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.
Brian P. Pellerin, Deborah Buszard, Alex Georgallas and Richard J. Nowakowski
Brian P. Pellerin, Deborah Buszard, David Iron, Charles G. Embree, Richard P. Marini, Douglas S. Nichols, Gerald H. Neilsen and Denise Neilsen
Tree fruit growers use chemical and mechanical thinning techniques in an attempt to maintain regular annual flower production and maximum repeatable yields of varieties susceptible to biennial bearing. If the percentage of floral buds an apple tree could produce without causing yield depression in subsequent years was known, it would be possible to better manage crop-thinning regimes. This study proposes that thinning is a partial transfer of potential flower buds from one year to the next year and estimates the maximum repeatable sequence of flower buds without biennial bearing. The conceptual framework is tested on a 50-year simulation with 0% to 100% transfer of thinned flower buds. Results indicate that the maximum repeatable sequence of flower buds rises sharply when the final years of the orchard approach and declines when the percent transfer of thinned buds is near 0%.