Isolation and biological control effects of cotton Verticilium wilt antagonist

Cotton Verticillium wilt is a soil-born fungi disease, resulting in severe yield loss of cotton world wide. Compared with the routine control on cotton Verticillium wilt, rhizobacteria-mediated biocontrol is a more effective alternative. Bacteria strains ZJ6 and ZJ1, which were antagonistic to Verticillium dahliae Kleb were screened and identified and their effects to control cotton Verticillium wilt were studied in pot experiments. Detection of antibiotic biosynthesis genes of the strains ZJ6 and ZJ1 were also done in this experiment. The results show that: 1) ZJ6 and ZJ1 are both identified as Bacillus subtilis according to their physiological and biochemical characteristics and 16S rDNA sequences. 2) The applications of ANT-ZJ6 and ANT-ZJ1 which are simply mixed (ANT-ZJ6 and ANT-ZJ1) or fermented (BOF-ZJ6 and BOF-ZJ1) respectively with organic fertilizers (pig manure compost∶amino acid fertilizer=1∶1) could control cotton Verticillium wilt effectively. The applications of ANT-ZJ6, ANT-ZJ1, BOF-ZJ6 and BOF-ZJ1 could decrease the incidence of cotton Verticillium wilt by 39.8%-64.1% and disease index by 56.3%-82.4%. The biocontrol efficiency to cotton Verticillium wilt by ANT-ZJ6 and BOF-ZJ6 is about 80%. BOF-ZJ6 or BOF-ZJ1 is more effective in control of cotton Verticillium wilt than that of ZJ6 or ZJ1 respectively. The biocontrol efficiency of BOF-ZJ1 is 20.8% higher than that of ANT-ZJ1. 3) The application of bioorganic fertilizer could change the microbial population of rhizosphere soil. After applications of BOF-ZJ6 and BOF-ZJ1, the populations of bacteria are increased by 7.1 and 8.5 times, actinomyces by 11.7 and 32.6 times, while the populations of fungi are decreased by 53.0% and 68.2%, Verticillium dahliae Kleb by 98.6% and 98.5% respectively, compared with those of control. 4) Genes bam, fenB, fenD, ituA, ituB, ituC and ituD, responsible for synthesis of antibiotics Bacillomycin, Fengycin and Iturin respectively, are detected in strain ZJ6 while Genes fenB, fenD, sboA and QK, responsible for synthesis of antibiotics Fengycin and Subtilisin respectively, are detected in strain ZJ1. It is concluded that the application of bacteria strains ZJ6 and ZJ1 being fermented with organic fertilizers is an effective approach in biocontrol against cotton Verticillium wilt.