Genetic diversity of african and worldwide strains of Ralstonia solanacearum as determined by PCR-Restriction Fragment Length Polymorphism analysis of the hrp gene region

Abstract

The genetic diversity among a worldwide collection of 120 strains of #Ralstonia 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 eight clusters. Each cluster included strains belonging to a single biovar, except for strains of biovars 3 and 4, which could not be separated. However, the biovar 1 strains showed rather extensive diversity since they were distributed into five clusters whereas 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 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, 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. (Résumé d'auteur