RESPONSES OF WATER STATUS AND FRUIT QUALITY OF JAPANESE PERSIMMON (DIOSPYROS KAKI) TO DROUGHT STRESS

To elucidate the relationship between leaf and fruit water status and the resulting fruit characteristics and level of drought stress, we investigated the responses of water status and fruit quality of container-grown Japanese persimmon (Diospyros kaki Thunb. ‘Nishiura’) to drought stress during three fruit growth stages. The pre-dawn water potential, osmotic potential, and turgor of mature leaves and fruit flesh (mesocarp) were determined using an isopiestic psychrometer. Regardless of the fruit growth stage, the leaf water potential of drought-stressed trees began to decrease from an unstressed value of approximately -0.4 to -0.3 MPa after drip irrigation was withdrawn. During fruit growth stage I (early rapid growth), the flesh water potential and turgor pressure of drought-stressed trees decreased rapidly after withholding irrigation. The firmness of fruit growing on drought-stressed trees was significantly lower than that of fruit from control trees (irrigated), and severe early fruit drop occurred. Even though the flesh water potential was similar in both treatments during fruit growth stage II (slow growth), the flesh osmotic potential was less negative in the stressed trees, so the flesh turgor in the stressed trees decreased below that in the control. On the other hand, drought stress during stage III (mature rapid growth) had little influence on the fruit water status. These results indicated that the responses of fruit water status to short-term drought stress in Japanese persimmon depended on the fruit growth stage.