Auxin Pulverizations Mitigate the Adverse Effect of Water Deficit on Grapevine (Vitis vinifera L.) Physiology and Development

Environmental stress factors such as water deficit and temperature extremes compromise grapevine physiology and reduce vegetative development. Foliar application of plant growth promoters, such as auxins, has emerged as promising approach to improve stress tolerance in vines. This study was performed to investigate the effects of leaf auxin (indole-3-butyric acid, IBA) pulverizations at various doses (0, 100, 200, 500 and 1000 ppm) on the physiology and growth features of ‘Spil Karasi’ grapevines subjected to different irrigation levels: full irrigation (FI: 100% of water holding capacity) and deficit irrigation (DI: 50% of FI) in soilless culture under a climate-controlled Venlo glasshouse. Auxin pulverizations were performed three times at 30-day intervals during the summer seasons of 2024 and 2025. DI irrigation depleted the physiology of the grapevines by increasing malondialdehyde (MDA) content and electrolyte leakage (EL), and decreasing stomatal conductance (gs) and leaf chlorophyll content. Disruption to plant physiology due to water deficit led to reduced vegetative development of the vines. However, auxin treatments mitigated the adverse effects of the water deficit as they decreased MDA and EL while supporting the gs and chlorophyll content. Finally, leaf and shoot growth of the vines were significantly promoted by foliar auxin treatment for two irrigation levels during both years. Among the tested doses, 200 ppm auxin was the most effective application for many parameters. Auxin pulverization, with particular regard to DI conditions, could be recommended to support vine physiology and growth.