Abstract
Among a group of tetraploid grape varieties which are genetically related to ‘Kyoho’ (Vitis vinifera L.×V. labrusca L.), ‘Kyoho’ and ‘Pione’ set a large number of seedless berries which hardly grew to the normal size of their seeded berries. Other varieties, such as ‘Beni Zuiho’, ‘Beni Izu’, ‘Red Qeen’ and ‘Honey Red’, usually set more seeded and fewer seedless berries. To study the cause of the production of seedless berries in these varieties, we investigated the completeness of floral organs and the penetration of pollen tubes into ovules.
Abnormal ovules and immature embryo sacs were observed more frequently in ‘Kyoho’ and ‘Pione’ than in the other varieties. Pollen grains lacking the generative and vegetative nucleus were also more frequent in ‘Kyoho’ and ‘Pione’, although pollen germinability on agar media was not related to the frequency of such nonfunctional pollen. The number of pollen tubes growing into intact pistils was markedly reduced at the middle and lower part of ovary tissue in all varieties. In ‘Kyoho’ and ‘Pione’, this reduction was more severe and fewer pollen tubes penetrated the ovules than in other varieties.
From these results, we concluded that the poor setting of seeded berries in ‘Kyoho’ and ‘Pione’ is due to the retarded development of ovules and the low ability of pollen tubes to fertilize ovules. It became apparent that in ‘Kyoho’ and ‘Pione’, many unfertilized ovaries develop into seedless berries, although the mechanisms are not clear.
