Enhancing Heat Tolerance in Maize Hybrids Using Bacterial Consortium: Modulation of Morpho-Physiological Traits and Antioxidant Mechanisms

Heat stress is one of the most detrimental abiotic stresses, causes significant reduction in plant growth and yield in tropical and sub-tropical regions. Mitigating the adverse effects is crucial for sustainable crop production and global food security. The use of bacterial consortia represents a promising and eco-friendly approach to enhance heat tolerance in plants, offering a biological strategy to improve resilience under climate-induced stress conditions. In this study, three heat-tolerant Bacillus species (Bacillus velezensis, Bacillus altitudinis and Bacillus cereus) and two maize hybrids DK-6103 (heat tolerant) and SW-1080 (heat sensitive) were selected from laboratory and glasshouse experiments. The bacterial strains were screened in laboratory at various heat stress levels (30°C, 40°C and 50°C for 96 h), while maize hybrids were evaluated in glasshouse conditions [30°C ± 3 (control) and 45°C ± 3 (heat stress) for 6 h per day over a period of 8 consecutive days]. Subsequently, the response of best performing heat-tolerant Bacillus spp. as individual and consortium was explored in selected maize hybrids under heat stress [45°C ± 3; 6 h/day over a period of 8 consecutive days] based on morpho-physiological and antioxidant activity. The results revealed that seed inoculation with a bacterial consortium of B. velezensis, B. altitudinis and B. cereus resulted significant improvements in plant growth, morpho-physiological traits and antioxidant mechanisms. Inoculation treatment demonstrated a rise in shoot and root length (39% and 30%) attributed to enhancements in net leaf photosynthetic rate (25%), soluble protein content (46%), superoxide dismutase (73%), catalase (94%) and proline content (151%) compared to the control. Additionally, seed inoculation also led to a reduction in leaf transpiration rate and malondialdehyde contents indicating a stress response in plants. Consortium-inoculated seedlings exhibited the highest increases in net leaf photosynthetic rate, soluble protein content, superoxide dismutase, catalase and proline under heat stress. It highlights the effectiveness of bacterial inoculation in enhancing thermotolerance in maize hybrids. In conclusion, seed inoculation with a bacterial consortium effectively enhances seedling growth, physiological traits, antioxidant activities and osmolytes production under heat stress.