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Cotton Verticillium wilt is a soilborne fungal disease, resulting in severe yield loss of cotton worldwide. Compared with the routine control on cotton Verticillium wilt, rhizobacteria-mediated biocontrol is a more effective alternative. Antagonistic bacteria' dissertation">Antagonistic bacteria strains were screened and identified. The control efficiency to cotton Verticillium wilt, the colonization ability of bacteria strains in rhizosphere soil and the effects on microorganism flora by application of bacteria strains simply and bioorganic fertilizer containing the screened bacteria strains were studied in pot experiments. Detection of antibiotic biosynthesis genes, cell wall degrading enzymes and volatile compounds of the strains were also done in this paper. The results obtained are as follows:(1) Two stains, which were gram positive, spore forming, fast growing in poor nutrient condition and antagonistic to Verticillium dahliae on plate, were screened and named as ZJ6 and ZJ1. They were both identified as Bacillus subtilis according to their physiological and biochemical chacteristics and 16S rDNAgene sequences.(2) The application of ZJ6 and ZJ1 which were simply mixed (ANT-ZJ6 and ANT-ZJ1) or fermented with organic fertilizers (pig manure compost:amino acid fertilizer=1:1) (BOF-ZJ6 and BOF-ZJ1) could control cotton Verticillium wilt effectively. Application of ANT-ZJ6, ANT-ZJ1, BOF-ZJ6 and BOF-ZJ1 could decrease the incidence of cotton Verticillium wilt by 39.8% to 64.1% and disease index by 56.3% to 82.4% as compared with the control. The biocontrol efficiencies against cotton Verticillium wilt by ANT-ZJ6 and BOF-ZJ6 were about 80%. BOF-ZJ6 or BOF-ZJ1 was more effective in control of cotton Verticillium wilt than that of ZJ6 or ZJ1 liquid broth, respectively. The biocontrol efficiency of BOF-ZJ1 was 20.8% higher than that of ANT-ZJ1.(3) The numbers of ZJ6 and ZJ1 decreased gradually after applied into soil. The numbers of ZJ6 and ZJ1 in treatments BOF-ZJ6 and BOF-ZJ1, in which ZJ6 and ZJ1 were fermented with organic fertilizer respectively for 4 days, were 28 times and 77 times higher than that in treatments ANT-ZJ6 and ANT-ZJ1, in which mixture of ZJ6 and ZJ1 and organic fertilizers were applied. Ability in colonization of rhizosphere soil by ZJ6 was stronger than that of ZJ1 in pot experiment. At the 50th day, the numbers of ZJ6 in treatments of ANT-ZJ6 and BOF-ZJ6 were 156 times and 56 times higher that that of ZJl in treatments of ANT-ZJ1 and BOF-ZJ1, respectively.(4) Application of ZJ6 and ZJ1 could reduce the number of Verticillium dahliae in rhizosphere soil. The numbers of Verticillium dahliae were decreased by 86.1% to 98.6% in the treatments of ANT-ZJ6, BOF-ZJ6, ANT-ZJ1 and BOF-ZJ1, compared with that of control.(5) Application bioorganic fertilizer could change the microbial composition of rhizosphere soil. After application of BOF-ZJ6 and BOF-ZJ1, the numbers of bacteria increased 7.1 and 8.5 times, while those of actinomyces increased 11.7 and 32.6 times, but fungi decreased 53.0% and 68.2%, respectively, as compared with the control.(6) Genes bam, fenB, fenD, ituA, ituB, ituC and ituD, responsible for synthesis of antibiotics Bacillomycin, Fengycin and Iturin were detected in strain ZJ6 while Genes fenB, fenD, sboA and QK, responsible for synthesis of antibiotics Fengycin and Subtilisin were detected in strain ZJ1.β-1,3-glucanase and volatile compounds were both detected in ZJ6 and ZJ1.
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