Effects of Shoot Vigor and SADH Application to Clusters Before Anthesis on Berry Set in Kyoho Grapes

In a poorly setting 4n cultivar, Kyoho, the shoots sprouting from the basal part of canes (weak shoots) were significantly shorter, set seeded berries faster, and had more seeds per seeded berry than the shoots from the apical part (strong shoots). Applying SADH to clusters alone before anthesis improved the set of seeded berries in both types of shoots with no significant effect on shoot elongation. Pollen tubes reaching ovules were more numerous in weak shoots than in strong ones and more numerous in SADH-treated clusters than in untreated clusters. In florets around blooming time, the level of total sugar was higher and total nitrogen lower in weak shoots than in strong ones, but total sugar was lower and nitrogen higher in SADH-treated clusters than in untreated clusters. The cause of poor set in vigorous vines of Kyoho is discussed based on these results.