Soil-borne antagonists for biological control of bacterial wilt disease caused by Ralstonia solanacearum in tomato and pepper.

Abstract

Bacterial wilt is an important disease of tomatoes and peppers, causing plant death and significant yield losses. Control methods include use of resistant varieties, crop rotation, etc. Biological control is desirable because control with other methods gives variable results. This paper describes the effectiveness of microbial antagonists isolated from soils. Of 73 isolated antagonists, eight were screened and evaluated in vitro and in vivo against Ralstonia solanacearum. They all significantly reduced disease symptoms. The effects of carbon and nitrogen source, incubation temperature and broth culture pH were evaluated for production of inhibitory substances. Results indicated that the optima were sucrose 2.5% (w/v), peptone 2% (w/v), temperature 28°C, and initial medium pH of 7. Three antagonists isolated from soil (Bacillus megaterium, Enterobacter cloacae, Pichia guillermondii) and Candida ethanolica showed high potential for disease suppression and also increased fruit weight, biomass and plant height. These results provide encouragement for continued research on biological control of bacterial wilt by antagonistic isolates from soil.