| On the basis of ecologic balance, the Complex Microbial Preparations, principal component of which was Gliocladium virens, were developed for control of damping-off of Pinus massoniana in this paper, and multiple, antagonistic microbes can play a cooperative role for use against this soilborne plant pathogen,which were expected to obtain. The major results are as follows:1. The antagonism of Gliocladium virens GVD against three strains of pathogenetic fungi causing seedling damping-off were studied with dual test, enclosed chamber test , scanning microscope,inhibitory activity and thermostability of crude extract of gliotoxin. The results indicated that GVD was competitive and parasitic to Rhizoctonia solani, Fusarium solani and Pythium sp; GVD expanded the hyphae cell of Rhizoctonia solani to ellipsoid. GVD growed parallel to Rhizoctonia solani and coiled itself round them.Many hyphae of Rhizoctonia solani were crinkle and shriveled. They were penetrated by GVD and collapsed; GVD coiled itself round hyphae of Fusarium solani and made their hyphae broken or deformed, and cytoplasm of Fusarium solani were oozing;GVD penetrated deformity hyphae of Pythium sp where they were lysis or broken; The inhibitory rates of nonvolatilizable metabolites from GVD were 100% against Rhizoctonia , Fusarium , Pythium ;the inhibitory rates of volatilizable metabolites from GVD were 26. 7%, 51. 5% and 43. 5% against Rhizoctonia, Fusarium, Pythium . The thermostability of crude extract of gliotoxin was under 100℃. The antagonism of Gliocladium virens GVD against Rhizoctonia solani, Fusariumspp and Pythium spp is evident.2. Bacillus spp (B-305),an antagonistic bacterium isolated from the soil, strongly inhibited the growth of three kinds of pathogenetic fungi causing seedling damping-off. The strains was preliminarily identified as Bacillus firmus on the basis standard of bacteria tests;Cultured on rotary shaker for 3 days, the CPU of this bacterium reached the largest value in log increasing at this time;Antagonistic substance which was strongly antagonistic to plant pathology fungi can be produced by B-305 strain which was cultured for 3 or 2 days. The inhibitory rates of nonvolatilizable metabolites from B-305 were 64.04%, 29. 59%, 99. 99% against Rhizoctonia solani, Fusarium solani , Pythium sp , which were cultured for 64 hours. The acid metabolites was produced in the die process of B-305 and this substances was antifungal;By enclosed chamber test, the inhibitory rates of volatilizable metabolites from B-305 were 8. 43%> 9.98%, 5.59% against Rhizoctonia solani, Fusarium solani, Pythium sp; The scanning electronic microscope revealed that the growth of Rhizoctonia solani was inhibited by nonvolatilizable metabolites from B-305, their cells of hyphae were expanded to ellipsoid or globular structure in the top or middle cell of hyphae, some hyphae were broken off, and the cytoplasm oozed out of the cells so that most of hyphae became crinkle and shriveled.3. The optimal medium for chlamydospore production was potato-dextrose liquid which was screened out from 8 kinds of mediums. In PD medium, the optimum culture conditions were pH3, 30℃, rotating in the light. The acid environment greatly enhanced chlamydospore formation and inhibited production of conidia entirely, and the numbers of chlamydospore production are 8.00 X 106 ^h/ml at these conditions for a week;Studies of chlamydospore germinating showed:The optimum germination pH value was pH6~pH8 and the optimum temperature of germination was 25℃;The germinating rate could reach above 90% after 48 hours;The optimal temperature for storing was under 5℃.4. The results of potted plant experiment showed: Bacterization of seed with B-305 cell suspention and chlamydospore powder of different weight applied tosterile soil had significant effect on incidence of Pinusmassonianadamping-off. The more chlamydospore powders, the greater controlling effect was strengthened . The controlling effect of complex antagonists was better than that of single antagonist...
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