| This paper presented a systematic study on the biological control of soilborne disease by Bacteria HSY-8-1 and the isolation, purification, and characterization of an antifungal substance.180 strains were isolated from roots of bean and resistant to heat. The antagonistic assay in plates showed that among which 52 strains were with antagonistic activities. And 16 strains of them exhibited the in vitro antagonistic activity to the main soilbome phtytopathogens: Fusarium ssp, Rhizoctionia solani and showed the biological control ability to soilborne disease in green-house experiments. Among them, strain HSY-8-1 showed rather high in vitro antagonistic activities to Fusarium ssp, and Rhizoctionia solani , as well as more available for control of other soilborne phytopathogens than other one.In vitro antagonistic test, antibiosis plays an important role in desease suppression by bacteria HSY-8-1. Its antifungal machanism was mainly disintegration of cell wall to make the hyphae abnormal and the spores germinate abnormally or can not germinate at all. The abonormal hyphal growth of Fusarium ssp.caused by the antifungal substance such as swollen tips , twisted, short growth and cytoplasm condensation was also observed.With (NH4)2SO4, fractional precipitation, DEAE-Sephadex Fast Flow chromatography and Sephadex G-100 chromatography followed by tracks of fraction antagonistic assay , an antifungal substance with in vitro anti-Fusarium ssp.activity was isolated and purified. The purified material had absorbtion peak at 275 nm, and was exhibited negative in biuret color reaction. However after hydrolyzed with HC1, this substance shown positive in the same reaction. Its active pH range is wide, from 4. 0 to more than 12. 0, relative more stable inhigh pH. Combining with its thermostion and resistance proteinases, it was suggested that this antifungal material was cyclic peptide. |
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