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Bacterial wilt caused by Ralstonia solanacearum is a serious soilborne disease in many economically important crops including tomato, potato, tobacco, and peppers. Compared with the routine control, biological control is a more effective way in suppression of this kind of soil-borne disease.To explore possibilities of biological control for capsicum wilt,16 antagonistic bacteria against Ralstonia solanacearum were isolated from the rhizosphere of healthy capsicum. The isolate a45 was screened as the most promising antagonist based on antagonistic activity, spore-forming, growth on poor-nutrient media and antibiotic sensitivity. The strain was identified as Bacillus subtilis based on physiological and biochemical characteristics and 16S r DNA gene sequence.The soil and capsicum seedlings were treated with the antagonist a45 and their effects were studied in the greenhouse. The mixture of pig manure compost and amino acid fertilizer was inoculated with 20%(V/W) of a45 culture and fermented for 4 days to produce a bio-organic fertilizer (BOF), in which there were about 1.0×1010g-1 of a45. Pot experiment was carried out in greenhouse and the soils previously inoculated with pathogen R. solanacearum (5.0×106g-1 soil) was amended either with BOF (5‰W/W,5.0×107 a45 g-1 soil) or with a45 liquid culture (LC,5.0×107 a45 g-1 soil) to evaluate the effect of the biocontrol agents in controlling wilt disease.The results obtained were listed as follows. Application of LC and BOF could reduce capsicum wilt incidence by 69.58% and 76.09%, respectively. Meanwhile, the capsicum growth-promoting effects by LC and BOF were also observed. The population of R. solanacearum in the rhizosphere soil of capsicum 30 days after application with LC and BOF was decreased by 20.6% and 25%, respectively compared with that of the control. The population of a45 decreased gradually after inoculation in soils added with LC and BOF. Organic fertilizer, however, significantly improved the survival of strain a45 when it was applied together with a45.Application of strain a45 and its bioorganic fertilizer could induce POD, CAT and SOD activity in the leaves of the capsicum, but could not influence the soluble protein content. Application of strain a45 and its bioorganic fertilizer could also significantly affect the quantities of the bacteria, actinomycetes and fungi, thus improving the structure of soil microbial population.Genes ItuA, ituB, ituC, ituD, Qk, bam and sboA responsible to synthesize antibiotics iturin, subtilisin QK, bacillomycin and subtilosin A were detected by PCR in strain a45, indicating that the potential for biological control of the pathogens of peppers by strain a45 was possibly due to the production of antibiotics.In conclusion, application of strain a45 and its bioorganic fertilizer could significantly.control bacterial wilt of peppers caused by Ralstonia solanacearum by producing many antibiotics after the strain successfully survived and reproduced in soils with the help of organic substrates applied together.
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