| The prevention and control of tomato bacterial wilt caused by Ralstonia solanacearum is a world-wide difficult problem. The objective of this experiment was to screen and identify antagonistic bacteria from tomato rhizospheric soil against R.solanacearum (mainly pathogenic strains SST-Y and G2M1.70), optimize fermentation conditions of antagonistic strains, and illuminate characteristics of antagonistic substances produced by antagonistic strains, and testify the effects of them against R.solanacearum by pot experiment.In this study, antagonistic bacteria against R.solanacearum were screened by the plate culture method. Tomato rhizopheric soil was randomly taken from the depth of 0cm to 20 cm, mixed and plated with gradient dilution. 284 strains were isolated, and 33 strains have the effects against Ralstonia solanacearum. After further screening by dotting and agar block method, 4 strains, YB1, YB6, YB22 and YB70, were selected. The strain YB6 suppressed the growth of R.solanacearum with the inhibition zone above 17mm. Only the strain YB6 had stable antagonistic effects after continuous 10 generations, and was selected as the objective of the following experiments.The strain was identified as Arthrobacter by traditional identification, members of which widely inhabit in soil, and are scarcely reported as antagonistic bacteria.The composition of culture media and fermentation conditions of YB6 were optimized with orthogonal test. The optimal combination of fermentation were as follows: the carbon source with sucrose at a concentration of 1.5%, the nitrogen sources with peptone and (NH4)2SO4 at concentrations of 1.0%,0.3%, respectively, the initial pH at 9.0, the inoculum concentration 3%, and shaker revolution 100 r/min, incubation temperature 30°C and incubation time with 3 days.Under the optimal conditions, the inhibition zone of the strain against SST-Y and G2M1.70 increased by 76.72%, 81.14%, respectively.In the stability test, the strain showed low stability to tested chemical agents, and super acid, super base, and above 1.5 mg/mL concentration of protease inactivated the strain. The strain was sensitive to heat, 60°C over the loss of antimicrobial activity, but showed stability to UV 5 h and light 35000 L.The bacterium liquid and the fermentation filtrate of the strain YB6 were stored at 4°Cand room temperature, respectively. It was found that the inhibition activity of both the bacteria liquid and the fermentation filtrate was higher when stored at room temperature than at 4°C, and the inhibition activity of the bacterium liquid was higher than that of the fermentation filtrate.In the production experiment of solid inoculum, the adsporption effect of organic carrier(Organic fertilizer, Corn flour, Peanut meal, peatmoss, Rice stems powder, Rice bran ) was better than that of inorganic carrier(Activated carbon, vermiculite ), and maize flour as the carrier of the strain showed highest adsorption activity, survival rate and inhibition activity. The pot experiment showed that the inhibition activity was highest by the dipping inoculum method in the period of transplanting, and the biocontrol rate reached 65.0%.The antimicrobial range test revealed that the strain showed inhibition activity against all of the eight tested pathogenic strains(Rhizoctonia solani Kuhn, Ustilago scitaminea Syd., Colletotrichum gloeosporioides, Botrytis cinerea Pers., Fusarium graminearum, Fusarium oxysporum f.sp.cubense, Xanthomonas compeatris pv. Oryzicola, Magnaporthe oryzea), especially to the sugarcane smut and the wheat scab, indicating that the strain is valuable in the development of biocontrol bacteria. |
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