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Specific Genes from the Potato Brown Rot Strains of Ralstonia solanacearum and Their Potential Use for Strain Detection

First and sixth authors: CIRAD, UMR PVBMT, Saint Pierre, La Réunion, F-97410 France; second, third, and seventh authors: CNRS-INRA, UMR LIPM, Castanet Tolosan, F-31326 France; and fourth and fifth authors: Cátedra de Microbiología. Facultad de Química, UDELAR, Gral. Flores 2124. CP 11800, Montevideo, Uruguay.

Ralstonia solanacearum is the agent of bacterial wilt infecting >200 different plant species covering >50 botanical families. The genus R. solanacearum can be classified into four phylotypes and each phylotype can be further subdivided into sequevars. The potato brown rot strains of R. solanacearum from phylotype IIB, sequevar 1 (IIB1), historically known as race 3, biovar 2 strains, are responsible for important economic losses to the potato industry and threaten ornamental crop production worldwide. Sensitive and specific detection methods are required to control this pathogen. This article provides a list of 70 genes and 15 intergenes specific to the potato brown rot strains of R. solanacearum from phylotype IIB1. This list was identified by comparative genomic hybridization on microarray and subsequent polymerase chain reaction validation with 14 IIB1 strains against 45 non-IIB1 strains that covered the known genetic diversity in R. solanacearum. The microarray used consisted of the previously described microarray representative of the phylotype I strain GMI1000, to which were added 660 70-mer oligonucleotides representative of new genomic islands detected in the phylotype IIB1 strain IPO1609. The brown rot strain-specific genes thus identified were organized in nine clusters covering 2 to 29 genes within the IPO1609 genome and 6 genes isolated along the genome. Of these specific genes, 29 were parts of mobile genetic elements. Considering the known instability of the R. solanacearum genome, we believe that multiple probes are required to consistently detect all IIB1 strains and we recommend the use of probes which are not part of genetic mobile elements.