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

2022

E15164

Increasing requirements for developing tools allowing fine strain traceability responsible for epidemics is tightly linked with the need to understand factors shaping pathogen populations and their environmental interactions. Bacterial wilt caused by the Ralstonia solanacearum species complex (RSSC) is one of the most important plant diseases (Mansfield et al., 2012) in tropical and sub-tropical regions. Sadly little or outdated, or no information on its epidemiology is reported in the literature, although alarming outbreaks are regularly reported as a disaster. A large set of phylotype I isolates (n = 2,608) was retrieved from diseased plants in fields across the South West Indian Ocean (SWIO) and Africa. This collection enabled further assessment of the epidemiological discriminating power of the previously published RS1-MLVA14 scheme. Thirteen markers were validated and characterized as not equally informative. Most had little infra-sequevar polymorphism and their performance depended on the sequevar. Strong correlation was found with a previously MLST scheme. However, 2-3% of sequevars were not correctly assigned through endoglucanase gene sequence. Discriminant Analysis of Principal Components (DAPC) revealed four groups with strong phylogenetic relatedness to sequevars 31, 33, and 18. Phylotype I-31 isolates were highly prevalent in the SWIO and Africa, but their dissemination pathways remain unclear. Tanzania and Mauritius showed the greatest diversity of RSSC strains, as the four DAPC groups were retrieved. Mauritius was the sole territory harboring a vast Phylogenetic diversity and all DAPC groups. More research is still needed to understand the high prevalence of phylotype I-31 at such a large geographic scale.

online, PHYTOPATHOLOGY

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