Screening Of Antagonistic Endophytic Bacteria Of Camellia Oleifera And Preliminary Study On Its Biocontrol Mechanism

Anthracnose,soft rot and seed decay are important diseases of Camellia oleifera during planting and postharvest storage.At present,the control of these diseases is mainly based on chemical pesticides,but chemical pesticides are prone to drug resistance and pollute the environment.Endophytic bacteria form a reciprocal coexistence relationship with the host in the process of co-evolution,and have the ability to easily colonize,inhibit the growth of pathogenic bacteria,promote plant growth,and improve the survival rate of plants.Therefore,the use of endophytic bacteria to control important diseases of C.oleifera has great development potential.In this study,the main varieties of C.oleifera planted in Hunan,Guangxi,Jiangxi and Hainan provinces were used as experimental materials to isolate and screen the endophytic bacteria with antibacterial and growth-promoting effects from the tissues(roots and leaves)of C.oleifera,and preliminarily analyzing the bacteriostatic and growth-promoting mechanisms of these endophytic bacteria.The main research results are as follows:(1)A total of 155 endophyte strains were isolated from healthy C.oleifera tissues(leaves and roots)collected from Changsha City,Hunan Province,Youxian County,Hunan Province,Fenyi County,Jiangxi Province,Nanning City,Guangxi Province,and Chengmai County,Hainan Province,which including 95 strains of root endophytes and 60 strains of leaf endophytes.60 endophytic strains with inhibitory effects on Colletotrichum fructicola,Agricodochium camelliae and Penicillium sp.were screened by medium plate method.Among them,41 endophytic strains had antagonistic effect on C.fructicola,among which AG-5 had the highest inhibition rate of 80.39%;13 strains of endophytic bacteria had antagonistic effect on A.camelliae.,of which AY-14 had the highest antibacterial rate of 76.43%.Six endophytic strains had antagonistic effects on Penicillium sp.The antibacterial rates of strains AG-10 reached 66.97%.The antibacterial effect of endophytic bacteria fermentation liquid was measured that the 60 endophytic bacteria fermentation liquid also had antibacterial effect on plant pathogens.(2)The ability of nitrogen fixation,phosphorus solubilization,potassium solubilization plant auxin secretion(IAA)of 60 endophytic bacteria were determined.28 endophytic strains with nitrogen fixation ability were screened out,and strain AY-3 had the highest nitrogenase activity(25.14 U/L).16 endophytic strains had the ability to dissolve inorganic phosphorus,and AG-14 had the highest phosphorus content(1.401μg/mL).18 endophytic strains had the ability to dissolve organophosphorus,and AG-5 had the highest phosphorus content(1.299 μg/mL).According to the presence or absence of potassium cycle,18 endophytic strains were screened with the ability to release potassium,among which strain AG-4 had the highest potassium removal efficiency of 61.06%.29 endophytic strains could secrete IAA,and the content of IAA in the supernatant of AG-15 was the highest(54.19 mg/L).Combined with the antagonistic experiment,6 endophytic strains with excellent antibacterial and growth promoting ability were screened out,which were AG-5,AG-10,AG-15,AY-2,AY-5 and AY-14 respectively.(3)The endophytic strains AG-5,AG-10,AG-15,AY-2,AY-5,and AY-14 with excellent bacteriostatic and growth-promoting effects were identified by morphological observation,physiological and biochemical test and molecular biology analysis.The results showed that the endophytic strains AY-2,AY-5 and AG-5 were Bacillus.The endophytic strains AG-10,AG-15 and AY-14 were Lysinibacillus.(4)The inhibition mechanism and induced resistance of 6 endophytic strains were studied.The results showed that antagonistic strains AG-5,AG-10,AG-15,AY-2,AY-5 and AY-14 could distort and swell the mycelia of C.fructicola,A.camelliae and Penicillium sp.respectively,and affect the normal growth of mycelia.After treatment with antagonistic growth-promoting endophytes,the content of soluble protein in the mycelium of pathogenic bacteria decreased,the production of pyruvate was inhibited and the content of reducing sugar decreased.The activities of SOD,POD and CAT in C.oleifera plants were significantly increased by induction.