Screening And Fermentation Of Antagonistic Microorganisms Against Fusarium Wilt Of Cucumber

Cucumber fusarium wilt is caused by Fusarium Oxysporum cucumber biotypes（Fusarium oxysporum f.sp.cucumerinum Owen）.The cucumber is infected through the Rhizosphere.It is one of the soil borne diseases which causes the serious reduction of cucumber production.Chemical pesticides are mainly used to prevent and control wilt disease in our country at present.With increasing cares about environmental pollution and food safty,safe and effective biological control is main approach to prevent and control plant diseases.In this study,antagonistic microbial strains against fusarium wilt were screened,and the fermentation technology of two antagonistic microbial strains were investigated.The main results are as follows:The 10 strains were screened by primary screening and secondary screening,which had better antagonistic effect on Fusarium Oxysporum.Strain D1（Paenibacillus polymyxa D1）and B3 had the best antibacterial effect.The both diameter of inhibition zone was more than 30 mm.Most of the strains had the synergistic antagonistic effect.Strain D1 and B3 were very effective and the diameter of inhibition zone reached to 42.52 mm.Strain B3 was identified as Bacillus amyloliquefaciens by molecular identification.Cellulosase could be produced by strains D1 and B3.Cellulosase activities of both strains were more than 70 U/mL,which were favorable for colonization in soil.Solid state fermentation technology of P.polymyxa D1 was investigated using pear residue as main raw material.Fresh pear residues contained much sugar and were suitable to cultivate P.polymyxa in solid state fermentaion.The bacteria cells grew well when pear residue and wheat bran mixed with proportion in 10:4.Adding soybean meal,urea and NaNO3 could significantly increased viable cell number and spore number in pear residues fermentation medium,of which soybean meal was the most effective.The cell growth and formation of spores could be significantly promoted by 0.5% KH2PO4.The number of spores decreased as medium voulme increased.The optimal cultivation conditions of P.polymyxa D1 were: inocultion 10%,cultivation temperature 34°C,cultivation time 120 h.The number of viable cell and spores rate were 5.61×109 CFU/g and 93.88% respectively under the optimal cultivation conditions.Cultivation conditions of B.amyloliquefaciens B3 were investigated.When fructose,glucose,maltose,lactose and sucrose were used as carbon source,the cells grew well.Glucose was the best carbon source.When starch and dextrin were used as carbon source,B.amyloliquefaciens B3 grew solwly.The optimal glucose concentration in the medium was 50 g/L.When yeast extract,peptone,beef extract,corn syrup,urea,potassium nitrate,ammonium sulfate were used as nitrogen source,the effects of nitrogen source on the growth of B.amyloliquefaciens B3 were studied,It was found that the growth of the cells was the best when the beef extract（25 g/L）.Urea,KNO3 and（NH4）2SO4 obviously inhibited the growth of B.amyloliquefaciens B3.NaCl、KCl、CaCO3 and KH2PO4 could significantly promot the cell growth.The growth of the cell was significantly inhibited by FeSO4 and CuSO4.The best culture medium of B.amyloliquefaciens B3 were: glucose 50.0 g/L,beef extract 25.0 g/L,KH2PO4 4.0 g/L,KCl 6.5 g/L and NaCl 5.0 g/L.The best cultivation conditions were: inoculation 2%,culture temperature 34°C,rotation speed 230 r/min.The number of viable cell obtained reached 1.05×10¹⁰ CFU/mL.