Endophytic Bacillus strains enhance chickpea growth and performance under controlled and field conditions

Endophytic Bacillus species are known to improve legume symbiosis and plant performance through an array of mechanisms. This study evaluated the potential of endophytic Bacillus strains (B. firmus, B. subtilis, and B. tequilensis) to promote growth and productivity of chickpea (Cicer arietinum L) grown under rainfed conditions. Among the Bacillus strains evaluated for in vitro plant growth-promoting traits, B. firmus exhibited the highest potential for phosphate solubilization (pH drop to 5.0) and indole-3-acetic acid (IAA) production (28.9 PPM). Seed biopriming with Bacillus strains enhanced antioxidant accumulation in chickpea seedlings, with B. subtilis markedly boosting key antioxidant enzymes, while B. tequilensis and B. firmus exerted distinct tissue-specific effects, as revealed by principal component analysis (PCA). At the critical threshold of 20% polyethylene glycol (PEG 6000), which inhibit chickpea seed germination, B. firmus and B. tequilensis maintained viability and biopriming chickpea seeds with these strains restored germination (25% and 41.7%, respectively), whereas UnInoculated and B. subtilis bioprimed seeds failed to germinate. In a controlled pot study, B. firmus inoculation enhanced chickpea biomass, increasing root and shoot growth by 37.4% and 27.7%, respectively, over the UnInoculated control. Field study showed that co-inoculation of B. firmus with Mesorhizobium ciceri enhanced leghemoglobin content (79.6%), nodule biomass (69.0%), nutrient uptake (N: 13.8%, P: 20.3%), plant biomass (14%) and seed yield (8%) over the absolute control. Ordination analysis clearly indicated that co-inoculation of M. ciceri with B. firmus had the strongest effect on chickpea performance under field conditions. Our findings establish B. firmus as a promising bioinoculant for improving chickpea productivity under rainfed conditions.