Screening Efficient Biocontrol Bacteria To Prevent Watermelon Fusarium Wilt And Researching On The Mechanism Of Function

All around the world,watermelon is planted,and watermelons suffer from different pathogens causeing diseases in various stages of growth and development.Watermelon Fusarium wilt i5 a soil bome disease.Its pathogen is uwsarium oxysporum f.sp.niveu.At present,the prevention and control of Watermelon Fusariumn wilt is mainly achieved by breeding of disease-resistant varieties and grafting methods.However,breeding an excellent diseas-resistant variety usually need longer time.Although grafting technology also affects the quality of watermelon,especially the sweetness.When Watermelon Fusarium wilt happens,the main way that prevents Watermelon Fusarium wilt is to use chelical agents.Although the chemical agents can control Watermelon Fusariiun wilt to a certain extent,the extensive use of chemical agents causes serious problem such as enviroment pollution and chemical pesticide residue.With a large amount of chemical agents using,the resistance to chemical agents of pathogens is also gradually expressed,which raises the risk of increasing drug resistance in turn.The above reasons indicate that chemical control methods have become weaker.In recent years,study of biocontrol bacteria has become more and more mature,how to effectively control plant diseases by biocontrol bacteria is attracting more and more attention.The use of biocontrol bacteria to prevent plant diseases will not cause environmental pollution,soil structure damage,or the resistance to drug of pathogenic bacteria emergence,which conform to the strategy of green development and recycling development.Therefore,the aim of this study is to screen biocontrol bacterium to prevent Watermelon Fusarium Wilt and preliminarily explore the mechanism of biocontrol.First,from more than 2000 biocontrol bacterias,we screened 13 effectual biocontrol bacterias and a bacterial strain that have no antagonism by using the hydrolytic enzymatic activity experiment and plate antagonistic experiment mainly.Through disease prevention and growth promotion experiments in greenhouse,we found Fll and HSSN09 not only improve the watermelon growth but also reduce incidence rate of watermelon Fusarium wilt.Combining results of hydrolytic enzymatic activity experiment and plate antagonistic experiment,we finally identified two biocontrol strains by gyrb gene,Fll and HSSN09,which have better effects.Through identification,the two biocontrol strains were Bacillus velezensis and Bacillus amyloliquefaciens.After Real-time PCR and enzyme assays(Catalase CAT,Peroxidase POD,total peroxide dismutase SOD)being performed,we found F and HSSN09 can activate the resistance genes of the SA and JA pathways and various enzyme related resistance in watermelon root.So we conclude Fll and HSSN09 can enianee the watermelon resistance to Fusarium oxysporum.For the biocontrol bacteria Fll,we uses transcriptional sequencing analysis technology to explore the mechanism of prevention and control of Fusarium oxysporum from a point of view that a molecular biology and transcriptional regulation mechanism.We analyzed the GO function and pathway function.It is found that Fll can mobilize the expression of genes related to biological processes,cell components and molecular functions,and the highest expression of gene expression in the catalytic activity of the 2 level GO function classification is reached to 4995.In the pathway,Fll bacteria are mainly involved in the synthesis of endoplasmic reticulum proteins and amino acids,carbon metabolism and RNA transport.Analysis of gene expression shows that Fll can activate many resistance genes in watermelon,In addition,the we found that the Bacillus subtilis BsEl which is screened at the early stage of the laboratory,has a good swimming ability,Whether for Watermelon Fusarium wilt or wheat scab,BsE1 has a certain control effect.Therefore,this study also conducted the construction of the random insert mutant library of BsE1,screen mutants with significant changes in swimming activity.We found 14 mutants,then compared with wild type,the motility of the 14 mutants decreased significantly.Through greenhouse experiment,BsE1 also showed good control effect of wheat and watermelon.So we speculated it is a strain with potential of biocontrol.