Description of phylotype II ecotypes within Ralstonia solanacearum species complex : diversity and evolution

Abstract

The studied model is the vascular plant pathogen Ralstonia solanacearum, with a particular focus on phylotype II strains. This telluric bacterium has a wide diversity, both on genotypic and phenotypic levels. Its evolving classification reflects the need to clarify its unusual biodiversity and seek to identify ecotype structure in this species complex, i.e., groups of strains with both genotypic and specific biological traits. Within the framework of this model pathosystem, we initially focused on deeply revisiting pathotypes among ecotypes, although well described in the literature, or describing new ecotypes (African phylotype III). We observed high phenotypic convergence between strains from phylotype III from the African highlands and Brown rot strains from phylotype IIB-1, both able to trigger wilt symptoms on potato and other Solanaceae at cold temperatures. Adaptation of diverse strains for cold tolerance led us to investigate the R. solanacearum situation in Europe and more specifically in the Mediterranean regions. This strategy allowed us to appreciate the significant divergence towards pathogenicity (virulence and aggressiveness) on Solanaceae within clonal-like structure of strains in the Brown rot ecotype, which also established latent interactions in the banana vascular system. In the mean time, phenotypes of banana pathogenic strains unifying the Moko ecotype, was also revisited on Solanaceae, and was able to trigger symptoms on both susceptible and resistant genetic resources to bacterial wilt. All these experimental data yielded selection criteria for choosing three new candidate strains in the R. solanacearum species complex for complete genome sequencing. Our genomic comparative approach allowed us to describe the first pangenome of this pathogen: all targeted identified genes of this species complex. These data were analyzed by various bioinformatic approaches and allowed us to design a complete reshaping of R. solanacearum species