Antagonistic potentiality of native rhizobacterial isolates against root rot disease of okra, incited by Rhizoctonia solani

Among seventy isolates, antagonistic twenty one representing biovars of Pseudomonas fluorescens (biovars I, II, III, and V) were collected from the rhizosphere of okra, chilli, ground nut, brinjal, cabbage and tomato from different agro-ecological regions of West Bengal and were subjected to evaluate for their antifungal activity under in vitro condition against Rhizoctonia solani, the most important soil-borne plant pathogen two isolates, PF-8 and PF-7 effectively inhibited the mycelial growth of Rhizoctonia solani (72.05 and 68.25%, respectively) in dual culture method. The vigour index of okra was also recorded maximum for the isolate PF-8 (2415.7) followed by PF-7 (2063.25). Mechanisms of fungal inhibition were elucidated by tracing secondary-metabolite production of the rhizobacterial isolates. Most of the isolates expressed a specific mechanism of antagonism, as represented by production of pigments, Siderophores, cyanide (HCN), Indole Acetic acid (IAA) and Salicylic Acid (SA) production, and Phosphate solubilization. Rhizobacterial isolate PF-8 was found to be effective as seed and soil treatment for management of root rot disease of okra. The antagonistic nature of fluorescent pseudomonads against fungal pathogens can be assigned to design a potential candidate for development of agriculture sector to be used in biological control of soil borne plant pathogens.   Key words: Fluroscent pseudomonads, secondary metabolites, Rhizoctonia solani, okra root rot.