The Effect of Gibberellic Acid, Defoliation and Cluster Thining on the Cluster Compactness of Table Grape (Vitis vinifera L. cv. Yaghooti)

This research was carried out in three separate experiments based on a randomized complete block design with four replications. In the first experiment, GA3 (0, 10, 20, and 30 mg L-1) was sprayed 10 days befor flowering. The second experiment, consisted of four levels of defoliation including; non-defoliation (control), defoliation of two nodes below the frutful branches, defoliation of four nodes below the frutful branches and defoliation of six nodes below the frutful branches one weeks before the stage of full bloom . The third experiment consists of four levels of cluster thinning including; no thinning (control), removal of 1 cm from the cluster end, 2 cm  from the cluster end and brushing of the clusters before the stage of full bloom. Comparison of the three experiments in term of cluster compactness showed mean cluster compactness of 5.6, 6.3 and 6.8 by application of GA3, defoliation and cluster thinning, respectively. The results showed that, the defoliation of the six nodes below the frutful branches and brushing of the cluster could decrease the cluster compression while GA3 significantly increase the length of the main and sub axes of the cluster and decrease the number of berries. Finally, it is recommended to use 30 mg L-1 GA3 10 days before flowering to reduce the cluster compactness.