ABSTRACT
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% NaCl and 2% sucrose concentration and after 72 hr of incubation at 30°C temperature. A. vinelandii showed 44% higher yield of antifungal metabolite under optimized conditions. The minimum inhibitory concentration was 10 µg 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.
ABSTRACT
A total of 187 endophytic fungi were isolated from 11 plant species, which were collected from 11 locations in Korea. Their antifungal activities were screened in vivo by antifungal bioassays after they were cultured in potato dextrose broth and rice solid media. Antifungal activity against plant pathogenic fungi such as Magnaporthe grisea (rice blast), Corticium sasaki (rice sheath blight), Botrytis cinerea (tomato gray mold), Phytophthora infestans (tomato late blight), Puccinia recondita (wheat leaf rust), and Blumeria graminis f. sp. hordei (barley powdery mildew) was determined in vivo by observing the inhibition of plant disease development. Twenty (11.7%) endophytic fungi fermentation broths were able to control, by more than 90%, at least one of the six plant diseases tested. Among 187 liquid broths, the F0010 strain isolated from Abies holophylla had the most potent disease control activity; it showed control values of more than 90% against five plant diseases, except for tomato late blight. On the other hand, fourteen (7.5%) solid culture extracts exhibited potent disease control values of more than 90% against one of six plant diseases. The screening results of this study strongly suggested that metabolites of plant endophytic fungi could be good potential sources for screening programs of bioactive natural products.