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Broad Diversity of Ralstonia solanacearum Strains in Cameroon

In 2005, an extensive survey of bacterial wilt in Cameroon collected 110 strains of Ralstonia solanacearum from wilting tomato, potato, pepper, huckleberry (Solanum scabrum), sesame, and amaranth. The genetic diversity and phylogeny of selected strains from Cameroon were assessed by multiplex--polymerase chain reaction (PCR), race 3/biovar 2--specific PCR, and sequence analyses of the mutS and egl genes. These data were compared with those from 33 reference strains covering the known diversity within the R. solanacearum species complex. Strains isolated in Cameroon clustered into three of the four known phylotypes: I (Asian), II (American), and III (African). Lowland tomato strains belonged to phylotype I and were quite homogeneous. The strains belonging to phylotype II were genetically diverse, and partitioned into subclusters IIA and IIB (sequevar 1, race 3/biovar 2). Cameroon strains in the African phylotype III were distinct from reference strains from Zimbabwe or the Indian Ocean, highlighting the genetic diversity present within this phylotype. Strains from potatoes growing in the highlands of West Cameroon fell into both phylotypes II (race 3/biovar 2) and III. These phylotype II and III highland strains attacked both potato and tomato and could therefore pose an economic threat to potato and tomato crops throughout Central Africa. This is the first comprehensive report on the genetic diversity of R. solanacearum strains in Cameroon.