カキ‘富有’果実の肥大生長と果柄部維管束の発達について

Abstract

This experiment was conducted to reappraise more thoroughly the development of Japanese persimmon fruit, Diospyros kaki cv. Fuyu, by measuring the growth rate and the relative growth rate (RGR) of fruit diameter and weight, in relation to the vascular development of the fruit stalk.Cumulative diameter and weight increases have a double sigmoid pattern corresponding with changes in growth rate. Fruit development was classified into three distinct stages. Stage I was completed by early August, 10 weeks after anthesis. The increase to a peak in the growth rate of fruit diameter preceded by several weeks the peak in the growth rate of fresh fruit weight. Furthermore, the maximum rate of fresh weight growth occurred one week earlier than the maximum rate of dry weight growth. The whole fruit declined in dry matter percentage during the middle of this period when fruit diameter increased rapidly. The low percentage of dry matter in the fruit lasted during the period of July, when the growth rate of fresh weigh typically increased. On the other hand, the fruit increased in dry matter percentage during the two weeks in the early period of stage I, accompanying tannin cell development.During stage II, in which the overall growth rate slowed down markedly, the fruit increased in dry matter percentage. Both seed weight and the dry matter percentage of seed increased markedly during this stage.During stage III, a period of vapid growth, fruit continued to grow and to increase in dry matter percentage for as long as it was left on the tree. Initially in stage III, a rapid increase of fruit diameter commenced almost simultaneously with the weight increase.The rate of fruit diameter increase was higher in stage I than in stage III, but the rate of fresh weight growth was nearly the same in stage I and III. Contrarily, the dry weight increase in stage III was markedly higher than in stage I.There appeared to be little difference in the fruit growth curves among fruits which had different numbers of seeds, although there was a significant positive correlation between seed and fruit weight until July, during the early stage of fruit development.The maximum peak of the RGR of fruit diameter and fruit weight appeared several days after full bloom, and a small RGR peak appeared again during the ripening stage.The growth of the stalk diameter increased markedly during stage I of the fruit development, and lasted until mid-August. The differentiation of vascular tissue (transverse section)in the fruit stalk had already begun one month before blooming. However, this development was only slight: xylem vessel diameter averaged about 9μm and phloem differentiation had progressed enough to display a large nucleus. Thereafter, vascular tissue (xylem vessels, sieve tubes and companion cells) was developed strikingly until blooming, and continued to grow markedly until approximately 4 weeks after blooming. Although the growth of vascular tissue appeared to slow down gradually during the decelerated period of fruit growth, it increased again duting the ripening stage. The development of the vascular bundle in the stalk region corresponded to the fruit growth.