The 2011 ASHS Annual Conference

Chilling requirement is the primary determinant of a peach cultivar’s zone of adaptation. The chilling requirement is defined as the number of hours below 7 °C needed by flower and vegetative buds to overcome endodormancy. A peach cultivar’s chilling requirement determines its bloom date and cropping potential. Within a location, cultivars with lower chilling requirements bloom early and their crops can be at risk from late spring frosts.  In contrast, cultivars with high chilling requirements may not receive sufficient chill hours for normal flowering, fruiting, and resumption of vegetative growth.  Most commercial peach cultivars have chilling requirements in the 650-850 chill hour range and are not adapted to Florida. Development of commercial quality low chill (100-450 chill hour) cultivars adapted to the chilling ranges typical of Florida, required the hybridization of primitive low chill peach germplasm with high chill commercial quality cultivars.  The limited genetic diversity available within commercial low chill germplasm requires the continued use of high chill germplasm as a source of novel traits. The use of high chill germplasm in crosses typically leads to a series of developmental abnormalities in the seedling progeny that have to be corrected.