Cucumber Seedling Damping-off Biocontrol And Pathogenic Molecular Identification Of Antagonistic Bacteria

Seedling damping-off of cucumber has been a important soil-borne disease in cucumber. In Zhejiang provience, this disease causes cucumber seedling damping-off seriously, and makes large economy losses. Its main pathogen is Pythium aphanidermatum, and the pathogen has produced resistance to chemistry fungicide Metalaxy. In order to avoid the environmental pollution it is necessary to use biological control. In this dissertation, using antagonism on petri dish, promoting seed germination growth and pot testing to screen biocontrol agents that can control seedling damping-off of cucumber.Using three methods to test BCA X3, XI3, PEP66, PEP188, PEP231, 396, 391, 879, 678Y, 678W, CN31 to promote cucumber growth and control seedling damping-off of cucumber.In antagonism on petri dish testing, we got two antagonist X3 and X13, they antagonize not only to Pythium aphanidermatum, but to Pythium ultimiim, to Fusarium oxysporam f. sp. melonis caused Fusarium wilt of melon and to F. graminearum caused Fusarium head blight of Barley. Their antagonistic ablity was showed some broad spectrum. Both strain X3 and X13 showed strong inhibitory effection during the pathogens of seedling damping-off growth under the optimum temperature at 18 -25 .In promoting seed germination and buds growth, strain 879 is the best one. The promoting seed germination growth is at 26.24%. And X3, X13, CN31 have some effect on germination, while strain PEP188 inhibit the bud growth. In pot testing, X13 showed the same result that control seedling damping-off of cucumber as that of Metalaxy. Strain 879 showed some effect on that. However, X3 did not show effective enough as X13.The identification of strain X3 and X13 by morphological characterization, culturing pattern, physiology and biochemistry characteristics were done. The results showed that both strain X3 and X13 similar to Pseudomonas aeruginosa described byBergey's Manual of Determinative Bacteriology (Eighth Edition). But the identification through BIOLOG, the result was that X3 belongs to P. spinosa and XI3 is strain of P. aentginosa. And then the 16S rDNA determination and analysis was used for further identification, the 16S rDNA genes of X3 and X13 were got. Then the genes were sent to genbank by blast and search homologous. The result showed that X3 and X13 with the most sequence similarity to strain P. aeruginosa PA01(AE004844) recorded by Genbank, the similarity were at 99% and 100% respectively. Using biological soft DNA star to analysis, comparing the 16S rDNA sequences of X3 and X13 with that of Pseudomonas's recorded in Genbank, both X3 and X13 belong to the same branch with P. aeruginosa in phylogenetic tree. The result tested is that both strains X3 and X13 is the same strain in P. aeruginosa.The formulation of three plant growth promoting rhizobacteria (PGPR) strains PEP66, PEP 188, PEP231 from rhizosphere which cooperated with Australia, and then formulation for the mixture of three strains was determined. The formulation is consist of xanthan gum as bond and attapulgite as carrier. The three PGPR strains reach to maximum quantity after 28-30 hours when fermenting in liquid culture medium. Using pot testing in green house to test the formulation effect to control of seedling damping-off of cucumber, the result was not effective.