Effects of High Temperature in the Nighttime and Shading in the Daytime on the Early Drop of Apple Fruit^|^lsquo;Starking Delicious^|^rsquo;

Abstract

The daily rate of fruit growth and elongation of the terminal shoots increased under the high night temperature (HNT). Fruit abscission was induced on the trees under HNT from 27 days, and 34 days after full bloom (AFB). Under shading from 20 days, 27 days and 34 days AFB, the daily rate of fruit growth decreased and fruit abscission was induced. The reducing sugar content per fruit was lower in the fruits under shading, in the fruits with interrupted growth and a yellow peduncle. Ethylene evolution and carbon dioxide production per fruit weight were greater at the early stage of fruit development and increased with the increase of the environmental temperature. AVG application inhibited ethylene evolution and reduced the fruit abscission under a HNT, but hardly under shading. From these results, it appears that fruit abscission under HNT was caused by the consumption of the nutrients associated with the increase of the vegetative growth and respiration rate and by the amount of ethylene evolved under a high temperature in the nighttime, while fruit abscission under shading was considerably affected by the reduction of the supply of metabolites.