The Influence of Chilling and Heat Accumulation on Bud Break and Flowering in Kiwifruit (Actinidia deliciosa cv. Hayward)

Climate change has affected the rates of chilling and heat accumulation, which are vital for flowering and production in temperate fruit trees. In this study, the chilling requirement of kiwifruit was analyzed by using the dynamic (CP) and chilling hours (CH) model, and the heat requirement was analyzed by using the growing degree Hours (GDH) model. The results shown that high temperatures at bud swell or woolly bud phase led to the acceleration of the different stages of bud phenology. Also, reduction of chilling requirement delays the events of bud phenology. In addition, a linear and significant relation was observed between chilling requirement and heat accumulation. So, the flowering time of kiwifruit cultivar “Hayward” was significantly affected by the timing and interaction of received chilling and heat accumulation. In the cuttings that received 954 and 1194 chilling hours, the heat requirement for breaking vegetative buds was 10543 GDH and 8251 GDH respectively. With cold-continuing, the heat requirement for breaking buds decreased, and flowering was done in shorter periods. The obtained results showed that the amount of chill recieved is effective in the percentage of bud break, and the number of flower buds formed. Also, the chilling requirements for maximum bud breaking were about 725 CH, and the chilling requirements for maximum flowering were above 954 CH in Hayward cultivar.