| Agricultural antibiotic was produced by microorganism in secondary metabolism and used for controlling agricultural pest As an important group of agricultural application microorganism,about 70%antibiotics were produced from actinomycetes,and the secondary metabolites were the important source of agricultural antibiotics.Strawberry root rot was one of soil-borne pathogens,caused by many pathogen microorganism,which could harm plant roots to make roots rot and lamina withering,finally caused the whole plant disease.This phenomenon had seriously restricted the development of strawberry cultivation industry.At present,strawberry root rot controlled by using biological control method was the research hotspot.Streptomyces albospinus CT205 was antagonistic actinomyces strain separated and preserved by our laboratory,and it had strong inhibition effect and a broad antimicrobial spectrum.In this paper,the liquid fermentation medium and conditions of Streptomyces albospinus CT205 were optimized,and the active substance from the fermentation broth was separated,purficated and determinate,then the solid state fermentation medium for S albospinus CT205 was optimized and microbial agent was preparated,at last the biological control of S.albospinus CT205 against the strawberry root rot by pot experiments and field experiments were investigated.The results were as follows:with single-factorial evaluation and orthogonal experimental design,the optimal ingredients of fermentation medium and suitable fermentation conditions in shake flask were determined with antibacterial activity of fermentation broth to Saccharomyces cerevisiae,and take mycelia quantity as indicators,the optimal fermentation medium was sucrose 2.0%,starch 3.0%,peptone 0.2%,soybean meal 0.8%,MgSO4·7H2O 0.05%,K2HPO4·7H2O 0.05%,NaCl 0.2%,CaCO3 0.3%.The optimal fermentation conditions were initial pH was 8.0,fermentation temperature was 28-30℃,inoculation amount was 9%-11%,broth content was 100ml/500ml.The active substance from fermentation broth was separated by the thin layer chromatography(TLC,GF254),and the results indicated that only component 4 had antibacterial activity to both S.cerevisiae and F.oxysporum Y3,after biological detection,the Rf value of the active substance was 0.68.Component 4 was scanned by ultraviolet for further research,and a strong UV absorption peak was found at wavelength λ=258 nm.Component 4 was further isolated and purified with high performance liquid chromatography(HPLC)to obtain a white crystal substance which had antibacterial activity.The molecular weight of white crystal substance was speculated possible 273.2、317.2 and 436.1 by a mass spectrometry.Through the optimization of solid state fermentation formula for strain CT205,the optimum formula was obtained.The mass ratio of vermicompost and wheat bran was 1:1,the volume ratio of material and water was 1:0.8,fermentation temperature was 28℃,the fermentation time was 4-6 day in the platters,strain CT205 microbial agent was obtained,and the spores number reached to 2.28×109 CFU g-1.Then the microbial agent was used for strawberry pot experiments and strawberry field experiments.The strawberry pot experiment was carried out in the Qilin town of Nanjing,whose results showed that the control effect on strawberry root rot disease of using CT205 liquid agents and CT025 solid agents alone were 78.57%and 88.10%respectively,while the biomass,the enzyme activity of plants and the soil enzyme activity of each treatment plants were measured,the results showed that whether the liquid agents or solid agents had significant promoting effect on strawberry plant.And the plant catalase(CAT)were 115.45 U g-1 and 471.54 U g-1 when the liquid agents and solid agents were applied separately,CAT were 24 times and 98 times compared with control respectively.The plant superoxide dismutase(SOD)were 490.52 U/g and 481.77 U/g respectively,which was 5.03%and 3.16%higher than control respectively.Otherwise the soil urease were 305.35 mg/(g·24h)and 230.99 mg/(g·24h)respectively,which was 53.27%and 15.58%higher than the control respectively.In addition,the rhizosphere soil microbial quantity were measured by fluorescence quantitative PCR method,results showed that either the treatment applied CT205 liquid agents or the treatment applied solid agents,the number of bacteria and fungi all were lower than the control.The strawberry field experiment was carried out in the strawberry technology park of Fujiabian of Lishui district in Nanjing,whose results showed that the treatment with strain CT205 solid agents could effectively control strawberry root rot disease,the disease control rate was 69.3%. |
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