Relation between Early Drop of Apple Fruit, Ethylene Evolution and Formation of Abscission Layer

Abstract

Early fruit drop in ‘McIntosh Red’ apples was enhanced by 30 days of high night temperature (25°C) beginning on the 10th day after full bloom. A reduced rate of fruit enlargement for two days indicated the imminence of fruit drop; abscission occured 6 to 10 days later. The fruit drop process was divided into four stages stage A, potential fruit drop as indicated by the reduced rate of fruit enlargement; stage B, two days after potential fruit drop; stage C, four days after potential fruit drop; stage D, abscission. There was no difference in ethylene evolution between fruits of stage A and persistent fruits. However, the stage of fruit drop advanced from B to C, ethylene evolution increased. Few fruit at stage A had formed an abscission layer but those which had, evolved more ethylene than those which had not. These results suggest that ethylene evolution and abscission layer formation are not the primary factors causing the early drop of apple fruit but are part of the ageing process which occurs with the advance of the fruit drop process.