Study On Antagonistic Mechanisms And Biocontrol Effect Of Strain Bai-g1 Against Fusarium Wilt In Banana

An antagonistic bacterium strain against Fusarium oxysporum f. sp. cubense race 4 was isolated from the soils of Cambodia, named bai-g1(Paenibacillus sp). Identifying strain bai-g1, optimizing fermentation, studying the inhibiting mechanism, extracting the antimicrobial substance and testing in pot plot were finished.Through the testing of morphology, physiological and biochemical signature, sequences of 16SrDNA, the strain bai-g1 maybe belong to the Paenibacillus cereus.Through the single factor and orthogonal test respectively, the optimum fermented conditions of strain bai-g1 were determined to produce the antimicrobial substance. The result showed the optimized media components of bai-g1 contained 2% inoculation volume, beef extract 0.4%, glucose 0.25%, sodium nitrate 0.25%, pH 7.0, cultured at 28℃, 150rpm for 72h.The strain and germfree fermented filtrate posed significant inhibition to F. oxysporum f.sp.cubense. The studies demonstrated that the strain can break down the hyphae, for example, mycelial digestion, large fault, local prominent deformity, end of the enlargement, the outflow of protoplasm. The germfree fermented filtrate can inhibit conidial germination, for example, microspore plasmolysis, cytoplasm condensation, lower germination rate. The diameter of inhibition zone went to 21.3mm on PDA plate. The diluted germfree fermented filtrate of 10 times had 94.4% inhibition rates to conidial germination.The inhibition effect maintained stable when the antimicrobial substance was treated with heat,acid and alkali. The diameter of inhibition zone went to 15.0mm when the germfree fermented filtrate dealt with 121℃after 10min and the antimicrobial activity was stable when the value of pH was adjusted to the range of pH 2～9. Precipitating the germfree fermented filtrate by 60% saturated ammonium sulfate was the ideal method to gain the antimicrobial extract. The result showed the antimicrobial substance was protein. The molecular mass of the protection with inhibition were 29.0KD,33.5KD . The antagonistic bacterium could produce Chitinase and the Chitinase was very sensitive to the proteinase K, pepsin, and trypsin.A pot experiment was used on the banana roots inoculated seedlings of eight processing, biocontrol effect on banana wilt of the strain bai-g1 reached 81.5%, the concentration of antagonistic bacteria for the 2.0×10~6 cfu / ml. The bai-g1 against usarium wilt disease in banana can be achieved to alleviate and improve plant resistance to disease, to promote the growth of banana seedlings, showing a good prospect.