Screening And Identification Of Biocontrol Microorganism Against Rice Blast,caused By Magnaporthe Oryzae

Rice blast,caused by Magnaporthe oryzae,is a worldwide devastating fungal disease that seriously damaged the yield and quality of rice and affected the safety of grain production.At present,chemical control is still the main measure to combat this disease.However,it has caused serious problems in environmental pollution and edible safety.Alternatively,using biocontrol microorganism originated from rice plants to control rice disease can overcome the shortcomings of chemical control and meet the requirements of modern agricultural production.This approach can be called“come from the rice and benefit the rice”.The main purpose of this study is to screen microbial strains that shared excellent antagonism to rice blast fungus,and then to identify the strains,to test the biological antimicrobial spectrum,the antimicrobial effect of the metabolic product,and the prevention and treatment effects to leaf blast as well.The main results are as follows:1.Screening and identification of the antagonistic bacteria of rice blast fungus.In this study,464 strains were isolated from the healthy rice and its rhizosphere soil among the rice blast infected rice hills.When filtered with two rounds of screening using M.oryzae as indicator fungus,strains RS10,RS39,and RS85 showed an inhibition rate of92.73%,89.62%and 91.01%,respectively,on the mycelium growth of M.oryzae.Combined the analysis of morphology,physiology and biochemistry,and the 16S r DNA sequences,the three strains of RS10,RS39,and RS85 were all identified as Bacillus subtilis.2.Biological characteristics of strains RS10,RS39 and RS85.The antimicrobial spectrum assays performed on 10 pathogens demonstrated that the strains of RS10,RS39 and RS85 had no effect on bacteria,but had also antimicrobial effect on the fungus except for blast fungus,displaying inhibition activities to Sclerotinia sclerotiorum with inhibition rates of 85.16%,67.74%,and 81.94%,respectively.The antagonism screening against M.oryzae on metabolites of the three strains showed that,as the smallest volume of these metabolites accounted for 15%of the PDA medium,the inhibition activities were positive showing inhibition rates of 85.28%,80.55%and 81.32%respectively.3.Control effect of strain RS10 on rice blast leaf blast in Greenhouse.The control efficacy against the rice leaf blast were tested by sequential inoculation of conidial suspension of M.oryzae,followed by the compound of fermentation liquid of RS10and thallus of RS10,pure thallus of RS10,and the sterilized fermentation liquid,respectively.Results showed that the control efficiency were optimal when these RS10 associated materials were sprayed,3 days post-inoculation of the M.oryzae,in concentration of1×10~8cfu/m L,1×10~9cfu/m L,and 10 times diluent,respectively.The control efficiency were90.12%、87.43%and 88.94%(1×10~8cfu/m L RS10 fermentation liquid,the best value is90.12%).Moreover,another control efficacy test also conducted.It obtained the optimal control efficiency of 88.24%,87.61%and 84.83%(1×10~8cfu/m L RS10 fermentation liquid,the best value is 88.24%),respectively,by inoculation the same compound of fermentation liquid and thallus,pure thallus,and the sterilized fermentation liquid of RS10 3 days prior to inoculation of the conidial suspension of M.oryzae in the same concentration of1×10~8cfu/m L,1×10~9cfu/m L,and 10 times diluent,respectively.