Microbial inoculants improve growth in Zea mays L. under drought stress by up-regulating antioxidant, mineral acquisition, and ultrastructure modulations

Drought-induced stress poses a formidable impediment to agricultural productivity, compromising crop growth and yield. While the utilization of arbuscular micorrhizal fungi (AMF) consortium, plant growth promoting bacteria (PGPB) consortium, and Piriformospora indica inoculum shows promise in mitigating drought effects, a rigorous scientific assessment of their relative efficacy is lacking. This study thus investigates the comparative effects of P. indica , AMF consortium, and PGPB consortium inoculation on nutrient assimilation, ultrastructural adjustments, metabolic responses, and antioxidant defenses in drought-exposed maize plants. A completely randomized block design was employed, subjecting plants to varying drought stress levels (75%, 55%, 45%, and 35% of soil field capacity (FC)) in a greenhouse. The study analyzed multiple aspects, including growth parameters, nutrient levels, physiological responses, osmolyte content, antioxidant defense mechanisms, and leaf ultrastructure. Inoculation with AMF, P. indica , and PGPB yielded substantial enhancements in growth metrics like plant height, biomass accrual, leaf area expansion, stomatal conductance, photosynthetic activity, internal CO 2 dynamics, and transpiration rate, particularly evident across all drought stress intensities. Notably, microbial treatments counteracted nutrient deficiencies induced by drought, with augmented levels of osmolytes (total sugars, trehalose, glycine betaine), proteins, attenuated lipoxygenase enzyme (LOX) activity, ion leakage, and lipid peroxidation relative to non-inoculated plants. Elevated enzymatic activity of antioxidants, including ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), in addition to elevated non-enzymatic antioxidants (proline, α-tocopherol, polyamines), was evident in microbial-inoculated plants. Furthermore, microbial inoculation ameliorated drought-induced ultrastructural alterations. Noteworthy disparities in drought resilience were observed among inoculants, with PGPB displaying the highest robustness, followed by AMF and P. indica . This research underscores the substantial potential of microbial inoculants in fostering sustainable agriculture practices in drought-challenged contexts.