LAUSR

Because of the winter in Egypt is short and does not meet the chilling requirements of buds, the delay in opening the buds of lateopining apple trees until late winter exposes them to damage under the influence of high temperature and/or delays them in entering in dormancy in the following year leads to some physiological defects that may result in weakness and death. This threatens the lateopining apple productivity in Egypt.1,2 Apple trees that do not receive adequate winter chill show poor bud break, uneven and delayed bloom that impact negatively on tree architecture and fruit production. Previous research indicates that the endodormancy progression of such trees differs from trees grown under adequate winter chill condition.3 The majority of trees in temperate climates fulfill a chilling requirement (CR) in so as to overcome endodormancy.4 Therefore, the CR could dissent by species, varieties, or growing regions.5–8 Cultivars with low CR bloom and ripen earlier, whereas those with high CR bloom and ripen later.9–13 For temperate-zone fruit species such as apricot, when winter cold requirements are not adequately satisfied, negative repercussions on productivity occur.14 CR constrains the acceptable areas of cultivation of the various commercially important tree species and cultivars around the world. If chilling requirement don’t appear to be met, irregular, delayed and asynchronous growth, flowering and fruit set are discovered inside the subsequent season.15–17