Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author. QUANTITATIVE INHERITANCE STUDIES OF GRAIN MATURATION AND GERMINATION IN THREE WHEAT CROSSES. A THESIS PRESENTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY AT MASSEY UNIVERSITY VINICH SEREEPRASERT 1990 i ABSTRACT The pattern of grain maturation and germinability was studied in three wheat crosses ripening in warm and cool environments . Two white grained and two red grained wheat cultivars with varying resistance to preharvest sprouting were used as parents in three crosses . The white grained wheats were Tordo , "resistant" to sprouting through gibberellin insensit ivity, and Gabo, a standard cultivar susceptible to sprouting . The two red grained wheats were Karamu and Sonora 64A, the former being sprouting resistant while the latter was susceptible . Tordo was the common parent in all three crosses . Six generations, P 1 , P 2 , F2 , F3 , BC1 (P1 )s1 and BC1 (P2 )Sl from each cross were grown in a glasshouse and were transferred into controlled climate rooms at booting stage , being arranged in a randomized complete block experiment with three replications . The patterns of grain development were measured from serial samples of the grains from ears which had been tagged at anthesis. The changes in grain dry weight, moisture content, germination and a-amylase activities were measured at intervals from just after anthesis until maturity; and the patterns were described using regression analysis against age of grain (in days after anthesis) . The functions of best fitted were used to estimate nine key stages of grain development , which were : harvest ripeness, amylase maturity, GA amylase maturity, median germination, germination maturity, median embryo maturity, embryo maturity, grain colour maturity and grain weight maturity. Gene effects were estimated for these variables, and also for maximum grain coat colour, grain weight at harvest ripeness, maximum dry weight, a-amylase activities at harvest ripeness and at embryo maturity, standard germination and potential germination at harvest ripeness . The gene effects were fitted using Hayman' s Generation Means Analysis . The full twelve parameter model (digenic epistasis, environment and their interactions included) were used to explain the ii phenotypic variations among the six genetic populations ripening in the two environments. The gene effects estimated were used to assist in making recommendation for breeding for preharvest sprouting resistance . The experimental result s showed that cool environment prolonged the time to reach most developmental stages compared to the warm environment . Harvest ripeness (12.5 % grain mo isture) occurred after grain weight maturity (time to 90 % maximum grain weight ) but before the time when the grains reached their maximum dry weight . Embryo maturity, as a measure of ability of the grains to germinate when the dormancy had been bypassed, was considered the important component for germinability. Germinative a-amylase at harvest ripeness was the variable most consistently correlated with germination at harvest ripeness . The gene actions for the derived variables appeared to be complicated, with epistasis and epistasis x environment effects being significant mo re often than the additive or dominance effects . The gene actions for the maximum grain colour and percent sterility were also studied . For the maximum colour score the result indicated that there was interallelic interaction between the "classical'' gene for grain redness and unknown genes . The breeding strategies for preharvest sprouting re sistance were discussed based on the actions of the genes for the characters . Briefly it appeared that producing hybrids would enhance the earliness in many maturity characters which would indirectly resulted in more susceptible genotypes. To improve resist ance to preharvest sprouting, selection for cha racters like low a-amylase activities at harvest ripeness, low standard germination and potential germination at harvest ripeness, or late embryo maturity was recommended. These characters were controlled by many genes which interacted and showed epistasis effect and also the gene effects we re dependent on environmental condition . Effectiveness in selection would be specific to a particular environment . The selection for cultivar resistant to preharvest sprouting based on these characters should be deferred until later generations when the plants had reached iii high level of homozygosity. The selection for low a-amylase and low germination at harvest ripeness would give more reliable protection against preharvest sprouting damage . iv ACKNOWLEDG NT EME I would like to express my deep gratitude to my chief supervisor, Dr. I.L. Gordon for his patient guidance, and close supervision through the course of this study . I also feel deeply grateful to Dr. J.M. McEwan of the Crop Research Division, D.S.I.R. and Dr. P. Coolbear of the Seed Technology Centre for their valuable discussions, criticisms and thoroughly examining the manuscript . I would like to thank Mr . Ian Warrington of the Plant Physiology Division for providing the glasshouse and climate room facilities . All assistance from staff at the Climate Laboratory was highly appreciated. I am personally indebted to Dr. D.R. Smith for his help in providing the F 1 seeds and computer programs used in this work . The help from Mr Wichien Chatupote, Mr Pirote Wiriyacharee and Dr. Quingfeng Li in preparing the graphic work in the Appendices was received with gratitude . Their help and encouragement were so valuable to me . Finally I would like to express my sincere thanks to the New Zeal and Government for their financial support during my stay in New Zeal and and to the Thai Government for granting me study leave . V TABLE OF CONTENTS page ABSTRACT i ACKNOWLEDGEMENTS iv TABLE OF CONTENTS V LIST OF TABLES ix LIST OF FIGURES xiv LIST OF APPENDICES xviii CHAPTER 1. INTRODUCTION : THE NATURE AND OCCURRENCE OF PREHARVEST SPROUT ING 1 CHAPTER 2. REVIEW OF LITERATURE 5 I. The Nature of Seed Dormancy 5 II . Dormancy of Wheat Grain 6 II.l Structure of the Wheat Grain 6 II.2 Role of Grain Coat 8 II .3 Hormonal Effect on Grain Dormancy 12 II. 3.1 Gibberellic Acid 12 I I.3. 2 Abscisic Ac id 17 II .3.3 Cytokinins 19 III. Preharvest Sprouting in Wheat 20 IV . Temperature Effects on Grain Deve lopme nt and Preharvest Sprouting 25 IV.l Effects on Grain Development 25 IV .2 Effects on Grain Dormancy and Preharvest Sprouting 25 V. a-Amylase 26 V.l a-Amylase in Germinating Grain of Wheat 28 VI . Endosperm Degradation 30 VII . Genetics of Preharvest Sprouting 32 VII .1 Grain Coat Colour 32 VII .2 GA Insensitivity 33 VII .3 a-Amylase Genes 34 VII .4 Inheritance of Dormancy and Preharvest Sprouting Characters 34 VIII. Generation Mean Analysis 35 vi IX. Other Method of Inheritance Studies 39 IX.l Diallel 39 IX.2 Other Designs 41 CHAPTER 3. MATERIALS AND METHODS 42 I. Cultivars and Generations 43 II. Generation Advance 44 III. Experimental Materials 44 IV. Experimental Details in the Controlled Climate Rooms 45 IV .1 Temperature 46 IV .2 Light 46 IV .3 Nutrient 46 IV. 4 C02 46 IV.5 Insect and Disease Cont rol 46 V. Samp ling of the Ears 47 VI . Attributes Measured 47 VI .l Grain Dry We ight and Grain Moisture Content 47 VI .2 Harvest Ripeness 48 VI .3 Standard Germination and Potent ial Ge rmination 48 VI .4 Grain Colour Score 49 VI .5 a-Amylase Concentrations 50 VI .5.1 Base a-amylase 50 VI .5.2 Germinative a-Amylase 50 VI .5.3 Gibberellin a-Amylase 50 VII . Data Analysis 51 VII.l Estimat ing Data from Regression Equations 51 VII.l.l Moisture Content 52 VII .1.2 Grain Dry Weight 53 VII.l.3 Standard Germination and Potential Germination 54 VII.l.4 Estimated Dormancy Percentages . 55 VII .1.5 Grain Colour Scour 56 VII.1.6 a-Amylase Data 57 VII.l.6.1 Base a-Amylase 57 VII.l.6.2 Germinative a-Amylase and GA3-Induced a-Amylase 57 VII .2 Analysis of Variance 59 VII.3 Generation Mean Ana lysis 61 vii CHAPTER 4. RESULTS 66 I. Timing of Events During Grain Development and Ripening 66 I.1 Definitions 66 I.2 Cross 1's Results 67 I.3 Cross 2's Results 71 I.4 Cross 3' s Results 76 I.5 Comparisons of Tordo' s Maturity Characters Between Crosses 80 II . Germination Percentages at Harvest Ripeness 82 II .1 Cross 1's Results 82 II .2 Cross 2's Results 84 I I.3 Cross 3' s Results 86 II.4 Comparison Among Crosses 88 III. Grain Dry Weight at Harvest Ripeness and Maximum Grain Dry Weight 89 III.1 Cross 1's Results 89 III .2 Cross 2's Results 91 III. 3 Cross 3' s Results 92 IV. a-Amylase Contents in the Grains at Harvest Ripeness and Embryo Maturity 95 IV .1 Cross 1's Results 95 IV .2 Cross 2's Results 101 IV .3 Cross 3' s Results 108 V. Maximum Colour Score . 116 VI . Sterility Percentage . 119 VII. Generation Mean Analysis . 121 VII .1 Generation Mean Analysis of Maximum Colour Score . 122 VII .2 Germinative a-Amylase at Harvest Ripeness . 125 VII .3 Harvest Ripeness and a-Amylase Maturities . 126 VII .4 Median Embryo Maturity and Embryo Maturity. 129 VII .5 Dry we ight Maturity and Grain Colour Maturity 134 VII . 6 Germinat ions at Harvest Ripeness 136 VII .7 Grain Dry Weight 139 viii VII .8 Base a-Amylases 140 VII .9 Germinative a-Amylase at Embryo Maturity 143 VII .10 GA3 a-Amylases 144 VII .ll Percent Sterility 146 CHAPTER 5.