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Epidemiological surveillance of plant pathogens based on genotyping methods is mandatory to improve disease management strategies. In the Southwest Indian Ocean (SWIO) islands, bacterial wilt (BW) caused by the Ralstonia solanacearum species complex (RSSC) is hampering the production of many sustainable and cash crops. To thoroughly analyze the genetic diversity of the RSSC in the SWIO, we performed a wide sampling survey (in Comoros, Mauritius, Reunion, Rodrigues, and Seychelles) that yielded 1,704 isolates from 129 plots, mainly from solanaceous crops. Classification of the isolates to the four major RSSC phylogenetic groups, named phylotypes, showed that 87% were phylotype I, representing the most prevalent strain in each of the SWIO islands. Additionally, 9.7% were phylotype II, and 3.3% were phylotype III; however, these isolates were found only in Reunion. Phylotype IV (2 isolates), known to be restricted to Indonesia-Australia-Japan, was reported in Mauritius, representing the first report of this group in the SWIO. Partial endoglucanase (egl) sequencing, based on the selection of 145 isolates covering the geographic and host diversity in the SWIO (also including strains from Mayotte and Madagascar), revealed 14 sequevars with Reunion and Mauritius displaying the highest sequevar diversity. Through a multilocus sequence analysis (MLSA) scheme based on the partial sequencing of 6 housekeeping genes (gdhA, gyrB, rplB, leuS, adk, and mutS) and 1 virulence-associated gene (egl), we inferred the phylogenetic relationships between these 145 SWIO isolates and 90 worldwide RSSC reference strains. Phylotype I was the most recombinogenic, although recombination events were detected among all phylotypes. A multilocus sequence typing (MLST) scheme identified 29 sequence types (STs) with variable geographic distributions in the SWIO. The outstanding epidemiologic feature was STI-13 (sequevar I-31), which was overrepresented in the SWIO and obviously reflected a lineage strongly adapted to the SWIO environment. A goeBURST analysis identified eight clonal complexes (CCs) including SWIO isolates, four CCs being geographically restricted to the SWIO, and four CCs being widespread beyond the SWIO. This work, which highlights notable genetic links between African and SWIO strains, provides a basis for the epidemiological surveillance of RSSC and will contribute to BW management in the SWIO.

The Ralstonia solanacearum species complex (Rssc) encompasses strains that are highly destructive worldwide on a wide hast range. This soilborne bacterial plant pathogen invades the roots and colonizes the xylem vessels causing bacterial wilt (BW) diseases. Strains are distributed into four phylogenetic groups, called phylotypes, differing in geographical origin of the strains: phylotype I (Asia), phylotype II (America), phylotype III (Africa) and phylotype IV (Australia - lndonesia - Japan). Each phylotype is subdivided into sequevars based on partial sequencing of the endoglucanase (egl) gene (Fegan and Prior, 2005). In the South-West lndian Ocean (SWIO) islands, although the Rssc is regularly reported no recent data is available about its genetic diversity and population structure. To thoroughly analyze the genetic diversity of the Rssc in the SWIO, we collected a significant collection of Rssc strains mainly from Solanaceae: Reunion (n=789, 41 sites), Mauritius (n=785, 30 sites), Rodrigues (n=S1, 3 sites), Mayotte (n=166, 24 sites), Seychelles (n=92, 9 sites) and Comoros (n=S, to be completed). Using the Multiplex-PCR (Fegan and Prior, 2005), we revealed that the four phylotypes are present with variable distribution depending on the SWIO islands and variable proportions: phylotype 1 (86.7%), phylotype II (9.7%), phylotype Ill (3.5%) and two strains from phylotype IV (0.1%). Partial egl sequencing based on a selection of strains that covered the geographic and hast diversity showed the unexpected overrepresentation of one sequevar (1-31). Further characterizations are ongoing through (i) a MLSA/MLST (Multilocus sequence analysis/typing) based on partial amplification of 7 genes (gdhA, mutS, adK, feus, rp/B, gyrB, and egl) and (ii) the development of a new MLVA (Multilocus variable number of tandem repeat analysis) scheme. Results of bath approaches will be discussed du ring the presentation.