Screening,Identification And Primary Investigation Of The Biocontrol Mechanism Of Antaganism Against Botrytis Cinerea From Tomato

Dilution method was used to isolate bacteria from four different samples: soil, leaf, root and flower. Totally, 315 strains were obtained. Plate method combined with leaf梔isc methods was applied to screen antagonists. After primary screening by Plate-method, 95 strains were aquired. In the following screening, 44 strains were obtaind through leaf-disc method, among which 12 strains strongly inhibited the growth of the Botrytis cinerea. 2 strains that could spread quickly on the plate without nutrition and inhibit Botrytis cinerea completely were obtained from the second screening through leaf-disc method. The third leaf-disc assay demonstrated that the two strains could completely and duratively inhibit Botrytis cinerea. Three of six strains with stronger inhibition activities were isolated from the surface of the leaf. The two strongest strains were isolated from the healthy plants in the disease field.The results of the identification demonstrated that both the morphological and biochemical characters were accordant with that of Bacillus subtilis. Therefore, B21 was primarily identified as Bacillus subtilis.Duel-culture method was used to assay the inhibition spectrum of the bacteria. The results demonstrated that B21 was a potential antagonist with wider spectrum. Inaddition to Botrytis cinerea, it also inhibited growth of verticillium dahliae and other pathogens.Shake-flask method was used to screen the best condition for fermenting. The results indicated that the best condition of fermenting was: the medium PS, temperature 30X3, rotating speed 200, original pH value 6, fermenting time 36 hours. With this conditions, the inhibitive substance had the strongest inhibitive activity against Botrytis cinerea from tomato .The results of the greenhouse showed that even the spores of Botrytis cinerea were inoculated 24 hours ahead, the fermented liquor of the strain B21 without being diluted could remarkabely inhibit the occurance of gray mould. The control effect was better than that of the fungicide which was generally used. Therefore, B21 was supposed to be an effective biocontrol agent.Bioncontrol mechanisms were study primarily by Plate and Leaf-disc methods combined with Tissue-transpanrency method. Tissue-transparency assay was conducted on onion inner coat. The result showed that the germination of the spore and the growth of the hyphae were both inhibited by B21. The spores were deformed. The results of the Leaf-disc method displayed the same results. Thereafter, we could concluded that Bacillus subtilis B21 could secret some kind of inhibitive substance which lead to the thickness of the mecylium. The substance could produce cavity in the cell wall which lead to the flow-out of the protoplasm and the fragmentation of the mycelium.Mycelium-growth method was used to qualitify the inhibitive substance.56Primary study showed that 80% saturation of the (NH^SQj precipitate the most of the inhibitive substance. It was primarily identified as polypeptide.