Effect of gibberellin on seedless Vitis vinifera

Experiments were performed in 1958 on three seedless varieties of Vitis vinifera to determine their responses to gibberellin. Berry-growth curves of Black Corinth and Thompson Seedless were double sigmoid when growth increments in diameter were plotted. Gibberellin increased berry diameter but did not alter the general shape of the curves.

On clusters of Black Corinth or Thompson Seedless, only the treated portions responded to gibberellin. In Black Corinth, increasing concentrations from 1 to 100 ppm of gibberellin usually progressively increased berry size and length-to-width ratio. Black Corinth showed little increase in size of berry as a result of compound absorbed by leaves. The percentage increase in length of young Thompson Seedless clusters dipped in gibberellin was greatest in the apical portion and least in the basal (peduncle).

Thompson Seedless vines were sprayed with gibberellin at 10, 25, or 50 ppm, at four prebloom stages. Length of cluster was increased by the second application. Weight of fruit was sometimes decreased by gibberellin, but in two of four instances in which crop level could be eliminated as a factor, maturation was hastened. Gibberellin at 1 ppm and higher, applied after shatter, increased berry size of Thompson Seedless. The compound at 1,000 ppm injured the berries, but not the foliage and shoots. Largest berries resulted from combined gibberellin and girdling. The largest berries in Thompson Seedless were produced by spraying at the shatter stage; later sprayings produced progressively smaller berries. Gibberellin absorbed by leaves had only a small effect on enlargement of fruit.

Gibberellin increased berry size of Black Monukka.