MANIPULATION OF PERSIMMON FRUIT RIPENING BY THE COMBINED APPLICATION OF GIBBERLLIN (GA₃) AND PACLOBUTRAZOL (PBZ).

The normal commercial harvesting period of the 'Triumph' persimmon is two weeks in November. Previous studies have shown that this term can be extended by at least another two weeks, following the application of GA₃ eithin the month preceding harvest. There is an additional advantage to this treatment, in that it also extends the storage and shelf-life of the fruit. Its disadvantage lies in the fact that the extended harvest season endangers the fruit remaining in the orchard by exposing it to the hazards of hailstorms and heavy rainfall, which lay the foundations for the subsequent development of excessive decay. A greater advantage is therefore to be expected in extending the harvest season by inducing precocious ripening. The objective of this study was to achieve an earlier harvest, with the aid of PBZ, and to enable an extended storage season by following it with a preharvest GA₃ treatment. PBZ application in May induced precocious ripening of 'Triumph' persimmons by 2 to 4 weeks, in different locations. The first visible evidence was an early change in the ground color of the fruit from green to orange. The growth rate of the fruit was enhanced, so that there was non loss in yield due to reduced fruit size. Much of the fruit was more highly colored and the softening rate of this fruit was accelerated and its storage and shelf-life curtailed. The accelerated ripening rate was effectively arrested by a preharvest GA₃ spray, at the same dose that is required for delaying the ripening of fruit on untreated trees. The enhanced and retarded rates of fruit softening were significantly correlated to CMCase activity in vacuum - 2M NaCl extracts from whole fruit slices. The possibility that CMCase synthesis or activation is regulated by GA₃ is under examination. In conclusion, ripening of persimmon fruits can be manipulated by the interplay of the two antogonistic plant growth regulators. The implication is that the harvesting and marketing season of 'Triumph' persimmons can be extended at both ends by applying PBZ to the roots in the spring and GA₃ to the canopy in the autumn.