Leyla Karapınar, rman Fereydouni and Sara Al-Khafaji

The phytochemical profile of grapevine (Vitis vinifera L.) leaves represents a critical determinant of plant defence capability, metabolic regulation, and overall physiological resilience. Among various bio stimulants, salicylic acid (SA) has emerged as an effective endogenous signalling compound known to modulate secondary metabolite synthesis and enhance tolerance against biotic and abiotic stresses. However, the comparative impact of SA on the phytochemical behaviour of specific cultivars, particularly Halwani and Kamali, remains insufficiently characterised. This research investigates the influence of foliar-applied salicylic acid on major phytochemical constituents total phenols, flavonoids, tannins, chlorophyll pigments, and antioxidant capacity in leaves of Halwani and Kamali grapevines cultivated under similar Agro-ecological conditions. Experimental treatments were structured using varied SA concentrations to determine dose-dependent responses and identify optimal physiological thresholds. The results indicated that SA application enhanced total phenolic content and flavonoid accumulation in both cultivars, though Halwani displayed a more pronounced increase in antioxidant activity, suggesting higher metabolic responsiveness. Additionally, SA regulated chlorophyll stability and tannin biosynthesis, demonstrating its role in improving photosynthetic efficiency and structural defence compounds. Kamali exhibited moderate improvement in chlorophyll a and b compared to Halwani, indicating cultivar-dependent variation in pigment metabolism. The findings emphasize that exogenous SA acts as a metabolic elicitor capable of modulating phytochemical pathways, thereby enhancing the functional quality of grapevine foliage. Understanding these cultivar-specific responses offers valuable insight for viticultural management strategies aimed at improving plant health, stress tolerance, and biochemical productivity. This research contributes to the growing evidence supporting SA as a sustainable, low-cost, and effective bioregulator for improving phytochemical composition in grapevines, with implications for both primary production and value-added leaf-based nutraceutical applications.

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