Classification of Apple Genetic Resources Using Early Fruit Abscission Pattern

Abstract

Apple trees generally have heavy bloom and fruit set, producing a surplus of fruit that cannot be supported to maturity. Fruit thinning is necessary for improving fruit size and quality, but chemical thinning can be inconsistent in effectiveness and hand thinning is very laborious and expensive. Therefore, self-abscising cultivars in which fruits abscise themselves within a cluster can be useful for time- and labor-saving commercial production. Based on the fruit abscission pattern from full bloom to 30 days after full bloom, 48 apple genetic resources were classified into three groups: 1) a non-abscising group, in which no fruits were abscised; 2) a June drop group, in which the abscission process occurred non-selectively in clusters; and 3) a self-abscising group, in which only the central or the last fruit in a cluster remained to grow, and the others were abscised. Most cultivars in the self-abscising group showed a fruit abscission pattern, in which the central fruit dominated over lateral fruits in a cluster, inducing their growth inhibition and final abscission. Exceptionally, in Malus coronaria'Charlottae', the central fruit did not dominate the lateral fruits, but was abscised first within a cluster. The date of full bloom and fruit weight were significantly related to fruit abscission - fruit abscission was delayed with early dates of full bloom and smaller fruit size.