Biocontrol potential of Pseudomonas stutzeri endophyte from Withania somnifera (Ashwagandha) seed extract against pathogenic Fusarium oxysporum and Rhizoctonia solani

Agricultural crops are susceptible to abiotic and biotic factors. Among biotic factors, plant pathogens attacks are prominent and significantly reduce the crop productivity and production. Long term application of synthetic pesticides in agriculture not only causes resistance development in pathogens but also deteriorates the soil quality and pollutes the ecosystem. In the current study, an investigation has been made with an objective to isolate an endophytic bacterium from Withania somnifera seed and evaluate its potential biocontrol activity against soil-borne pathogens like Fusarium oxysporum var. ciceri and Rhizoctonia solani. The molecular approach of bacterium identification using 16S rRNA sequencing methods includes kit based DNA extraction and PCR amplification and the isolated endophytic bacterium was identified as Pseudomonas stutzeri. In dual culture assay, the endophytic bacterium P. stutzeri PSIISS-1 effectively suppressed growth of pathogenic fungi F. oxysporum var. ciceri (61.0%) and R. solani (53.3%), respectively. In vivo studies were conducted with initial microbial inoculum size of 10⁸cell/ml and the studies revealed that the bacterium P. stutzeri PSIISS-1 co-inoculated with R. solani had significantly inhibited the sheath blight disease with the efficacy of 76% in susceptible paddy MTU-7029. Simultaneously, co-inoculation of P. stutzeri PSIISS-1 along with the pathogen F. oxysporum var. ciceri in chickpea JG-14 variety resulted in reduction of wilt symptom up to 80.45%. Bacterial inhibitions against the pathogens were corroborated with chitinase, protease and lipase enzymatic activities. Based on the results obtained from the study, P. stutzeri showed biocontrol activity against plant pathogens which can be used as potential bio-pesticides.