Flower types, pollen morphology and germination, fertilization, and berry set in Vitis coignetiae Pulliat

Commercial vineyards of Vitis coignetiae Pulliat, a wild dioecious grape species, have been planted to produce berries for wine making. Studies were conducted in an attempt to identify the factors causing irregular bearing in this grape vine. Flower types, morphology and germinability of pollen, ovule fertilization process and correlation between pollinizer distance and berry set were analyzed. Both sexual morphs presented distinct flower and pollen morphology. Only pollen from male plants germinated on agar medium. Each pollen grain had three furrows and germ pores on its surface. Pollen from female plants were nonfunctional and lacked furrows and germ pores. At full bloom pistils from female plants contained perfect ovules but showed only a small number of pollen tubes growing down their style after hand pollination. Examination of abscised pistils during the week following anthesis revealed ovules were poorly fertilized, indicating that deficiency in fertilization must be a factor contributing to lower yield. No correlation was found between pollinizers distance and berry set.