Field control efficiency of tobacco specific bio-organic fertilizer on tobacco bacterial wilt

【Objectives】Tobacco bacterial wilt is one of the most serious soil-borne diseases for tobacco production. The biocontrol of tobacco bacterial wilt has become a hot topic recently. To investigate effect of specific bio-organic fertilizers on biocontrol of tobacco bacterial wilt, a two-year field experiment was conducted to investigate the biocontrol efficiency and soil microbial community.【Methods】 In this experiment, two antagonistic strains (L-25 and L-9) with strong inhibitory effects on Ralstonia solanacearum in vitro were isolated from rhizosphere soil in a severely wilt-diseased field. Two solid bio-organic fertilizers (BOF) were secondly fermented by the two antagonists, strain L-25 and L-9. A two-year field experiment was conducted in Anhui Province. The biocontrol efficiency was investigated at 50 d and 105 d after tobacco transplanting. The effects of the bioorganic fertilizers on soil microbial community and tobacco yield were measured and analyzed. In order to reveal the biocontrol mechanism of the bioorganic fertilizers, the colony counting method, biolog phenotype analysis and denaturing gradient gel electrophoresis (DGGE) were used to analyze microbial population, functional and structural diversity of microorganisms, respectively in rhizosphere soil after the application of the bioorganic fertilizers.【Results】1）At 50 d after the transplanting, compared with the control, the control efficiencies of the BOF treatments reach to 82.2% and 96.2% for the first and second year, respectively, and to 75.2% for the first year and 95.4% for the second year at 105 d after the transplanting. 2）The tobacco yields are increased to 2212.5 kg/ha and 1475.5 kg/ha in the first and second year in the BOF treatments which are about 2.4 times and 2.6 times of control, respectively. 3） The populations of rhizosphere cultivated bacteria and actinomycetes of the BOF treatments are significantly higher than those of the control, while the counts of fungi of the BOF treatments are significantly lower than those of the control (P＜0.05). In the first year, the populations of antagonists are increased by 241.8 times and 13.4 times of the control in 50 d and 105 d after the transplanting in the BOF treatments, while the populations of pathogen are 19.7% and 56.6% of the control, respectively. In the second year, the counts of antagonists are increased by 111.0 times and 26.7 times of the control in 50 d and 105 d after the transplanting in the BOF treatments. However, the pathogen counts in the BOF treatments are 9.1% and 31.4% of the control. 4）The Shannon Index, Simpson Index and Mclntosh Index of soil microbial community of the BOF treatments are significantly higher than those of the control in both 50 d and 105 d after the transplanting in the two years. 5）There are significant differences of soil microbial structural diversity between the BOF treatments and the control. The denaturing gradient gel electrophoresis (DGGE) patterns of soil bacteria and fungi of the BOF treatments and the control treatment belong to two corresponding clusters，which suggests that bacterial species are increased and fungi species are decreased under the application of BOF. 【Conclusions】The application of tobacco specific BOF in the severely wiltdiseased tobacco field can significantly reduce the wilt disease incidence and thus increase tobacco yield. Bioorganic fertilizer depresses the population of the pathogen and increases the counts of antagonists. Meanwhile, it can increase the functional diversity of the soil microbial community and improve the microbial structural diversity. Therefore, the soil micro-ecology keeps balanced.