Use of GA3 toincrease bunch size in crop forced table grapes

Abstract

Crop forcing of table grapes has been proposed as a technique to be used when yield is lost due to late frosts or hail. It consists of forcing the sprouting of fruiting buds during the same season they were formed, through pruning and removal of the apex, leaves, and bunches of the plant. However, the resulting bunch is smaller than the normal bunches. The objective of this study is to use gibberellic acid (GA3) to increase bunch size in Red Globe plants subjected to crop forcing technique. The trial was conducted in an 18-year-old Red Globe vines, trained to an overhead trellis. The plants were pruned in mid-December, removing shoot tips, leaves, females, and bunches. These plants had also been traditionally pruned in winter. The treatments consisted of a Control without GA3 and the spray application of GA3 CF1: 2ppm between 100% flowering and start of setting, and CF2: 2 ppm in 15cm shoot +20 ppm in berry size of 10-14mm. The trial design was completely randomized, with 5 replicates per treatment. Data were analysed using ANOVA, and the mean separation was performed using Tukey's test. There were no significant differences between Control, CF1 and CF2 in terms of bunch weight, number of berries per bunch and berry weight, however CF2 tended to have higher bunch weight and number of berries than the control, while CF1 had lower bunch weight and number of berries compared to the control. On the other hand, the length of the rachis, internodes and wings of the CF2 bunches increased significantly. These results indicate that the application of 2 ppm of GA3 in a 15 cm shoot + 20 ppm of GA3 in a berry size of 10-14mm improves the architecture of the table grape bunch with forced sprouting and therefore the quality of the bunch.