Isolation And Identification Of An Antagonistic Bacterium A2 And Its Control Effect On Blumeria Graminis F. Sp. Tritici

The dissertation describes the isolation of a Bacillus strain A2 from the soil of protected farmland, as well as the identification of the strain based on its morphological, physiological characteristics and the homological analysis of 16S rDNA sequence, the optimization of fermentation conditions, and the screening for its biological activities. The main conclusions as follow:⑴Using different media, 38 colonies were obtained by the infinite dilution on plate followed by 12 colonies with antagonistic activity screened out using the Botrytis cinerea and Magnaporthe grisea inhibition model. After 10 generations, A2 was only strain which still keeping up its inhibitory ability to phytopathogenic fungi.⑵Antagonistic Spectrum of Bacillus strain A2 was studied by means of Duel-culture method. The results showed that Bacillus strain A2 had a wider antimicrobial spectrum, it exhibited an inhibitory ability to 20 species of phytopathogenic fungi (29.00%-86.00% inhibition ratio) and its inhibition zone of Botrytis cinerea and Magnaporthe grisea achieved 17.00mm,15.83mm respectively.⑶A2 strain was identified as Bacillus subtilis based on the results of morphological, physiological characteristics and the homological analysis of 16S rDNA sequence. The phylogenetic tree built on the 16S rDNA sequence indicated A2 strain was the nearest to B.subtilis. The study of morphology, physiological and biochemical characteristics showed it can produce amylase, fluidity glutin, and showed the positive reaction in the litmus milk test, suggesting A2 strain had the common characteristics of Bacillus subtilis.⑷Fermentation conditions were reasonably optimized in the research, including fermentation temperature, fermentation time, inoculation dose, the makeup and pH of culture medium and so on. The strain grows well in much wider temperature and pH ranges, with 28℃and 7as the optimum. The optional ratio in liquid fermentation is 3:1 with cane sugar as carbon source and beef peptone as nitrogen source.⑸A2 strain showed strong inhibitory activity against the hypha growth and spore germination of Magnaporthe grisea,Valsa mali,Pythium graminicola and Fusarium oxysporum f.sp.vasinfectum. A series of diluted culture supernatant of A2 strain had been tested and the results showed that the hypha can hardly grow,and spore germination was completely suppressed. The growth of hypha was deformed by A2 strain. With their tips bulged or attenuated, the hypha grew twisty, ramulose, yielded a large number of round cystids and their protoplasm agglomerated.⑹In pot plant experiments, A2 strain and its culture supernatant showed significant control efficacies (over 29.00 % ) against Blumeria graminis f. sp. tritici, and the control efficacy of admixture of them was much better. The control efficacy of fermentation broth of A2 strain achieved 72.22%, when the control efficacy of culture supernatant of A2 strain was 29.24%.