Study On The Mutants Induced By UV Radiation Affecting Hyperparasitic Streptomyces Strain F46 And PR

The spores of hyperparasitic Streptomyces strains PR and F46 were irradiated with UV light to improve the control effects against plant diseases. The lethality rate of UV light to the spore of hyperparasites strains PR and F46 was determined. The irradiated time for strains PR and F46 were 7 min and 3 min respectively when obtaining 95% lethality rate. Two mutants PR-7-2 and F46-3-7 were screened based on the inhibiting effects to the target pathogens. The color of substrate mycelia of mutants was always white or colorless, which were absolute different from the original strains. The production of spore of mutants was as much as 2.2 times of the original strains', but the mutants showed reduced growth. Eleven pathogens were used to test the antagonistic effects of the two mutants. The results showed that the two mutants had different inhibiting effects on those pathogens, and they, as their original strains, had better inhibiting effects on low pathogenic fungi. The mutants had better effect on target pathogens than the original strains. The mutants could maintain those characters after 8 successive generations on the PDA. The mutants had different tolerance to the 8 tested fungicides commonly used in the field. The results showed that PR-7-2 could use in the field with matalaxyl, quintozene, procymidone, triadinfon, and F46-3-7 with thiophanate, quintozene, carbendazim procymidone, triadinfon. The ecological studies with the two mutants showed that strain PR-7-2, the same to the original strain PR, only survived several in the three media. But strain F46-3-7 could survive in the soil added with the mycelia of M. piriformis, and the number could increase. The two mutants were able to colonize in the cucumber seedling, and the colony ability of the two mutants was better than their original strains. They could move in the body of cucumber seedling and always move to the top of cucumber seedling. Biocontrol potential of the two mutants against apple postharvested decay demonstrated the two mutants have better inhibiting effects on the pathogens than their original strains at 15℃and 25℃. The resules showed that the control efficacy of both the mutants and their original strains against pathogens over 50%.