Exogenous putrescine and calcium nitrate alleviate water deficit stress in sesamum indicum L. by modulating antioxidant defense and nutrient homeostasis

Water deficit is a major constraint for sesame ( Sesamum indicum L.) production in arid and semi-arid regions. This study evaluated the effects of foliar application of calcium nitrate )Ca(NO₃)₂; 0, 5, and 10 mM( and putrescine (Put; 0 and 0.5 mM) on the physiological and biochemical responses of sesame under three irrigation regimes (100%, 75%, and 50% of crop water requirement) during the 2018–2019 growing seasons. The experiment was conducted under field conditions using a split-plot factorial design with three replications. Severe water deficit (50% irrigation) significantly reduced chlorophyll content by 38.6%, relative water content by 27.2%, and membrane stability index by 28.6% compared with full irrigation ( P ≤ 0.01). Foliar application of 10 mM Ca(NO₃)₂ increased total chlorophyll by 19.3% and relative water content by 17.1% ( P ≤ 0.05), whereas 0.5 mM Put improved membrane stability by 30.8% under severe stress ( P ≤ 0.01). Both treatments reduced electrolyte leakage by 18–23% and increased leaf calcium content by up to 60.6%, soluble carbohydrates by 45.6%, proline by 34.3%, catalase activity by 32.8%, and peroxidase activity by 27.4%. Significant interaction effects were detected for chlorophyll and calcium content ( P ≤ 0.01). This study provides field-based evidence that the combined foliar application of Ca(NO₃)₂ and Put can mitigate drought-induced injury in sesame through coordinated improvements in water status, membrane stability, and antioxidant defense. These findings suggest that this treatment combination may serve as a practical complementary agronomic strategy for improving sesame performance under water-limited conditions.