Screening And Mechanism Of Disease Biocontrol Agents Of Fusarium Studied

China is the biggist country of production and consumption watermelon. The watermelon Fusarium wilt is a soil-born vascular disease caused by Fusarium oxysporum f. sp. niveum, This diease has become one of the main diseases of watermelon and distribute in every watermelon production district, especially serious in continuous cropping watermelon district. The watermelon Fusarium wilt has become one of the main obstacles of watermelon production in China. There are some prevention and control strategies, such as disease resistance breeding, crop rotation, grafting in root, chemical control, biological control, physical prevention and so on. Biological control is considered to be one of the most promising methods, because of the special contributions of endophytic bacteria to biological control, it is attractive to use this type of bacteria as an alternative tool to control soilborne vascular wilt disease. In order to screen endogenous bacteria resources with effective control efficiency against watermelon fusarium wilt and explored their biocontrol mechanism, we carried out the experiments.Through antagonistic ability test of the living bacteria or extracellular metabolites,7strains with strong antagonistic ability against Fusarium oxysporum f. sp. niveum were selected from355rhizosphere or plant endophytic bacteria strains. These7strains had extensive inhibition spectrum and effectively controlled watermelon Fusarium wilt in pot experiment. The control efficiency of srtain Jaas edl, Jaas ed2and Jaas ed3were75.1%,64.1%and63.2%respectively, and more significant than that of chemical fungicide chlorothalonil. In field experiment strain Jaas edl, Jaas ed2, and Jaas ed3still could control watermelon Fusarium wilt, and the control efficiency of strain Jaas ed2was64.9%. Based on their morphology, physiological and biochemical characteristics and16S-rDNA sequence analysis,the strain Jaas ed2was identified to be Bacillius subtilis,with GenBank accession number JX849658, the strain Jaas ed3was identified to be Paenibacillus polymyxa with GenBank accession number JX849659, and the strain Jaas edl of our laboratory had been identified as Bacillus subtilisIn addition, the biocontrol mechanism of these3strains of endophytic bacteria strains Jaas ed1, Jaas ed2, Jaas ed3has been studied. The results showed that these three endophytic bacteria strains could promote the growth of watermelon seedling, the function of the strain Jaas ed3is the most obviously, it could increase the watermelon seedling plant height by34.15%, increase fresh weight by48.41%. These3endophytic bacteria strains tagged with rifampicin resistance could colonize in watermelon seedling for12d at least. Furthermore strain Jaas ed1marked with GFP could colonize in watermelon root and vascular bundle of stem, and the number of root colonization was significantly more than that of vascular bundles in the stem. In addition, we found that endophytic bacteria strains Jaas edl could produce volatile substances which can inhibit the growth of the pathogenic fungus, inhibite botrytis cinerea infection in vitro on tomato leaves and have fresh-keeping effection for postharvest strawberry.