Effect of Ethephon and Gibberellin on Maturation of Ungirdled Thompson Seedless Grapes

Abstract

Thompson Seedless grapevines were sprayed with either ethephon at 100, 250, and 500 ppm at véraison or with KGA₃ at 5, 25, and 50 ppm one week after fruit-set. All fruits were harvested at about 19°Brix. Ethephon-treated grapes matured 16 days earlier than did the controls, and KGA₃ retarded maturation 32 days beyond that of the non-treated vines. Thus the harvesting period for this cultivar was extended by about 48 days.

Ethephon application had no effect on yield, cluster weight, berry weight, or size. However, KGA₃ produced increases in the above-mentioned parameters. A high juice percent resulted from the application of these compounds, but ethephon treatments gave the higher values. Moreover, higher values in the °Brix/ acid ratio, and lower ones in acidity, were caused by ethephon. GA₃ increased acidity, but decreased the °Brix/acid ratio.