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 Ralsto nia solanacearum was assessed by restriction fragment length polymorphism ( RFLP) analysis of amplified fragments from the hrp gene region. Five amplif ied fragments appeared to be specific to R. solanacearum. Fifteen different profiles were identified among the 120 bacterial strains, and a hierarchic al cluster analysis distributed them into eight clusters. Each duster inclu ded strains belonging to a single biovar, except for strains of biovars 3 a nd 4, which could not be separated. However, the biovar 1 strains showed ra ther extensive diversity since they were distributed into five dusters wher eas the biovar 2 and the biovar 3 and 4 strains were gathered into one and two clusters, respectively. PCR-RFLP analysis of the hrp gene region confir med the results of previous studies which split the species into an "Americ anum" division including biovar I and 2 strains and an "Asiaticum" division including biovar 3 and 4 strains. However, the present study showed that m ost of the biovar 1 strains, originating from African countries (Reunion Is land, Madagascar, Zimbabwe, and Angola) and being included in a separate cl uster, belong to the "Asiaticum" rather than to the "Americanum" division. These African strains could thus have evolved separately from other biovar 1 strains originating from the Americas.