Growth rate of apple fruits as a method of predicting their abscission

Abstract

A study on the fruit growth rate of apple cultivars Golden Delicious and Granny Smith as observed from day 5 to day 25 after petal fall revealed that a decrease in growth rate and fruit growth break can be used as a relatively reliable method for the early evaluation of natural fruit drop.

Fruit growth to a diameter of about 5 mm was slow (about 1 mm/day), and subsequently, from a diameter of 5 to 15 mm, the growth was more rapid and almost linear (mean value being 5.5 mm/day).

The fruits experiencing growth break during the first shed period reached a size of 4.5-5.5 mm, and those whose growth broke during the second shed period (June drop) were 8-12 mm in size. At least 4 days elapsed between the moment of growth break and fruit dropping.

A decrease in fruit growth rate can serve as a fairly reliable indicator of approaching fruit drop at a stage when the fruits have reached a size of 5 mm. In fruits that are about to drop, the growth break occurs 2-4 days after the growth rate decrease down to 50% of the growth rate
of surviving fruits.