Implications of exogenous allantoin in enhancing growth and development of Vitis vinifera L. cultivars under semi-arid condition

Elucidating the physiological enhancement mechanisms of grapevines through biostimulant applications is essential for developing optimized viticulture practices in modern agriculture. However, comprehensive knowledge about how foliar allantoin supplementation modulates growth parameters, fruit quality, and secondary metabolite profiles across different cultivars remains limited. We investigated reproductive growth, photosynthetic capacity, and biochemical dynamics in Vitis vinifera L. cultivars Sultana and Merlot subjected to graduated allantoin concentrations (0, 10, 20, and 30 mM), followed by detailed morphological and metabolomic profiling. Data were analyzed using two-way ANOVA followed by LSD and Duncan's tests (p < 0.01 and p < 0.05). Cultivar and allantoin application significantly influenced all measured parameters (p < 0.01), with notable interaction effects observed for panicle weight, berry development, and chlorophyll content among morphological traits, and phenolic compounds, anthocyanins, and carbohydrates among biochemical parameters. Allantoin-supplemented plants consistently demonstrated superior performance metrics, maintaining higher reproductive success (panicle weight increases up to 151% in Sultana), enhanced berry quality parameters (TSS improvement reaching 23.9 °Brix), and more robust photosynthetic capacity under optimal treatment compared to controls. Enhancement of secondary metabolite biosynthesis was also more pronounced in treated vines, with better accumulation of phenolic compounds, anthocyanins, and improved antioxidant status reflected by reduced MDA levels. Metabolic profiling revealed distinct cultivar-specific response patterns, with Sultana demonstrating superior responsiveness in reproductive and vegetative parameters, while Merlot showed enhanced secondary metabolite accumulation and stress tolerance indicators. Correlation analysis explained strong relationships between morphological traits (berry length-berry weight r = 0.94), demonstrating coordinated developmental responses to allantoin treatment. We conclude that allantoin foliar application significantly enhances grapevine productivity and berry quality through comprehensive improvement of growth, physiological, and biochemical pathways. These findings have direct applications for viticulture management, particularly in semi-arid regions where optimizing yield and fruit quality through bio stimulant application can enhance vineyard productivity without extensive modifications to existing practices. The differential responses between cultivars provide insights for variety-specific bio stimulant strategies, while the quantitative enhancement profiles identified offer valuable parameters for optimizing vineyard management practices under diverse environmental conditions.