Mitigating Drought Stress in Maize: Synergistic Effects of Zinc Sulfate and Pseudomonas spp. on Physiological and Biochemical Responses

This study aimed to evaluate the synergistic effects of zinc sulfate and <i>Pseudomonas</i> spp. in terms of mitigating drought stress in maize (<i>Zea mays</i> L.) by analyzing physiological, biochemical, and morphological responses under field conditions. A two-year (2018-2019) field experiment investigated two irrigation levels (optimal and moderate stress) and twelve treatment combinations of zinc sulfate application methods (without fertilizer, soil, foliar, and seed priming) with zinc-solubilizing bacteria (no bacteria, <i>Pseudomonas fluorescens</i>, and <i>Pseudomonas aeruginosa</i>). Drought stress significantly reduced chlorophyll content, increased oxidative damage, and impaired membrane stability, leading to a 42.4% increase in electrolyte leakage and a 10.9% reduction in leaf area index. However, the combined application of zinc sulfate and <i>P. fluorescens</i>, and <i>P. aeruginosa</i> mitigated these effects, with seed priming showing the most significant improvements. Specifically, seed priming with zinc sulfate and <i>P. fluorescens</i> increased catalase activity by 76% under non-stress conditions and 24% under drought stress. Principal component analysis revealed that treatments combining zinc sulfate and <i>P. fluorescens</i>, and <i>P. aeruginosa</i> were strongly associated with improved chlorophyll content, carotenoid content, and grain yield while also enhancing osmotic adjustment and antioxidant enzyme activity. These findings highlight the potential of the use of zinc sulfate and <i>P. fluorescens</i> as well as <i>P. aeruginosa</i> as sustainable strategies for enhancing maize drought tolerance, mainly through seed priming and soil application methods.