2 TYPES OF UNFRUITFULNESS FOUND IN ARTIFICIAL POLLINATION EXPERIMENTSOF APPLE

Two types of unfruitfulness were found in our apple breeding programs; one was in the reciprocal cross between 'Kizashi' and 'Golden Delicio us' and the other in the crosses of HCR6T132, a strain bred in Purdue university, U. S. A., with pollen of other cultivars. The reciprocal c ross between 'Kizashi' and 'Golden Delicious' resulted in very low rat es of fruit set. Microscopic examinations revealed that pollen of both cultivars germinated normally on the stigma, but their tubes ceased g rowth in the upper part of the style; a number of pollen tubes formed swollen tips, indicating that the sterility was controlled by gametoph ytic incompatibility mechanisms. HCR6T132 yielded a high rate of fruit set when it was used as a pollen parent, whereas it failed as a seed parent. The unfruitfulness of the strain as a seed parent could not be ascribed to the incompatibility, because there was no difference in p ollen tube behavior, compared with the cross compatible combinations. It was found that the fruit set was reduced when HCR6T132 flowers were emasculated (petals and anthers were removed) just before pollination ; the injured flowers evolved much more ethylene than the intact ones. On intact flowers, the strains retains its fruitfulness, as did the t reatment with AVG (aminoethoxyvinyl glycine), an ethylene synthesis in hibitor, to the emasculated flowers. These results revealed that the s train is probably very sensitive to ethylene and/or produces much woun d ethylene, and that the unfruitfulness is ascribed to ethylene induce d by emasculation.