isolation and characterization of bacillus sp with in-vitro antagonistic activity against fusarium oxysporum from rhizosphere of tomato

the present investigation was carried out to isolate and characterize antagonistic bacteria against wilt causing fungal pathogen i.e. fusarium oxysporum, from the rhizosphere of tomato. fifty-six bacterial strains were isolated from the rhizosphere soil samples of healthy tomato fields, collected from different locations of faridabad district, haryana, india. out of these, ten isolates were found to be antagonistic against the tested fungal pathogen i.e. fusarium oxysporum, under in-vitro conditions. on the basis of percentage inhibition of radial growth of fusarium oxysporum, isolate tnam5 was found to be the most effective antagonistic rhizobacteria. based on its morphological and biochemical properties along with 16s rrna sequence analysis, it was identified as a bacillus sp., with close nucleotide identity to bacillus subtilis group. average percentage inhibition given by this isolate was 47.77% and it was found to produce diffusible and volatile antifungal metabolites along with hydrogen cyanide and ammonia. effect of physiological parameters on the growth and antagonistic behavior of the potential isolates was also examined. optimal conditions for antagonistic activity were found to be 28ºc and ph 6.5, while the maximum growth was observed at 35ºc and ph 7.0. however, increase in salinity did not significantly affect (p> 0.05) the antagonistic behavior or growth of the isolates and they were found to withstand nacl concentration up to 8.0% (w/v). the present study, hence, provides a potential biocontrol agent for fusarium oxysporum, however, field studies of this isolate as soil inoculant in tomato are required in order to establish its actual performance.