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How diverse is the Ralstonia solanacearum species complex in the South-West lndian Ocean islands?

Yahiaoui N., Ravelomanantsoa S., Cheron J.J., Chesneau T., Brutus S., Petrousse B., Benimadhu S., Jeetah R., Azali Hamza A., Jaufeerally-Fakim Y., Cottineau J.S., Costet L., Robene I., Hostachy B., Guérin F., Cellier G., Prior P., Poussier S.. 2016. In : 12èmes Rencontres Plantes-Bactéries - Book of Abstracts. Paris : SFP, p. 94-94. Rencontres Plantes-Bactéries. 12, 2016-01-11/2016-01-15, Aussois (France).

Ralstonia solanocearum is a species complex (Rssc), distributed worldwide and economically destructive. This soilborne bacterial plant pathogen encompasses an unusually wide host range. The pathogen invades the roots and the xylem vessels causing bacterial wilt (BW) diseases. Four phylogenetic groups called phylotypes structured the Rssc that relates to their geographic origin of evolution: phylotype I (Asia), phylotype II (America), phylotype III (Africa), and phylotype IV (Indonesia-Japan). In the South-West Indian Ocean (SWIO) islands, although R solanocearum is regularly reported, no recent data is available about its genetic diversity and structure. Our main objectives are then to get a significant collection of R.solanacearum strains to thoroughly analyze the genetic diversity of the strains; characterize the evolutionary forces that shape populations; and evaluate genetic resources for resistance to BW. Presently, 2971 R.solanocearum strains have been collected mainly from Solanaceae: Madagscar* (n=1224), Reunion (n=F789), Mauritius (n=693), Mayotte (n=166), Seychelles (n=92), and Comoros (n=5, to be completed). A preliminary broad molecular typing was done using the multiplex PCR (Fegan and Prior 2005)**, showing 46.6% of phylotype I, 42.3% of phylotype II, 11% of phylotype III, and 0.1% of phylotype IV. A selection of 126 strains that covered the geographic and host diversity was organized to assess phylogenetic relationships. Maximum Likelihood tree (PhyML) was performed on the partial endoglucanase (egl) amplification, along with a set of 1 OO international reference strains. Further characterizations are ongoing through a MLSA scheme based on partial amplification of 6 genes; gdhA, mutS, adK, leuS, rplB and gyrB. This is the first report of a large scale survey in the SWIO. Surprisingly we showed that phylotype I-31 is mainly represented and found in every prospected territory in the SWIO. Also Phylotype IV was first described in Mauritius.

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