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Cirad

The Ralstonia solanacearum species complex : genetic diversity, phylogeny and molecular typing of strains with a particular attention to emerging strains and bacterial wilts of banana known as moko disease, bugtok disease and blodd disease

Prior P., Wicker E., Fegan M.. 2005. In : 08 - 02/09/05, Manizales, Colombia/Corpoica. II Seminario Internacional sobre produccion, comercializacion e industrializacion de platano, 28. s.l. : s.n., 1 p.. Seminario Internacional sobre Produccion, Comercializacion e Industrializacion de Platano. 2, 2005-08-28/2005-09-02, Manizales (Colombie).

Ralstonia solanacearum is a ubiquitous, highly variable and adaptable plant pathogen distributed worldwide with a large and expanding host range. R. solanacearum (Rs) and its close relatives, the blood disease bacterium and R. syzygii, constitute a species complex, a diverse group of closely related isolates that represent more than one species. Biovar (Bv) typing and race assessment are methods commonly used for assessing the diversity of Rs strains. However, recent genetic evidence has indicated that these phenotypically-based schemes are not sufficient to encompass the diversity of strains represented in the species Rs. A classification system based upon phylogenetic analysis of sequence data generated from the 16S-23S internal transcribed spacer (ITS) region, the endoglucanase gene and the mutS gene has recently been developed. From the phylogenetic analysis of the sequence data the Rs species complex can be subdivided into four monophyletic clusters of strains, termed phylotypes. Phylotype I includes strains belonging to Bv 3, 4, and 5, primarily originating from Asia. Phylotype II includes strains belonging to Bv 1, 2 and 2T, primarily originating from America. The Rs race 3 potato pathogen, which has a worldwide distribution, and the race 2 banana pathogen are both members of phylotype Il. Phylotype III contains strains primarily isolated from Africa and surrounding islands, and belonging to to Bv 1 and 2T. Phylotype IV contains Rs strains isolated primarily from Indonesia belonging to Bv 1, 2 and 2T and also contains the blood disease bacterium and R. syzygii. Each phylotype is composed of a number of groups of strains, with highly conserved endoglucanase and mutS gene sequences, termed sequevars. The phylotyping scheme is highly discriminatory, flexible, additive, and should allow a better prediction of the properties of strains. Multiplex PCR protocols have been designed for identifying the phylotype to which a strain belongs and to provide identification of strains with different pathotypes: H/B MLG24, SFR/A MLG25, and heliconia/tomato/banana MLG28 (sequevars 3, 4 and 6, respectively). A case study is presented on epidemiology of an emerging anthurium/cucurbit pathotype from Martinique (sequevar4NP) which may infect Musa (especially capable in infecting plantain banana). This in turn will aid in the development of strategies for the successful control of the many bacterial wilts caused by R. solanacearum. Based on this recent knowledge, a global and long term bacterial wilt project has recently been launched in Reunion Is. under the leadership of CIRAD, details of this project will be presented. (Texte intégral)
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