Screening Of Antagonistic Bacterium Against Alternaria Alternata And Determination Of Control Effect Of The Bacterium On Alternaria Alternata

Alternaria Alternata is one of main diseases of tobacco, which causes huge economic losses in China every year. At present, biological control is the most potential method of controlling the Alternaria Alternata diseases. Some Antagonistic Bacteriums found in the soil and leaves around tobacco can inhibit pathogenic organisms, promote the growth of tobacco and induce the expression of systemic acquired resistance, so they are widely used in controlling plant diseases.86 strains which had effection on Alternaria Alternata were isloated from health tobacco leaves collected from Liu Yang of Hunan province in this experiment.4 strains in 86 strains which had the better antagonistic effect on Alternaria Alternata were selected by preliminary screening and Rescreening, in which the stain 07 had the best control on the germination of Alternaria spore and the growth of mycelium. The rate of spore germination and confrontation between the culture plate is 68.2% and 72.1% separately.The strain B07 is identified as Bacillus brevis according to its morphology and biochemical characteristics.Through the research of fermentation conditions of strain B07, the result showed the best condition for strain B07 is to culture the strain in 100 mL medium with the pH 7.0 for 48 h in 28℃, and the best fermentation medium for strain B07 contains KH2PO40.7‰, bean cake powder 25%o, fish meal 3%o, CaCO32‰.The research on the mechanism of the zymotic fluid of strain B07 showed that it could inhibite the germination of Alternaria alternata and the growth of spore. And the result also showed that the activity of peroxide enzyme(POD) and polypheno loxidase(PPO) related to resistance in tobacco leaves which were treated by the zymotic fluid of strain B07 increased..The control effect tests of the zymotic fluid of strain B07 showed the average control efficacy is 61.9% in vitro experiment,69.3% in the test of greenhouse with 10 times the zymotic fluid and 59.6% to 77.15% separately in the test of field.The research of biochemical characteristics and culture conditions of the 07 strain, the further research as the activity impact of enzyme and the number of the strains on tobacco leaves is worthy for the biological control of Alternaria Alternata in future.