Study On The Isolation,Identification And Antimicrobial Activity Of Endophytic Actinomycetes Against Cucumber Fusarium Wilt

Cucumber fusarium wilt is caused by Fusarium oxysporum f.sp.cucumerinum owen infecting cucumber root.It is the most important soil-borne diseases in cucumber industry.In production,cucumber fusarium wilt seriously affected the cucumber yield and quality and was difficult to control.As the main component of the plant root micro ecosystem,the changes of the endophytic actinomycetes structure and richness have a great influence on the health of the host plant.At the same time,endophytic actinomyces can also affect the growth of host plants through its own metabolites.Therefore,it has a vital significance to understand the cucumber root endophytic actinomycetes community structure and richness under different physiological conditions and obtain endophytic actinomycetes to control cucumber fusarium wilt.The aim was to explore the cucumber root endophytic actinomyces community structure and look for bio-control endophytic actinomyces as the main starting point.Endophytic actinomycetes ofr cucumber plants roots infected by Fusarium oxysporum f.sp.cucumerinum owen and adjacent healthy plants roots as the research object,using five different separation medium to isolate endophytic actinomyces of samples of three groups.Based on the morphological identification and the plate count method,the differences of the composition and abundance of endophytic actinomycetes in healthy and diseased cucumber plant roots were determined.Considering the result of bioactive against Fusarium oxysporum f.sp.cucumerinum owen,strain separation sources and the comparison of richness,the strongest active endophytic actinomycet HAAG3-11 which presented in both healthy and diseased cucumber roots was chosen as the research object.The field seedling test showed the colonization ability and the control effect.The research provides the data support and practical experience for the development and utilization of cucumber roots endophytic actinomycetes.The main results of this study are as follows:(1)With the three groups diseased and the adjacent healthy cucumber root as separate source,a total of 163 different strains of endophytic actinomycetes were isolated.By comparing the study found that: the total number of the endophytic actinomycetes was large and the community structure was rich in the healthy plant,the community structure was poor and the overall number was small in the diseased plant.There were some duplicates endophytic actinomycetes isolated from healthy and diseased cucumber roots.Healthy and diseased cucumber roots have their own unique strains.The data showed that the micro system in the root of cucumber and richness of endophytic actinomycetes were significantly changed after infection by cucumber fusarium wilt.At the same time,the diseased plants roots can recruit endophytic actinomycetes.(2)In vitro antagonism activity assay showed,163 endophytic actinomycetes against Fusarium oxysporum f.sp.cucumerinum owen were screened,7 active endophytic actinomycetes were obtained.The inhibitory action in the 7 endophytic actinomycetes,6 strains(HGS1-1,HGS3-17,HAAG3-8,HGS2-18,HCPA2-26,HAAG3-4)from the healthy plant roots,1 strain(HAAG3-11)from the diseased and healthy plant roots.The endophytic actinomycet HAAG3-11 has a maximum inhibition effect on Fusarium oxysporum f.sp.cucumerinum.In addition,the endophytic actinomycet HAAG3-11 also showed a good inhibitory effect on other plant pathogenic fungi.(3)Endophytic actinomycet HAAG3-11 was the dominant endophytic actinomycetes in the diseased plant roots,and exist in both healthy plant(0.434 × 10 cfu/g)exists in plant root of cucumber blight(0.68×102 cfu/g).The richness of diseased plant roots was much higher than that of healthy plant roots,which indicated that diseased plant roots had a recruitment effect on endophytic actinomycet HAAG3-11.(4)The polyphasic approach identification of the endophytic actinomycet HAAG3-11,develop characteristic identification by morphological and chemotaxonomic of identification,and finally confirm the endophytic actinomycet HAAG3-11 belong to Streptomyces.(5)The result of the cucumber seedling colonization ability experiment showed that the endophytic actinomycet HAAG3-11 has good root colonization ability in cucumber roots,and colonization ability increases with colonization time increasing.The colonization ability of endophytic actinomycet HAAG3-11 reached the strongest in twenty-eighth days after inoculation,and the number of colonization was much higher than that of endophytic actinomycet HAAG3-11 in the isolated source.According the cucumber seedling assay,endophytic actinomycetes HAAG3-11 had obvious inhibitory effect on cucumber fusarium wilt disease incidence and disease index were both significantly reduced.It is a biocontrol endophytic actinomycetes with good development prospect.In conclusion,the results showed that the endophytic actinomycetes community structure in the roots of cucumber were significantly changed after infected by Fusarium oxysporum f.sp.cucumerinum owen,which resulted in the decrease of the spices and the richness of the endophytic actinomyces.Compared with diseased cucumber plant roots,more active strains were obtained from healthy plant roots.The highest activity endophytic actinomycet HAAG3-11 was screened out by in vitro antagonism activity assay experiment,which showed good colonization ability in the cucumber seedling colonization ability experiment.In the control experiment of seedling stage,the endophytic actinomycet HAAG3-11 showed good resistance to disease.It has been identified that endophytic actinomycet HAAG3-11 is a kind of Streptomyces with good biocontrol potential.