Genetic diversity of Xanthomonas citri pv. citri causing citrus canker in Asia

Three PCR-based methods were used to assess the genetic diversity of 239 strains of Xanthomonas citri pv. citri (Xcc) causing citrus canker in Asia, including some strains from international collections. Data from amplified fragment length polymorphism (AFLP) analysis alter Sacl/Mspl restriction, insertion sequenceligation mediated-PCR (IS-LM-PCR) targeting 3 IS (ISXac-1, -2 and -3) and variable number of tandem repeats (VNTRs) using 14 minisatellite loci grouped into a multiple-locus VNTR analysis (MLVA) were collected by automated capillary electrophoresis. All three methods discriminated between Xcc-A strains exhibiting a broad host range on different cirrus species, and Xcc-A* strains with a more restricted host range, mainly on limes. Pathogenicity profiles were confirmed by inoculation on a range of hosts that differentiated these strains using a detached leaf assay. Xcc-A* was detected in South-East Asia, with a larger geographical distribution than previously known. The different genetic clusters of Xcc-A* that could be identified mostly correlated with geographical origin. Xcc-Aw strains from Florida were closely related to Xcc-A* both genetically and pathologically and they could be synonyms. The 239 Xcc strains were best discriminated by VNTRs, yielding 211 different haplotypes, followed by ISLM-PCR (149 haplotypes) and AFLP (97 haplotypes). IS-LMPCR and MLVA appeared to be most appropriate for genotyping Xcc strains on a small geographical scale. The three methods were very informative and data analysis could be highly automated, making them useful for population structure analysis and convenient for addressing issues about the epidemiology of this quarantine pathogen. (Texte intégral