Daily Dynamics of Sugar and Phenol Contents in Apple Fruitlets during June Drop

Abstract

The occurrence of the abscission signal in young developing fruits on apple trees (Malus domestica) was studied. Apple has a natural system of fruitlet shedding, so called June drop. Although physiological fruit drop is unable to guarantee production of marketable apples and avoid alternate bearing, knowledge of this is a key background for successful fruit thinning. A study was carried out on apple trees cv. ‘Golden Delicious’ during June drop. On three dates (beginning, middle and after June drop), the daily dynamics of HPLC detected individual sugar and spectrophotometrically detected total phenolic contents were investigated in central (K) and lateral (L) fruitlets. The results of daily dynamics showed the highest sugar contents at 2 p.m. On the final sampling date, on 2nd July 2015, we observed a significant difference between sugar contents at 2 p.m. and the morning and afternoon measurements. Contents of sugars in K and L fruitlets were not significantly different. Total phenolic content at the beginning of June drop was higher than at the end. There was no statistically significant difference between K and L in an individual time period, while there were statistically significant differences in total phenolic content among the sampling dates. Although sugar and phenolic contents in K and L fruitlets were rarely statistically different, their contents changed during June drop. In general, sugar contents increased and phenolic contents decreased during the process, while the daily dynamic depended on weather conditions.