Polyphasic taxonomic revision of the Ralstonia solanacearum species complex: proposal to emend the descriptions of Ralstonia solanacearum and Ralstonia syzygii and reclassify current R. syzygii strains as Ralstonia syzygii subsp. syzygii subsp. nov., R. solanacearum phylotype IV strains as Ralstonia syzygii subsp. indonesiensis subsp. nov., banana blood disease bacterium strains as Ralstonia syzygii subsp. celebesensis subsp. nov. and R. solanacearum phylotype I and III strains as Ralstonia pse

Abstract

The Ralstonia solanacearum species complex has long been recognized as a group of phenotypically diverse strains that can be subdivided into four phylotypes. Using a polyphasic taxonomic approach on an extensive set of strains, this study provides evidence for a taxonomic and nomenclatural revision of members of this complex. Data obtained from phylogenetic analysis of 16S-23S rRNA ITS gene sequences, 16S–23S rRNA intergenic spacer (ITS) region sequences and partial endoglucanase (egl) gene sequences and DNA–DNA hybridizations demonstrate that the R. solanacearum species complex comprises three genospecies. One of these includes the type strain of Ralstonia solanacearum and consists of strains of R. solanacearum phylotype II only. The second genospecies includes the type strain of Ralstonia syzygii and contains only phylotype IV strains. This genospecies is subdivided into three distinct groups, namely R. syzygii , the causal agent of Sumatra disease on clove trees in Indonesia, R. solanacearum phylotype IV strains isolated from different host plants mostly from Indonesia, and strains of the blood disease bacterium (BDB), the causal agent of the banana blood disease, a bacterial wilt disease in Indonesia that affects bananas and plantains. The last genospecies is composed of R. solanacearum strains that belong to phylotypes I and III. As these genospecies are also supported by phenotypic data that allow the differentiation of the three genospecies, the following taxonomic proposals are made: emendation of the descriptions of Ralstonia solanacearum and Ralstonia syzygii and descriptions of Ralstonia syzygii subsp. nov. (type strain R 001T = LMG 10661T = DSM 7385T) for the current R. syzygii strains, Ralstonia syzygii subsp. indonesiensis subsp. nov. (type strain UQRS 464T = LMG 27703T = DSM 27478T) for the current R. solanacearum phylotype IV strains, Ralstonia syzygii subsp. celebesensis subsp. nov. (type strain UQRS 627T = LMG 27706T = DSM 27477T) for the BDB strains and Ralstonia pseudosolanacearum sp. nov. (type strain UQRS 461T = LMG 9673T = NCPPB 1029T) for the strains of R. solanacearum phylotypes I and III.

Técnicas para el aislamiento, identificación y caracterización molecular de cepas de Ralstonia solanacearum relacionadas a Moko del plátano

“…Existe una alta variabilidad dentro de la especie, por lo que R. solanacearum es considerada una "especie complejo", abreviado como RSSC por sus siglas en inglés "Ralstonia solanacearum species complex" (Safni et al, 2014;Prior et al, 2016). Una especie complejo es definida como un grupo de aislados relacionados cercanamente, cuyos miembros individuales pueden representar más de una especie (Fegan y Prior, 2005).…”

“…There is a high variability within the species, therefore R. solanacearum is considered a "species complex", abbreviated as RSSC, for "Ralstonia solanacearum species complex" (Safni et al, 2014;Prior et al, 2016). A species complex is defined as a group of closely-related isolations, the individual members of which can represent more than one species (Fegan and Prior, 2005).…”

“…Since R. solanacearum makes up a heterogenous group of strains with a high genetic and phenotypic diversity, its classification has been under constant reconsideration for 50 years (Hayward, 1964;Fegan and Prior, 2005;Safni et al, 2014;Prior et al, 2016). Classification into biovars does not reflect the genetic background of the strains, so a genetic classification scheme is currently used, hierachically organized into the categories of phylotypes and sequevars (Fegan and Prior, 2005;Prior et al, 2016 Hayward, 2001;Champoiseau et al, 2009).…”

Occurrence and diversity of Ralstonia solanacearum populations in Brazil

“…nov. (SAFNI et al, 2014). The authors also divide the species R. syzygii into three distinct groups (Table 3).…”

“…According to this classification, pathogenic profiles (pathoprofiles) would group the behavior of strains within a group of host plants of several species, while the pathotypes would group the strains according to their virulence within a single host species. Another classification suggests the division of R. solanacearum into new species (REMENANT et al, 2011;ALLEN et al, 2014;SAFNI et al, 2014). In the first putative proposal (REMENANT et al, 2011), only phylotype II strains would be classified as R. solanacearum, while phylotypes I and III would be included in the new species R. sequeirae and phylotype IV in R. haywardii.…”