Efficacy of bacteriocinogenic strains of Xanthomonas oryzae pv. oryzae on the incidence of bacterial blight disease of rice (Oryza sativa L.)

Abstract

A total of 144 isolates of Xanthomonas oryzae pv. oryzae were screened for bacteriocin production against 30 indicator strains of X. oryzae pv. oryzae. Forty isolates showed broad-spectrum inhibitory activity against 20–27 indicators, presumably because of the production of bacteriocin compounds. The selected isolates were screened for bacteriocin production at 29 °C and tested for virulence on rice differentials. Since all of the isolates were pathogenic, nonpathogenic bacteria were generated through N-methyl-N-nitro-N-nitrosoguanidine mutagenesis and by repeated subculturing. Epiphytic colonization and survival of pathogens and of nonpathogenic bacteriocin producers on rice plants were monitored, using mutants resistant to streptomycin and rifampicin. An improved method of pathogen inoculation was developed and used to evaluate biological control. Treatment with nonpathogenic bacteriocin-producing bacteria resulted in reductions of bacterial blight incidence up to 31–99% in greenhouse tests and 11–73% in the screenhouse. Bacterial leaf streak severity was reduced 4–20% in the greenhouse and disease incidence was reduced 20–39% in the screenhouse. Key words: bacteriocin, biological control, Xanthomonas oryzae pv. oryzae, mutagenesis, rice.