Genetic diversity of African and worldwide strains of Ralstonia solanacearum as determined by PCR-restriction fragment length polymorphism analysis of the hrp gene region.
The genetic diversity among a worldwide collection of 120 strains of R. solanacearum was assessed by restriction fragment length polymorphism (RFLP) analysis of amplified fragments from the hrp gene region. Five amplified fragments appeared to be specific to R. solanacearum. Fifteen different profiles were identified among the 120 bacterial strains, and a hierarchical cluster analysis distributed them into 8 clusters. Each cluster included strains belonging to a single biovar, except for strains of biovars 3 and 4, which could not be separated. The biovar 1 strains showed extensive diversity, with the strains distributed into 5 clusters. Biovar 2 and biovar 3 and 4 strains were gathered into 1 and 2 clusters, respectively. Polymerase chain reaction-RFLP analysis of the hrp gene region confirmed the results of previous studies, which split the species into an "Americanum" division (including biovar 1 and 2 strains) and an "Asiaticum" division (including biovar 3 and 4 strains). However, the present study showed that most of the biovar 1 strains, originating from African countries (Reunion Island, Madagascar, Zimbabwe and Angola) and being included in a separate cluster, belonged to the "Asiaticum" rather than the "Americanum" division. It is suggested that the African strains could have evolved separately from other biovar 1 strains originating from the Americas.