Auxin synthesis-encoding transgene enhances grape fecundity.

Grape (Vitis vinifera) yield is largely dependent on the fecundity of the cultivar. The average number of inflorescences per shoot(i.e. shoot fruitfulness) is a trait related to fecundity of each grapevine. Berry number and weight per bunch are other featuresaffecting grape yield. An ovule-specific auxin-synthesizing (DefH9-iaaM) transgene that increases the indole-3-acetic acidcontent of grape transgenic berries was transformed into cultivars Silcora and Thompson Seedless, which differ in the averagenumber of inflorescences per shoots. Thompson Seedless naturally has very low shoot fruitfulness, whereas Silcora hasmedium shoot fruitfulness. The average number of inflorescences per shoot in DefH9-iaaM Thompson Seedless was doubledcompared to its wild-type control. Berry number per bunch was increased in both transgenic cultivars. The quality andnutritional value of transgenic berries were substantially equivalent to their control fruits. The data presented indicate thatauxin enhances fecundity in grapes, thus enabling to increase yield with lower production costs.