A novel framework to consider endogenous hormonal control of apple tree flowering

Abstract

Inhibition of flower initiation by nearby developing fruits is one of the main causes of biennial bearing in apple trees. This localized inhibition may depend on a critical ratio of inhibitor and promoter hormones that inhibits flowering of apical meristems. A model is proposed to explain this phenomenon. In the model, it is assumed that seeds and leaves act as point sources and export inhibiting and promoting hormones to apical meristems. The model assumes critical ratios of promoting and inhibiting hormones determine whether an apical meristem flowers or not and this may be a cause of biennial bearing. Thus, the spatial arrangement of shoot apical meristems on a limb is perhaps critical in determining whether meristems initiate flower clusters. This article presents a novel framework to view the hormone hypotheses of biennial bearing in apple trees and how management strategies such as flower removal could be used to achieve regular numbers of flower clusters over consecutive years.