Amplified fragment length polymorphism and multilocus sequence analysis-based genotypic relatedness among pathogenic variants of Xanthomonas citri pv. citri and Xanthomonas campestris pv. bilvae

Abstract

Three pathogenic variants (i.e. pathotypes) have been described withinXanthomonas citripv.citri, the causal agent of Asiatic citrus canker. Pathotype A strains naturally infect a wide range ofCitrusspecies and members of some related genera. In contrast, pathotypes A* and Awhave narrow host ranges within the genusCitrusand have been isolated from Mexican lime (Citrus aurantifoliaL.) and from Mexican lime and alemow (Citrus macrophyllaL.), respectively. We used amplified fragment length polymorphism (AFLP) and multilocus sequence analysis (MLSA) based on four partial housekeeping gene sequences (atpD,dnaK,efpandgyrB) for the genotypic classification ofXanthomonas citripv.citriand the poorly characterized citrus pathogenXanthomonas campestrispv.bilvae. A Mantel test showed that genetic distances derived from AFLP and MLSA were highly correlated.X. campestrispv.bilvaeshowed a close relatedness to the type strain ofX. citri, indicating that this pathovar should be reclassified asX. citripv.bilvae. All pathotype A* and Awstrains were most closely related toX. citripv.citristrains with a wide host range (pathotype A), confirming previous DNA–DNA hybridization data. Pathotype Awshould be considered a junior synonym of pathotype A* on the basis of pathogenicity tests, AFLP, MLSA and PCR using pathovar-specific primers. Evolutionary genome divergences computed from AFLP data suggested that pathotype A* (including Awstrains) is a group of strains that shows a wider genetic diversity than pathotype A.