Morphophysiological and antioxidant responses of different grape cultivars from the Caspian Basin under varying water deficit conditions

The study investigated the effects of water deficit on the morphophysiological and antioxidant responses of seven grape cultivars from the Caspian Basin. Three-bud cuttings from grapevine cultivars were prepared, rooted in sawdust, and transplanted into pots with soil, sand, and peat. A factorial experiment design, considering three water deficit levels (100 % as control, 70 %, 40 % field capacity [FC]) and seven cultivars, was performed. Morphophysiological and antioxidant responses were measured at the onset of visible drought symptoms, enabling a comparative evaluation of cultivar-specific adaptations to water stress. As water deficit increased, shoot length, leaf fresh and dry weights decreased, with the lowest values observed under the 40 % FC treatment. Interestingly, the Muscat Yamtazini cultivar maintained the highest total chlorophyll content in the 70 % FC treatment. Cultivar and water deficit also had significant main effects on internode length and lateral shoot length. The Bidane Sefid cultivar exhibited the highest internode length but the lowest lateral shoot length. Water deficit treatments reduced internode length and drastically decreased lateral shoot length, with the 40 % FC treatment having the lowest lateral shoot length. Water deficit treatments significantly affected stem diameter, lateral shoot number, and canopy temperature. The 40 % FC treatment resulted in the lowest stem diameter and lateral shoot number, while displaying the highest canopy temperature. Relative water content (RWC) of leaves and roots and membrane stability index (MSI) decreased with increasing water deficit. The Qazagiski Ramphi and Chefte cultivars maintained the highest leaf and root RWC under water deficit, while the Chefte cultivar had the lowest MSI. Leaf and root proline content, total protein, and hydrogen peroxide showed significant interaction effects between cultivar and water deficit. Antioxidant enzyme activities increased with drought stress, and the Muscat Yamtazini, Kishmish Hisrao, and Qazagiski Ramphi cultivars exhibited distinct responses. Based on their performance under drought stress, the studied cultivars were ranked, with Muscat Yamtazini being the most tolerant, followed by Kishmish Hisrao and Qazagiski Ramphi.