Inhibitory effects of UV mutants of Streptomyces corchorusii and Streptomyces spiroverticillatus on bean and banana wilt pathogens

Abstract

The purpose of this investigation was to produce improved mutants of Streptomyces corchorusii and Streptomyces spiroverticillatus, using a UV-irradiation regime, which are effective against the causal pathogens of the Fusarium wilt of French bean and the bacterial wilt of banana, respectively. Seven out of the 11 mutants obtained from S. corchorusii were active antagonists against Fusarium oxysporum f.sp. phaseoli; mutant 155 was the most effective. All five mutants obtained from S. spiroverticillatus showed inhibitory effects against Pseudomonas solanacearum; mutant 281 was the most potent. Spore germination, germ-tube elongation, growth, and sporulation of F. oxysporum f.sp. phaseoli were significantly inhibited in the different concentrations of filtrates of either wild or mutant 155 of S. corchorusii in vitro with the mutant being more effective; maximum inhibition was at 80% concentration. The filtrate of either wild or mutant 281 of S. spiroverticillatus sharply decreased the number of colonies of P. solanacearum as its concentration increased up to 80%, at which no growth was obtained. The in vivo utilization of S. corchorusii in the biocontrol of Fusarium wilt of French bean revealed that soaking seeds in filtrate of the antagonistic strain prior to sowing was the most effective treatment and that mutant 155 reduced disease incidence by 83.4% (43.3% for the wild type) compared with the untreated control, in addition to improving plant growth. Key words: antagonism, UV irradiation, mutation, Streptomyces spp., Fusarium wilt, bacterial wilt, French bean, banana.