Physiological and Multivariate Characterization of Chitosan-Indiced Drought Tolerance in Groundnut (Arachis hypogaea L.) Seedlings

Abstract

Early-stage drought stress severely limits seedling establishment in groundnut (Arachis hypogaea L.), necessitating effective biostimulant-based approaches to enhance drought tolerance. This study aimed to identify the optimum foliar concentration of chitosan for improving seedling growth and physiological performance under contrasting moisture regimes using integrated multivariate analyses. A factorial completely randomised design with three replications was employed, comprising two moisture regimes (well-watered and water-stressed) and six chitosan concentrations (0, 100, 200, 300, 400, and 500 ppm). Chitosan was applied as a foliar spray at 15 days after sowing, and growth, biomass, relative leaf water content (RLWC), membrane stability index (MSI), and cellular metabolic activity were evaluated after 15 days. Chitosan significantly enhanced all measured traits under both moisture conditions, with responses increasing up to 300 ppm before declining at higher concentrations. The 300 ppm treatment produced the highest shoot length (27.01 cm), root length (19.55 cm), fresh biomass (3.32 g seedling⁻¹), RLWC (84.83%), MSI (83.00%), and cellular metabolic activity (2.14 A₄₈₅ g⁻¹ FW). Pearson's correlation analysis revealed strong positive associations among growth, biomass accumulation, water status, membrane stability, and cellular metabolic activity, while principal component analysis explained 87.2% of the total variation. The Composite Performance Index (CPI), integrated with quadratic regression, predicted optimum chitosan concentrations of approximately 322 ppm under water stress and 300 ppm under well-watered conditions. As both predicted optima closely corresponded to the tested 300 ppm treatment, this concentration was identified as the practical optimum. These findings demonstrate that foliar application of chitosan at 300 ppm effectively enhances seedling vigour and physiological resilience under both drought-stressed and well-watered conditions, providing a scientifically validated dose for future greenhouse and field evaluation.