Genotype-Dependent Effects of Zinc Oxide Nanoparticles on Physiological and Biochemical Traits of Withania coagulans under Water Stress

\This study evaluated the effects of zinc oxide nanoparticles on the physiological responses of different ecotypes of Withania coagulans (Stocks) Dunal under conditions of limited moisture and drought stress. A factorial greenhouse experiment was conducted to assess the impacts of three irrigation regimes (optimal, mild at 70% field capacity, and severe at 40% field capacity) and foliar zinc spray treatments on four ecotypes of W. coagulans. The application of zinc significantly enhanced chlorophyll content in plants under severe drought stress, especially in the Faroj ecotype which maintained higher chlorophyll levels compared to other ecotypes. The accumulation of anthocyanins, which protect plants from stress, increased progressively with the severity of drought stress and was further potentiated by zinc application, particularly in the Saravan and Sarbaz ecotypes that exhibited higher anthocyanin levels. The stress biomarker MDA, indicating lipid peroxidation, rose under drought stress but decreased following zinc application, demonstrating zinc's antioxidant activity in reducing membrane damage. The activities of key antioxidant enzymes varied among the different ecotypes of W. coagulans in their response to both zinc application and drought stress level. Under mild stress, the Saravan ecotype displayed a greater enhancement of all three antioxidant enzymes SOD, CAT and POX with zinc application. Overall, the results highlight that zinc supplementation can alleviate the negative impacts of drought stress on key physiological and biochemical processes in W. coagulans in a manner dependent on the ecotype and severity of water limitation, underscoring opportunities to develop drought-tolerant cultivars through zinc-based nutritional strategies.