FRUIT SET AND THE EFFECTIVE POLLINATION PERIOD IN APPLE AND PEAR AS AFFECTED BY BLOOM AND POST-BLOOM TEMPERATURE.

Under controlled temperature conditions fruit set and the effective pollination period (EPP) of pear cv. Doyenné du Comice and apple cv. Golden Delicious were studied at 4 temperature regimes, i.e. 13°(bloom)-13°C (post-bloom), 13–17, 17–17, and 17–13. The post-bloom temperature was applied from 1 day after the end of bloom. Fruit set was determined 3 and 6 weeks after bloom. Fruit set at 3 weeks was very high in pear and apple. There were hardly any differences between the various temperature regimes. A severe fruit drop occurred between 3 and 6 weeks after bloom when post-bloom temperature was high. The effect of bloom temperature on fruit set was very small. The data for pear indicate that the EPP is extended somewhat at the high bloom temperature. In apple the EPP was about the same in all treatments. The data suggest that final fruit set in Doyenné du Comice as well as in Golden Delicious is mainly determined by the post-bloom temperature. Bloom temperature is not relevant as long as pollination and the EPP do not limit fruit set.