Chilling Hour Requirement for Flower Bud Expansion of Two Rabbiteye and One Highbush Blueberry Shoots

Abstract Three hundred shoots with flower buds were collected from three blueberry types to determine the influence of chilling hours on flower bud expansion. The three types were rabbiteye blueberry ( Vaccinium ashei Reade ) ‘Brightwell’ and clone T-110, and low-chill highbush blueberry ( V. corymbosum L. ) ‘Georgiagem’. Chilling hours in this study ranged from 0 to 700 and were defined as accumulated hours of temperatures < 7.2°C. Flower bud expansion of all three blueberry types was influenced significantly by levels of accumulated chilling. The mathematical relationships between bud width and chilling hours were either linear or quadratic. Largest bud expansion occurred after 400 chilling hours for ‘Brightwell’ and ‘Georgiagem’ and after 550 hr for T-110. Overall, ‘Brightwell’ had the smallest bud width, ‘Georgiagem’ was intermediate, and T-110 the largest.