Impact of chilling requirements on metabolic changes in nitrogenous compounds in buds during and after dormancy releasing in early and late (Malus sylvestris, Mill) apple varieties

In order to produce the physiological bases for choosing early-flowering varieties that may avoid the insufficient winter chilling requirements in Egypt. The early and lateopining apple variety Barkhar, Local and Strakhan (Malus sylvestris) were used to study the relation between seasonal changes in nitrogenous compounds and flower opining date according to chilling requirements for each variety. 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. Results showed less bud burst in late varieties than in early ones. In the former, there were increased in nitrogenous compounds (soluble nitrogen, total nitrogen, arginine and total free amino acids) at budburst in all varieties. As dormancy begins, storage proteins are synthesized, coinciding with a reduction in the levels of nitrogen and free amino acids. Consequently, as dormancy breaks, these storage proteins are degraded, and an increase in the concentrations of nitrogen and amino acids occurs, in order to support new growth. 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 nitrogenous compound pattern throughout bud development compared to early varieties.