Comparative effects of ZnSO₄ and ZnO-NPs in improving cotton growth and yield under drought stress at early reproductive stage

Drought episodes, especially during the reproductive stages, have posed a significant threat to cotton production on a global scale. Finding an efficient solution that would bring immediate advantages to cotton producers has received unprecedented interest from the research community. Mineral supplements can play an important role in combating drought, while also improving fiber yield and cotton quality. The current study evaluated the comparative effectiveness of zinc sulphate (ZnSO₄·7 H₂O; 1.0 g Kg⁻¹ potting mix) and zinc oxide-nanoparticle (ZnO-NP; 0.1 g Kg⁻¹ potting mix) supplements in improving cotton drought tolerance and yield attributes. Supplementation of zinc (Zn) to potting mix, particularly in the form of ZnO-NPs, increased cotton growth, root and shoot biomass, and hydration status during drought. Both Zn supplements boosted the enzymatic antioxidant system and contributed to membrane integrity by minimizing drought-induced oxidative damage. Gene expression analysis using RT-qPCR also showed high corroboration with the antioxidant activity assay data. ZnO-NP-supplemented plants showed better performance in mineral uptake and accumulation than ZnSO₄-supplemented plants under both well-watered and drought conditions. In terms of yield, ZnO-NP-supplemented plants outperformed ZnSO₄-supplemented plants in both drought and well-watered circumstances. The correlation network analysis also provides evidence of Zn-mediated coordination of antioxidant defense system and yield performance. Altogether, the findings of the present study suggest that ZnO-NPs have better potential than ZnSO₄ in mitigating the harmful effects of drought on cotton to enhance its performance under soil conditions with restricted water availability.