Screening And Metabolites Of Antagonistic Actinomycetes Against Fusarium Oxysporum F.sp.Lycopersici

Fusarium wilt,one of the main diseases on tomato,seriously reduces tomato's production and quality in the world.Chemical method is the main measure to prevent and control this disease,but it can lead to a series of problems such as environmental pollution,pesticide residues and resistance,when the fungicides were used in large amounts and for a long time.Therefore,people have gradually paid more and more attention to biological control measures which is environmentally friendly.To obtain high inhibiting activity antagonistic strain is the basis of antibacterial agent research and development.Previous studies have shown that several kinds of actinomycetes can produce antagonistic substances to inhibit the growth of many plant pathogens effectively.In order to get some strains that have strong antagonism effect on Fusarium oxysporum f.sp.Lycopersici(FOL)for further biofungicides development,many actinomycetes isolated from the rhizosphere soil in Jiangsu province were screened by the methods of confrontation culture and growth rate inhibiting.Mycelium morphology,cultural properties,physiological and biochemical characteristics and ITS sequences of the strain 2-1-2F-1,showing the best inhibiting ability to FOL,were used to identify it.The fermentation conditions of it were optimized,and the properties of its metabolites were studied.Results were showed as follows:1.Eight high antagonistic actinomycetes strains were screened,and the strain named 2-1-2F-1 had the best comprehensive antagonism against FOL with an inhibiting band of 8.8 mm width.This strain had a more wide antifungal spectrum and good inhibitory effects on Bipolaris zizaniae,Botrytis cinerea,F.oxysporum f.sp.vasinfectum,Colletotrichum gloeosporioides,F.oxysporum f.sp.cucumerinum,F graminearum,F.graminearum and Pseudomonas syringae pv.actinidia.When the strain was incubated in the medium for 5 days,the inhibition rate of its supernatant to FOL was 72.45%.2.Colony color of the strain 2-1-2F-1 was light purple gray,and the aerial hyphae of it had multi branches.Microscopic observation showed that the spore hyphae of the strain were linear or spiral,and the spores of it were round or oval with the size of 1.2?4.7×0.6?1.2 ?m.The substrate mycelium of the strain was yellow and could not produce soluble pigment.In addition,the strain could liquefy gelatin,hydrolyze starch and cellulose,and induce milk coagulation and peptonization,but not produce hydrogen sulfide.The strain could grow on the medium containing 5%NaCl and utilize glucose,fructose,inositol,L-rhamnose monohydrate and L-arabinose as carbon source,but not D(+)-sucrose xylose,mannitol or raffinose.16S rDNA sequence of this strain was 100%homology with Streptomyces lavendulae.In conclusion,all the results above indicated that the strain 2-1-2F-1 belonged to S.lavendulae.3.The optimal conditions for incubating the strain 2-1-2F-1 were inoculating 5 mycelium discs with diameter of 6 mm into 100 mL No.4 culture solution(10 g of soybean cake powder,10 g of glucose,3.0 g of peptone,2.5 g of NaCl,2.0 g of CaCO3,1 L of H2O,pH 7.0)at 30? with 180 r/min continuous shaking for 5 days.4.Antibacterial substances produced by the strain 2-1-2F-1 had no volatility.Substances extracted from culture supernatant by acetone could coarsen and break the mycelia of FOL,and expand the tip of the mycelium into balls.When the metabolite was condensed 50 times,the width of the antibacterial band against FOL could extend to 13.5 mm.Physical and chemical properties tests showed that antagonistic substances produced by the strain 2-1-2F-1 contained traces carbohydrate with strong polarity,and were not proteins and lipids.In addition,the inhibition activities of the antagonistic substances could be inactivated by 36.25%at pH 11.0,but had not effects when it was treated by chloroform,protease and strong acid.222 nm was the peak absorption wave length,and no peak value in the detection of NMR.