Effect of gibberellin on seeded Vitis vinifera, and its translocation within the vine

Four seeded grape varieties were treated, at various stages of development, with gibberellic acid as a water-soluble potassium salt (80 per cent active ingredient). The compound was applied by dipping, spraying, or painting, in amounts ranging from 1 to 100 ppm. The experiments were concerned with determining the proper concentration and time of application for producing loose clusters with a minimum of shot berries, and with translocation of gibberellin within the vine.

Dipping of Zinfandel clusters and spraying of entire vines at various prebloom, bloom, and postbloom stages gave varying results, including elongation and loosening of clusters; shot berries; accelerated flowering, fruit coloration, and ripening; a higher percentage of soluble solids; a decrease in rot; and some reduction of crop.

Carignane vines sprayed, at six stages of development, with gibberellin at 1 to 50 ppm, gave results similar to those for Zinfandel. There was loss of crop weight because of fewer berries in sprayed clusters.

In the translocation experiments, gibberellin was not translocated from one shoot to another, judging by its effect on shoot elongation. Red Malaga shoots about 3 feet long showed just as much additional growth when only the apical 6 inches were sprayed as when the whole shoot was sprayed. In 6-inch Carignane shoots, more gibberellin reached the apex when the basal leaf was treated than when an apical leaf was treated. An experiment in which foliage and/or clusters of Zinfandel were treated showed that much cluster elongation and shot berry development resulted from compound absorbed by the leaves.