Effects of Pruning Levels on Physiological Fruit Drop and Fruit Development in 'Shimizuhakuto' Peach

Using 'Shimizuhakuto' peach trees maintained by light (LP) and heavy (HP) prunings, fruit development and shoot growth were investigated in relation ro physiological fruit drop. The rate of split-pit fruits was significantly lower in LP trees than in HP trees, and the rate of dropped fruit in the former was also lower than in the latter although there was no significant. In LP trees shoot growth ceased by the end of May, while in HP trees the shoots continued to elongate until the end of June, corresponding to the end of stage 2 of fruit development. There was no significant difference in enlargement of normal and pit-split fruits between HP and LP trees. However, the enlargement of dropped fruits was more vigorous than those of pit-split fruit in HP and was by contrast inferior in LP trees. The growth of embryo in the fruits of HP trees was smaller than in those of LP trees from the beginning of stage 2, and the size of embryos of pit-split fruit were less than 50% in size compared to normal fruits in HP trees during stage 3. On the other hand, embryo of pit-split fruits in LP trees showed a similar growth to normal fruits until the end of stage 2. There was no difference in the size of endosperm and embryo of dropped fruit between HP and LP trees. Based on these results, ther possible causes whereby light pruning might decrease physiological fruit drop in peach are discussed.