Effects of Gibberellic Acid and Girdling on ‘Thompson Seedless’ and ‘Ruby Seedless’ Table Grapes in Morocco

Abstract ‘ Thompson Seedless’ and ‘Ruby Seedless’ vines were girdled and/or treated at bloom with GA 3 (‘Thompson Seedless’ at 5 ppm and ‘Ruby Seedless’ at 1, 5, and 20 ppm), and/or at fruit set (just after berry shatter) at 20 and 40 ppm. Results for ‘Thompson Seedless’ grapes ( Vitis vinifera L.) indicate a significant increase in berry weight resulting from GA 3 spray or girdling at fruit set. The greatest increase was obtained from a combination of girdling and GA 3 spray. Soluble solids and titratable acidity were not significantly affected. Results for ‘Ruby Seedless’ grapes indicate significant fruit thinning at 5 and 20 ppm but not at 1 ppm. No increase in berry size was recorded, but a significant increase in soluble solids and a decrease in acidity were obtained with bloom-sprayed vines at 5 and 20 ppm.