Promotion of Berry Set in Grapes by Growth Retardants

The prebloom application of SADH (succinic acid-2, 2-dimethyl hydrazide) to clusters of Kyoho (V×L) by spraying at 2500 ppm was as effective for increasing the set of seeded berries as foliar treatment at the same concentration or prebloom shoot pinching. The spraying on cluster had no inhibitory effect on shoot growth during bloom and set stages. Nearly the same trend as above was observed in Muscat of Alexandria (V) to which CCC (2-chloroethyl trimethylammonium chloride) was applied at 200 ppm. These results reconfirmed those of our earlier study. In both cultivars, the application of the growth retardants to either clusters or leaves distinctly reduced the gibberellin activity in florets at the beginning of bloom, whereas the shoot pinching raised the activity in Muscat or did not affect it in Kyoho. On the other hand, the cytokinin activity in florets was markedly enhanced by the retardant applications and the shoot pinching in both cultivars.These results indicate that reduction of shoot growth is not essential to exert the promotive effect of growth retardants on the set of seeded berries and that the increased level of cytokinin activity in florets induced by the chemicals is causally associated with the promoted berry set.