Résumé
Xanthomonas albilineans causes leaf scald, a lethal disease of sugarcane. This bacterium exhibits distinctive pathogenic mechanisms, ecology and taxonomy when compared to other species of Xanthomonas. For example, X. albilineans is missing two loci required for pathogenicity in other plant ·pathogenic species of Xanlhol11onas: the xanthan gum biosynthesis and the Hrp (for Hypersensitive response and pathogenicily) TTss (for Type ThreeSecretion System) gene clusters. X albilineans also exhibits a large intra-species variability which was previously described using different genetic markers, including PFGE (for PulsedField Gel Electrophoresis) ( 1). Aerial transmission of the pathogen has been shown to occur in several sugarcane producing locations of the world (including Florida, Guadeloupe, Louisiana, Mauritius, Taiwan, and Texas), and was associated with outbreaks of the disease in the late 1980's. Strain s of X albilineans involved in these out breaks were shown to belong to a single PFGE group called PFGE-B (1). A former study revealed high variation in pathogenicity among 19 PFGE-B strains isolated in Guadeloupe in 2003 (2). These 19 strains, which differ in their capacity to colonize sugarcane stalks and/or to cause foliar symptoms, were distributed into 4 colonization groups (CG): CG-I to CG-IV with CG-I including the least aggressive strains and CG-IV the most aggressive strains. AFLP analyses were performed using 9 of these 19 strains which span the variability o f pathogenicity (CG- I la CG-IV), and results revealed that these 9 strain s were genetically c10sely related. However, no relationship was found between the AFLP genetic variation and the variation in pathogcnicity (2). In the present stud y, we sequenced these nine strains in order to identify SNP (for Single Nucleotide Polymorphism) associated with the distribution of the strains into the 4 groups of colonization. (Résumé d' auteur)