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The Influence of Chilling and Heat Accumulation on Bloom Timing, Bloom Length and Crop Yield in Almonds (Prunus Dulcis (Mill.))

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The Influence of Chilling and Heat Accumulation on Bloom Timing, Bloom Length and Crop Yield in Almonds (Prunus Dulcis (Mill.)) THE INFLUENCE OF CHILLING AND HEAT ACCUMULATION ON BLOOM TIMING, BLOOM LENGTH AND CROP YIELD IN ALMONDS (Prunus dulcis (Mill.)) A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment of the Requirement for the Degree of Master of Science in Agriculture, Specialization in Crop Science by Melanie Marie Covert December, 2011 ©2011 Melanie Marie Covert ALL RIGHTS RESERVED ii COMMITTEE MEMBERSHIP TITLE: The Influence of Chilling and Heat Accumulation on Bloom Timing, Bloom Length and Crop Yield in Almonds (Prunus dulcis (Mill.)) AUTHOR: Melanie Marie Covert DATE SUBMITTED: December, 2011 COMMITTEE CHAIR: Dr. Mary E. Pedersen, Associate Dean of the College of Agricultural, Food and Environmental Sciences COMMITTEE MEMBER: Dr. Lauren Garner, Associate Professor, Horticulture and Crop Sciences COMMITTEE MEMBER: Dr. Jeffery Wong, Associate Professor, Horticulture and Crop Sciences iii ABSTRACT The Influence of Chilling and Heat Accumulation on Bloom Timing, Bloom Length and Crop Yield in Almonds (Prunus dulcis (Mill.)) Melanie Marie Covert Almonds are one of the first commercial nut trees to bloom in early spring and thus are susceptible to temperature patterns prior to and during bloom which affect bloom timing, bloom length, pollination and nut set. Data used in this project include yearly dates of 90% bloom from 1996-2006, bloom length in days and final crop yields in pounds per tree for Nonpareil and Mission varieties. Data were collected from the University of California Cooperative Extension reports on the 1993-2006 Regional Almond Variety Trials in Butte, San Joaquin and Kern Counties. Temperature pattern models in the form of Chill Hours (Chill Hour Model), Chill Units (Chill Unit Model), Chill Portions (Chill Portion Model) and Growing Degree Hours (GDH°) (Heat Model) prior to bloom were used to predict the date of 90% bloom for each variety, site and year. Temperature model results were compared to averaged actual dates of 90% bloom by site and variety used to predict bloom timing (Calendar Model). The relationship between bloom length in days and GDH° during bloom and the relationship between bloom length, GDH° during bloom and final crop yields were also evaluated. The average error in predicting the 90% bloom date for both Nonpareil and Mission was smaller using the Calendar Model compared to the four temperature pattern models. The Chill Portion model did not have significantly higher average error in predicting the date of 90% bloom than the Calendar model in Nonpareil. The Chill Unit and Chill Portion models had smaller errors in predicting 90% bloom date than the Chill Hour or GDH° model in Mission. GDH° during bloom was positively correlated with bloom length. GDH° during the first four days of Nonpareil bloom was significantly correlated with crop yields, with each additional GDH° during bloom correlated with a 0.4 lbs./tree increase in crop yield. Further research is needed on specific temperature thresholds and their relationship to physiological changes during almond bloom and pollination. The practice of monitoring chilling and heat accumulation will allow growers to anticipate bloom, prepare to optimize bee activity during bloom, and plan for possible crop yield variations due to adverse weather conditions during bloom in almonds. Keywords: Almonds, Tree Physiology, Flowering, Yield, Growing Degree Days, Chilling Requirement iv ACKNOWLEDGEMENTS I would like to thank the many people who have helped guide me to Cal Poly and through the process of completing this project. Firstly, I would like to express my gratitude to Farm Advisor Joe Connell and Bob Curtis, Senior Manager of Production Research and the Almond Board of California, who were instrumental in inspiring, formulating and funding this project. This project would not have been possible without their gracious generosity and support. I would like to sincerely thank Dr. Mary Pedersen, my Graduate Advisor, who provided many meetings’ worth of much needed advice, confidence and encouragement throughout my time as a Master’s student. I would like to thank Dr. Mark Shelton, who along with Dr. Pedersen, was instrumental in my arrival at Cal Poly and has provided additional counsel to me. I am very grateful to Dr. Steven Rein, for his time and expertise in the statistical design and analysis phases of this project. I would like to express my appreciation for the members of my committee, Dr. Garner and Dr. Wong, for contributing their knowledge of perennial tree crops and plant physiology to this project. A special thank you to my mother Tamara, father Craig, step-father Ray, and my best friend and boyfriend Chris for their unending patience, positivity and love throughout this journey. Thank you to my invaluable friends in San Luis Obispo for their constant support and mentorship. Most importantly I would like to thank God for His strength, stamina and purpose in completing this thesis project. v TABLE OF CONTENTS Page LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ............................................................................................................ x I. INTRODUCTION ........................................................................................................... 1 Objective 1. Evaluate correlations between temperature patterns prior to bloom and bloom timing ................................................................................................................... 3 Objective 2: Evaluate correlations between temperature patterns during bloom and bloom length ................................................................................................................... 4 Objective 3: Evaluate correlations between the length of bloom, temperature patterns during bloom, and corresponding yields ......................................................................... 4 II. REVIEW OF LITERATURE......................................................................................... 5 Almond History .............................................................................................................. 5 Origin and Botanical Classification ............................................................................ 5 California Almond Production .................................................................................... 8 Orchard Planning, Design and Development............................................................ 12 Seasonal Processes .................................................................................................... 14 Almond Growth and Development ............................................................................... 17 Dormancy .................................................................................................................. 19 Temperature and Growth .......................................................................................... 24 Almond Bloom.............................................................................................................. 30 Annual Reproductive Cycle ...................................................................................... 30 Bloom Timing ........................................................................................................... 34 Bee Pollination .......................................................................................................... 41 Yield .............................................................................................................................. 43 Fruit Set and the Effective Pollination Period (EPP) ................................................ 44 Pollen Grain Germination, Pollen Tube Growth and Ovary Fertilization ................ 45 Fruit and Nut Development ...................................................................................... 46 Temperature and Yield ............................................................................................. 48 Conclusion .................................................................................................................... 50 III. MATERIALS AND METHODS ................................................................................ 51 Project Descriptions ...................................................................................................... 51 Regional Almond Variety Trials (1993-2006 RAVT) .............................................. 51 Almond Bloom Project ............................................................................................. 52 Hypotheses .................................................................................................................... 53 vi Objective 1. Evaluate correlations between temperature patterns prior to bloom and bloom timing ................................................................................................................. 53 Objective 2: Evaluate correlations between temperature patterns during bloom and bloom length ................................................................................................................. 53 Objective 3: Evaluate correlations between the length of bloom, temperature patterns during bloom, and corresponding yields ....................................................................... 54 Differences between Nonpareil and Mission ...............................................................
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