| The bacterial wilt caused by Ralstonia solanacearum is one of the most important diseases in the crop. The microecological attentuation of the R. solanacearum caused by the biocontrol agent Bacillus cereus ANTI-8098A was studied in this paper, including the differentiation of pathogenicity of R. solanacearum and its distribution in the plant, physiological and biochemistry characteristics of ANTI-8098A and its fermentation characteristics and technique, the microecological attentuation of R. solanacearum caused by the selection of biocontrol agent between virulent and avirulent R. solanacearum populations under the different conditions, and the biocontrol effects of microecological attenuation to the bacterial wilt disease.Pathogenicity test to a large amount of R. solanacearum strains collected from the field showed that the obvious differentiation of pathogenicity existed among them, even in the different strains from the same plant. Studies on the distribution of R. solanacearum in infected plants at different stages indicated that the concentration of pathogenic bacterium decreased with the increase of the plant height. In addition R. solanacearum was found in the healthy peanut, which could exist and reproduce in the plant but unable to cause the disease symptom, the stable virulent and avirulent strains were obtained as the standard strains for the following experiments through isolation, purification and several times of subculture.The conditions of fermentative culture for biocontrol strains Bacillus cereus ANTI-8098A were studied. The results indicated that: the optimum conditions for bacterial growth were in 250mL flask with 25mL medium of pH 7.5 shaking at the speed of 200rpm at 28±1℃. The concentration of spore was up to18.2x 108cfu/ml at 36h after inoculation of 10% liquid culture under this condition. To improve the level of ANTI-8098A fermentation, a control system was designed and constructed to control fermentation parameters such as temperature, rotating speed, DO and pH. The program control could be set to change fermentative parameters at different stages of fermentation according to the simulative setup scheme. A telecontrol subsystem based on TCP/IP network was developed to execute the remote control of the fermentation system. When the fermentation is done in 50L fermenter under the control of this system, the concentration of 57.62× 108cfu/ml could be achieved in 40 hours.The significant differences were found in the inhibition test for the bacterial-wilt-disease biocontrol agent ANTI-8098A to virulent and avinilent strains of R. solanacearum. The 50% lethal concentration of ANTI-8098A to virulent strain of R. solanacearum was 12.4%, 33.3% lower than that to the avirulent strain. The inhibition rate of ANTI-8098A to the virulent strain was 0.158, 40.6% higher than that to the avirulent strain. The inhibition differences of the strain ANTI-8098A to the virulent and avirulent strains resulted in the attenuation by microecological selection that killed the virulent strain and preserved the avirulent strain, preventing the disease outbreak. It was the first time to find the attenuation of the strain ANTI-8098A in R. solanacearum.Fermentative products of the virulent strain of R. solanacearum were treated by the series dilution of the fermentative product of Bacillus cereus ANTI-8098A, and inoculated to tissue-cultured tomato seedlings and potted eggplant seedlings, The results showed that the control effects was up to 100.0% with 100-200 times dilution, as 85.0% in tomoto and 75.0% in eggplant with 300 times dilution. The R. solanacearum introduced into potted seedlings of tomato and eggplant by watering the root with the ferment liquid of R. solanacearum could be controlled effectively by watering the root with the ferment liquid of biocontrol agent ANTI-8098A.
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