Response of certain varieties of Vitis vinifera to gibberellin

Two seedless and five seeded grape varieties were treated with the watersoluble potassium salt of gibberellic acid at different stages of the vines’ development. Applications were made by dipping clusters or by spraying shoots or entire vines; concentrations ranged from 0.1 to 1,000 ppm. In all varieties shoot growth was stimulated, and internodes were elongated. Treatment of Black Corinth resulted in an excellent set of large berries, and at the higher concentrations berries were elongated. In Thompson Seedless some treatments hastened flowering and produced more elongated clusters and peduncles, others resulted in increased berry size. Flowering was also hastened in Zinfandel and shoots were elongated. Tokay responded with longer leaves and elongated cluster parts. In Ribier and Red Malaga no beneficial results were obtained by dipping clusters, but spraying often hastened coloration slightly and sometimes produced higher Balling readings. Dipping flower clusters of Muscat of Alexandria failed to increase the percentage of set. Considerable numbers of shot berries resulted from some treatments of Thompson Seedless, Zinfandel, Tokay, and Ribier.