Effect of shoot vigor on the development of transmitting tissue and pollen tube growth in pistils of tetraploid grape, cv. Pione

Effects of shoot vigor on the development of transmitting tissue (TT) and pollen tube growth in pistils of Pione grapevines (a hybrid of Vitis vinifera L. and V. labrusca L., tetraploid) were investigated anatomically. Shoot vigor was reduced by root zone restriction and pre-bloom shoot tipping, and was increased by severe winter pruning and application of high concentration fertilizer. The TT development in long and short shoots of the vines without root restriction was also compared. In cross sections of the upper and middle ovaries, a thicker TT and more pollen tubes were found in root zone-restricted vines compared to unrestricted vines. Also, thicker TT and more pollen tubes were observed in less vigorous, short shoots of unrestricted vines. Tipping did not improve the TT development. However, spur pruning and application of high concentration fertilizer to root zone-restricted vines did not inhibit the TT development and pollen tube growth, though shoots grew vigorously. From these results, we conclude that promoted TT development in less vigorous shoots of Pione grapevines allows for more pollen tubes to penetrate into the ovary, resulting in the production of acceptable clusters with a sufficient number of seeded berries.