Water Potentials and Water Fluxes into Fruit at the Initial Time of Development of Hard End Disorder in ‘Bartlett’ Pear

Abstract

In order to clarify the water relationships of the occurrence of hard end disorder in ‘Bartlett’ pear, the water potentials of leaves, fruits and stems and water influx into the fruit at the initial time of development of the disorder were investigated.
1. The stem water potentials were almost constant during the fruit growing season. The leaf water potentials fell after the end of July, but it showed large fluctuations before mid-July. The fruit water potentials fell gradually after the end of July, but it seldom fell greatly at the initial time of development of the disorder. In addition, there was no difference in water potentials between the normal trees and the tree affected by hard end.
2. The ratios of the water influx into the fruit per day to the fruit weight or the daily increase of fruit weight were evidently low at the initial time of development of the disorder (from mid-June to the beginning of July). However, there was no difference in the ratios between the normal trees and the affected tree, and the stronger the leaf water stress, the greater the drop in the ratios.
3. From these results, it seemed that the low ratios of the water influx into the fruit to the daily increase of fruit weight during the period from mid-June to the beginning of July tend to result in Ca deficiency of the fruit and the hard end disorder develop at this period in some trees grown in poor conditions which permit only insufficient Ca absorption.