Investigation of antagonistic effect of Bacillus subtilis on biological control of sugar beet damping - off disease

Due to the high antagonistic activity of bacterium, Bacillus subtilis (Ehrenberg) Cohn, three isolates (B.s.Ham, 204 and 202) were selected and their efficacy were studied in control of sugar beet damping–off caused by Rhizoctonia solani, in in vitro and in vivo conditions. In dual culture on PDA, all isolates of B.subtilis inhibited mycelial growth of R.solani. Significantly, volatile metabolites of B.subtilis isolates reduced mycelial growth of R.solani. Inhibitory ability of volatile metabolites of B.subtilis isolates were studied in different culture media. In this experiment, isolate B.s.Ham on PDA with inhibition percent of 62.22%, had the best effect in reduction of mycelial growth of R.solani. Inhibitory effect of five concentration (2%-5%-10%-15%-25%) of culture filtrates of bacterial isolates were studied and it was found that isolate B.s.Ham in 25% concentration with 73.70% was the most effective in inhibition of mycelial growth of R.solani. In green house experiments, we found that seed coating or soil drenching by antagonistic agents, 30 days after sowing, had a good effect in mortality and there were significant differences among treatments. Among isolates, B.s.Ham with 64.59% in comparison to the infected control had the best effect on control of this disease. Overall, soil drenching of antagonistic bacteria was more effective than seed coating, in reducing of sugar beet damping-off.