Improvement of Crossbreeding Seed Number and Germination Rate in Tetraploid Grapes through Utilization of Flower Clusters on Lateral Shoots

Abstract

Crossbreeding of tetraploid grapes including ‘Pione’ and ‘Aurora Black’ using primary flowers is inefficient due to the poor fruit set, low seed germination rate, and short period for effective pollination. In this study, we investigated the usefulness of lateral flower clusters (secondary flowers arising from lateral shoots) compared with primary flower clusters. In spur-pruned cultivation, the flowering season of lateral flower clusters lasts for approximately one month after the full bloom of primary flower clusters. The number of seeds per lateral flower cluster obtained by natural crossing increased, and the germination rate was higher than that of primary flower clusters on moderately growing shoots. Furthermore, when compared with primary flower clusters on weakly growing shoots, the number of seeds per lateral flower cluster and the germination rate were either comparable or superior, depending on the node position. In addition, we compared the pollen germination rate between the primary and lateral flower clusters. As a result, pollen from primary flower clusters stored in a refrigerator after collection showed higher germination rates than that from lateral flower clusters. When the lateral flower clusters of ‘Pione’ and ‘Aurora Black’ were used for crossbreeding, the number of full seeds per fruit cluster and seed germination rate were higher compared with those from weak primary shoots. These results indicate that lateral flower clusters are valuable for crossbreeding of tetraploid grapes.