Isolation,Identification And Biocontrol Effect Of Antagonistic Bacteria Against Magnaporthe Oryzae

Outbreaks of rice blast disease are a serious and recurrent problem in all rice-growing regions in the world,and the disease is extremely difficult to control.Rice blast,caused by the fungus Magnaporthe oryzae,is therefore a significant economic problem.It cause10%-30%loss to rise each year.Rice blast seriously threatens the safety of food production.At present,based on the China Plant Protection Policy of"prevention first,comprehensive control",agricultural control measures of breeding and planting resistant varieties as well as adopting chemical control measures,such as chemical agents,are conducted to comprehensively control rice blast.However,these control measures are imperfect.Because of the problems and limitations existing in agricultural control measures and chemical control measures,biological control that is environmentally friendly,non-toxic,harmless,and non-easy to develop disease resistance serving as an alternative measure for disease prevention and control has gradually become the focus of research.Biological control bears the advantages of low-cost,long-lasting,safe to the environment and organisms,as well as environmental friendly.Therefore,it is necessary to promote microorganisms to control plant diseases,for it provides a cost-effective way to prevent and control plant diseases without side effects.In order to explore the control effect of bacteria with rice blast,this study isolated bacteria,and employed plate confrontation experiment to screen and identify the bacteria with antagonistic effect against M.oryzae.And the study preliminarily explored the control effect of the obtained biocontrol bacteria against M.oryzae and the growth-promoting effect of the obtained biocontrol bacteria on rice.The main findings are as follows:The study isolated and purified 176 strains of bacteria,and conducted plate confrontation experiment of the obtained bacteria against M.oryzae.Finally,2 strains of bacteria with good antagonism against M.oryzae were screened out,and named V-23 andⅢ-6.The study amplified and sequenced the extracted genomic DNA of strain V-23 and strainⅢ-6 by gyr B primers,and establishes a phylogenetic tree by MEGA neighbor joining method,which confirmed that V-23 is Pseudomonas aeruginosa andⅢ-6 is Bacillus amyloliquefaciens.By testing the antibacterial activity of V-23 andⅢ-6 against other pathogenic fungi,oomycetes and bacteria,it is found that these two kinds of bacteria show a relatively broad-spectrum antagonistic effect.And V-23 shows stronger antibacterial activity against pathogenic fungi,whileⅢ-6 shows stronger antibacterial activity against pathogenic oomycetes.The lipopeptide substance produced by the antagonistic strain V-23is extracted by acid-precipitation.The lipopeptide substance of V-23 is analyzed by high performance liquid chromatography,and it is preliminarily confirmed that the active substance may be phenazine-1-carboxylic acid.Further research finds that the live bacteria and secondary metabolites of V-23 andⅢ-6 can inhibit the formation of appressorium of M.oryzae.The critical concentrations of V-23 andⅢ-6 that inhibits the formation of appressorium of M.oryzae（24 h）are 1.9×10³CFU/m L and 1×10²CFU/m L.At the same time,it is found that both bacterial fermentation liquid and filtrate of V-23 andⅢ-6(OD₆₀₀=1)show obvious control effect against rice blast,and the protective effect of them is significantly higher than the therapeutic effect.In addition,it is found that all different concentrations of V-23 andⅢ-6 can promote the growth of plant height,root length and stem weight of rice.And the optimal growth-promoting concentration of V-23 andⅢ-6 are OD₆₀₀=0.1 and OD₆₀₀=0.05.In summary,bacteria P.aeruginosa V-23 and B.amyloliquefaciensⅢ-6 with good effect against rice blast were isolated in this study.And both of them show broad-spectrum antagonistic effect,protective and therapeutic effect against rice blast,and good growth promoting effect of rice.The research results provide a theoretical and experimental basis for further exploring the prevention mechanisms and strategies of V-23 andⅢ-6 against rice blast.