AN ABSTRACT OF THE THESIS OF ROBERT HENRY ARON for the degree DOCTOR OFPHILOSOPHY (Name of student) (Degree) in Geography presented on (Major department) ate)' Title:CHILLING AS A FACTOR IN CROP LOCATION WITH PARTICULAR REFERENCE TO DECIDUOUS ORCHARDS IN CALIFORNIA Abstract approved: Redacted for Privacy James F. Lahey Several empirical formulas that may be used to estimate avail- able chilling are presented in this study.Many climatic parameters were considered in the derivation of these formulas.One equation employing only maximum and minimum temperatures hada coefficients of correlation (R) and R2 values of .978 and .957, respectively.This equation was used in estimating the availability of chilling at 273 stations throughout California.Using these estimates and considering such factors as altitude and marine influences, the availability of chilling throughout California was mapped. Factors that influence the effectiveness of the chilling received such as low and high temperatures, high light intensity, shade, fog, cloud cover, topography and wind were analyzed. Which temperatures are most effective in satisfying theplant's chilling requirement, the amount required by different varieties, the effects and consequences of inadequate chilling, and treatments which may ameliorate the effects of inadequate chilling were considered. Hormonal and physical and anatomical plant response changes occurring during rest were discussed. Chilling as a Factor in Crop Location with Particular Reference to Deciduous Orchards in California by Robert Henry Aron A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy June 1975 APPROVED: Redacted for Privacy Pfessor of Geography U in charge of major Redacted for Privacy Head of Department of Geography 14 y Redacted for Privacy Dean of Graduate School Date thesis is presented Typed by Lyndalu Sikes and Ilene M. Anderton for Robert Henry Aron ACKNOWLEDGMENTS The author expresses his thanks to the many individuals who offered their time and knowledge during the research and writing of this study. For their invaluable assistance during the very early phases of this study, the author wishes to thank Dr. John Kimura, Professor of Geography at the California State University at Long Beach for his encouragement when initial problems appeared overwhelming; Dr. Mary Smoke, Associate Professor of Mathematics at California State University at Long Beach, with whose aid these problems were overcome, and Mr. Don Rough, Farm Advisor for San Joaquin County for his encouragement to pursue this study further. Dr. Rodney Steiner, Professor of Geography at California State University at Long Beach, is thanked for his assistance in the mapping of chilling hours. During the research of this study, the author is indebted to the expertise of many agricultural researchers for their time in clarify- ing aspects of their research and/or of plant processes related to this study. Elizabeth Stoebel is thanked for typing and correcting the grammer of the first draft. Dr. Granville Jensen, Professor of Geography at Oregon State University, is thanked for his help in the translation of the many Spanish-written articles important to this study. To my research committee I extend a special word of gratitude: Dr. James F. Lahey, the Chairman, for his time during all stages of this study and particularly during the writing of the final draft. Dr. Leslie Fuchigami advanced many cogent suggestions and worth- while criticisms.I wish to acknowledge and thank the other members of my research committee; Dr. Robert Bard for his incisive questioning and valuable writing suggestions, Dr. Richard M. High- smith Jr. for his guidance during the coarse of my program, and Dr. Jong Lee, the graduate representative, for his time and for reviewing the drafts of this dissertation. Thanks are also due to the Oregon State University Computer Center for a research grant which covered all computer operation costs. Last but certainly not least,I wish to thank my good friend Bradley Roy Sands, Ph. D. candidate in Statistics at Oregon State University, for his advice and help with statistical procedures. TABLE OF CONTENTS Chapter Page I INTRODUCTORY STATEMENT 1 II DECIDUOUS TREES' RESPONSES: CHILLING REQUIREMENT; WHEN CHILLING IS EFFECTIVE; HOW MUCH IS REQUIRED AND THE EFFECTS OF LIMITED AMOUNTS OF CHILLING 5 A.Introduction 5 B.Plant Responses Associated with Rest 10 1. Hormonal Changes 10 2. Anatomical and Physical Response Changes 19 a. The Effects of Photoperiod 19 b. The Role of Bud Scales 27 c. Changes in the Morphology and Physical Responses during the Dormant Period 29 1. Pre -Rest 29 2. Rest 30 3. Post-Rest 37 d. Vegis's Theory 38 e.Summation 40 C. Temperatures Effective in Meeting the Plants Chilling Requirement 41 1. Temperatures Effective for Chilling 41 2. Actual Bud Temperature Versus Air Temperature and When These Tem- peratures are Effective as Chilling 44 D. The Chilling Requirement of Deciduous Fruit and Nut Trees 52 E.Effects of Inadequate Chilling 57 F.Treatments that can have an Effect on a Tree's Chilling Requirement 64 1. Botanical Treatments 64 a. B ree ding 64 b. Other Physiological Treatments 68 1. Rootstock 68 2. Treatments Which Alter the Vegetative Condition 73 2. Chemical and Oil Sprays 74 Chapter Page III. CHILLING ESTIMATION 81 A. Formulation of Empirical Equations for the Estimation of Chilling 81 B. Climatic Factors Influencing the Effective- ness of the Chilling to Which a Plant is Exposed 92 1. Low Temperatures 92 2. High Temperatures 94 3. Light 100 a. Light Intensity 100 b. Photoperiod 100 4. Rainfall 101 C.Factors Affecting Bud Temperature 102 1. Shade 102 2. Fog 105 3. Cloud Cover 107 4. Humidity 107 5. Marine Influence 111 6. Topography 112 7. Wind 112 D. Areal Distribution of the Mean Number of Hours Under 45°F. Throughout California as Determined by Equation I 114 Analysis of the Availability of Chilling Throughout California as Interpreted Through the Maps and Site Evaluation 115 a. Elevation 116 b. Marine Influence 118 c. Inversions 121 1. Marine 121 2.Nocturnal 121 d. Latitude 122 e. Urban Heat Island 122 IV. CONCLUSION AND RECOMMENDATIONS FOR FURTHER RESEARCH 124 SELECTED BIBLIOGRAPHY 129 APPENDIX I 159 APPENDIX II 172 APPENDIX III 176 APPENDIX IV 186 LIST OF TABLES Table Page 1 Apricot cultivar:tRaananat at Mashave Sade, 1969 under various spray treatments. 79 2 The effect of different light conditions on leaf bud opening of the Redhaven peach. 104 3 Distribution of differences in daily maximum temperatures, expressed as a percentage of the total number of observations when comparing the highest and lowest maximums recorded by thermo- couples in apricot flower buds with the maximums recorded by shelter and black bulb thermographs and a thermocouple exposed in air. 188 4 Distribution of differences in daily minimum tem- perature, expressed as a percentage of the total number of observations when comparing the highest and lowest minimums recorded by thermocouples in apricot flower buds with the minimums recorded by shelter and black bulb thermographs and a thermocouple exposed in air. 190 5 Distribution of differences in daily normal mean temperature, expressed as a percentage of the total number of observations when comparing the highest and lowest normal means recorded by thermocouples in apricot flower buds with the normal means recorded by shelter and black bulb thermographs and a thermocouple exposed in air. 192 6 Distribution of differences in daily frequency mean temperature, expressed as a percentage of the total number of observations when comparing the highest and lowest frequency means recorded by thermo- couples in apricot flower buds with the frequency means recorded by shelter and black bulb thermo- graphs and a thermocouple exposed in air. 194 LIST OF FIGURES Figure Page 1 Gibberellin promotes the germination of lettuce seed in the dark. 14 2 A model for the hormonal mechanisms of seed dormancy and germination using gibberellin, cytokinin, and inhibitor. 15 3 Histograms indicating the growth-promoting and growth inhibiting activities in extracts of Betula pubescens seedlings. 21 4 Stem elongation of Betula pubescens seedlings and inhibitory activities from the extracts of the seedlings. 22 5 Flow diagram showing the effect of day length on the production of GA or ABA via the phyto- chrome system. 24 6 Desmayo and Loarre 2 almond flower bud growth curves. 33 7 Diagrammatic representation of the various types of narrowing and widening of the temperature range for germination and bud break at times of change in growth activity. 39 8 Graph of the coefficients for the correlations of bud drop with the hours of shelter and black bulb temperatures under 45 degrees F. accumulated after September 1 to the dates indicated. 47 9 Effect of one hour per day under 45°F.on the date of bloom of an apricot flower bud. 51 10 Effect of inadequate chilling on bloom date. 58 11 Theoretical monthly distribution of hours below 45°F. 84 Figure Page 12 Theoretical linear fit of monthly distribution of hours below 45oF. 84 13 Actual monthly distribution of hours below 45°F. during California winters. 84 14 Initial linear fit of actual monthly data of hours below 45oF. from California 84 15 Iterative linear fit of actual monthly data from California. 84 16 Effect of one growth unit (warm) per day on the date of bloom of an apricot flower bud. 98 17 Generalized representation of absorptivity for water vapor and carbon dioxide, as a function of wavelength. 109 18 Five station winter moving mean normal lapse rates for the San Joaquin Valley. 119 19 Five station winter moving mean normal lapse rates for the Sacramento Valley. 120 20 Increasing wind speed with initial conditions of a wind speed at one mile per hour and air-bud temperature difference equal to 25o.