The effect of chemical and physical thinning on some characteristics of Yaghooti ‎grape cluster

Yaghooti grape is the most important horticultural crop in the Sistan region that the cluster compactness of this grape has affected its marketability. The aim of this experiment was to investigate the effect of chemical and physical thinning on the compactness of Yaghooti grape cluster and also evaluate its economic efficiency. This experiment has been conducted in three projects in the form of randomized complete blocks design with three replications. The first experiment consisted of four levels of GA3 (0 (control), 10, 20 and 30 mg.L-1), the second experiment consisted of four levels of defoliation (non-defoliation (control), defoliation of two nodes lower fertile branches, defoliation of four nodes lower fertile branches, and defoliation of six nodes lower fertile branches) and the third experiment consisted of four levels of cluster thinning (no thinning (control), removal of 1 cm from the end of the cluster, removal of 2 cm from the end of the cluster and brushing the clusters). Mean comparison of the cluster compactness in 3 experiments showed that the use of 30 mg.l-1 gibberellic acid caused the greatest reduction in cluster compaction. The benefit/cost of using gibberellic acid and defoliation was significant, however it was not significant for cluster thinning. Mean comparison of utilizing gibberellic acid and defoliation showed that the highest benefit/cost was related to all levels of gibberellic acid application. The benefit/cost of using 30 mg.l-1 gibberellin was 31.4% and 41.5% higher than 20 and 10 mg.l-1 gibberellin application, respectively. In general, applying 30 mg.l-1 gibberellin increased 85.2% of benefit/cost compared to the defoliation of six nodes and it is recommended to decrease the cluster compactness.