Screening Of Biocontrol Strains Against Rice Blast And Analysis Of Bioactive Compounds

In this paper,bacteria isolated from soil and plant roots were used as research objects.Strains with antagonistic effects against plant pathogenic fungi were screened by Oxford Cup method.Active strains were identified and its biocontrol effect was evaluated.Then the active substance in fermentation broth of active strain was analyzed and its antifungal effect was investigated,which provided a basis for the development of biological control agent.The details were as followed:1.Petroleum ether,n-butanol,and ethyl acetate were used to extract the fermentation broth of the 11 strains in sequence.The Oxford cup method was used to investigate the activity of 33 kinds of extracts against 11 plant pathogenic fungi.The ethyl acetate extracts of strain WRN032 fermentation broth had a strong inhibitory effect on Magnaporthe oryzae.When the concentration was 1.0mg/mL,the inhibition zone diameter was 22.31mm.2.Active strain was identified and its biocontrol effects was evaluated.Through the results of physiological and biochemical tests and 16S rRNA identification,the strain WRN032 was identified as Bacillus tequilensis.The ethyl acetate extracts of its fermentation broth had strong biocontrol effect on Magnaporthe oryzae.As the concentrations increased,the relative inhibition rate obviously increased.When the minimum concentration was 0.0625 mg/m L,the inhibitory rate was 60.5%.The active substances were stable at temperature of 25～80°C and p H of 1.0～7.0,and were not sensitive to ultraviolet light.When stored at room temperature for 48h,the antifungal effect of the active substances were basically unchanged.3.The ethyl acetate extracts of Bacillus tequilensis WRN032 fermentation broth were analyzed by HPLC.The active substance was identified by mass spectrometry and its antifungal effect was evaluated.The optimized chromatographic conditions were:chromatographic column of Unitary C₁₈,detection wavelength of 275nm,acetonitrile-water（0.1%acetic acid）as mobile phase for gradient elution,segmented flow rate,column temperature of 25℃.Methodological investigation results showed that the method was stable and reliable,which can be used for the analysis of this sample and separation of active substances.The inhibitory effect of the purified active substance against Magnaporthe oryzae was similar to 75% tricyclazole wettable powder,which showed the antifungal effect of purified substance was strong.The relative molecular mass of this compound was about 340.2.