Genetic diversity of Ralstonia solanacearum as assessed by PCR-RFLP of thehrp gene region, AFLP and 16S rRNA sequence analysis, and identification of an African subdivision

The genetic diversity among strains in a worldwide collection of Ralstonia solanacearum. causal agent of bacterial wilt was assessed by using three di fferent molecular methods. PCR-RFLP analysis of the hrp gene region was ext ended from previous studies to include additional strains and showed that f ive amplicons were produced not only with all R. solanacearum strains but a lso with strains of the closely related bacteria Pseudomonas syzygii and th e blood disease bacterium (BDB). however the three bacterial taxa could be discriminated by specific restriction profiles. The PCR-RFLP clustering, wh ich agreed with the biovar classification and the geographical origin of st rains, was confirmed by AFLP. Moreover, AFLP permitted very fine discrimina tion between different isolates and was able to differentiate strains that were not distinguishable by PCR-RFLP. AFLP and PCR-RFLP analyses confirmed the results of previous investigations which split the species into two div isions, but revealed a further subdivision. This observation was further su pported by 16S rRNA sequence data, which grouped biovar 1 strains originati ng from the southern part of Africa.