Diversity of Brazilian biovar 2 strains of Ralstonia solanacearum

Ralstonia solanacearum is responsible for bacterial wilt disease. Specific and accurate identification of this pathogen is essential for protection of susceptible crops as well as breeding resistant varieties. Historically, R. solanacearum has been classified into biovars based on the use of sugar and alcohol as carbon sources, into races based on its ability to infect different hosts, more recently into phylotypes based on the intergenic transcribed sequence of the ribosomal RNA genes 16S and 23S and into sequevars based on the endoglucanase gene (egl) sequence. Race 3 biovar 2 (R3Bv2) is widespread in South and Central America, and in Brazil it is present in all potato-producing regions as the most prevalent strain. In this study, we classified 53 Brazilian R. solanacearum biovar 2 (Bv2) strains by traditional and molecular methods. PCR with specific primers confirmed all 53 bacterial strains as belonging to the R. solanacearum species complex, and all were classified as biovar 2A or 2T based on acidification of sugars and alcohols. Multiplex phylotype PCR assigned all strains to phylotype II. Phylogenetic analysis of egl sequences showed that most Bv2 strains from Brazil analyzed in this study did not cluster with known sequevars and are less clonal than the R3Bv2 strains reported for other countries. This is the first study to address the diversity of a collection of Brazilian R. solanacearum strains using the phylotype and sequevar classification scheme.