The present investigation was carried out during 2019 and 2020 seasons to study the effect of GA3 and some natural plant compounds on growth and fruiting of Thompson Seedless grapevines. The experiment was arranged in a randomized complete block design in which the study involved six treatments with three replications, one vine each.
Pruning wood weight, leaf area and total leaf chlorophyll were significantly increased by spraying either GA3, humic acid, selenium, turmeric or roselle extracts compared to water sprayed ones (control). Spraying humic acid, turmeric or selenium were very effective on improving vegetative growth, yield/vine, and cluster traits. Moreover, these treatments significantly improved the berry quality in terms of increasing the berry weight, total soluble solids, reducing sugars of berries compared to unsprayed ones. The best results were obtained on the vines that sprayed with 0.1% humic acid or turmeric extract. No significant differences were obtained among humic acid turmeric or selenium spraying. It could be concluded that spraying humic turmeric or selenium at 0.1% three times annually was necessary to get high yield with good cluster and berry quality of Thompson Seedless grapevines. Moreover, such treatments more effective to overcome the adverse effect of using GA3 i.e. delay the berry ripening and reducing full coloration of colored cultivars.