Strain characterization and 16S‐23S probe development for differentiating geographically dispersed isolates of the phytopathogen Ralstonia solanacearum

Abstract

The causative agent of potato brown rot and bacterial wilt, Ralstonia solanacearum, results in serious world-wide economic losses, particularly in the tropics. In the last decade, however, the incidence of bacterial wilt in potatoes grown in Northern Europe has increased, presenting an interesting epidemiological puzzle. Its occurrence may be as a result of changes in agricultural practice or the emergence of a novel bacterial variety, better adapted to cooler conditions. To understand the distribution and genetic diversity of this phytopathogen, we have analysed a collection of 82 isolates from Europe and tropical regions. Both phenotypic [SDS-PAGE (sodium dodecyl sulphate polyacrylamide gel electrophoresis) profiling, FAME (fatty acid methyl esters) analysis, growth profiles and EPS (exopolysaccharide) production] and genotypic [16S rRNA RFLP (restriction fragment length polymorphism), ARDRA (amplified ribosomal DNA restriction analysis) and sequence analysis of 16S-23S rRNA ITS and flanking regions] methods were compared. Principal component analysis of FAME profiles clustered isolates into three groups and ARDRA of a 0.85 kb amplified fragment from the 16S-23S ITS region differentiated isolates into four groups. Using sequence analysis, specific primers were designed within the variable region 147-170 of the 23S rRNA. These primers, RsolT2 and RsolT3, respectively, differentiated isolates into two distinct clusters as described previously by Wullings and colleagues (Wullings et al., 1998). The European strains (Biovar 2, race 3) analysed in this study specifically hybridized with RsolT3, and showed considerable genetic homogeneity when compared with strains of other races from 'the rest of the world'. These data indicate the possible selection and proliferation of a 'European'-adapted variant.

Genetic diversity of Ralstonia solanacearum strains from China assessed by PCR-based fingerprints to unravel host plant- and site-dependent distribution patterns

“…All strains also displayed a distinct fliC ‐RFLP pattern and belonged to the same sequevar. This unusual stability of the BOX patterns has already been reported by several studies (Cook et al , 1989; Timms‐Wilson et al , 2001; Xu et al , 2009). These biovar 2 strains are most often isolated from potato and supposedly originated from the cool Andean highlands.…”

Phylogeny and Population Structure of Brown Rot- and Moko Disease-Causing Strains of Ralstonia solanacearum Phylotype II

“…The investigation first focused on cold-tolerant phylotype IIB-1 strains, which represent a serious threat for potato production in Europe and temperate regions of the world. These strains were formerly known to present a clonal structure (20,23,27,38), and considerable diversity associated with the geographical distribution of strains was inferred in this study. Analysis showed two major clusters, but surprisingly, whereas the inference of phylogeny reflected a separation between sequevar 1 and 2 strains (phylotype II), the Bayesian population structure assessment method grouped strains from the Andean region together.…”

Detection and functional characterization of a large genomic deletion resulting in decreased pathogenicity in Ralstonia solanacearum race 3 biovar 2 strains

“…Due to their probable common origin in Andean highlands, isolates from around the world composing the R3bv2/Phylotype IIB1 subgroup are phenotypically and genetically homogenous (Timms‐Wilson et al ., 2001; Fegan and Prior, 2005; Guidot et al ., 2009). To date, two draft genome sequences of R3bv2 strains have been established: the one from strain UW551, isolated in Wisconsin from a wilted geranium grown from a cutting originating in Kenya (Gabriel et al ., 2006), and the one from strain IPO1609, isolated from potato in the Netherlands (van Elsas et al ., 2000; Guidot et al ., 2009).…”