Maize seed treatments with Bacillus methylotrophicus and Bacillus subtilis to mitigate the effects of water deficit

Rainfall has gradually decreased over time, accompanied by prolonged dry spells, which can reduce maize yields. Numerous studies have demonstrated the beneficial effects of plant growth-promoting bacteria, particularly species of the genus Bacillus, including Bacillus methylotrophicus and Bacillus subtilis, which enhance plant growth through phytohormone regulation and phosphate solubilization, thereby mitigating the effects of water deficit. In this context, the objective of this study was to evaluate the ability of B. methylotrophicus and B. subtilis to mitigate the effects of water deficit in maize. The experiment was conducted in a greenhouse using pots in a randomized block design with a 2 × 4 factorial arrangement and five replications. The factors consisted of two water regimes (100% field capacity—no water deficit; 50% field capacity—water deficit) and four seed treatments: control (no inoculation); Onix® (B. methylotrophicus 1 × 109 CFU mL−1; 3 mL kg−1), Rizos® (B. subtilis 3 × 109 CFU mL−1; 1.5 mL kg−1), and Onix® (3 mL kg−1) + Rizos® (1.5 mL kg−1). The maize hybrid DKB 255 PRO3 was evaluated for vegetative growth, biomass accumulation, and yield at 45, 60, and 90 days after emergence; electrolyte leakage and relative water content were also assessed. No significant differences were observed in the number of ears per plant or stem diameter among treatments, whereas plant height was greater under no-water-deficit conditions. Total fresh and dry matter biomass of plants treated with plant growth-promoting bacteria were equal to or greater than those of control plants under both water regimes. Plants at 50% field capacity exhibited higher electrolyte leakage and lower relative water content than those at 100% field capacity, except for seeds treated with Rizos®, which maintained relative water content similar to that observed under no-water-deficit conditions. Under water-deficit conditions, inoculation with Onix® and Rizos® generally resulted in superior performance for yield components. Under no-water-deficit conditions, the Onix® + Rizos® combination exhibited superior performance. The results indicate that B. subtilis and B. methylotrophicus can mitigate the effects of water deficit in maize.