Genetic Control of Dormancy and Chill Requirement In Peach

Perennial fruiting trees require sustained exposure to low, near freezing, temperatures before vigorous floral and vegetative bud break is possible after the resumption of warm temperatures in the spring. The depth of dormancy, duration of chilling required (the chilling requirement, CR) blooming date (BD) and heat requirement to break buds (HR) are determined by the climatic adaptation of the particular cultivar, thus limiting its geographic distribution. This limitation is particularly evident when attempting to introduce superior cultivars to regions with very warm winter temperatures. The physiological mechanisms for these important life history characters are partially understood however, the genetic pathways central to physiology remain poorly characterized and although breeding programs deliberately manipulate these characters, robust closely associated markers to the traits have not been available in the past.

      In this regard, we have developed a comprehensive mapping program directed at characterization of QTL controlling these characters. We used segregating populations of apricot (100 F₁ individuals, Newe Ya'ar Research Center, ARO) and peach (378 F₂ individuals, Clemson University) to discover discreet genomic loci that regulate CR, BD and HR.  We used the extensive genomic/genetic resources available for Prunus including the whole genome sequences of peach to successfully combine our apricot and peach genetic data to identify candidate genes for control of these phenological traits. In this regard, we have developed a model for dormancy control based on changes in the methylation status of the genome, and currently we are testing this hypothesis through whole genome and individual gene methylation  studies throughout the dormancy period. 

      Here, we present the results of these efforts and discuss the implications of these results to our fundamental understanding of the genetics of these traits and the application of this knowledge for manipulation of these characters in marker assisted breeding programs.