MICROBIAL SEED PRIMING MODULATES PHYSIO BIOCHEMICAL RESPONSES OF ORYZA SATIVA L. UNDER POLYETHYLENE GLYCOL-INDUCED DROUGHT STRESS

Abstract

Drought stress is a major constraint to rice production, adversely affecting seed germination, seedling establishment, growth and physiological functions. Microbial seed biopriming offers an environmentally sustainable approach for enhancing crop resilience under water-deficit conditions. The present study was conducted to evaluate the potential of selected plant growth-promoting bacterial inoculants for improving seed germination, seedling growth, water status, membrane stability and antioxidant defence in rice under polyethylene glycol (PEG 6000)-induced osmotic stress. Seeds of rice cultivars CO 53 and TKM 15 were bioprimed individually with 20% Azospirillum lipoferum, Bacillus megaterium, Paenibacillus mucilaginosus and Pseudomonas chlororaphis and compared with hydroprimed and untreated seeds. The treated seeds were evaluated under control conditions and PEG-induced osmotic potentials of −4 and −6 bar. Germination, seedling growth, vigour indices, dry matter production, relative water content (RWC), electrolyte leakage and antioxidant enzyme activities were assessed. Increasing osmotic stress progressively reduced germination, root and shoot growth, seedling vigour and dry matter production in both cultivars. However, microbial biopriming substantially alleviated the adverse effects of osmotic stress. Among the treatments, Azospirillum lipoferum consistently recorded superior performance, producing the highest germination percentage, seedling growth, vigour indices and dry matter production under both moderate and severe stress followed by Bacillus megaterium. In CO 53, A. lipoferum recorded 85 and 77% germination at −4 and −6 bar, respectively, compared with 73 and 64% in the untreated control. Similarly, in TKM 15, germination reached 79 and 74% under −4 and −6 bar, respectively, compared with 69 and 61% in the untreated control. The treatment also maintained higher RWC and reduced electrolyte leakage, indicating improved cellular hydration and membrane stability. Furthermore, A. lipoferum enhanced catalase, peroxidase and superoxide dismutase activities under increasing osmotic stress, suggesting improved antioxidant defence and reactive oxygen species scavenging. Overall, the findings demonstrate that microbial seed biopriming, particularly with A. lipoferum, effectively improves early-stage drought resilience in rice by sustaining seedling growth, water status, membrane integrity and antioxidant defence under PEG-induced osmotic stress.