Employing Leaf Removal and Spraying Gibberellic Acid (GA3) to Reduce Cluster Compactness Coefficient and Enhance Chemical and Physical Properties of Thompson seedless H4 Grapevines.

This investigation was carried out in the vineyard of the EL-Baramon experimental farm over two seasons (2021 and 2022). Horticultural Research Institute, Mansoura, Dakahlia Governorate, Egypt. The experiment was carried out on seven-year-old Thompson seedless grapevines (H4 strain). The vines were planted in clay soil using surface irrigation system, cane pruning, and trellising using the Spanish Baron technique. The purpose of this research was to decrease the compactness coefficient of clusters and improve the physical and chemical quality of clusters and berries in Thompson seedless grapes (H4 strain). A field experiment was conducted in a randomized complete design with four times of leaf removal individual or in combination with GA3, which applied by removing 6 leaves at the beginning of flowering, 25% of flowering, 50% of flowering and at 75% of flowering to compare the effect of these treatments on the performance of Thompson seedless grapevines (H4 strain) during 2021 and 2022 seasons. Results revealed that removing 6 leaves at the 75% of flowering + spraying GA3 at 10 ppm was the best in enhancing vegetative growth, total nitrogen in canes, carbohydrate contents in canes, yield and physical properties of cluster and berries, whereas the same treatments decreased the compactness coefficient, Botrytis incidence and Botrytis severity of the clusters. It can be concluded that removing 6 leaves at the 75% of flowering + spraying GA3 at 10 ppm lead to improve chemical and physical properties and reduce compactness coefficient of Thompson seedless grapevines (H4 strain).