Changes in water relations as related to the growth inhibition of persimmon fruit by calyx lope removal.

The role of calyx lobes in water relations of persimmon (Diospyros kaki L.) fruit and its involvement in fruit development were investigated on 'Sakushu-mishirazu' fruit by manually removing their calyx lobes at growth stage I, II, or III. Calyx lobe removal at growth stage I or II inhibited fruit development significantly, whereas treatment in the stage III had no effect on the fruit growth. At harvest, the water potential, of a whole fruit treated at stages I and II were -0.88 and -1.02 MPa, respectively, whereas that of the control was -1.35 MPa. However, the water potential of fruit whose calyx lobes were removed at stage III was not significantly different from that of control fruit. Similar result was obtained in osmotic potential, when the juice of frozen-thawed flesh was measured by osmometer. Osmotic potential of the treated and control fruits decreased with fruit development, but the rate of decrease was slower for the fruit whose calyx lobes were removed at stages I and II. The osmotic potentials of fruit treated at stages I and II were 1.20 and -1.57 MPa, whereas that of control was -1.74 MPa. Close relationship between growth inhibition and changes in water relations by calyx lobe removal was confirmed on Hiratanenashi' fruit whose calyx lobes were removed at the end of stage I. The water potential of the treated fruit at harvest measured at mid - day with a thermocouple psychrometer using a flesh disc was -2.24 MPa, whereas it was -2.45 MPa for the control. The seasonal trend of the water potential paralleled that of the growth inhibition Osmotic potential of treated 'Sakushu-mishirazu' fruits followed the same trend as water potential for the rest of the growing season. Thus, we attribute the inhibition of fruit growth by calyx removal that is related to the changes in water relations in the fruit.