| 59 strains of actinomycete were isolated from soil samples collected in Liquan Shanxi, Shangqiu Henan and Weihai Shandong. In the subsequent screening program of the fungicidal activity against Bacillus subtilis, 7 strains ( A3, A10, A19, B8, B20, B31, B38 ) exhibited fungicidal activity. Among these, strain A19 possesed the highest activity, the inhibition zone was diaphanous and its diameter reached 21cm.The bioassay results showed that the fermentation broth of strain A19 had 100% inhibition rate against Bipolaris sorokiniana; more than 80% inhibition rate against Botrytis cinerea, Bipolaria maydis and Exserlhilum turcicum; more than 70% inhibition rate against Alternaria longipes, Fusarium graminearum, Fusarium oxysporium and Colletotrichum gloeosporioides; about 60% inhibition rate against Fulvia fulvum and Curvularia lunata. By means of agar diffusion method, the diameter of inhibition zone against Bacillus subtilis, L-streptococcus and Staphylococcus aureus were 21.0mm, 20.0mm, 17.0mm, respectively. The results of pot tests indicated that the fermentation broth of strain A19 exhibited 54.3% protective efficacy and 65.0% therapeutic efficacy against Erysiphe graminis.The results of the stability test indicated that antimicrobial activity of the fermentation broth of strain A19 had few variety after cultivated 10 generations seriately. It was stable to temperature, but unstable to acid or alkali.Doskochilova Solvent System identification showed that the the active constituent of the fermentation broth was considered to be a kind of aureothricin. A compound 15-2 isolated from the fermentation products was identified as 7-hydroxy-3-isobutylhexahydropyrrolo[1,2-α]pyrazine-1,4-dione. The compound exhibited 6mm diameter of inhibition zone against Bacillus subtilis. By means of spore germination tests, the inhibition rate against Exserlhilum turcicum, Bipolaris sorokiniana and Alternaria longipes was 57.0%, 67.3% and 55.5%, respectively.
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