Molecular epidemiology of Ralstonia pseudosolanacearum Phylotype I strains in the South West Indian Ocean region and their relatedness to African strains

Increasing requirements for developing tools allowing fine traceability of strains responsible for epidemics is tightly linked with the need to understand factors shaping pathogen populations and their interactions with their environment. Bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) causes one of the most important plant diseases in tropical and sub-tropical regions. Sadly few, outdated or no information on its epidemiology is reported in the literature, although alarming outbreaks are regularly reported as a disaster both in terms of economical and sociological impact. A large set of isolate (n = 2,608) belonging to the Ralstonia solanacearum species complex Phylotype I strains was retrieved from diseased plants on the field across the South West Indian Ocean and Africa. This collection helped further assessing the epidemiological discriminating power of the RS1-MLVA14 scheme previously published. A total of 13 markers were validated and characterized as not equally informative, with little infra-sequevar polymorphism for most of them and performance-specific depending on the Phylotype I lineage considered. We strongly believed that the full characterization of the RS1-MLVA13 scheme will help for understanding the epidemiology of Phylotype I strains and that more research is needed in order to understand why the Phylotype I-31 is such a successful ecotype at such a large geographic scale.