Salicylic Acid Mitigates Salinity Stress in Grapevine Cultivars by Regulating Redox Homeostasis and Morpho-Physiological Traits

Grapevine (Vitis vinifera L.) is one of the world’s most economically important fruit crops, widely valued for fresh consumption, raisin and juice production, and its significant role in global horticulture. This study evaluated the morphological, physiological, and biochemical responses of several grapevine cultivars to salinity stress and foliar application of salicylic acid (SA) under greenhouse conditions in 2023. The experiment was arranged as a split–split plot design based on randomized complete block design with three replications. Measured traits included shoot and root fresh and dry biomass, plant height, root length, stem diameter, leaf thickness, proline content, antioxidant enzyme activities (peroxidase, catalase, superoxide dismutase, and glutathione reductase), malondialdehyde content, hydrogen peroxide, superoxide radicals, and total soluble sugars. Increasing salinity levels intensified oxidative stress and cellular damage, as indicated by significant increases in proline accumulation, antioxidant enzyme activities, electrolyte leakage, malondialdehyde, hydrogen peroxide, superoxide radicals, and total soluble sugars, concomitant with marked reductions in overall plant growth. In contrast, foliar application of SA effectively mitigated salinity‑induced damage across all stress levels and generally improved growth performance. The 300 mg/L SA treatment was particularly effective under severe salinity (90 mM NaCl), with the cultivar ‘Laleh Siah’ exhibiting an 11.77% increase in plant height compared with the other cultivars. Overall, the results demonstrated that SA at 300 mg/L substantially alleviates the adverse effects of salinity stress and enhances plant performance. Among the examinated cultivars, ‘Laleh Siah’ displayed the greatest salinity tolerance, whereas ‘Bidaneh Sefid’ proved the most sensitive.