Peach trees require quantitative exposure to winter chilling (chilling requirement, CR) for spring bloom. The chill accumulation time points are determined using weather data of air temperatures between 32 and 45 ºF, using various calculation methods such as the simple chill hour (CH) method or more sophisticated methods like Utah and Chill portions (CP) that account for negations of chilling due to warm weather during the dormancy. All these methods rely on air temperature and do not consider the soil temperature during the dormancy and its effect on the tree’s perception and account for chill accumulation. Peach flowers and developing fruit are highly sensitive to freezing temperatures and are killed following even a limited exposure. In the past decade, mild winters and early spring frosts have significantly reduced or eliminated the annual peach production in the southeast U.S. Low-chill winters have become increasingly common in the southeastern peach-producing regions, and when followed by warm springs, result in early bud break and early flowering, increasing the risk of crop loss to frost. Due to a replant issue caused by Armillaria root rot, almost all acreage under the new peach orchards in the southeast, including South Carolina, are planted on berms adopting root collar excavation as a method to extend the life of orchards on infested soil. We observed significant differences between the air temperature and temperature of undisrupted soil and soil within berms at various depths (3, 6, 12 and 18 in) during dormancy. The effect of observed temperature differences on ‘Cresthaven’ tree chill accumulation calculation and transition between endo- and eco-dormancy stages was investigated by collecting vegetative bud and root tissue from all four depths at six chill hour time points (400, 500, 600, 700, 800 and 900). Preliminary data show significant gene expression differences between bud and root tissue and different gene expression profiles related to the chill accumulation in each tissue. Detailed analyses of the gene expression profiles between the tissues at the different chill accumulation stages and their effect on chilling and heat accumulation, bloom time, and the transition between the dormancy stages in peaches will be discussed.
