Impact of Chilling Requirement on Budburst, Floral Development and Hormonal Level in Buds of Early and Late Apple Varieties (Malus sylvestris, Mill) under Natural Conditions

In order to produce the physiological bases for choosing early- flowering varieties that may avoid the depleted low winter temperatures, the early and late- opining apple variety Barkhar, Local and Strakhan (Malus sylvestris) were wont to study the relation between the seasonal changes and these balance of endogenous hormones and flower opining date. An improved understanding of the factors governing budburst and development, and their underlying mechanisms is crucial for management of trees performance and yielding. This study investigated variations in chilling requirements, bud burst and development in early and late varieties of apple trees. The budburst and hormonal profile of flower and vegetative buds of early and late varieties were additionally investigated. Results showed less bud burst in late varieties than in early ones. In the former, there were increased in promoters (indole-3-acetic acid and gibberellins) at budburst. Although endogenous inhibitors levels of abscisic acid were considerably reduced by bud development in all varieties. We conclude that late varieties (Strakhan) are less economical in manufacturing new growth, as indicated by less bud vigor at budburst than early varieties (Barkhar and local) and show a marked differential hormonal pattern throughout bud development compared to early varieties.