Allochthonous rhizobacterial inoculation of Vigna radiata promotes plant growth and anti-bacterial metabolite production

In the present study, rhizobacterial strains associated with paddy rhizosphere were screened for plant growth promotion efficacy against Vigna radiata. Plant growth promotion effect was determined by measuring indole acetic acid (IAA) phosphate solubilisation efficacy and antagonistic activity. Among the isolates, Azosprillum strain AZOSP -V1 strain (114.2 μg/mL) and the AZOSP-S1 strain (104.2 μg/mL) were known to produce maximum production of IAA. High phosphate solubilisation efficacy was recorded in the Pseudomonas fluorescens- PS-V4 strain. Antagonistic activity of rhizobacterial isolates was tested against plant pathogenic fungal strains Pythium sp, Fusarium oxysporum, Rhizoctonia solani and Trichosporium vesiculosum. Among the rhizobacterial strains, notable growth inhibition of all the tested fungal pathogens was recorded in Pseudomonas fluorescens and Bacillus megaterium treatment. Seed priming of the respective rhizobacterial strain supported seedlings' emergence plant growth promotion of V.radiata without inducing any undesirable oxidative stress. Further, rhizobacterial strains were screened for bioactive metabolites production. Among the strains, bioactive metabolites were extracted from Pseudomonas fluorescens strain PS-V4 which showed potential pesticidal and antibacterial activity against gram pod borer Helicoverpa armigera and plant pathogenic bacterial strain Xanthomonas campestris. Biocompatibility of the metabolites was also screened with the zebrafish model by measuring embryonic toxicity. No sign of toxic effect on all the embryonic stages of zebrafish treatment confirmed the best biocompatibility. The present study suggests the possible utilisation of allochthonous rhizobacteria as an effective biofertiliser and biocontrol agent to their high growth promotion, biocontrol efficacy, and coupled oxidative stress modulation.