Screening For Antagonistic Strains Of Bacillus Spp. And Study On TasA Gene

This dissertation studied the screening and identification of antagonistic strains of Bacillus spp., and discussed the mechnisms of Bacillus spp. to improve sweet patato' s resistance to Fusarium. oxysporumf. sp. batatas., which included increasing photosynthesis and promoting protective enzyme system. The main results were as follows:(1) Forty-one strains of Bacillus spp. were obtained from plant rhizosphere and their antagonistic effect on plant fungal and bacterial pathogens were tested. Among them, eleven strains with high inhibitory rate on plant pathogen were screened, which were AB, V3, SAI, 3-1, N8-b, 25-1, 25-5, 25-6, 25-9, 25-15 and 25-17. This research also explored the inhibition mechanism of Bacillus spp. on several pathogens, which were F. oxysporumf. sp. batatas, Alternaria brassicae, Colletotrichum musae, Rhizoctonia solani, Phytophthora capsici. The research of mechanism focused on inhibitory effects of strains 25-5, 25-6, 25-9, 25-15, 25-17 on F. oxysporum f. sp. batatas, Alternaria brassicae and those of strains 25-1, 25-17 on Colletotrichum musae. The results indicated as follows: with dual culture on plate method, significant anti-bacterial circle was observed; with concave slide method, in which the pathogen conidia were treated with bacterial culture filtrate, the germination rate of conidia decreased significantly. Coating bacterial culture filtrate and conidia suspension on the PDA plate, culture filtrate inhibited pathogen conidia' s formation. Observing strains with optical microscope and optical oil immersion lens showed that all of the strains could inhibit pathogen growth. The inhibition caused the increase of pathogen hyphae branches and the expansion of the top and central part. With continued inhibition, abnormal structures increased, the hypha became bead-like or with more branches, and the cells on the end of the hypha expensed to clusters, the hypha walls pierced so the contained substance leeked out, the cells collapsed and turned into hollow sphere bubble.(2)With Bacillus spp. strains 25-5, 25-6, 25-9, 25-15, 25-17 as materials, the photosynthetic mechanism and starting mechanism of protective enzyme system in the process of inoculating Baccillus spp. to increase sweet potato' s resistance to F. oxysporumf. sp. batatas, were investigated. The results indicated that for the sweet potato leaves treated with Baccillus spp.