Screening Of Antagonistic Bacteria Against Plant Pathogenic Fungi In Vermicompost And Its Mechanisms

Every year thousands of billion dollars in economic losses are caused by the plant pathogenic fungi which are very susceptible to plants in the process of agricultural production.So,how to control the disease and maintain the normal growth of plants,have been the hot topics in the study of scientific research workers.Chemical pesticides play a huge role in effectively control fungal diseases and can contribute to plant diseases in the prevention and treatment.But the overuse of chemical pesticides can cause soil,water and air pollution and increase the amount of pesticide residues in agricultural and sideline products,which direct harm to human health and life,but also cause the drug resistance of pathogenic fungi.These problems restrict the use of chemical pesticides,so it is urgent to find a new safe and effective way to control plant diseases.Through the screening of antagonistic microorganisms in vermicompost to control plant diseases,not only the drug resistance problems caused by the overuse of chemical pesticides can be solved,but also it can contribute to environmental safety and human health under certain conditions.In this paper,a broad-spectrum antagonistic bacterium was screened from the vermicompost by gradient dilution and plate confrontation methods.At the same time,the biocontrol effect and antagonistic mechanism of antagonistic bacteria were studied.The main research and findings are as below:Firstly,ten plant pathogenic fungi were used as the target fungi to isolate the antagonistic bacteria from vermicompost according to the methods of gradient dilution and dural culture.Results showed that 12 bacterial strains against Rhizoctornia solani,21 strains against Fusarium oxysporum f.sp.cucumerinum,3 strains against Phomopsis amygdali,and 3 strains against Botrytis cinerea were isolated.Among them,the strain M29(16S rRNA GenBank accession number:KU870670)had 95.3%inhibition rate on mycelium growth of.Rhizoctornia solani,91.2%inhibition rate on,and 89.4%inhibition rate on Verticillium dahliae and Botrytis cinerea.The strain M29 was identified as Bacillus subtilis after the morphological changes,physiological and biochemical indexes and 16S rRNA gene sequence analysis were considered.Secondly,the antagonistic activity of the secondary metabolites produced by the strain M29 was determined.The antifungal lipopeptides derived from antagonistic bacteria was extracted by acid precipitation method.It was found that the inhibition rate of different fungi was 37%-97%,the highest inhibition rate was 97%,and the inhibition rate of Aspergillus fumigatus was the lowest,which was about 37%.The inhibition ratio of volatile substances(VOCs)to hyphal growth was measured by plate back-off method and the inhibition ratio of Verticillium dahlia was 65%.VOCs had an obvious inhibition on the growth of Aspergillus fumigatus conidia and the production of pigment generated by various pathogenic fungi.Based on the GC-MS analysis,eleven VOCs including alcohols,acids,ketones,esters,ethers and hydrocarbons were identified,and the antifungal activity of purified compounds was tested against Botrytis cinerea in different concentrations.Results showed that when the standard concentration was 50?L,1-butanol,acetic acid butyl ester,1-heptylene-4-alcohol and 3-methyl-3-hexanol completely inhibited the mycelia growth of Botrytis cinerea in vitro,while furan-tetrahydro-2,5-dimethyl completely inhibited mycelia growth only at a high concentration of 100 ?L per dish of the standard substance.2,6-diisocyanato-l-methyl-benzene,1-propoxy-2-propanol and benzophenone could obviously inhibit the growth and spore germination of Botrytis cinerea,and caused the surface of mycelium to shrink,exfoliate,protoplast collapse or apoptosis.At last,the biocontrol effect of M29 strain and its volatile substances(VOCs)on tomato seedings was 91.2%and 94.4%,respectively.The pot experiment showed that the biocontrol effect of strain M29 on Botrytis cinerea was 71.5%.