Screening Antagonistic Bacteria Against Tomato Wilt And Research On Antibacterial Effect

Tomato wilt is a soil-borne disease caused by Fusarium oxysporum.,which has seriously affect the yield and quality of tomatoes.At present,the control of tomato wilt is still mainly rely on chemical control,However,long-term use of chemical pesticides will damage soil ecological environment.High concentration of pesticide residues will even endanger human health.In this era,the concept of green environmental protection and sustainable production is widely recognized,and non-toxic and pollution-free biological control measures are adopted.Vermicompost is particulate matter excreted by organic wastes after biological treatment by e arthworms.It contains a large number of nutrients needed for plant growth and a mass of beneficial microorganisms.Vermicompost is one of the rare "bacteria banks" in nature.The research of soil borne disease control by the beneficial microorganism in the vermicompost has been recognized by many domestic and foreign colleagues.The utilization of vermicompost resources broadens the research channels of the biological control of beneficial microorganisms.In this study,strains with inhibitory effect on tomato wilt were screened out from vermicompost.Their classified properties were identified,antibacterial mechanism was analyzed,and the optimum formula and conditions for fermentation cultivation were determined.The following research results were obtai ned:(1)Sixty-one strains of bacteria were screened out from vermicompost,which forty-two strains had inhibitory effect.The inhibitory rate of fourteen strains was over 30%.The best bacteriostatic effect was strain No.25(denoted as DX-25),which had a 66.09% inhibition rate on F.oxysporum in the plate test.And the bacteriostasis effect of DX-25 was stable.(2)Molecular identification of strain DX-25 showed that its 16 S r DNA sequence length was 1488 bp,and DX-25 was Bacillus velezensis by homologous comparison in Genbank.(3)Strain DX-25 has good broad-spectrum antibacterial effect which can effectively reduce the occurrence of tomato wilt.Under the potted condition,the therapeutic effect of DX-25 on tomato wilt was 61.82%,the control effect was 70.91%.Moreover,high concentration of DX-25 fermentation broth inhibited the germination of tomato seeds,while low concentration promoted the germination of tomato seeds.(4)DX-25 can effectively induce POD,CAT,SOD,PPO,PAL,GLU,CHT and LOX enzyme activities in tomato.DX-25 had stronger inducing ability for PPO,GLU,CHT and LOX enzyme activities than F.oxysporum,while weaker for POD,CAT,SOD and PAL activities.The inducing ability of DX-25 for PPO,GLU and CHT enzyme activities was faster by 2 4 h compared with that of F.oxysporum.The interaction of DX-25 and F.oxysporum had a synergistic effect on PPO and GLU enzyme activities,and the inducing time of PPO and GLU activities were earlier by 48 h and 24 h than that of the single inoculation of Fusarium oxysporum.(5)Through optimized culture,the inhibition rate of DX-25 on tomato wilt was increased from 66.09% to 74.17%.