Screening, Indentification And Application Of Tobacco Antagonistic Endophytic Bacteria Against Phytophthora Parasitica Var. Nicotianae

Six strains of Phytophthora parasitica var. nicotianae were isolated from disease tobaccos in Yongzhou and Ningxiang from heavy disease plots;. Pathogenicity was tested to six strains, the results shows the strain of phy3 have strong pathogenicity. We also studied the effect of several solutions for producing zoosporangium in Artificial culture condition, the result shows the hyphea culture with 0.1% KNO3 produced the most quantity of zoosporangiums. 120 Endophtic bacteria strains were isolated from healthy tobaccos from heavy disease plots in Yongzhou, Ningxiang and Liuyang. By Laboratory dual culture test, seventeen actinomycetes to Phytophthora parasitica var. nicotianae were screened. Among them eight endophytic bacteria showed relatively strong antagonistic actions. By inoculated to tobacco plants, six strains could be re-isolated from the inoculated plants, indicating that they were endophytic bacteria in tobacco. Culture these eight bacteria and Phytophthora parasitica var. nicotianae together, the result showed four endophytic bacteria YN-55, NN-3, YN-4 and YN-10 have the best antagonistic effects. The control effects were above 66%. According morphologic, physiological and biochemical characteries, strain YN-55, NN-3, YN-4 and YN-10 were identified.Some conditions for culture YN-55, NN-3, YN-4 and YN-10 were studied in shake flask (100ml in 150ml flask). The optimum cultivation PH and temperature for YN-55 were 6.5 and 27.5C respectively, for NN-3 were 7.5 and 27.5C respectively, for YN-4 and YN-10 were 7.0 and 27.5C respectively. The optimum cultivation time for NN-3 and YN-4 were 24h, for YN-10 was 26h.Ferment products of antagonistic bacteria YN-55, NN-3, YN-4 and YN-10 were applied at tobacco seedling in greenhouse in two tobacco cultivars. The greenhouse experimental results indicated that four endophytic bacteria YN-55, NN-3, YN-4 andYN-10 could control tobacco blank shank, and the control effects were between 30.4% and 51.4%. Among them, NN-3 shows the best control effect, the control effect were 51.4% and 39.1 % respectively.