Screening Of Antagonistic Endophytic Actinomycetes Against Phytophthora Capsici And Optimizing Conditions Of The Fermentation

Screening of 242 endophytic actinomycetes in plate showed that 62 strains were antagonistic against Phytophthora capsici. Of which 24 strains showed more than 5mm in inhibition zone. These, isolated from 9 plant species, including cucumber, burdock et al. were 10% of the total strains tasted. Re-screening by the cup-plate method, the cell-free fermentation of 6 strains were both antagonistic against P. capsici and P. sojae. Their diameter of inhibition zone was exceeded 20mm. Further investigation showed that the strain gCLA4 inhibited sporangia and zoospores production of P. capsici, respectively 100% and 96.2%. The inhibitory effect of the cell-free filtrate of gCLA4 fermentation 50 times dilution were 95.3% and 85.6% respectively. Pot experiments in greenhouse showed that the cell-free filtrate of gCLA4 fermentation have a good control efficacy to the pepper phytophthora blight in seedlings after inoculated with pathogen. Using gCLA4 cell-free filtrate 48h, 24h and 0h before inoculation, the biocontrol efficacy were 100%, 92.3% and 80.8% respectively investigated 7d after inoculation. The biocontrol efficacy was 77.8%, 55.6% and 36.1% respectively 14d after inoculation. The result showed that endophytic actinomycetes strain gCLA4 was a potential biocontrol agent in pepper Phytophthora blight control.Screen the optimal fermentation medium and the optimal culture condition for strain gCLA4. The optimal seed medium was Soybean Flour medium, culture time 36h. And the optimal conditions as the medium(%) was composed of glucose1, starch soluble0.4, glycerol0.2, soybean flour2, peptone0.4, (NH4)SO40.6, NaCl0.2, MgSO4·7H2O0.05, KH2PO40.05, CaCO30.1, pH6.5~7.0. The optimum fermentation condition for the strain: the optimum temperature was 28℃, 250mL shake bottle filled with 50mL liquid medium, inoculation volume was 12%, the agitation speed was 150r/min, fermentation time 96h.The investigation showed that the crude extracts of strain gCLA4 inhibited sporangia and zoospores production of P. capsici respectively 95.5% and 90.4%, also it suppressed mycelium growth of P. capsici, the inhibitory effect of 6mg/mL gCLA4 crude extracts was 95.6% respectively.