465 Dormancy Completion—A Dual Response

Most of the works evaluating dormancy completion relies on measuring the level of budbreaking or the time needed for buds to break in forcing conditions. In all cases, the evaluation of budbreak is limited to the initial stages of bud opening in both vegetative and floral buds. Very rarely the response of the new growth is determined. It is accepted that dormancy completion of the bud is of a qualitative nature of yes or no. This reasoning led to using excised branches that can not support normally a growing bud but may support the evaluation of the emerging buds. In practice, the effect of breaking bud dormancy is far reaching and has an impact on the development after budbreaking. Growth vigor is a characteristic tied to the rate of dormancy completion in a quantitative manner. After exposure to sufficient chilling growth is rapid and vigorous. When buds are exposed to warm winters, growth is sluggish and poor. Under certain conditions, budbreak may be high, but all vegetative buds will form rosettes. Likewise with floral buds, they may break satisfactorily but will not set normal fruit especially in stone fruit species. In a recent study of bud dormancy inheritance in apricots, budbreak showed a clear dominance of the low chilling characteristic; level of vegetative vigor showed a similar effect to the high and low chilling parents. Thus, two characteristics of dormancy completion should be considered. The first is the level of budbreak and the other is the vigor of the growing vegetative buds and the functionality of the flower buds, as both are affected by the conditions that induce dormancy completion.