Two types of unfruitfulness found in artificial pollination experiments of apple.

摘要

Reciprocal crosses between Kizashi and Golden Delicious resulted in very low rates of fruit set. Microscopic examinations revealed that pollen of both cultivars germinated normally on the stigma, but the pollen tubes ceased growth in the upper partof the style; a number of pollen tubes formed swollen tips, indicating that the sterility was controlled by gametophytic incompatibility mechanisms. Fruit set in crosses involving HCR6T132 was high when it was used as a pollen parent, but was absent whenit was used as a seed parent. This lack of fruit setting when HCR6T132 was used as a seed parent could not be ascribed to incompatibility, because there was no difference in pollen tube behaviour compared with the cross compatible combinations. It was found that the fruit set was reduced when HCR6T132 flowers were emasculated (petals and anthers removed) just before pollination; the injured flowers produced much more ethylene than intact ones. When intact flowers were used, the strain retained its fruit setting ability; this was also the case when emasculated flowers were treated with aminoethoxyvinyl glycine, an ethylene synthesis inhibitor. The results indicated that HCR6T132 is probably very sensitive to ethylene and/or produces much wound ethylene, and that the absence of fruit setting is ascribed to ethylene induced by emasculation.