Abstract:
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.
Keywords: Rhizobacteria, Biocontrol, Percentage inhibition, Tomato wilt.
