RELATIONSHIP BETWEEN FRUIT-DEVELOPMENT AND PHYSIOLOGICAL DROP OF PEACH FRUIT

Fruit development with particular reference to physiological fruit drop, which occurs between late Stage 2 and early Stage 3, was investigated on each of three (No. 1, 2, and 3), orchard-grown, bearing peach trees, 'Shimizu-hakuto' and 'Setouchi-hakuto'. The percentage of fruit drop in tree No. 3 of both cultivars was higher every year than that in the other two trees. The highest fruit drop of 36.3% occurred in tree No. 3 of 'Setouchi-hakuto'; in others it was less than 5%. On the same tree, increase in fruit weight, length, diameter, and width, pit length and diameter, and seed weight were larger during Stage 1 than they were in Stage 2. Among the test trees the percentages of split-pits and aborted-seeds were higher in tree Nd. 3 of 'Setouchi-hakuto' and in all trees of 'Shimizu-hakuto', No clear relationship between fruit drop and the occurrence of split-pits or aborted-seeds was observed. Seed of No. 3 'Setouchi-hakuto' tree aborted early. The percentage of fruits containing two seeds per fruit was not correlated with the % fruit drop. Although more ethylene was evolved by fruits of tree No. 3 of 'Setouchi-hakuto' throughout Stage 2, no clear-cut correlation occurred between the % fruit drop and ethylene production. In 'Setouchi-hakuto', no differences in total carbon in the leaves, flesh tissue, and seed were observed among the three trees, but total nitrogen content in leaves and seeds was lower in tree Nd. 3 than it was in the other two trees. The nitrogen content in,the seed decreased rapidly at the beginning of Stage 2 and continued until harvest. The nitrogen content in the flesh also decreased, but it did not differ among trees. A possible relationship between these observations and the occurrence of lune drop in peaches is discussed.