EFFECT OF CULTURE CONDITIONS ON THE ANTIMICROBIAL ACTIVITIES OF UV-MUTANTS OF STREPTOMYCES-CORCHORUSII AND S-SPIROVERTICILLATUS AGAINST BEAN AND BANANA WILT PATHOGENS

The potentiality of 36 strains of actinomycetes species isolated from fertile clay soils in Egypt for the production of antimicrobial substa nces against a variety of test organisms was investigated. Most of the isolated organisms inhibited gram positive, gram negative and acid fa st bacteria as well as yeasts and filamentous fungi. Nine isolates sho wed antagonistic activities against the French bean-wilt fungus Fusari um oxysporum f.sp. phaseoli, and 19 isolates antagonized the bacterial -wilt pathogen of banana Pseudomonas solanacearum in vitro. The most a ctive isolates against the preceding pathogens were identified as Stre ptomyces corchorusii and S. spiroverticillatus. These were subjected t o UV-irradiation treatment in order to induce mutants with increased a ntagonistic activities. Eleven mutants were obtained from S. corchorus ii and mutant M155 was the most active against the Fusarium-wilt patho gen on agar medium (diameter of inhibition zone was 15 mm after 10 day s compared with 9 mm for the wildtype). All five mutants obtained from S. spiroverticillatus were inhibitory to P. solanacearum; mutant M 28 1 was the most potent in liquid medium (diameter of inhibition zone wa s 24 mm after 2 days compared with 12 mm for the wild-type by the pape r disc method). Different concentrations of the ingredients of starch- nitrate medium stimulated by nearly 2-fold the inhibitory effects of M 155 and M281 as compared with their wild types. Under such conditions, S. corchorusii M155 lysed completely the mycelium of F. oxysporum f.s p. phaseoli after 10 days.