicon on cucumber plants grown in recirculating nutrient solution. Annals of Botany 58:343-351.

Adlan, H.A. 1969. Effect of pH, silicon and phosphorus treatments on growth and yield of papaya (Carica papaya L.). Ph.D. Dissertation. University of Hawaii. Hawaii, USA.

Agarie, S., H. Uchida, W. Agata, F. Kubota, and P.B. Kaufman. 1998. Effects of silicon on transpiration and leaf conductance in rice plants (Oryza sativa L.). Plant Production Science 1:89-95.

Agarwala, S.C., B.D. Nautiyal, and C. Chatterjee. 1986. Manganese, copper and molybdenum nutrition of papaya. Journal of Horticultural Science 61:397-405.

Ahmad, R.R., H.S. Zaheer, and S. Ismail. 1992. Role of silicon in salt tolerance of wheat (Triticum aestivum L.). Plant Science 85(1):43-50.

Ahmed, M., F.U. Hassen, U. Qadeer, and M.A. Aalam. 2011. Silicon application and drought tolerance mechanism of sorghum. African Journal of Agricultural Research 6(3):594-607.

Akamine, E.K. and T. Goo. 1971. Relationship between surface color development and total soluble solids in papaya. HortScience. 6:567-568.

Al-aghabary, K., Z. Zhu, and Q. Shi. 2004. Influence of silicon supply on chlorophyll content, chlorophyll fluorescence, and antioxidative enzyme activities in tomato plants under salt stress. J. Plant Nutrition 27:2101-2115.

Alexandre, A., J.D. Meunier, F. Colin, and J.M. Koud. 1997. Plant impact on the biogeochemical cycle of silicon and related weathering processes. Geochimica et Cosmochimica Acta 61(3):577-5682.

Allan, P. 2002. Carica papaya responses under cool subtropical growth conditions. Acta Horticulturae 575:757-763.

Almeida, F.T., S. Bernardo, E.F. Souza, S.L.D. Marin, and S. Grippa. 2003. Growth and yield of papaya under irrigation. Scientia Agricola 60(3):419-424.

276

Alva, A.K. 1993. Comparison of Mehlich 3, Mehlich 1, ammonium bicarbonate-DTPA, 1.0M ammonium acetate, and 0.2M ammonium chloride for extraction of calcium, magnesium, phosphorus, and potassium for a wide range of soils. Communications in Soil Science and Plant Analysis 24(7&8):603-612.

Alvarez, J. and L.E. Datnoff. 2001. The economics of silicon for integrated management and sustainable production of rice and sugarcane. pp:221-239. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Alvarez, J., L.E. Datnoff, and G.H. Snyder. 2004. The economics of silicon applications on rice and sugarcane in Florida. IFAS Extension. FE475. University of Florida. Gainesville, FL. 6 p.

Al-Yahyai, R., B. Schaffer, F.S. Davies, and R. Muñoz-Carpena. 2006. Characterization of soil- water retention of a very gravelly loam soil varied with determination method. Soil Science 171(2):85-93.

Amthor, J.S. 1989. Respiration and crop productivity. Book review. First edition. Springer- Verlag. New York, NY. 215 p.

An, J.F. and R.E. Paull. 1990. Storage temperature and ethylene influence on ripening of papaya fruit. Journal of the American Society for Horticultural Science 115:949-953.

Anderson, D.L. and O.Jr. Sosa. 2001. Effect of silicon on expression of resistance to sugarcane borer (Diatraea saccharalis). Proceedings Journal of the American Society of Sugarcane Technologists 21:43-50

Anderson, J., K. Pegg, L. Coates, L. Dann, T. Cooke, L. Smith, and J. Dean. 2004. Silicon and disease management in avocados. Talking Avocados 15(3):23-25.

Anderson, J.M., K.G. Pegg, E.K. Dann, A.W. Cooke, L.A. Smith, S.L. Willingham, F.R. Giblin, J.R. Dean, and L.M. Coates. 2005. New strategies for the integrated control of avocado fruit diseases. New Zealand and Australia Avocado Grower’s Conference ’05. Session 3. Pest Disease Control Strategies, Integrated Production Systems and the Impact on Market Access. 20-22 September 2005. Tauranga, New Zealand. 6 p.

AOAC International. 1995. Official methods of analysis of AOAC international. AOAC International. Arlington, VA.

Arnon, D.I. and P.R. Stout. 1939. The essentiality of certain elements in minute quantity for plants with special reference to copper. Plant Physiology 14:371-375.

277

Asher, C.J. 1991. Beneficial elements, functional nutrients, and possible new essential elements. pp:703-723. In: J.J. Mortvedt, F.R. Cox, L.M. Shuman, and R.M. Welch (eds.). Micronutrients in agriculture. The Soil Science Society of America. Book series no. 4. Madison, WI. 760 p.

Asmar, S.A., E.M. Castro, M. Pasqual, F.J. Pereira, and J.D.R. Soares. 2013. Changes in leaf anatomy and photosynthesis of micropropagated banana plantlets under different silicon sources. Scientia Horticulturae 161:328-332.

Awada, M. 1977. Relations of nitrogen, phosphorus, and potassium fertilization to nutrient composition of the petiole and growth of papaya. Journal of the American Society for Horticultural Science 102(4):413-418.

Awada, M. and W. Ikeda. 1957. Effect of water and nitrogen application on composition, growth, sugars in fruits, yield, and sex expression of the papaya plants (Carica papaya L.). Hawaii Agricultural Experimental Station. Technical Bulletin. No. 33.

Awada, M. and C. Long. 1969. The selection of the phosphorus index in papaya tissue analysis. Journal of the American Society for Horticultural Science. 94:501-504.

Awada, M. and C. Long. 1971a. Relation of petiole nitrogen levels to nitrogen fertilization and yield of papaya. Journal of the American Society for Horticultural Science 96(6):745- 749.

Awada, M. and C. Long. 1971b. The selection of the potassium index in papaya tissue analysis. Journal of the American Society for Horticultural Science 96(1):74-77

Awada, M. and C. Long. 1978. Relation of nitrogen and phosphorus fertilization to fruiting and petiole composition of ‘Solo’ papaya. Journal of the American Society for Horticultural Science 103(2):217-219.

Awada, M. and C. Long. 1980. Nitrogen and potassium fertilization effects on fruiting and petiole composition of 24- to 48-month old papaya plants. Journal of the American Society for Horticultural Science 105(4):505-507.

Awada, M. and R. Suehisa. 1970. Nutrient removal by papaya fruits. HortScience 5(3):182.

Awada, M., R. de la Peña, and R. Suehisa. 1986. Effects of nitrogen and potassium fertilization on growth, fruiting and petiole composition of bearing plants. Institute of Tropical Agriculture and Human Resources. University of Hawaii. Honolulu, Hawaii. Res. Ser. 043. 20 p.

Awada, M., R. Suehisa, and M.M. Padgett. 1979. Effects of drip irrigation and fertilization on vegetative growth, fruit yield, and mineral composition of the petioles and fruits of papaya. Agriculture Extension Station, University of Hawaii, Honolulu, Hawaii. 20 p.

278

Awada, M., R. Suehisa, and Y. Kanehiro. 1975. Effects of lime and phosphorus on yield, growth, and petiole composition of papaya. Journal of the American Society for Horticultural Science 100(3):294-298.

Ayres A.S. 1966. Calcium silicate slag as a growth stimulant for sugarcane on low silicon soils. Soil Science 101(3):216-227.

Aziz, T., M.A. Gill, and T. Rahmatullah. 2002. Silicon nutrition and crop production: A review. Pakistan Journal of Agricultural Sciences 39(3):181-187.

Badillo, V.M. (1993). Caricaceae. Segundo esquema. Revista de la Facultad de Agronomía, Universidad Central de Venezuela 43:1–111.

Baker, J.T., D.C. Gitz, P. Payton, D.F. Wanjura, and D.R. Upchurch. 2007. Using leaf gas exchange to quantify drought in cotton irrigated based on canopy temperature measurements. Agronomy Journal 99(3):637-644.

Barbosa-Filho, M.P., G.H. Snyder, C.L. Elliot, and L.E. Datnoff. 2001. Evaluation of soil test procedures for determining rice-available silicon. Communication in Soil Science and Plant Analysis 32(11&12):1779-1792.

Barber, D.A. and M.G.T. Shone. 1966. The absorption of silica from aqueous solutions by plants. Journal of Experimental Botany 17:569-578.

Barkai-Golan, R. 2001. Postharvest diseases of fruits and vegetables: Development and control. First edition. Elsevier Science B.V. Amsterdam, The Netherlands. 442 p.

Barker, A.V. and D.J. Pilbeam. 2007. Introduction. pp:3-18. In: A.L. Barker and D.J. Pilbeam (eds.). Handbook of plant nutrition. CRS Press / Taylor and Francis Group. Boca Raton, FL. 613 p.

Bauer, P., R. Elbaum, and I.M. Weiss. 2011. Calcium and silicon mineralization in land plants: Transport, structure and function. Plant Science 180:746-756.

Beadle, C.L. 1985. Plant growth analysis. pp:20-25. In: J. Coombs, D.O. Hall, S.P. Long, and J.M.O. Scurlock (eds.). Techniques in Bioproductivity and Photosynthesis. Pergamon Press, Oxford. England. 298 p.

Beckwith, R.S. and R. Reeve. 1963. Studies on soluble silica in soils. I. The sorption of silicic acid by soils and minerals. Australian Journal of Soil Research 1(2):157-168.

Beckwith, R.S. and R. Reeve. 1964. Studies on soluble silica in soils. II. The release of monosilicic acid from soils. Australian Journal of Soil Research 2(1):33-45.

279

Bekker, T., T. Aveling, C. Kaiser, N. Labuschangne, and T Regnier. 2007. Accumulation of total phenolics due to silicon application in roots of avocado trees infected with Phytophthora cinnamomi. Proceedings of the VI World Avocado Congress. ISBN-13:978-956-17- 0413-8. Viña del Mar, Chile. .

Bélanger, R.R., P.A. Bowen, D.L. Ehret, and J.G. Menzies. 1995. Soluble silicon: Its role on crop and disease management of greenhouse crops. Plant Disease - The American Phytopathological Society 79(4):329-336.

Bell, P.F. and T.F. Simmons. 1997. Silicon concentrations of biological standards. Soil Science Society of America Journal 61:321-322.

Benassi, A. 2006. Informes sobre a produção de mamão. TodaFruta. São Paulo, Brazil. (Released in 2006). Website: http://www.todafruta.com.br/portal/icNociaAberta.asp?idNoticiaAberta.asp ?idNoticia=14291&tipoNoticia=&status=3&r=Not?cia%20enviada%20com%20sucesso (Accessed December 12, 2013).

Berner, R.A. 1997. Geochemistry and geophysics: The rise of plant and their effect on weathering and atmospheric CO2. Science 276(5312):544-546.

Berthelsen, S. and G.H. Korndörfer. 2005. Methods for Si analysis in plant, soil and fertilizers. pp:86-93. In: G.H. Korndörfer (ed.). III Silicon in Agriculture Conference. Universidad Federal de Uberlândia (UFU). Uberlândia, Mina Gerais, Brazil. 155 p.

Berthelsen, S., A.D. Noble, and A.L. Garside. 1999. An assessment of soil and plant silicon levels in north Queensland. Proceedings of the Australian Society of Sugar Cane Technologists 21:92-100.

Berthelsen, S., A.D. Noble, and A.L. Garside. 2001. Silicon research down under: Past, present, and future. pp:241-2255. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Bi, Y., S.P. Tian, Y.R. Guo, Y.H. Ge, and G.Z. Qin. 2006. Sodium silicate reduces postharvest decay on Hami melons: Induced resistance and fungistatic effects. Plant Disease 90(3):279-283.

Birchall, J.D. 1995. The essentiality of silicon in biology. Chemical Society Reviews 24(5):351- 357.

Birchall, J.D. and C. Exley. 1992. pp:411-420. In: E. Merian and W. Haerdi (eds.). Metal compounds in environment and life. Science and Technology Letters. 4. Northwood, CRC Press. 526 p.

Blanpied, G.D., W.J. bramlage, D.H. Dewey, R.L. LaBelle, L.M. Massey, Jr., G.E. Mattus, W.C. Stiles, and A.E. Watada. 1978. A standardized method for collecting apple pressure test data. New York’s Food and Life Sciences Bulletin 74:1-8.

280

Bohn, H.L., B.L. McNeal, and G.A. O’Connor. 1979. Soil chemistry. John Wiley and Sons, Inc. New York, NY. 329 p.

Bonman, J.M., B.A. Estrada, and J.A. Bandong. 1989. Leaf and neck blast resistance in tropical lowland rice cultivars. Plant Disease 73:388-390.

Bosse, R.J., J.P. Bower, and I. Bertling. 2011. Pre- and post-harvest treatments on ‘Fuerte’ avocados to control anthracnose (Colletrotrichum gloeosporioides) during ripening. . South African Avocado Growers’ Association Yearbook 34:65-69.

Bowen, P.A., J.G. Menzies, D.L. Ehret, L. Samuels, and D.M. Glass. 1992. Soluble silicon sprays inhibit powdery mildew development on grape leaves. Journal of the American Society for Horticultural Science 117(6):906-912.

Brady, P.V. and J.V. Walther. 1989. Controls on silicate dissolution rates in neutral and basic pH solutions at 25oC. Geochimical et Cosmochimica Acta 53(11):2823-2830.

Brady, N.C. and R.R. Weil. 2009. Elements of the nature and properties of soils. Third edition. Prentice Hall Publisher. Upper Saddle River, NJ. 624 p.

Brecht, M.O., L.E. Datnoff, T.A. Kuchareck, and R.T. Nagata. 2007. The influence of silicon on the components of resistance to gray leaf spot in St. Augustine grass. Journal of Plant Nutrition 30:1005-1021.

Bron, I.U. and A.P. Jacomino. 2006. Ripening and quality of ‘Golden’ papaya fruit harvested at different maturity stages. Brazilian Journal of Plant Physiology 18(3):389-396.

Brown, S.K. and M.C. Bourne. 1988. Assessment of components of fruit firmness in selected sweet cherry genotypes. HortScience 23(5):902-904.

Brown, P.H., R.M. Welch, and E.E. Cary. 1987. Nickel: a micronutrient essential for higher plants. Plant Physiology 85:801-803.

Brummell, D.A. 2006. Cell wall disassembly in ripening fruit. Functional Plant Biology 33:103- 119.

Buck, G.B., G.H. Korndörfer, and L.E. Datnoff. 2011. Extractors for estimating plant available silicon from potential silicon fertilizer sources. Journal of Plant Nutrition 34:272-282.

Cai, K., D. Gao, J. Chen, and S. Luo. 2009. Probing the mechanisms of silicon-mediated pathogen resistance. Plant Signaling and Behavior 4(1):1-3.

Cámara, M.M., C. Díez, and M.E. Torija. 1993. Changes during ripening of papaya fruit in different storage systems. Food Chemistry 46:81-84.

281

Campostrini, E. and D.M. Glenn. 2007. Ecophysiology of papaya: a review. Brazilian Journal of Plant Physiology 19(4):413-424.

Campostrini, E. and O.K. Yamanishi. 2001a. Estimation of papaya leaf area using the central vein length. Scientia Agricola 58:39-42.

Campostrini, E. and O.K. Yamanishi. 2001b. Influence of mechanical root restriction on gas- exchange of four papaya genotypes. Brazilian Journal of Plant Physiology 13:129-138.

Campostrini, E., C.V. Pommer, and O.K. Yamanishi. 2010. Environmental factors causing physiological disorders in papaya plants. Acta Horticulturae 851:453-458.

Campostrini, E., H.C. Lima, J.G. de Oliveira, P.H. Monnerat, and C.S. Marinho. 2005. Teores de Ca e variãveis meteorológicas: Relações com a incidệncia da mancha fisiológica do mamão no norte fluminense. Fitossanidade. Bragantia, Campinas 64(4):601-613.

Carvalho, S.P., J.C. Moraes, and J.G. Carvalho. 1999. Silica effect on the resistance of sorghum [Sorghum bicolor (L.) Moench] to the greenbug [Schizaphis graminum (Rond.)] (Homoptera: Aphididade). Anais da Sociedade Entomológica do Brasil 28(3):505-510.

Chakraborty, S., A. von Tiedemann, and P.S. Teng. 2000. Climate change: potential impact on plant disease. Environmental Pollution 108:317-326.

Chan, Y.K. and R.E. Paull. 2008. Papaya (Carica papaya L.) Caricaceae. pp:237-247. In: J. Janick and R.E. Paull (eds.). Encyclopedia of fruit and nuts. CABI International. Wallingford, UK. 954 p.

Cheikh, N., P.W. Miller, and G. Kishore. 2000. Role of biotechnology in crop productivity in a changing environment. pp:432-436. In: K.R. Reddy and H.F. Hodges (eds.). Climate change and global crop productivity. CABI Publishing. New York, NY. 488 p.

Chen, C.H. and J. Lewin. 1969. Silicon as a nutrient element for Equisetum arvense. Canadian Journal of Botany. 47:125-131.

Chen, M., L.Q. Ma, and Y.C. Li. 1999. Concentrations of P, K, Al, Fe, Mn, Cu, Zn, and As in Marl soils from south Florida. Soil and Crop Science Society of Florida Proceedings 59:124-129.

Chen, J., R.D. Caldwell, C.A. Robinson, and R. Steinkamp. 2000a. Silicon: The estranged medium element. Environmental Horticulture Department, Florida Cooperative Extension Service. IFAS Extension. Bulletin 341. University of Florida. Gainesville, FL. 5 p.

Chen, J., R.D. Caldwell, C.A. Robinson, and R. Steinkamp. 2000b. Let’s put the Si back to soil. Part I. Plant Nutrition / Greenhouse Product News (GPN) 4:44-46.

282

Cherif, M., A. Asselin, and R.R. Bélanger. 1994. Defense responses induced by soluble silicon in cucumber roots infected by Pythium spp. Phytopathology 84:236-242.

Chia, C.L., M.S. Nishina, and D.O. Evans. 1989. Papaya. Commodity Fact Sheet PA-3(A). Hawaii Cooperative Extension Service. Hawaii Institute of Tropical Agriculture and Human Resources. University of Hawaii at Manoa. Honolulu, HI. 4 p.

Chitarra, M.I.F. and A.B. Chitarra. 1990. Pós-Colheita de frutos e hortaliças: Fisiologia e manuseio. Fundação de Apoio ao Ensino, Pesquisa e Extensão – Escola Superior de Agricultura de Lavras. Lavras, Minas Gerais, Brazil. 293 p.

Cibes, H.R. and S. Gaztambide. 1978. Mineral-deficiency symptoms displayed by papaya grown under controlled conditions. Journal of Agriculture of the University of Puerto Rico 62(4):413-423.

Clayton, M., B. Biasi, and B. Mitcham. 1998. New devices for measuring firmness of cherries. Perishables Handling Quarterly. Issue No. 95:1-4.

Colburn, B. and S. Goldweber. 1961. Preparation of oolitic limestone soil for agricultural use. Proceeding of the Florida State Horticultural Society 74:343-345.

Conley, D.J. 2002. Terrestrial ecosystems and the global biogeochemical silica cycle. (Pages 68:1-8). Global Biogeochemical Cycles 16(4):1121-1129

Clark, R.B., C.I. Flores, L.M. Gourley, and R.R. Duncan. 1990. Mineral element concentration and grain field of sorghum (Sorghum bicolor) and pearl millet (Pennisetum glaucom) grow on acid soil. pp:391-396. In: M.L. Van Beusichem (ed.). Plant nutrition – Physiology and applications. First edition. Kluwer Academic Publishers. Dordrecht, The Netherlands. 824 p.

Clarkson, D.T and J.B. Hanson. 1980. The mineral nutrition of higher plants. Annual Review of Plant Physiology 31:239-298.

Clemente, H.S. and T.E. Marler. 1996. Drought stress influences gas-exchange responses of papaya leaves to rapid changes in irradiance. Journal of the American Society for Horticultural Science 12:292-295.

Clements, H.F. 1965. The roles of calcium silicate slags in sugarcane growth. Rep. Hawaiian Sugar Technology. pp:103-126.

Cloud, P.E. Jr. 1965. Significance of the Gunflint (Precambrian) microflora: Photosynthetic oxygen may have had important local effects before becoming a major atmospheric gas. Science 148(3666):27-35.

283

Comstock, J., and M. Mencuccini. 1998. Control of stomatal conductance by leaf water potential in Hymenoclea salsola (T. & G.) a desert subshrub. Plant Cell and Environment 21:1029- 1038.

Cornelis, J.-T., J. Ranger, A. Iserentant, and B. Delvaux. 2010. Tree species impact the terrestrial cycle of silicon through various uptakes. Biogeochemistry 97:231-245.

Costa, A.N. da and A. de F.S. da Costa. 2003. Nutrição e adubação. pp:201-227. In: D. dos S. Martins, and A. de F.S. da Costa (eds.). A cultura do mamoeiro: Tecnologias de produção. INCAPER. Vitória, ES. Brazil. 497 p.

Crane, J.H. 2005. Papaya growing in the Florida home landscape. IFAS Extension. University of Florida. Gainesville, FL. 8 p.

Cull B.W. 1986. A phenological cycling approach to tree crop productivity research. pp:151-156. In: B.W. Cull and P.E. Page. Symposium on physiology of productivity of sub-tropical and tropical tree fruits. Acta Horticulturae No. 175. May 12-17, 1986. Brisbane, Australia. 376 p.

Cunha, R.J.P. and H.P. Haag. 1980. Nutrição mineral do mamoeiro. I. Curva de crescimento do mamoeiro (Carica papaya L.) em condições de campo. Anais Escola Superior de Agricultura “Luiz de Queiroz”/USP. Piracicaba – São Paulo, Brazil 37:81-97.

Currie, H.A. and C.C. Perry. 2007. Silica in plants: Biological, biochemical and chemical studies. Annals of Botany 100:1383-1389.

Dakora, F.D. and A. Nelwamondo. 2003. Silicon nutrition promotes root growth and tissue mechanical strength in symbiotic cowpea. Functional Plant Biology 30:947-953.

Dat, J.F., N. Capelli, H. Folzer, P. Bourgeade, and P.M. Badot. 2004. Sensing and signalling during plant flooding. Plant Physiology and Biochemistry 42:273-282.

Dann, E.K. and S. Muir. 2002. Peas in media with elevated plant-available silicon levels have higher activities of chitinase and β-1,3-glucanase, are less susceptible to a fungal leaf spot pathogen and accumulate more foliar silicon. Australasian Plant Pathology 31:9-13.

Datnoff, L.E., C.W. Deren, and G.H. Snyder. 1997. Silicon fertilization for disease management of rice in Florida. Crop Protection 16:525-531.

Datnoff, L.E., G.H. Snyder, and C.W. Deren. 1992. Influence of silicon fertilizer grades on blast and brown spot development and on rice yields. Plant Disease 76(10):1011-1013.

Datnoff, L.E., K.W. Seebold, and F.V.Correa-V. 2001. The use of silicon for integrated disease management: reducing fungicide applications and enhancing host plant resistance. pp:171-184. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

284

Datnoff, L.E., M.O. Brecht, T.A. Kucharek, and R.T. Nagata. 2002. The role of silicon in turfgrass disease management. pp:105-110. In: Abstract of the Second Silicon in Agriculture Conference. Tsuruoka, Japan. 428 p.

Datnoff, L.E., R.N. Raid, G.H. Snyder, and D.B. Jones. 1991. Effect of calcium silicate on blast and brown spot intensities and yields of rice. Plant Disease 75:729-732.

Davis, M.J. and Z. Ying. 2004. Development of papaya breeding lines with transgenic resistance to papaya ringspot virus. Plant Disease 88:352-358.

Davies, M.J., T.L. White and J.H. Crane. 2003. Papaya variety development in Florida. Proceedings of the Florida State Horticultural Society 116:4-6.

Davis, M.J., T.L. White, and J.H. Crane. 2004. Resistance to papaya ringspot virus in transgenic papaya breeding lines. Proceedings of the Florida State Horticultural Society 117:241- 245.

Dea, S. 2009. Establishment of favorable physical and environmental conditions for the optimization of the total product quality of fresh-cut ‘Kent’ mangoes. Ph.D. Dissertation. University of Florida. Gainesville, FL. 251 p.

Dean, J.L., P.Y.P. Tai, and E.H. Todd. 1979. Sugarcane rust in Florida. The Sugar Journal. 42:10.

Deren, C.W. 2001. Plant genotype, silicon concentration, and silicon-related responses. pp:149- 159. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Drees, L.R., L.P. Wilding, N.E. Smeck, and A.L. Senkayi. 1989. Silica in soils: Quartz and disordered silica polymorphs. pp. 913-974. In: J.B. Dixon, S.B. Weed, and R.C. Dinauer (eds.). Minerals in Soil Environment. Second edition. Soil Science Society of America, Madison, WI. 1,244 p.

Drew, M.C., C.-J. He, and P.W. Morgan. 2000. Programmed cell death and aerenchyma formation in roots. Trends in Plant Science 5:123-127. du Preez, P. 1970. The effect of silica on cane growth. Proceedings of the South African Sugar Technologists’ Association. 44:183-188.

Egrinya-Eneji, A., S. Inanaga, S. Muranaka, J. Li, T Hattori, P. An, and W. Tsuji. 2008. Growth and nutrient use in four grasses under drought stress as mediated by silicon fertilizers. Journal of Plant Nutrition 31:355-365.

Elawad, S.H. and V.E. Green. 1979. Silicon and the rice plant environment: A review of recent research. Il Riso 28:235-253

285

Elawad, S.H., G.J. Gascho, and J.J. Street. 1982. Response of sugarcane to silicate source and rate. I. Growth and yield. Agronomy Journal 74(3):481-484.

Elliot, C.L. and G.H. Snyder. 1991. Autoclave-induced digestion for colorimetric determination of silicon in rice straw. Journal of Agriculture and Food Chemistry 39:1118-1119.

El-Sharkawy, M.A., J.H. Cock, and A.D.P. Hernández. 1985. Stomatal response to air humidity and its relation to stomatal density in a wide range of warm climate species. Photosynthesis Research 7:137-149.

Epstein, E. 1994. The anomaly of silicon in plant biology. Proceeding of the National Academy of Sciences of the United States of America 91:11-17.

Epstein, E. 1999. Silicon. Annual Review of Plant Physiology and Plant Molecular Biology 50:641-664.

Epstein, E. 2000. The discovery of the essential elements. pp:1-16. In: S.-D. Kung and S.-F. Yang (eds.). Discoveries in Plant Biology. III. World Scientific Publishing Co. Inc. Singapore. 473 p.

Epstein, E. 2001. Silicon in plants: Facts vs. concepts. pp:1-15. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Epstein, E. 2005. Silicon in agriculture: A historical review. pp:12-15. In: G.H. Korndörfer (ed.). III Silicon in Agriculture Conference. Universidad Federal de Uberlândia (UFU). Uberlândia, Mina Gerais, Brazil. 155 p.

Epstein, E. 2009. Silicon: Its manifold roles in plants. Annals of Applied Biology 155:155-160.

Epstein E. and A.J. Bloom. 2005. Mineral nutrition of plants: Principles and perspectives. Second edition. Sinauer Associates. Sunderland, MA. 400 p.

Eswaran, A. and K. Manivannan. 2007. Effect of foliar application of lignite fly ash on the management of papaya leaf curl disease. Acta Horticulturae. 740:271-275.

Evans, E.A., F.H. Ballen, and J.H. Crane. 2012. An overview of US papaya production, trade, and consumption. FE914. Florida Cooperative Extension Service. Institute of Food and Agricultural Sciences, University of Florida. Gainesville, FL. 8 p

Exley, C. 1998. Silicon in life: A bioinorganic solution to bioorganic essentiality. Journal of Inorganic Biochemistry 69:139-144.

Exley, C. and J.D. Birchall. 1992. The cellular toxicity of aluminum. Journal of Theoretical Biology 159(1):83-98.

286

FAOSTAT. 2011. USA’s Papaya production database. FAO Statistics Division. (Released in 2010) Website: http://faostat.fao.org/site/567/DesktopDefault.aspx?PageID=567#ancor. (Accessed December 12, 2013).

FAOSTAT. 2012. Medium-term prospects for agricultural commodities. Tropical fruits. Database FAO. Economic and Social Development Department. (Released in 2012) Website: http://www.fao.org/docrep/006/y5143e/y5143e1a.htm. (Accessed December 20, 2013).

Faure, G. 1991. Principles and applications of inorganic geochemistry. Macmillan Coll Div. New York, NY. 500 p.

Fauteux, F., W. Rémus-Borel, J.G. Menzies, and R.R. Bélanger. 2005. Silicon and plant disease resistance against pathogenic fungi. Federation of European Microbiological Societies (FEMS): Microbiology Letters 249:1-6.

Fawe, A., J.G. Menzies, M. Chérif, and R.R. Bélanger. 2001. Silicon and disease resistance in dicotyledons. pp:159-169. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Ferrão, J.E.M. 1992. A aventura das plantas e os descobrimentos Portugueses. Instituto de Investigação Científica Tropical, Comissão Nacional para as Comemorações dos Descobrimentos Portugueses, and Fundação Berardo. Lisbon, Portugal. 247 p.

Ferreira-Coelho, E., M.A. Coelho-Filho, and J. Lopes-Cruz. 2007. Orientações prácticas para a fertirrigação do mamoeiro. Circular Técnica, 85. Mandioca e Fruticultura Tropical Endereço. Cruz das Almas, BA. 6 p.

Fitch, M.M.M. 2005. Carica papaya Papaya. pp:174-207. In: R.E. Litz (ed.). Biotechnology of fruit and nut crops. CABI Publishing. Wallingford, UK 723 p.

Flexas, J., and H. Medrano. 2002. Drought-inhibition of photosynthesis in C3 plants: Stomatal and non-stomatal limitations revisited. Annals of Botany 89:183-189.

Fortunato, A.A., F. Avila-Rodrigues, and K.J. Teles do Nascimento. 2012. Physiological and biochemical aspects of the resistance of banana plants to fusarium wilt potentiated by silicon. Biochemistry and Cell Biology. Phytopathology 102(10):957-966.

Foulger, J.H. 1927. The colorimetric estimation of silicon in tissues by Isaacs’s method. Colorimetric Estimation of Silicon. Department of Biochemistry, University of Cincinnati 49:429-435.

Fox, R.L., J.A. Silva, D.L. Plucknett, and D.Y. Teranishi. 1969. Soluble and total silicon in sugarcane. Plant and Soil 30(1):81-92.

287

Fox, R.L., J.A. Silva, O.R. Younge, D.L. Plucknett, and G.D. Sherman. 1967. Soil and plant silicon and silicate responses by sugarcane. Soil Science Society of America Journal 31(6):775-779.

Francis, F.J. 1980. Color quality evaluation of horticultural crops. HortScience 15:58-59.

Fuggate, P., C. Wongs-Aree, S. Noichinda, and S. Kanlayanarat. 2010. Quality and volatile attributes of attached and detached “Pluk Mai Lie” papaya during fruit ripening. Scientia Horticulturae 126:120-129.

Fuhrer, J. 2003. Agroecosystem responses to combinations of elevated CO2, ozone, and global climate change. Agriculture, Ecosystems and Environment 97:1-20.

Galán-Saúco, V.G. and J.M.F. Farré-Massip. 2006. Tropical and subtropical fruit production in Spain. Chronica Horticulturae 46:26-30.

Galán-Saúco, V.G. and M.C.R. Rodríguez-Pastor. 2007. Greenhouse cultivation of papaya. Acta Horticulturae 740:191-195.

Gaillard, J.P. 1972. Approches sur la fertilization du papayer solo au Cammeroun. Fruits 27:353- 360.

Gao, X., C. Zou, L. Wang, and F. Zhang. 2004. Silicon improves water use efficiency in maize. Journal of Plant Nutrition 27:1457-1470.

Gascho, G.J. and H.J. Andreis. 1974. Sugar cane response to calcium silicate slag applied to organic and sand soils. Proceedings of the International Congress Society of Sugar Cane Technologists 15(2):543-551.

Goenaga, R., H. Irizarry, and E.Rivera-Amador. 2001. Yield and fruit quality of papaya cultivars grwon at two locations in Puerto Rico. Journal of Agriculture of the University of Puerto Rico 85(3 & 4):127-134.

Gonçalvez de Oliveira, J. and A. Pierre-Vitória. 2011. Papaya: Nutritional and pharmacological characterization, and quality loss due to physiological disorders. An overview. Food Research International 44:1306-1313.

Gong, H.J., D.P. Randall, and T.J. Flowers. 2006. Silicon deposition in the root reduces sodium uptake in rice (Oryza sativa L.) seedlings by reducing bypass flow. Plant, Cell and Environment 29:1970-1979.

Gong, H.J., K.M. Chen, G.C. Chen, S.M. Wang, and C.L. Zhang.. 2003. Effect of silicon on growth of wheat under drought. Journal of Plant Nutrition 26(5):1055-1063.

Gong, H.J., X.Y. Zhu, K.M. Chen, S.M. Wang, and C.L. Zhang. 2005. Silicon alleviates oxidative damage of wheat plants in pots under drought. Plant Science 169:313-321.

288

Gong, H.J., K.M. Chen, Z.G. Zhao, G.C. Chen, and W.J. Zhou. 2008. Effects of silicon on defense of wheat against oxidative stress under drought at different developmental stages. Biologia Plantarum 52(3):592-596.

Guével, M.-H., J.G. Menzies, and R.R. Bélanger. 2007. Effect of root and foliar applications of soluble silicon on powdery mildew control and growth of wheat plants. European Journal of Plant Pathology 119:429-436.

Gunztzer, F., C. Keller, and J.D. Meunier. 2010. Determination of the silicon concentration in plant material using Tiron extraction. New Phytologist 188(3):902-906.

Guo, Y., L. Liu, J. Zhao, and Y. Bi. 2007. Use of silicon oxide and sodium silicate for controlling Trichothecium roseum postharvest rot in Chinese cantaloupe (Cucumis melo L.). International Journal of Food Science and Technology 42(8):1012-1018.

Haneklaus, S., E. Bloem, and E. Schnug. 2008. History of sulfur deficiency in crops. pp:45-58. In: J. Jez (ed.). Sulfur: A missing link between soils, crops, and nutrition. Agronomy Monograph No. 50. ASA-CSSA-SSSA Publisher. Madison, WI. 329 p.

Hanlon, E.A., J.S. González, and J.M. Bartos. 1998. IFAS Extension Soil Testing Lab (ESTL) and Analytical Research Lab (ARL) chemical procedures and training manual. University of Florida Cir. 812. Gainesville, FL.

Hardisson, A., C. Rubio, A. Baez, M.M. Martin, and R. Alvarez. 2001. Mineral composition of the papaya (Carica papaya var. sunrise) from Tenerife island. European Food Research and Technology 212:175-181.

Harkness, R.W. 1960. Papaya growing in Florida. Circ. 133A. Agric. Extension Service, Gainesville, FL. 8 p.

Harty, J.M. 2009. Development and evaluation of an antisense ACC-Oxidase (CMACO-1) ‘Galia’ F1 hybrid muskmelon (Cucumis melo L. var. reticulatus Ser.). Ph.D. Dissertation. University of Florida. Gainesville, FL. 210 p.

Hattori, T., S. Inanaga, E. Tanimoto, A. Lux, M. Loxová, and Y. Sugimoto. 2003. Silicon- induced changes in viscoelastic properties of sorghum root cell walls. Plan and Cell Physiology 44(7):743-749.

Hattori, T., S. Inanaga, H. Araki, P. An, S. Morita, M. Loxová, and A. Lux. 2005. Application of silicon enhanced drought tolerance in Sorghum bicolor. Physiologia Plantarum 123:459- 466.

Haysom, M.B. and Z.A. Ostatek-Boczynski. 2006. Rapid, wet oxidation procedure for the estimation of silicon in plant tissue. Communication in Soil Science and Plant Analysis 37:2299-2306.

289

Henriet, C., X. Draye, I. Oppitz, R. Swennen, and B. Delvaux. 2006. Effect, distribution and uptake of silicon in banana (Musa spp.) under optimal controlled conditions. Plant Soil 287:359-374.

Henriet, C., N. de Jaeger, M. Dorel, S. Opfergelt, and B. Delvaux. 2008. The reserve of weatherable primary silicates impacts the accumulation of biogenic silicon in volcanic ash soils. Biogeochemistry 90:209-223.

Hernández R.O. 2008. Estudio de evaluación de desempeño del silicio en un cultivo de papaya. U.T. Bastidas Agudelo-AVE International Col. LTDA. Cali, Colombia. 24 p.

Hildebrand, M., K. Dahlin, and B.E. Volcani. 1998. Characterization of a silicon transporter gene family in Cylindrotheca fusiformis: sequences, expression analysis, and identification of homologs in other diatoms. Molecular and General Genetics 260-480-486.

Hodson, M.J., P.J. White, A. Mead, and M.R. Broadley. 2005. Phylogenetic variation in the silicon composition of plants. Annals of Botany 96:1027-1046.

Huber, D.M. and S. Haneklaus. 2007. Managing nutrition to control plant disease. Landbauforschung Volkenrode 57(4):313-322.

Ikeda, M. and L.T. Si. 1976. Optimal soil pH values for the vegetative growth of papaya (Carica papaya L.). Japanese Journal of Tropical Agriculture 20(2):115.

Iler, R.K. 1979. The chemistry of silica: Solubility, polymerization, colloid and surface properties and biochemistry of silica. Wiley-Interscience - Division of John Wiley and Sons, Inc. New York, NY. 866 p.

Islam, M.S. 2008. Soil fertility history, present status and future secenario in Bangladesh. Bangladesh Journal of Agriculture and Environment. Special Issue 4:129-151.

Jauhari, O.S., R.A. Mishra, and C.B. Tewari. 1974. Nutrient uptake of banana (Musa paradisiaca L.) var. ‘Basrai Dwarf’. Indian Journal of Agricultural Chemistry 7:73-79.

Jellinek, G. 1985. Sensory evaluation of foods: theory and practice. Ellis Horwood, Ltd., VCH Publishers. Deerfield Beach, FL. 429 p.

Jeyakumar, P., M. Kavino, and N. Kumar. 2007. Physiological performance of papaya cultivars under abiotic stress conditions. Acta Horticulturae 740:209-214.

Jones, L.H. and K.A. Handreck. 1963. Effects of iron and aluminum oxides on silica in solution in soils. Nature 198(4883):852-853.

Jones, L.H. and K.A. Handreck. 1965. Studies of silica in the oat plant. III. Uptake of silica from soils by the plant. Plant and Soil 23(1):79-96.

290

Jones, L.H. and K.A. Handreck. 1967. Silica in soils, plants, and animals. Advances in Agronomy 19:107-149.

Jones, R.L. and G.B. Dreher. 1996. Silicon. pp:627-637. In: D.L. Sparks (ed.). Methods of soil analysis. Part 3 - Chemical methods. Soil Science Society of America (SSSA) Book Series No. 5. Madison, WI. 1264 p.

Jones, W.W. and H. Kubota. 1940. Some chemical and respirational changes in the papaya fruit during ripening and the effects of cold storage on these changes. Plant Physiology 15:711-717.

Kader, A.A. 1997. Papaya: Recommendations for maintaining postharvest quality. Postharvest Technology: Maintaining Produce Quality and Safety. UCDavis, Univeristy of California. Source: Perishables Handling #90. Released in May 1997. Website: http://www.postharvest.ucdavis.edu/PFfruits/Papaya/ (Accessed December 8, 2013).

Kader, A.A., N.F. Sommer, and M.L. Arpaia. 2002. Postharvest handling systems: Tropical fruits. pp:390-393. In: A.A. Kader (ed.). Postharvest technology of horticultural crops. Third edition. Agriculture and Natural Resources, University of California. Publication No. 3311. Oakland, CA. 535 p.

Kao, M-W. S. 2011. Influence of harvest maturity and pre-storage conditioning on quality of meeting and non-melting flesh peaches. Ph.D. Dissertation. University of Florida. Gainesville, FL. 230 p.

Kaluwa, K., I. Bertling, and J.P. Bower. 2011. Effect of postharvest Si application on ‘Hass’ avocado fruit physiology. pp:565-571. In: J. Wesonga and R. Kahane (eds.). Proceedings of the First all African Horticultural Congress. International Society for Horticultural Science (ISHS) - Acta Horticulturae 911. Nairobi, Kenya. 578 p.

Kaluwa, K., I. Bertling, J.P. Bower, and S.Z. Tesfay. 2010. Silicon application effects on ‘Hass’ avocado fruit physiology. South African Avocado Growers Association Yearbook. 33:44-47.

Kapanadze, I.S. and G.S. Khasaya. 1988. Some biological characteristics of pawpaw trees. Subtropicheskie Kul'tury, No. 1:136-140.

Kato, N. and N. Owa. 1997. Evaluation of Si availability in slag fertilizers by an extraction method using a cation exchange resin. Soil Science and Plant Nutrition 43:351-359.

Katz, A. 1968. The direct and rapid determination of alumina and silica in silicate rocks and minerals by atomic absorption spectroscopy. The American Mineralogist 53:283-289.

Kaufman, P.B., L.B. Petering, and J.G. Smith. 1970. Ultrastructural development of cork-silica cell pairs in avena internodal epidermis. Botanical Gazette 131(3):173-185.

291

Kaya, C., L. Tuna, and D. Higgs. 2006. Effect of silicon on plant growth and mineral nutrition of maize grown under water stress conditions. Journal of Plant Nutrition 29:1469-1480.

Keeping, M.G. and J.H. Meyer. 2002. Calcium silicate enhances resistance of sugarcane to the African stalk borer [Eldana saccharina (Walker) Lepidoptera: Pyralidae)]. Agricultural and Forest Entomology 4:265-274.

Keeping, M.G. and J.H. Meyer. 2003. Effect of four sources of silicon on resistance of sugarcane varieties to Eldana saccharina (Lepidoptera: Pyralidae). Proceedings of the South African Sugar Technologists’ Association 7:99-103.

Khalid, R.A. and J.A. Silva. 1980. Residual effect of calcium silicate on pH, phosphorus and aluminum in tropical soil profile. Soil Science and Plant Nutrition 26:87-98.

Khalid, R.A., J.A. Silva, and R.L. Fox. 1978. Residual effects of calcium silicate in tropical soils. I: Fate of applied silicon during five years cropping. Soil Science Society of America Journal 42:89-94.

Khan, D. and A. Roy. 1964. P-uptake and fiber cell dimensions of the jute plants as affected by silicate treatment. Plant Soil 20:331-336.

Kiggundu, N., K.W. Migliaccio, B. Schaffer, Y. Li, and J. Crane. 2011. Water saving, nutrient leaching, and fruit yield in a young avocado orchard as affected by irrigation and nutrient management. Irrigation Science 30:275-286.

Kim, S.G., K.W. Kim, E.W. Park, and D. Choi. 2002. Silicon-induced cell wall fortification of rice leaves: A possible cellular mechanism of enhanced host resistance to blast. Genetics and Resistance 92(10):1095-1103.

King, E.J. 1928. The estimation of silica in tissues. Journal of Biological Chemistry 80:25-31.

Kohyama, K., A. Nagata, Y. Tamaki, and N. Sakurai. 2009. Comparison of human-bite and instrument puncture tests of cucumber texture. Postharvest Biology and Technology 52:243-246.

Korndörfer, G.H. and I. Lepsch. 2001. Effect of silicon on plant growth and crop yield. pp:133- 147. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Kumar, N., P. Jeyakumar, and M.I. Manivannan. 2008. Balanced fertilization for sustainable yield and quality in tropical fruit crops. Special edition. Bangladesh Journal of Agriculture and Environment 4:69-80.

Kumar, N., K. Soorianathasundaram, N. Meenakshi, M.I. Manivannan, J. Suresh, and V. Nosov. 2010. Balanced fertilization in papaya (Carica papaya L.) for higher yield and quality. Acta Horticulturae 851:357-362.

292

Kvedaras, O.L., M.G. Keeping, R. Goebel, and M. Byrne. 2005. Effects of silicon on the African Stalk Borer, Eldana saccharina (Lepidoptera: Pyralidae) in sugarcane. Proceedings of the South African Sugar Technologists’ Association 79:359-362.

Laing, M.D., M.C. Gatarayiha, and A. Adandonon. 2006. Silicon use for pest control in agriculture: A review. Proceedings of the 80th. Annual Congress of the South African Sugar Technologists’ Association. July 18-20, 2006. Durban, South Africa 80:278-286.

Lassoudiére, A. 1968. Le papayer: Description e genetique. Fruits 23(11):585-596.

Levitt, J. 1980. Responses of plants to environmental stresses: Chilling, freezing and high temperature stresses. 1. pp:102-106. Physiological Ecology. Academic Press, Inc. Second Edition. New York, NY. 697 p.

Lewin, J.C. 1995. Silicon metabolism in diatoms II: sources of silicon for growth of Navicula pelliculosa. Plant Physiology. 30:129-134.

Lewin, J.C. and B.E. Reimann. 1969. Silicon and plant growth. Annual Review of Plant Physiology 20:289-304.

Li, Y.C. 2001. Calcareous soils in Miami-Dade County. Soil and Water document SL-183. Florida Cooperative Extension Service. Institute of Food and Agricultural Sciences, University of Florida. Gainesville, FL. 3 p.

Liang, Y., W. Sun, Y.G. Zhu, and P. Christie. 2007. Mechanisms of silicon-mediated alleviation in higher plants: A review. Environmental Pollution 147:422-428.

Liang, Y.C., Q. Chen, Q. Liu, W.H. Zhang, and R.X. Ding. 2003. Exogenous silicon (Si) increases antioxidant enzyme activity and reduces lipid peroxidation in roots of salt- stressed barley (Hordeum vulgare L.). Journal of Plant Physiology 160(10):1157-1164.

Liang, Y.C., H. Hua, Y.G. Zhu, J. Zhang, C.M. Cheng, and V. Römheld. 2006. Importance of plant species and external silicon concentration to active silicon uptake and transport. New Phytologist 172(1):63-72.

Lindsay, W.L. 2001. Chemical equilibria in soils. Second edition. The Blackburn Press. Caldwell, NJ. 449 p.

Litz, R.E. 1984. Papaya. pp:349-368. In: W.R. Sharp, D.A. Evans, P.V. Ammirato, and Y. Yamada (eds.). Macmillan Publishing Co. New York, NY. 644 p.

Lorenzi, H., L.B. Bacher, M. T. Côrtes de Lacerda, and S.F. Sartori. 2006. Brazilian fruits & cultivated exotics (for consuming in natura). Instituto Plantarum de Estudos Da Flora LTDA. Nova Odessa – Sao Paulo, Brazil. 672 p.

293

Lu, R. and J.A. Abbott. 2004. Force/deformation techniques for measuring texture. Part II. Instrumental techniques for analyzing texture. pp:107-145. In: D. Kilcast (ed.). Texture in food. Volume 2: Solid foods. Chapter 5. Woodhead Publishing in Food Science and Technology. CRC Woodhead Publishing Limited. Cambridge, England. 537 p.

Lucas, Y. 2001. The role of plants in controlling rates and products of weathering: Importance of biological pumping. Annual Review of Earth Planetary Science 29:135-163.

Lux, A., M. Luxová, S. Morita, J. Abe, and S. Inanaga. 1999. Endodermal silicification in developing seminal roots of lowland and upland cultivars of rice (Oryza sativa L.). Canadian Journal of Botany 77:955-960.

Lux, A., M. Luxová, J. Abe, T. Hattori, S. Inanaga and Y. Sugimoto. 2002. Silification in sorghum (Sorghum bicolor) cultivars with different drought tolerance. Physiologia Plantarum 115(1):87-92.

Lux, A., M. Luxová, J. Abe, E. Tanimoto, T. Hattori, and S. Inanaga. 2003. The dynamic of silicon deposition in the sorghum root endodermis. New Phytologist 158(3):437-441.

Ma, J.F. 2004. Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses. Soil Science and Plant Nutrition 50(1):11-18.

Ma, J.F., Y. Miyake, and E. Takahashi. 2001a. Silicon as a beneficial element for crop plants. pp:17-39. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Ma, J.F., S. Goto, K. Tamai, and M. Ichii. 2001b. Role of root hairs and lateral roots in silicon uptake by rice. Plant Physiology 127:1773-1780.

Ma, J.F., A. Higashitani, K. Sato, and K. Tateda. 2003. Genotypic variation in silicon content of barley grain. Plant Soil 249:383-387.

Ma, J.F., K. Nishimura, and E. Takahashi. 1989. Effect of silicon on the growth of rice plant at different growth stages. Soil Science and Plant Nutrition 35:347.

Ma, J.F. and E. Takahashi. 2002. Soil, fertilizer, and plant silicon research in Japan. Elsevier Science B.V. Amsterdam, The Netherlands. 281 p.

Ma, J.F., K. Tamai, N. Yamaji, N. Mitani, S. Konishi, M. Katsuhara, M. Ishiguro, Y. Murata, and M. Yano. 2006. A silicon transporter in rice. Nature 440:688-691.

Ma, J.F. and N. Yamaji. 2006. Silicon uptake and accumulation in higher plants. Trends in Plant Science 11(8):392-397.

Ma, J.F. and N. Yamaji. 2008. Functions and transport of silicon in plants. Cellular and Molecular Life Sciences 65:3049-3057.

294

Ma, J.F., N. Yamaji, K. Tamai, and N. Mitani. 2007a. Genotypic difference in silicon uptake and expression of silicon transporter genes in rice. Plant Physiology 145:919-924.

Ma, J.F., N. Yamaji, N. Mitani, K. Tamai, S. Konishi, T. Fujiwara, M. Katsuhara, and M. Yano. 2007b. An efflux transporter of silicon in rice. Nature 448:209-213.

Magness, J.R. and G.F. Taylor. 1925. An improved type of pressure tester for the determination of fruit maturity. U.S. Department of Agriculture. Dept. Circ. No. 350.

Mahouachi, J., A.R. Socorro, and M. Talón. 2006. Responses of papaya seedlings (Carica papaya L.) to water stress and rehydration: growth, photosynthesis and mineral nutrient imbalance Plant Soil 281:137-146.

Mahouachi, J., V. Arbona, and A.G. Gómez-Cadenas. 2007. Hormonal changes in papaya seedlings subjected to progressive water stress and re-watering. Plant Growth Regulation 53:43-51.

Mali, M. and N.C. Aery. 2009. Effect of silicon on growth, biochemical constituents and mineral nutrition of cowpwa (Vigna unguiculata (L) Walp.). Communication in Soil Science and Plant Analysis 40:1041-1052.

Mann, S., C.C. Perry, R.J.P. Williams, C.A. Fyfe, G.C. Gobbi, and G.J. Kennedy. 1983. The characterization of the nature of silica in biological systems. Journal of the Chemical Society, Chemical Communications 1314:168-170.

Manshardt, R.M. 1999. UH Rainbow papaya. University of Hawaii. Germplasm, NPH-1. CTAHR, Cooperative Extension Service. Honolulu, HI. 2 p.

Manshardt, R.M. and F.T.-P. Zee. 1994. Papaya germplasm and breeding in Hawaii. Fruit Varieties Journal 48(3):146-152.

Manshardt, R.M. and R.A. Drew. 1998. Biotechnology of papaya. Acta Horticulturae 461:65-73.

Marani, A., D.N. Baker, V.R. Reddy, and J.M. McKinion. 1985. Effect of water stress on canopy senescence and carbon exchange rates in cotton. Crop Science 25:798-802.

Marinho, C.S., M.A.B. de Oliveira, P.H. Monnerat, R. Vianni, and J.F. Maldonado. 2001. Fontes e doses de nitrogênio e a qualidade dos frutos de mamoeiro. Scientia Agricola 58:345- 348.

Marler, T.E. 1998. Solution pH influences on growth and mineral element concentrations of ‘Waimanalo’ papaya seedlings. Journal of Plant Nutrition 21(12):2601-2612.

Marler, T.E. and H.M. Discekici. 1997. Root development of ‘Red Lady’ papaya plants grown on a hillside. Plant and Soil 195:37-42.

295

Marler, T.E. and M.V. Mickelbart. 1998. Drought, leaf gas exchange, and chlorophyll fluorescence of field-grown papaya. Journal of the American Society for Horticultural Science 123(4):714-718.

Marler, T.E. and R. de la Cruz. 2001. Chemical factors enhancing papaya root growth in a tropical volcanic acid subsoil. HortScience 36(6):1037-1038.

Marler, T.E., R. de la Cruz, and A.L. Blas. 2002. Iron deficiency induced changes in iron reductase activity in papaya roots. Journal of the American Society for Horticultural Science 127(2):184-187.

Marler, T.E., A.P. George, R.J. Nissen, and P.C. Andersen. 1994. Miscellaneous tropical fruits: papaya. pp:216-224 In: B. Shaffer and P.C. Andersen. Handbook of environmental physiology of fruit crops, Volume II.: Sub-tropical and tropical crops. CRC Press, Inc. Boca Raton, FL. 310 p.

Marschner, H. 1995. Mineral nutrition of higher plants. Academic Press. Second edition. London, UK. 889 p.

Martin, F.W., C.W. Campbell, and R.M. Ruberté. 1987. Perennial edible fruits of the tropics: An inventory. United States Department of Agriculture (USDA) – Agricultural Research Service. Agriculture Handbook No. 642. Washington, DC. 247 p.

Massey, F.P. and S.E. Hartley. 2006. Experimental demonstration of the antiherbivore effects of silica in grasses: impacts on foliage digestibility and vole growth rates. Proceedings of the Royal Society London B 273:2299-2304.

Matichenkov, V.V. and A.A. Kosobrukhov. 2004. Si effect on the plant resistance to salt toxicity. Conserving Soil and Water for Society: Sharing Solutions. 13th. International Soil Conservation Organisation Conference. ISCO 2004. Brisbane, July 2004. Queensland, Australia. Paper No. 626:1-4.

Matichenkov, V.V. and D.V. Calvert. 2002. Silicon as a beneficial element for sugarcane. Journal American Society of Sugarcane Technologists 22:21-30.

Matichenkov, V.V. and E.A. Bocharnikova. 2001. The relationship between silicon and soil physical and chemical properties. pp:209-219. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Matichenkow, V.V. and E.A. Bocharnikova. 2004. Si in horticultural industry. pp:217-228. In: R. Dris and S.M. Jain (eds.). Production practices and quality assessment of food crops. Vol. 2: Plant Mineral Nutrition and Pesticide Management. Kluwer Academic Publishers. Amsterdan, The Netherland. 283 p

296

Matichenkov, V.V. and G.H. Snyder. 1996. The mobile silicon compounds in some South Florida soils. Eurasian Soil Science 24:1165-1173.

Matichenkov, V.V. and M.Y. Ammosova. 1996. Effect of amorphous silica on soil properties of a sod-podzolic soil. Eurasian Soil Science 28:87-99.

Matichenkov, V.V., Y.M. Ammosova, and E.A. Bocharnikova. 1997. The method for determination of plant-available silica in soil. Agrochemistry 1:76-84.

Matichenkov, V.V., D.V. Calvert, and G.H. Snyder. 1999. Silicon fertilizers for citrus in Florida. Proceedings of the Florida State Horticultural Society 112:5-8.

Matichenkov, V.V., E. Bocharnikova, and D. Calvert. 2001. Response of citrus to silicon soil amendments. Proceedings of the Florida State Horticultural Society 114:94-97.

Matichenkov, V.V., E.A. Bocharnikova, D.V. Calvert, and G.H. Snyder. 2000. Comparison study of soil silicon status in sandy soils of south Florida. Soil Crop Science Society Florida Proceedings 59:132-137.

Matoh, T., P. Kairusmee, and E. Takahashi. 1986. Salt-induced damage to rice plants and alleviation effecto of silicate. Soil Science and Plant Nutrition 32(2):295-304.

McGuire, R.G. 1992. Reporting of objective color measurements. HortScience 27:1254-1255.

McKeague, J.A. and M.G. Cline. 1963a. Silica in soils. Avances in Agronomy 15:339-396.

McKeague, J.A. and M.G. Cline. 1963b. Silica in soil solutions. I. The form and concentration of dissolved silica in aqueous extracts of some soils. Canadian Journal of Soil Science 43:70-82.

McKeague, J.A. and M.G. Cline. 1963c. Silica in soil solutions. II. The adsorption of monosilicic acid by soil and other substances. Canadian Journal of Soil Science 43:83-96.

McKersie, B.D., Y. Chen, M. de Beus, S.R. Bowley, and C. Bowler. 1993. Superoxide dismutase enhances tolerance of freezing stress in transgenic alfalfa (Medicago sativa L.). Plant Physiology 103(4):1155-1163.

Medina-Gonzales, O.A., R.L. Fox, and R.P. Bosshart. 1988. Solubility and availability to sugarcane (Saccharum spp.) of two silicate materials. Fertilizer Research. 16(1):3-13.

Medlicott, A.P. 1990. Product specifications and post-harvest handling for fruits, vegetables and root crops exported from the Caribbean. CARICOM Export Development Project. Caribbean Community (CARICOM) Secretariat. Turkeyen, Greater Georgetown, Guyana. 94 p.

297

Mehlich, A. 1938. Use of triethanolamine acetate-barium hydroxide buffer for the determination of some base exchanges properties and lime requirement of soil. Soil Science Society of America, Proceedings 29:374-378.

Meilgaard, M.C., G.V. Civille, and B.T. Carr. 2006. Sensory evaluation techniques. Fourth edition. CRC Press. Boca Raton, FL. 464 p.

Melo, S.P., G.H. Korndörfer, C.M. Korndörfer, R.M.Q. Lana, and D.G. Santan. 2003. Silicon accumulation and water deficient tolerance in grasses. Scientia Agricola 60(4):755-759.

Mengel, K. and E.A. Kirkby. 1987. Principles of plant nutrition. International Potash Institute. Fourth edition. Bern, Switzerland. 687 p.

Menzies, J., P. Bowen, D. Ehret, and A.D.M. Glass. 1992. Foliar applications of potassium silicate reduce severity of powdery mildew on cucumber, muskmelon, and zucchini squash. Journal of the American Society for Horticultural Science 117(6):902-905.

Merhaut, D.J. 2007. Magnesium. pp:145-181. In: A.L. Barker and D.J. Pilbeam (eds.). Handbook of plant nutrition. CRS Press / Taylor and Francis Group. Boca Raton, FL. 613 p.

Meyer, J.H. and M.G. Keeping. 2000. Review of research into the role of silicon for sugarcane production. Proceedings of the Congress of the South African Sugar Technologists Association (SAUS) 74:29-40.

Migliaccio, K.W., B. Schaffer, J.H. Crane, and F.S. Davies. 2010. Plant response to evapotranspiration and soil water sensor irrigation scheduling methods for papaya production in south Florida. Agricultural Water Management 97:1452-1460.

Miranda, S. de P., D. de F. Albernaz, G. Rodrigues Gagundes, S. Bevilaqua Rangel, and O. Kiyoshi Yamanishi. 2003. Características físico-químicas e vida pós-colheita de mamão (Carica papaya L.), cv. Canaã, produzido no município de São Desidério-BA. Proceedings of the Interamerican Society for Tropical Horticulture 47:225-227.

Mitani, N. and J.F. Ma. 2005. Uptake system of silicon in different plant species. Journal of Experimental Botany 56(414):1255-1261.

Mitani, N., J.F. Ma, and T. Iwashita. 2005. Identification of the silicon form in xylem sap of rice (Oryza sativa L.). Plant Cell Physiology 46(2):279-283.

Mitcham, B., M. Cantwell, and A. Kader. 1996. Methods for determining quality of fresh commodities. Perishables Handling Newsletter. Issue No. 85. 5 p.

Mitcham E.J., M. Clayton, and W.V. Biasi. 1998. Comparison of devices for measuring cherry fruit firmness. HortScience 33(4):723-727.

298

Mitcham, B., M. Clayton, B. Biasi, and S. Southwick. 1997. Evaluation of four cherry firmness measuring devices. Washington State University (WSU) Tree Fruit Research & Extension Center - Postharvest Information Network. Released in March 1997. (Released in 1997. Website: http://postharvest.tfrec.wsu.edu/pages/PC97I (Accessed December 10, 2013).

Miyake, Y. and E. Takahashi. 1978. Silicon deficiency of tomato plant. Soil Science Plant Nutrients 24(2):175-189.

Miyake, Y. and E. Takahashi. 1983a. Effect of silicon on the growth of solution cultured cucumber plant. Soil Science and Plant Nutrition 29(1):71-83.

Miyake, Y. and E. Takahashi. 1983b. Effect of silicon on the growth of cucumber plant in soil culture. Soil Science and Plant Nutrition 29(4):463-471.

Miyake, Y. and E. Takahashi. 1985. Effect of silicon on the growth of soybean plants in a solution culture. Soil Science and Plant Nutrition 31:625-636.

Miyake, Y. and E. Takahashi. 1986. Effect of silicon on the growth and fruit production of strawberry plants in a solution culture. Soil Science and Plant Nutrition 32(2):321-326.

Morton, J.F. 1987. Papaya. pp:336-346. In: J.F. Morton (ed.). Fruits of warm climates. Creative Resource Systems, Inc. Winterville, NC. 505 p.

Mossler, M.A. and J.H. Crane. 2008. Crop profile for papaya in Florida. Revised document. CIR 1402. IFAS Extension, University of Florida. Gainesville, FL. 11 p.

Mossler, M.A. and J.H. Crane. 2009. Florida crop / Pest management profile: Papaya. Revised document. CIR 1402. IFAS Extension, University of Florida. Gainesville, FL. 8 p.

Motomura, H., T. Fujii, and M. Suzuki. 2004. Silica deposition in relation to ageing of leaf tissues in Sasa veitchii (Carriére) Rehder (Poaceae: Bambusoideae). Annals of Botany 93:235-248.

Motomura, H., K. Hikosaka, and M. Suzuki. 2008. Relationships between photosynthetic activity and silica accumulation with ages of leaf in Sasa veitchii (Poaceae, Bambusoideae). Annals of Botany 101:463-468.

Nakasone, H.Y. 1986. Papaya. pp:277-299. In: S.P. Monselise (ed.). Handbook of fruit set and development. CRC Press. Boca Raton, FL. 584 p.

Nakasone, H.Y. and R.E. Paull. 1998. Tropical Fruits. Crop Production Science in Horticulture No. 7. Chapter 10:239-269. CABI Publishing. Wallingford, UK. 445 p.

299

NASS - Hawaii. 2011. Economic, Statistics, and Market Information System. (Release in 2010). Website:http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?docum entID=1377 (Accessed August 11, 2014).

Nautiyal, B.D., C.P. Sharma, and S.C. Agarwala. 1986. Iron, zinc and boron deficiency in papaya. Scientia Horticulturae 29:115-123. Nazeeb, M. and W.J. Broughton. 1978. Storage conditions and ripening of papaya ‘Bentong’ and ‘Taiping’. Scientia Horticulturae 9:265-277.

Neumann, D. and U. zur Nieden. 2001. Silicon and heavy metal tolerance of higher plants. Phytochemistry 56:685-692.

Neumann, D., O. Lichtenberger, W. Schwleger, and U. zur Nieden. 1997. Silicon storage in selected dycotyledons. Botanica Acta 110:282-290.

Nishina, M., F. Zee, R. Ebesu, A. Arakaki, R. Hamasaki, S. Fuduka, N. Nagata, C.L. Chia, W. Nishijima, R. Mau, and R. Uchida. 2000. Papaya production in Hawaii. Cooperative Extension Service. C.T.A.H.R. – University of Hawaii. F&N-3:1-8.

Noble, C.V., R.W. Drew, and J.D. Slabaugh. 1996. Soil Survey of Dade County Area, Florida. United States Department of Agriculture – National Resources of Conservation Service. National Cooperative Soil Survey Publication. Washington, DC. 64 p.

Nonaka, K. and K. Takahashi. 1990. A method of assessing the need of silicate fertilizers in paddy soils. XIV International Congress of Soil Science 4:513-514.

Nunes, B.N., A.G. Cruz, J.A.F. Faria, A.S. Sant’Ana; R. Silva, and M.R.L. Moura. 2010. A survey on the sanitary condition of commercial foods of plant origin solid in Brazil. Food Control 21:50-54.

Okuda, A. and E. Takahashi. 1961. Studies on the physiological role of silicon in crop plant. Part 2. Effect of silicon supplying period on the growth of rice plant and its nutrients uptake. Journal of Science Soil and Manure, Japan 32:481-488 [J,E]1

Okuda, A. and E. Takahashi. 1961b. Studies on the physiological role of silicon in crop plant. Part 4. Effect of silicon on the growth of barley, tomato, radish, green onion, Chinese cabbage and their nutrients uptake. Journal of Science Soil and Manure, Japan 32:623-626 [J,E]2

Okuda, A. and E. Takahashi. 1965. The role of silicon. pp:123-146. In: The mineral nutrition of the rice plant: Symposium, International Rice Research Institute (IRRI) The Johns Hopkins Press. Baltimore, MD. 494 p.

1 & 2 [J,E]: Legend at the end of the reference indicates paper written in Japanese with English summary.

300

Oliveira, A.M.G. 2002. Mamão. pp:112-114. In: A.L. Borges, E.F. Coelho, and A.V. Trindade (eds.). Fertirrigação em fruteiras tropicais. 1. EMBRAPA Mandioca e Fruticultura. Relatório Técnico. Cruz das Almas, BA. Brazil. 256 p.

Oliveira, A.M.G. and R.C. Caldas. 2004. Produção do mamoeiro em função de adubação com nitrogênio, fósforo e potássio. Revista Brasileira de Fruticultura 26:160-163.

Orr, K.J., H. Denning, and C.D. Miller. 1953. The sugar and ascorbic acid content of papayas in relation to fruit quality. Food Research 18:532-537.

Oviedo, G.F. 1535. Historia general y natural de las Indias. Volumen 3. Published by: La Real Academia de la Historia Española. Madrid, España. 643 p.

Palmer, S., E. Scott, J. Stangoulis, and A.J. Able. 2006. The effect of foliar-applied Ca and Si on the severity of powdery mildew in two strawberry cultivars. Acta Horticulturae 708:135- 139.

Parry, D., M.J. Hodson, and A.G. Sangster. 1984. Some recent advances in studies of silicon in higher plants. Philosophical Transactions of the Royal Society London B 304:537-549.

Paull, R.E. 1995. Preharvest factors and the heat sensitivity of field-grown ripening papaya fruit. Postharvest Biology and Technology 6:167-175.

Paull, R.E. and N.J. Chen. 1983. Postharvest variation in cell wall-degrading enzymes of papaya (Carica papaya L.) during fruit ripening. Plant Physiology 72:382-385.

Paull, R.E. and O. Duarte. 2011. Tropical fruits. Volume 1. Crop Production Science in Horticulture, No. 20. Second edition. CAB International (CABI). Cambridge, MA. 400 p.

Paull, R.E., W. Nishijima, R. Marcelino, and C. Cavaletto. 1997. Postharvest handling and losses during marketing of papaya (Carica papaya L.). Postharvest Biology and Technology 11(3):165-179.

Pedigo, L.P. and M. Rice. 2008. Conventional insecticides. pp:381-440. In: L.P. Pedigo and M. Rice (eds.). Entomology and Pest Management. Sixth edition. Prentice Hall. Upper Saddle River, N.J. 816 p.

Peña, J.E. and F.A. Johnson. 2006. Insect management in papaya. Entomology document ENY- 414. Revised document. Florida Cooperative Extension Service. Institute of Food and Agricultural Sciences, University of Florida. Gainesville, FL. 5 p.

Pereira, H.S., G.H. Korndörfer, W.F. Moura, and G.F. Corrêa. 2003. Extractors of available silicon in slags and fertilizers. Revista Brasileira de Ciência do Solo 27:265-274.

301

Persley, D.M. and R.C. Ploetz. 2003. Diseases of papaya. pp:373-412. In: R.C. Ploetz. Diseases of Tropical Fruit Crops. CABI Publishing. Cambridge, MA. 527 p.

Piperno, D.R. 2006. Phytoliths: A comprehensive guide for archaeologist and paleoecologists. Chapter 1. Rowman AltaMira Press. Lamham, MD. 239 p.

Piperno, D.R, and D.M. Pearsall. 1998. The silica bodies of tropical American grasses: Morphology, taxonomy, and implications for grass systematics and fossil phytolith identification. Smithsonian Contributions to Botany 85:1-40.

Piperno, D.R., D.M Pearsall, R. Benfer, Jr., L. Kealhofer, Z. Zhao, and Q. Jiang. 1999. Phytolith morphology. Science 283:1265-1266.

Plucknett, D.L. 1969. The use of soluble silicates in Hawaiian agriculture. Australian Society of Soil Science. Science. Queenland Branch. CSIRO Cunningham Laboratory – University of Queensland Papers, Department of Agriculture. St. Lucia, Brisbane, Australia 1(6):203223

Protain, S., A. Wilson, and M. Mohammed. 2004. The ripening of Carica papaya L. as affected by 1-Methylcyclopropene (1-MCP). Proceedings of the Caribbean Food Crops Society 40:79-87.

Proulx, E., M.C.N. Nunes, J.P. Emond, and J.K. Brecht. 2005. Quality attributes limiting papaya postharvest life at chilling and non-chilling temperatures. Proceedings of the Florida State Horticulture Society 118:389-395.

Prychid, C.J., P.J. Rudall, and M. Gregory. 2003. Systematics and biology of silica bodies in monocotyledons. The Botanical Review 69:377-440.

Rafi, M.M., E. Epstein, and R.H. Falk. 1997. Silicon deprivation causes physical abnormalities in wheat (Triticum aestivum L.). Journal of Plant Physiology 151:497-501.

Raid, R.N. and J.C. Comstock. 2006. Sugarcane rust disease. Agronomy document SS-AGR- 207. Revised document. Florida Cooperative Extension Service. Institute of Food and Agricultural Sciences, University of Florida. Gainesville, FL. 3 p.

Rajbhar, Y.P., G. Singh, and M. Lal. 2010. Effect of N, P. K and spacing on growth and yield of papaya (Carica papaya L.) cv. Pant Papaya 1. Acta Horticulturae 851:425-428.

Rao R.B. and Y.C. Li. 2003. Nitrogen mineralization of cover crop residues in calcareous gravelly soils. Communications in Soil Science and Plant Analysis 34:299-313.

Raven, J.A. 1983. The transport and function of silicon in plants. Biological Reviews 58:179- 207.

302

Raven, J.A. 2001. Silicon transport at the cell and tissue level. pp:41-55. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Raven, J.A. 2003. Cycling silicon: The role of accumulation in plants. New Phytologist 158(3):419-421.

Ray, J.D., R.W. Gesch, T.R. Sinclair, and L.H. Allen, Jr. 2002. The effect of vapor pressure deficit on maize transpiration response to a drying soil. Plant Soil 239:113-121.

Rayment, G.E. and F.R. Higginson. 1992. Australian Laboratory Handbook of Soil and Water Chemical Methods. Inkhata Press, Melbourne, Australia. 330 p.

Realpe, O.H.R. and H.M.L. Laane. 2008. Effect of the foliar application of soluble oligomeric silicic acid and low dose boric acid on papaya trees. pp:88. In: M. Laing, M. Keeping and O. Kvedaras (eds.). Silicon in Agriculture Conference: 4th. International Conference, October 26-31, 2008. A poster on silicon in plants – general. Abstract # 94. Wild Coast, Port Edward, KwaZulu-Natal, South Africa. 109 p.

Rehm, G.W. and A.C. Caldwell. 1968. Sulphur supplying capacity of soils and the relationship to soil type. Soil Science 105:355-361.

Richmond, K.E. and M. Sussman. 2003. Got silicon? The non-essential beneficial plant nutrient. Current Opinion 6:268-272.

Rieger, M. 2012. Papaya tree – Carica papaya. Fruit Crops. Released in 2012. Website: http://www.fruit-crops.com/papaya-carica papaya/ (Accessed August 12, 2014).

Ritchie, S.W., H.T. Nguyen, and A.S. Holaday. 1990. Leaf water content and gas-exchange parameters of two wheat genotypes differing in drought resistance. Crop Science 30:105- 111.

Rivera-Pastrana, D., E.M Yahia, and G.A. González-Aguilar. 2010. Phenolic and carotenoid profiles of papaya fruit (Carica papaya L.) and their contents under low temperature storage. Journal of the Science of Food and Agriculture 90:2358-2365.

Rodrigues, F.A. and L.E. Datnoff. 2005. Silicon and rice disease management. Review. Fitopatologia Brasileira 30(5):457-469.

Rodrigues, F.A., F.X.R. Vale, L.E. Datnoff, A.S. Prabhu, and G.H. Korndörfer. 2003. Effect of rice growth stages and silicon on sheath blight development. Phytopathology 93(3):256- 261.

Romero-Aranda, R., T. Soria, and J. Cuartero. 2001. Tomato plant-water uptake and plant-water relationships under saline growth conditions. Plant Science 160(2)(3):265-272.

303

Rosenzweig, C. and M.L. Parry. 1994. Potential impact of climate change on world food supply. Nature 367:133-138.

Sadzawka, R.M.A. and S. Aomine. 1977. Adsorption of silica in river waters by soils in central Chile. Soil Science and Plant Nutrition 23:297-309.

Samson, J.A.R. 1986. Papaya. pp:256-269. In: J.A. Samson (ed.). Tropical fruits (Tropical Agricultural Series). Second Edition. Blackwell Publishing Co. Oxford, OX, UK. 335 p.

Samuels, A.L., A.D.M. Glass, D.L. Ehret, and J.G. Menzies. 1991. Mobility and deposition of silicon in cucumber-plants. Plant, Cell and Environment 14(5):485-492.

Sanclemente, M.A., B. Schaffer, P.M. Gil, F.S.Davies, and J.H. Crane. 2013. Leaf removal before flooding influences recovery of avocado (Persea americana Mill.) trees from flooding stress. Scienctia Horticulturae 150:154-163.

Sangster, A.G. and D.W. Parry. 1981. Ultrastructure of silicon deposits in higher plants. pp:383- 407. In: T.L. Simpson and B.E. Volcani (eds.). Silicon and siliceous structures in biological systems. Springer-Verlag Publisher. New York, NY. 587 p.

Sangster, A.G. and M.J. Hodson. 1986. Silica in higher plants. pp:90-111. In: D. Evered and M. O’Connor (eds.). Silicon biochemistry. CIBA Foundation Symposium No. 121. John Wiley and Sons. Chichester, West Sussex, UK. 272 p.

Sangster, A.G., M.J. Hodson, and H.J. Tubb. 2001. Silicon deposition in higher plants. pp:85- 113. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Sankat, C.K. and R. Maharaj. 1997. Papaya. pp:167-189. In: S.K. Mitra (ed.). Postharvest physiology and storage of tropical and subtropical fruits. CABI Publishing. Wallingford, UK. 423 p.

Sartori de Camargo, M., L. Amorim, A. Rodrigues-Gomex, Jr. 2013. Silicon fertilization decreases brown rust indicence in sugarcane. Crop Protection 53:72-79.

SAS Institute, Inc. 1982. SAS User’s guide: Statistics. SAS Institute, Inc. Cary, NC. USA.

Sauer, C.O. 1966. The early Spanish main. University of California Press. Berkeley, CA. 306 p.

Savant, N.K., G.H. Snyder, and L.E. Datnoff. 1997a. Silicon management and sustainable rice production. Advances in Agronomy 58:151-199.

Savant, N.K., L.E. Datnoff, and G.H. Snyder. 1997b. Depletion of plant-available silicon in soils: a possible cause of declining rice yields. Communication in Soil Science and Plant Analysis 28(13&14):1245-1252.

304

Savant, N.K., G.H. Korndorfer, L.E. Datnoff, and G.H. Snyder. 1999. Silicon nutrition and sugarcane production: A review. Journal of Plant Nutrition 22(12):1853-1903.

Schery, R.W. 1952. Plants for man. Prentice Hall, Inc. Plant Science Series. Englewood Cliffs, NJ. 564 p.

Schwartz, M.C. 1942. Photometric determination of silica in the presence of phosphates. Industrial and Engineering Chemistry: Analytical Edition 14(11):893-895.

Seebold, K.W., T.A. Kucharek, L.E. Datnoff, F.J. Correa-Victoria, and M.A. Marchetti. 2001. The influence of silicon on components of resistance of blast in susceptible, partially resistant, and resistant cultivars of rice. Phytophatology 91(1):63-69.

Senaratna, T., C.E. Mackay, B.D. McKersie, and R.A. Fletcher. 1988. Uniconazole-induced chilling tolerance in tomato and its relationship to antioxidant content. Journal of Plant Physiology 133:56-61.

Shakoor, S.A. 2014. Silicon to silica bodies and their potential roles: An overview. International Journal of Agricultural Sciences 4(2):111-120.

Sibbernsen, E. and K.A. Mott. 2010. Stomatal responses to flooding of the intercellular spaces suggest a vapor-phase signal between the mesophyll and the guard cells. Plant Physiology 153:1435-1442.

Sims, C. 2010. Texture analysis. A laboratory for FOS 4722C & 6126C. Fall semester. Food Science Department, University of Florida. Gainesville, FL. 3 pages.

Slaughter, D. and J. Thompson. 2007. Evaluating nondestructive firmness detectors for pears. Good Fruit Grower. Released in 2007. Website: http://www.goodfruit.com / Good-Fruit- Grower/February-1st-2007/Evaluating-Nondestructive-Firmness-Detectors-for-Pears/ (Accessed December 10, 2013).

Smith, D.K. 1998. Opal, cristobalite, and tridymite: Noncrystallinity versus crystallinity, nomenclature of the silica mineral and bibliography. Powder Diffraction 13(1):2-19.

Snyder, G.H. 2001. Methods for silicon analysis in plants, soils, and fertilizers. pp:185-196. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Snyder, G.H., D.B. Jones, and G.J. Gascho. 1986. Silicon fertilization of rice on Everglades histosols. Soil Science Society of America Journal 50:1259-1263.

Snyder, G.H., V.V. Matichenkov, and L.E. Datnoff. 2007. Silicon. pp:551-568. In: A.L. Barker and D.J. Pilbeam (eds.). Handbook of plant nutrition. CRS Press / Taylor and Francis Group. Boca Raton, FL. 613 p.

305

Snyder, G.H., D.W. Rich, C.L. Elliot, and M.P. Barbosa-Filho. 2004. Evaluation of candidate silicon fertilizers. Soil and Crop Science Society Florida Proceedings 64:52-54.

Stanisavljević, N.S., D.B. Nikolić, Ž.S. Jovanović, J.T. Samardžić, S.R. Radovićand, and V.R. Maksimović. 2011. Antioxidative enzymes in the response of buckwheat (Fagopyrum esculentum Moench) to complete submergence. Archives of Biological Sciences, Belgrade 63(2):399-405.

Steponkus, P.L. 1984. Role of the plasma membrane in freezing injury and cold acclimation. Annual Review of Plant Physiology 35:543-584.

Stone, H. and J.L. Sidel. 2004. Sensory evaluation practices. Fourth edition. Elsevier Academic Press. San Diego, CA. 408 p.

Storey, W.B. 1985. Carica papaya. pp:147-157. In: H.H. Abraham (ed.). Handbook of flowering. II. CRC Press, Inc. Boca Raton, FL. 544 p. .

Storey, W.B. 1987. Papaya. pp:374-392. In: F.D. Ferwerda and F. Wit (ed.). Genotecnia de Cultivos Tropicales Perennes. First edition. Editorial: A.G.T. Editor, S.A. México, D.F., México. 520 p.

Subbarao, D.V. and A. Perraju. 1976. Resistance in some rice strains to first-instar larvae of Tryporyza incertulas (Walker) in relation to plant nutrients and anatomical structure of the plants. International Rice Research Newsletter. 1:14-15.

Sudhakar, P.C., J.P. Singh, Y. Sing, and R. Singh. 2006. Effect of graded fertility levels and silicon sources on crop yield, uptake and nutrient-use efficiency in rice (Oryza sativa L.) 51(3):186-188.

Suojala-Ahlfors. 2005. Fruit firmness of pickling cucumber cultivars. HortTechnology 15(4):777-781.

Tahir, M.A., T. Aziz, and T. Rahmatullah. 2011. Silicon-induced growth and yield enhancement in two wheat genotypes differing in salinity tolerance. Communications in Soil Science and Plant Analysis 42(1):395-407.

Tahir, M.A., Q. Rahmatullah, T. Aziz, M. Ashraf, S. Kanwal, and M.A. Maqsood. 2006. Beneficial effects of silicon in wheat (Triticum aestivum L.) under salinity stress. Pakistan Journal of Botany 38(5):1715-1722.

Taiz, L. and E. Zeiger. 2006. Plant physiology. Fourth edition. Sinauer Associates, Inc. Sunderland, MA. 700 p.

306

Takahashi, E. 1996. Uptake mode and physiological functions of silica. pp:99-122. In: T. Matsuo, K. Kumazawa, R. Ishii, K. Ishihara, and H. Hirata (eds.). Science of the rice plant: Physiology. Volume 2. Food and Agriculture Policy Research Center Publisher. Tokyo, Japan. 1240 p.

Takahashi, E., J.F. Ma, and Y. Miyake. 1990. The possibility of silicon as an essential element for higher plants. Comments on Modern Chemistry. Part B. Comments on Agricultural and Food Chemistry 2(2):99-122.

Tamai, K., G. Wu, M. Ichii, and J.F. Ma. 2002. Isolation and characterization of a rice mutant defective in Si uptake. pp:154-156. In: Proceedings of the Second Silicon in Agriculture Conference. August 22-26, 2002. Tsuruoka, Yamagata, Japan.

Tamimi, Y.N. and R.L. Voss. 1970. Mineral accumulation in corn-grain as affected by rates of P and CaSiO3 fertilization. pp:45. In: P.P. Rotar (ed.). Abstracts of publications and research. IV. Soil Science. Department of Agronomy and Soil Science, College of Tropical Agriculture. University of Hawaii. Departmental Paper 30, Period: 1960-1974. Honolulu, HI. 58 p.

Teetes, G.L. 2009. Plant resistance to insects: A fundamental component of IPM. Electronic Lecture in Radcliffe’s IPM World Texbook. University of Minnesota. (Released in 2009). Website: http://ipmworld.umn.edu/chapters/teetes.htm. (Accessed August 11, 2014).

Terra de Almeida, F., B. Salassier, E. Fernandes de Sousa, S. Lúcio, D. Marin, and S. Grippa. 2003. Growth and yield of papaya under irrigation. Scientia Agrícola 60(3):419-424.

Tesfay, S.Z., I. Bertling, and J.P. Bower. 2011. Effects of postharvest potassium silicate application on phenolics and other anti-oxidant systems aligned to avocado fruit quality. Postharvest Biology and Technology 60:92-99.

Texeira da Silva, J.A., Z. Rashid, D.T. Nhut, D. Sivakumar, A. Gera, M. Texeira Souza Jr., and P.F. Tennant. 2007. Papaya (Carica papaya L.): Biology and biotechnology. Trend and Forestry Science and Biotechnology 1(1):47-73.

Thomas, M.B., J. Ferguson, and J.H. Crane. 1995. Identification of N, K, Mg, Mn, Zn, and Fe deficiency symptoms of carambola, lychee, and papaya grown in sand culture. Proceedings of the Florida State Horticultural Society 108:370-373.

Tian, S.P., G.Z. Qin, and Y. Xu. 2005. Synergistic effects of combining biocontrol agents with silicon against postharvest diseases of jujube fruit. Journal of Food Protection 68(3):544- 550.

Tian, S., G. Qin, B. Li, Q. Wang. 2007. Synergistic effects of combining microbial biocontrol agents with silicon against postharvest diseases of fruits. pp:38-46. In: P. Belorini (ed.). Novel approaches for the control of postharvest diseases and disorders. Proceedings of the International Congress. 3-5 May, 2007. Bologna, Italy.

307

Tilgner, D.J. 1971. A retrospective view of sensory analysis and some considerations for the future. Advance Food Research 19:216-277.

Torres-Neto, A., E. Campostrini, J. Gonçalves de Oliveira, and O.K. Yamanishi. 2002. Portable chlorophyll meter for the quantification of photosynthetic pigments, nitrogen and the possible use for assessment of the photochemical process in Carica papaya L. Brazilian Journal of Plant Physiology 14(3):203-210.

Towsend, G.R. and F.S. Andrews. 1940. Florida Agricultural Experiment Station Annual Report. 170 p.

Trenholm, L.E., L.E. Datnoff, and R.T. Nagata. 2004. Influence of silicon on drought and shade tolerance of St. Augustinegrass. HortTechnology 14(4):487-490.

US Food Market Estimator. 2012. (Releasead in 2012). Website: http://www.ctre.iastate.edu/ marketsize/Default.aspx (Accessed August 12, 2014).

USDA NASS – Hawaii. 2012a. Agricultural Census U.S.D.A. (Released in 2013). Website:http://www.agcensus.usda.gov/publications/2012/Full Report/Outlying_areas/prv1.pdf (Accessed August 12, 2014).

USDA NASS – Hawaii. 2012b. Agricultural Census USDA. (Released in 2013). Website: http://www.agcensus.usda.gov/publications/2012/Full_Report/Volume_1,_Chapter_2_US _State_Level_/st99_2_031_.pdf (Accessed August 12, 2014).

Van der Vorm, P.D.J. 1980. Uptake of Si by five plants species, as influenced by variations in Si-supply. Plant and Soil 56:153-156.

Van Soest, P.J. 2006. Rice straw, the role of silica and treatments to improve quality. Animal Feed Science Technology 130:137-171.

Vandemark, G.J. 1999. Transgenic plants for the improvement of field characteristics limiting crop production. pp:219-273. In: O. Paredes-López (ed.). Molecular biotechnology for plant food production. Chapter 6. Technomic Publishing Company, Inc. Lancaster, PA 626 p.

Van Droogenbroeck, B., P. Breyne, P. Goetghebeur, E. Romeijin-Peeters, T. Kyndt, and G. Gheysen. 2002. 1995. AFLP analysis of the genetic relationships among papaya and its wild relatives (Caricaceae) from Ecuador. Theoretical and Applied Genetics 105(2-3): 289-297.

Veerannah, L. and P. Selvaraj. 1984. Studies on growth, dry matter partitioning and pattern of nutrient uptake in papaya. Proceeding of the National Seminar on Papaya and Papain Production. March 26-27. Department of Fruit Crops, Horticultural College and Research Institute. Tamil Nadu Agricultural University (TNAU). Coimbatore, India. pp:76-78.

308

Ventura, J.A., H. Costa and J.S. Tatagiba. 2003. Manejo das doençã do mamoeiro. pp:231-308. In: D.S. Martins and A.F. Costa (eds.). A cultura do mamoeiro: Tecnologias de produção. INCAPER. Vitória, Espirito Santo (ES), Brazil. 497 p.

Vinci, G., F. Botre, G. Mele, and G. Ruggieri. 1995. Ascorbic acid in exotic fruits: a liquid chromatographic investigation. Food Chemistry. 53:211-214.

Voisey, P.W. 1977. Examination of operational aspects of fruit pressure tests. Canadian Institute of Food Science Technology 10:284-294.

Volk, R.J. and R.L. Weintraub. 1958. Microdetermination of silicon in plants. Analytical Chemistry 30(5):1011-1014.

Voogt, W. and C. Sonneveld. 2001. Silicon in horticultural crops grown in soilless culture. pp:115-131. In: L.E. Datnoff, G.H. Snyder, and G.H. Korndörfer (eds.). Silicon in agriculture. Elsevier Science B.V. Amsterdam, The Netherlands. 403 p.

Waldron, K.W. 2004. Plant structure and fruit and vegetable texture. Part III. Understanding and improving the texture of particular foods. pp:241-258. In: D. Kilcast (ed.). Texture in food. Volume 2: Solid foods. Chapter 10. Woodhead Publishing in Food Science and Technology. CRC Woodhead Publishing Limited. Cambridge, England. 537 p.

Walker, G.K. and J.E. Richards. 1985. Transpiration efficiency in relation to nutrient status. Agronomy Journal 77:263-269.

Wall, M.M. 2006. Ascorbic acid, vitamin A, and mineral composition of banana (Musa sp.) and papaya (Carica papaya) cultivars grown in Hawaii. Journal of Food Composition and Analysis. 19:434-445.

Wang, Y., A. Stass, and W.J. Horst. 2004. Apoplastic binding of aluminum is involved in silicon-induced amelioration of aluminum toxicity in maize. Plant Physiology 136(3):3762-3770.

Wang, Q., W. Klassen, Y.C. Li, and M. Codallo. 2009. Cover crops and organic mulch to improve tomato yields and soil fertility. Agronomy Journal 101(2):345-351.

Watson, B. 1997. Agronomy/Agroclimatology notes for the production of papaya. Soil and Crop Evaluation Project. Ministry of Agriculture, Forests, Fisheries and Meteorology, Australia (MAFFA). Australian Agency for International Development. Sidney, Australia. 15 p.

Williams, R.J. 1986. Introduction to silicon chemistry and biochemistry. pp:24-39. In: D. Evered and M. O’Connor (eds.). Silicon biochemistry. CIBA Foundation Symposium No. 121. John Wiley and Sons. Chichester, West Sussex, UK. 272 p.

309

Wills, R.B.H. and S.B. Widjanarko. 1995. Changes in physiology, composition and sensory characteristics of Australian papaya during ripening. Australian Journal of Experimental Agriculture 35:1173-1176.

Wills, R., B. McGlasson, D. Graham, and D. Joyce. 1998. Postharvest: An introduction to the physiology and handling of fruit, vegetables and ornamentals. University of New South Wales Press, Ltd. – CAB International. Sydney, Australia. 262 p.

Winslow, M. D. 1992. Silicon, disease resistance, and yield of rice genotypes under upland cultural conditions. Crop Science 32:1208-1213.

Wolf, B. 1982a. An improved universal extracting solution and its use for diagnosing soil fertility. Communications in Soil Science and Plant Analysis 13(12):1005-1033.

Wolf, B. 1982b. A comprehensive system of leaf analysis and its use for diagnosing crop nutrient status. Communications in Soil Science and Plant Analysis 13(12):1035-1059

Woolley, J.T. 1957. Sodium and silicon as nutrients for the tomato plant. Plant Physiology. Ph.D. Dissertation. University of California, Berkeley. CA, USA.

Wright, A.L., Y. Wang, and K.R. Reddy. 2008. A loss-on-ignition method to assess soil organic C in calcareous Everglades wetlands. Communications in Soil Science and Plant Analysis 39:3074-3083.

Wu, Q.-S., X.-Y. Wan, N. Su, Z.-J. Cheng, J.-K. Wang, C.-L. Lei, X. Zhang, L. Jiang, J.-F. Ma, and J.-M. Wan. 2006. Genetic dissection of silicon uptake ability in rice (Oryza sativa L.). Plant Science 171(4):441-448.

Wutscher, H.K. 1989. Growth and mineral nutrition of young orange trees grown with high levels of silicon. HortScience 24:275-277.

Yadava, U.L., A.J. Burris, and D. McCray. 1990. Papaya: a potential annual crop under middle Georgia conditions. pp:364-366. In: J. Janick and J.E. Simon (eds.). Advances in new crops Timber Press. Portland, OR. 560 p.

Yang, B., Y.C. Li, Y.H. Ge, and Y. Wang. 2009. Induces resistance in melons by elicitors for the control of postharvest diseases. pp:31-42. In: D. Prusky, M. Lodovica Gullino (eds.). Post-harvest pathology. Plant Pathology in the 21st Century – Contributions to the 9th. International Congress 2. Springer. New York, NY. 211 p.

Yee, W., E.K. Akamine, G.M. Aoki, R.A. Hamilton, F.H. Haramoto, R.B. Hine, O.V. Holtzmann, J.T. Ishida, J.T. Keeler, and H.Y. Nakasone. 1970. Papayas in Hawaii. Cooperative Extension Service. University of Hawaii. Circular # 436. Honolulu, HI. 57 p.

310

Yeo, A.R., S.A. Flowers, G. Rao, K. Welfare, K. Senanayake, and N. Flowers. 1999. Silicon reduces sodium uptake in rice (Oryza sativa L.) in saline conditions and this is accounted for by a reduction in the transpirational bypass flow. Plant, Cell and Environment 22(5):559-565.

Yoshida, S. 1975. The physiology of silicon in rice. Food and Fertilizer Technology Center. Technical Bulletin. Taipei City, Taiwan. 25:1-27.

Yoshida, S., S.A. Navaser, and E.A. Ramirez. 1969. Effect of silica and nitrogen supply on some leaf characters of the rice plant. Plant and Soil 31:48-56.

Yoshida, S., Y. Ohnishi, and K. Kitagishi. 1962a. Chemical forms, mobility and deposition of silicon in rice plant. Soil Science and Plant Nutrition 8(3):81-92.

Yoshida, S., Y. Ohnishi, and K. Kitagishi. 1962b. Histochemistry of silicon in rice plant. III. The presence of cuticle-silica layer in the epidermal tissue. Soil Science and Plant Nutrition 8(2):1-5.

Zargar, S.M. and A. Agnihotri. 2013. Impact of silicon on various agro-morphological and physiological parameters in maize and revealing its role in enhancing water stress tolerance. Emirates Journal of Food and Agriculture 25(2):138-141.

Zhu, Z.J., G. Wei, J. Li, Q. Qian, and J. Yu. 2004. Silicon alleviates salt stress and increases antioxidant enzymes activity in leaves of salt-stressed cucumber (Cucumis sativus L.). Plant Science 167(3):527-533.

Zhu, Z.J., Y.C. Liang, Y.F. Ding, and Z.J. Li. 2006. Effects of silicon on photosynthesis and its related physiological parameters in two winter wheat cultivars under cold stress. Scientia Agricola Sinica 39:1780-1788.

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BIOGRAPHICAL SKETCH

Octavio Augusto Menocal Barberena was born in Granada, Nicaragua, on 1961. He attended Centro Escolar Carlos A. Bravo elementary school and completed his high school education at the Instituto Nacional de Oriente in 1978. He graduated as an Engineer of

Agricultural Sciences from the Universidad Nacional Autónoma (U.N.A.N.), Managua,

Nicaragua, in 1984. From 1980 to 1981 he served as a teaching assistant in an introductory mathematics course for undergraduates at the Facultad de Ciencias Agropecuarias (U.N.A.N.).

He began his career as a field researcher and extension agent, serving from 1984 to 1994 in different enterprises and institutions belonging to the Nicaraguan Government. As an officer of the Ministry of Agriculture, he gained experience in rubber, corn, beans, rice, tobacco, vegetables, and fruit crops production. In 1994, working for the Nicaraguan Institute for

Agricultural Research (Instituto Nicaragüense de Tecnología Agropecuaria, INTA) he concentrated on pitahaya, pineapple, papaya, ’Tahiti’ lime, avocado, and mango production. At the Bluefields Experimental Station he gained additional experience as specialist in fruit crops.

After being awarded an INTA scholarship to pursue a Master of Science degree in 1995, he studied English at the Intensive English and Orientation Program (IEOP) at Iowa State

University, Ames, Iowa and at the English Language Institute (ELI) of the University of Florida in Gainesville, FL. In January 1997, he was accepted by the Graduate School of the University of Florida and the Horticultural Sciences Department. Dr. William (Bill) Castle was his major professor and he conducted research on citrus at the Water Conserv II facilities at Winter

Garden, FL., graduating with the degree of Master of Science in April 1999.

Upon completion of his Master of Science graduate program, Octavio Augusto returned to Nicaragua to apply the knowledge received during his graduate study. At the beginning of

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2001, after working for INTA as a non-traditional researcher for about 1.5-years, he was promoted to the National Research Director position and had a successful professional career.

In January 2008, he took a position with the Mango Quality Project conducted by the

Horticultural Sciences Department of the University of Florida and the National Mango Board,

Orlando, Florida. In January 2009, he was accepted into a Ph.D. program to continue his education in the same department with Dr. José Xavier Chaparro as his major professor and Dr.

Jeff K. Brecht as his co-advisor. However after two-years, Octavio changed his plans and moved to the Tropical Research and Education Center (TREC) in Homestead, FL where he continued his program under Dr. Jonathan H. Crane’s advice.

Octavio Augusto Menocal Barberena is married to the former Norma del Socorro

Sandoval-Balladares, and they have two children, Octavio Augusto, who studied agriculture and graduated as an Agronomist Engineer in December 2011 from the Panamerican Agricultural

School of ‘El Zamorano’ in Honduras, and Norman Francisco who is currently an undergraduate student at ‘El Zamorano’, Honduras.

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