Effect of Seed Number on Preharvest Drop and Fruit Mass of Three Apple Cultivars

Abstract

The factors controlling preharvest drop are poorly understood. The number of viable seeds in apple fruit has been associated with fruits retained following June drop. Three experiments were conducted to determine the effect of seed number on time of preharvest drop. In two experiments treatments were imposed to induce variability in seed numbers. Trees of `Redchief Delicious' were covered with 92% shade fabric for 0, 1, 2, or 3 days when fruits averaged 13 mm in diameter. In a second experiment `Redchief Delicious', `Smoothee', and `Commander York' flowers had 0, 1, 2, 3, 4, or all 5 stigmas excised at early “popcorn” stage and the remaining stigmas were hand-pollinated. The third experiment investigated drop of the same three cultivars as affected by the natural variability in seed number. Fruits were gathered from under the trees daily from 26 Aug. until all the fruits had fallen from the trees. Fruits were weighed and the number of filled, large aborted and small aborted seeds were counted. Neither total number of seeds, number of filled seeds, total number of aborted seeds, number of large aborted seeds nor number of small aborted seeds explained any appreciable amount of the variation in date of drop (R2 < 0.13). Fruit mass was positively related to seed number for `Delicious', but not for `Smoothee' or `York'.