2018 ASHS Annual Conference

Bud break timing in peach (Prunus persica [L.] Batsch) is determined by the fulfillment of a chilling requirement (CR) and a heat requirement (HR) for development. Genotypic variation in CR has been well-characterized in peach. Potential variation in HR among varieties has received less attention, in part due to the overlap of effective temperatures for CR and HR and dynamic modification of HR by continued chilling accumulation beyond the minimum threshold CR for bud break. HR could vary in the magnitude of growing degree hours (GDH) and/or the base temperature for accumulating GDH. We estimated the GDH and base temperature for floral bud break by forcing replicate stem cuttings at constant temperatures of 12, 14, 16, 18, and 20 °C and analyzing the effect of temperature on the inverse of hours accumulated to reach median bud break (defined by appearance of sepal or petal coloration). We evaluated >40 varieties (representing a range of CR) in which chilling had been saturated after 1800 h at 3 °C. Varieties differed in both GDH requirement and apparent base temperature for GDH accumulation. Phenotyping the separate components of HR without the confounding effect of unsaturated chilling was possible. This will allow standardized HR phenotyping in germplasm as a foundation for breeding delayed bloom and frost exposure avoidance. One variety was evaluated through a range of partial to fully satisfied chilling accumulations. Chilling accumulation reduced GDH while also altering base temperature for GDH accumulation. Improved descriptions of variety specific dynamics of GDH and base temperature response to chilling may allow improved bloom date modeling in peach.