Indigenous rhizospheric microbes mitigate root-knot disease and promote physiological, biochemical, and defense responses in green gram.

The efficacy of indigenous microbial isolates (IMIs), namely Trichoderma atroviride AMUTATROV-31, T. asperelloides AMUTASPD-51, T. harzianum AMUTHZ-72, T. viride AMUTVR-61, Purpureocillium lilacinum AMUPL-31, Pochonia chlamydosporia AMUPC-31, Bacillus subtilis AMUBS-80, and Pseudomonas fluorescens AMUPF-80 isolated from the rhizosphere of green gram soils in Aligarh, India, was evaluated for their potential to mitigate root-knot disease caused by Meloidogyne incognita. The isolates were purified using single-spore or single-colony techniques and identified through morphological and molecular techniques. The effectiveness of seed treatments (4 mL kg-1 seeds; 2.0 to 3.2 × 106 CFU/mL), the spore suspension (SS), and culture filtrate (CF) of IMIs was evaluated under pot conditions. Inoculation with M. incognita (2000 J2 per pot) significantly reduced the plant growth (20-24%), yield (16-36%), functional nodules (18%), leghaemoglobin (21%), leaf pigments (28-36%), seed protein (21%) and leaf photosynthesis (28%) of green gram cv. SML-668, while increased the non-functional nodulation (19%), phenolic compounds (9-27%), defense enzymes (17-20%), stress-related metabolites (36-38%), stomatal conductance and transpiration (21-25%) over control. The treatments with the SS of P. lilacinum AMUPL-31 and P. chlamydosporia AMUPC-31 significantly reduced the galling (54-61%), egg mass production (36-58%), fecundity (34-44%), reproduction factor (46-64%), multiplication factor (58-77%), and soil population (46-66%) of M. incognita over control. The microbial treatments promoted the above variables of plant growth, grain yield (18-32%), nodulation (20-42%), and photosynthesis rate (14-20%) in nematode infected green gram compared to the infected control. The SS of T. harzianum AMUTHZ-72 and T. viride AMUTVR-61 demonstrated potential for commercial application, as these treatments significantly suppressed the root galling and nematode reproduction (14-70%), and improved the yield of green gram (12-28%).