Heat Requirement from Blooming to Maturing in Apricot Cultivars

Abstract

Heat requirement from blooming to maturing in 15 apricot cultivars grown in the Belgrade region was determined by the Growing Degree Days method (GDD), using 8-year-phenological data. Two methods for calculating daily mean air temperatures were evaluated: (1) the mean of the maximum and minimum daily temperature (Max/Min), and (2) the mean of three equally spaced hourly observations weighted with the last observation (Weighted). The least coefficient of variation in GDD method was applied to obtain the best lower and upper threshold temperatures. The obtained the best lower threshold temperature varied from 0 degrees C in cultivar 'Kishiniev Early' to 7 degrees C in cultivar 'Roxana'. Calculations of daily mean air temperatures by Weighted method resulted in a smaller coefficient of variation than Max/Min method. Introduction of the upper threshold led to an increase of the coefficient of variation in GDD. The number of days from full blossoming to maturing ranged from 82 to 112. Taking 3 degrees C as the base temperature (the mean value of all cultivars studied), the accumulated GDD between these two phenological stages varied from 1056 (in 'Senetate') to 1648 (in 'Kecskemet Rose').