Identification and production of Azotobacter vinelandii and its antifungal activity against Fusarium oxysporum.

The phytopathogenic Fusarium species are one of the leading causes of loss in agricultural productivity. In search of an efficient bacterial antagonist, 19 soil isolates of Azotobacter sp. were screened for antagonistic activity against Fusarium oxysporum by agar well diffusion assay. The potential strain was identified as Azotobacter vinelandii by 16S rRNA sequencing. Optimum conditions for culturing A. vinelandii to obtain maximum antifungal activity were determined by varying temperature, pH, incubation period and NaCl and sucrose concentration. Maximum inhibition of F. oxysporum was observed at pH 7 and 8, 1% NaCI and 2% sucrose concentration and after 72 hr of incubation at 30 degrees C temperature. A. vinelandii showed 44% higher yield of antifungal metabolite under optimized conditions. The minimum inhibitory concentration was 10 microg ml(-1) for F. oxysporum. The FTIR analysis of purified metabolite showed presence of aldehyde, C-N, ester, aromatic ring, P-H stretch, and C-N stretch of alkyl amine in the structure. The purified antifungal metabolite of A. vinelandii showed effect on spore germination and mycelia morphology of F. oxysporum. The study revealed significance of A. vinelandii in controlling F. oxysporum and its promising application as a biocontrol agent in agriculture.