We report here the complete genome sequences of two Ralstonia pseu-dosolanacearum strains, isolated from the warm northeast region of Brazil. They display divergent (compatible versus incompatible) interactions with the resistant tomato line Hawaii 7996. Polymorphisms were detected in a subset of effector genes that might be associated with these contrasting phenotypes. R alstonia pseudosolanacearum is a soilborne pathogen and one of the main causal agents of the bacterial wilt (BW) disease of tomato (Solanum lycopersicum L.) and other crops (1). R. pseudosolanacearum is currently classified as a distinct species within the R. solanacearum complex, which comprises strains of phylotypes I and III (2-5). Although they are of putative exotic origin, R. pseudosolanacearum phylotype I isolates are currently disseminated in Brazil (north, northeast, and central regions) and infect mainly Solanaceae crops (tomato, peppers, eggplant, and scarlet eggplant) (6, 7). In this study, two tomato-infecting R. pseudosolanacearum strains from the warm Brazilian northeast region were sequenced in order to analyze candidate genes associated with their divergent (compatible versus incompatible) interactions with the tomato line Hawaii 7996, which is the main breeding source of BW resistance in this vegetable crop (8, 9). Strain RS 476 (sequevar I-18 from Maranhão state) is characterized by its ability to induce severe BW symptoms on Hawaii 7996 (60% incidence), whereas strain CRMRs218 (also sequevar I-18 from Pernambuco state) is able to induce severe BW symptoms in a wide range of tomato cultivars, but it is avirulent to Hawaii 7996.

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A detection assay for Ralstonia solanacearum in soil and weeds was developed by combining immunocapture and the polymerase chain reaction (IC-PCR). Anti-R. solanacearum polyclonal antibodies were produced in a white female rabbit and Dynal Ò superparamagnetic beads were coated with purified immu-noglobulinG (IgG). Using IC-PCR, the 718 bp target DNA was amplified at a detection threshold of approximately 10 4 colony-forming units (CFU) bacteria per millilitre of suspension. DNA was not amplified in soil suspensions derived from autoclaved and non-autoclaved soils, which contained R. solanacearum at 1-10 5 CFU/g soil. However, a positive PCR result was obtained when bacteria in the soil suspensions were first enriched in nutrient broth. IC-PCR detected R. solanacearum in tomato stems 24 h after inoculation by stem puncture with a suspension containing approximately 10 5 CFU/ml. IC-PCR detected the bacterium in 28 of 55 (51%) weeds and 10 of 32 (31%) soil samples. Of the weeds, Physalis minima, Amaranthus spinosus and Euphorbia hirta had the highest incidence of infection. R. solanacearum was not detected in soil taken from fallow fields, but it was discovered in some weed species. Symptomless tomato and pepper plants collected from the fields in which tomato bacterial wilt had previously occurred were found to contain R. solanacearum. These discoveries suggest that weeds and latent hosts may play a role in the survival of R. solanacearum between cropping cycles. U. S.

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