Exploitation of indigenous fluorescent pseudomonads against stem and pod rot of groundnut caused by Sclerotium rolfsii

Stem and pod rot of groundnut is an economically important soil borne disease caused by Sclerotium rolfsii Sacc. The present study aimed to evaluate the indigenous bacterial bio control agent Pseudomonas fluorescens strains having multiple traits related to bio control and plant growth promoting activity. Healthy rhizospheric soil from groundnut field was collected from different North Karnataka districts. Nineteen strains of P. fluorescens were isolated by serial dilution technique on King’s B medium. The antagonistic potential of nineteen strains was tested against S. rolfsii by using dual culture technique. The per cent inhibition was highly variable among the nineteen strains of P. fluorescens ranging from 2.59 to 75.18 per cent. Maximum mycelial inhibition of S. rolfsii was recorded by the strain PF-2 (75.18%) followed by PF-3 (72.96%), PF-6 (69.62%) and least inhibition was recorded by PF-13 (2.59%). Five superior strains of P. fluorescens showed fluorescens under UV light, yellowish green pigmentation, rod shaped cells under microscope. Five superior strains were subjected for various biochemical tests and all the isolates were positive for biochemical characterization such as Gram staining, endospore production, catalase, starch hydrolysis, urease test, casein hydrolysis and gelatin liquefy action and negative for KOH and in dole test. Further, these strains were subjected for plant growth promoting traits such as HCN production, IAA production, siderophore production and volatile compounds production. Among these, the strainsviz., PF-2 and PF-3 were scored as strong with respect to antagonism and growth promotion. The strainsPF-6, PF-7 and PF-10 were scored as moderate with light brown colour. Among the tested strains of P. fluorescens, the isolates PF-2 and PF-3 were recorded higher production of siderophore, isolates PF-6, PF-7 and PF-10 showed moderate production of siderophore. The strain PF-2 of P. fluorescens showed highest per cent of mycelial inhibition of S. rolfsii indicating higher production of volatile compounds, followed by PF-3 and PF-6. Whereas, the least mycelial inhibition was recorded by the isolate PF-10 indicating less production of volatile compounds.