Isolation,Selection And Fermentation Of Antagonistic Actinomycetes To Suppress Cucumber Fusarium Wilt

Fusarium oxysporum f.sp.cucumerinum?FOC?is a destructive pathogen of cucumber,which caused a serious cucumber Fusarium wilt worldwidely.Biocontrol is one way to manage this disease.The purpose of this study is to find a multifunctional strain to control cucumber wilt disease and promote plants growth.Isolation and selection of antagonistic actinomycetes.In this study,493 strains of actinomycetes were isolated from total 39 samples including 21 vegetable soil,6 composts,5 vegetables and 7medicinal plants by dilution-plating method.Among 27 antagonistic strains with an inhibition zone diameter over 18mm against FOC growth,three actinomycetes strains,HNMH-3-1,HNSG-4-2 and HS57,were selected because of their great suppression against FOC via antibiotics and volatiles as demonstrated in dual-culture.The inhibition rates of the three strains against FOC were79.2%,67.6%,and 52.4%,respectively.The three strains were initially identified as S.parvus,S.nigrescens or S.lydicus and S.nigrescens or S.lydicus.The control efficacy of antagonistic actinomycetes in greenhouse.Greenhouse test showed that the three actinomycetes HNSG-4-2,HNMH-3-1 and HS57 performed good control efficacy at the concentration of 1×10⁷ CFU/mL,1×10⁶ CFU/mL and 1×10⁷ CFU/mL,the control efficacy was 97.9%,63.3%and 51.0%,respectively.At the spore concentration of 1×10⁷ CFU/mL,both strains HNSG-4-2and HNMH-3-1 promoted the growth of seedlings.In comparison with control,strain HNSG-4-2promoted the stem width,dry weight and root dry weight at the rate of 93.1%,102.0%and 166.7%,respectively.Similarly,strain HNMH-3-1 increased the cucumber height,dry weight and root dry weight by 71.5%,41.8%and 100.0%,respectively.Fermentation techniques of strain HS57.In industrial production purpose,the liquid culture medium and fermentation technology for the spore formation of strain HS57 were studied to facilitate its large-scale production.The optimum organic nitrogen source,carbon source and inorganic salt for sporulation was soybean meal,soluble starch,and MgSO₄?7H₂O,respectively.The particle size of the components in the medium had an effect on the mycelial growth and sporulation of strain HS57,and the small particles 850?m were more favorable for sporulation.At the end of fermentation of starin HS57,pH was over 7.8,acid-adjusting could not improve the spore survival ability.After centrifugation and the re-suspension with sterilized water,the spores could survive at the initial level.Soild preparation of HS57 was made by the mixing the fermentation broth with diatomite or diatomite and rice husk powder?V:V=2:1?,with final spore concentration at 10⁹ CFU/g.Survival tests showed that drying at room temperature?20-24??was better for spore survival than that of drying at 40?.The determination of the survival spores amount in the agents kept at 4?,room temperature and 26?,respectively,indicated that the spores could survive better at lower temperature at 4?or room temperature?10²0??,with a3-times and 22-times reduction,respectively,after 6 months,whereas the spores number reduced52-times at 26?.In a conclusion,the above results indicated that strain HS57 is of great potential to be used as a biocontrol agent to suppress Fusarium wilt disease with both of its antagonistic activity,growth promoting ability,and good charcters for large-scale production.