Breaking Bud Rest on Detached Apple Shoots: Effects of Wounding and Ethylene1

Abstract Buds of ‘Golden Delicious’ apple ( Malus domestica Borkh.) were in deep rest between October 25 and December 20, 1976, although the uppermost bud on decapitated (apical and basal cuts) shoot segments developed at all sampling dates. Increases in rate of development of the uppermost bud, as well as in % break of lower buds after completion of deep rest, were both linear with time. Increases in % budbreak with time occurred in a basipetal direction, suggesting a gradient of increasingly deep rest from shoot apex to base. Development of the uppermost bud on decapitated shoots during deep rest was a result of the apical cut, and was not influenced by the original position of that bud on the intact shoot. The bud above the basal cut developed only on shoots with the terminal bud intact (basal cut only). Notching above a second bud on decapitated shoots did cause that bud to develop in addition to the uppermost bud. Results are discussed on the basis of a 2 stage rest model, rest gradient and apical dominance. There was no evidence for a role of ethylene in wounding or dinitro-orthocresol-stimulated budbreak. In addition, neither ethylene-releasing chemicals nor silver or cobalt had any influence on budbreak when applied to shoots at 2 dates during the rest period.