THE INFLUENCE OF PUTRESCINE ON FRUIT SET AND FRUIT SIZE IN 'HOUSUI' JAPANESE PEAR

To set fruit and improve fruit size and fruit shape, in Japan, hand-pollination is practiced with the main cultivars of Japanese pear. Nevertheless, this practice involves intensive labor and increases the production costs. Nowadays, in Japan, it is becoming necessary to reduce such labour intensive tasks and hence the costs of production of Japanese pear. Thus, the objective of this work was to test if application of putrescine before hand-pollination improves the fruit set and fruit size in the ‘Housui’ cultivar of Japanese pear. In 2003, three putrescine treatments (0 or control, 0.01 and 1.0 mM) were applied on ‘Housui’ flowers to observe the effect on fruit set during 8 days after flower anthesis, and also on final fruit size. Additionally, with the same putrescine treatments, early-, normal- and late-thinning was practiced to measure final fruit size. The results showed that putrescine increased the fruit set only in late-pollinated flowers; that is, 7 and 8 days after anthesis. This increase of fruit set was possible due to a higher pollen germination percentage in the putrescine-treated stigmas, as observed on in vitro pollination tests. Although fruit size was clearly influenced by the period of thinning, it was not influenced by putrescine treatments in either experiment. This work suggests that applications of putrescine might help farmers to hand-pollinate about 2 days more than the normal period, without risk of failing to set fruit.