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How diverse is the Ralstonia solanacearum species complex in the South-West India 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 : Book of abstracts of the 6th International Bacterial Wilt Symposium. Toulouse : INRA, p. 104-104. International Bacterial Wilt Symposium. 6, 2016-07-03/2016-07-07, Toulouse (France).

Ralstonia solanacearum is a species complex (Rssc), distributed worldwide and economically destructive. This soilborne bacterial plant pathogen encompasses an unusually wide hast range. The pathogen invades the roots and colonizes the xylem vessels causing bacterial wilt (BW) diseases. Strains distributed into four phylogenetic groups, based on ITS sequences called phylotypes that relates to geographical origin: phylotype 1 (Asia), phylotype Il (America), phylotype Ill (Africa), and phylotype IV (lndonesia-Japan). ln the South-West lndian Ocean (SWIO) islands, although R. solanacearum is regularly reported, no recent data is available about its genetic diversity and structure. Our main objectives are then to ge a significant collection of R. solanacearum strains to thoroughly analyze this genetic diversity; characterize the evolutionary forces that shape populations; and evaluate genetic resources for resistance to BW. 2971 R. solanacearum strains have been collected mainly from Solanaceae: Madagascar* (n=1224), Reunion (n=789), Mauritius (n=785), Mayotte (n=166), Seychelles (n=92), Rodrigues (n=Sl) and Comoros (n=S, to be completed). A preliminary broad molecular typing was done using the multiplex PCR (Fegan and Prier, 2005) showing 49.5% of phylotype I, 40 of phylotype Il, 10.4% of phylotype Ill, and 2 strains 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 th partial endoglucanase (egl) amplification, along with a set of 100 international reference strains. Further characterizations are ongoing through a MLSA/MLST** scheme based on partial amplification of 7 genes; gdhA, mutS, adK, leuS, rplB, gyrB and egl. This is the first report of a large scale survey in the SWIO. lnterestingly we reported here the predominance of one sequevar (1-31) among the SWIO strains whereas the phylotype I is known to encompass a broad genetic basis (16 sequevars) Also sequevar IV-10 was described in Mauritius for the first time.

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