Plant growth enhancement and suppression of Macrophomina phaseolina causing charcoal rot of peanut by fluorescent Pseudomonas

A plant growth-promoting bacterial strain, GRC(2), was isolated from potato rhizosphere and characterized as fluorescent Pseudomonas. It produced a hydroxamate-type siderophore in iron-deficient tryptic soy medium. The production of hydrocyanic acid and indole acetic acid was also recorded under normal growth conditions. The strain showed a strong antagonistic effect against Macrophomina phaseolina, a charcoal rot pathogen of peanut, when co-cultured on tryptic soy agar medium. The growth inhibition of M. phaseolina was 74% after 5 days of incubation. Bacterization of peanut seeds with fluorescent Pseudomonas GRC(2) resulted in increased seed germination, early seedling growth, fresh nodule weight, grain yield and reduced charcoal rot disease of peanut in M. phaseolina-infested soil as compared with control. A streptomycin-resistant marker of the bacterium GRC(2)(strep+) was used to monitor root colonization, which positively confirmed the efficient colonization of peanut root. Seed bacterization reduced charcoal rot disease in M. phaseolina-infested soil as compared with the control by 99%, making the organism a potential biocontrol agent against charcoal rot of peanut.