Characterization of phenotypically distinct strains of Xanthomonas axonopodis pv. citri from southwest Asia

Strains of #Xanthomonas axonopodis# pv. #citri# were isolated from Mexican lime (#Citrits aurantifolia#) trees in several countries in southwest Asia. These strains produced typical erumpent bacterial canker lesions on Mexican lime but not on grapefruit (#C. paradisi#). Lesions on grapefruit were watersoaked and blister-like in contrast to the typical erumpent lesions seen after artificial inoculation with all described pathotypes of #X. axonopodis# pv. #citri#. This group of strains hydrolysed gelatin and casein and grew in the presence of 3% NaCl as is typical of #X. axonopodis# pv. #citri# pathotype A. RFLP analyses and DNA probe hybridization assays also gave results consistent with #X. axonopodis# pv. #citri# pathotype A. Metabolic fingerprints prepared with the Biolog(R) system showed similarities as well as differences to #X. axonopodis# pv. #citri# pathotype A. In spite of the physiological and genetic similarities to pathotype A of #X. axonopodis# pv. #citri#, these strains had no or very little affinity for polyclonal antiserum prepared against any of the reference strains of #X. axonopodis# pv. #citri# and also did not react with monoclonal antibody A1, an antibody that detects all strains of pathotype A of #X axonopodis# pv. #citri#. These strains were also insensitive to bacteriophage Cp3 like #X. axonopodis# pv. #citri# pathotype A and unlike #X. axonopodis# pv. #citri# pathotype B. We conclude that these strains, designated Xcc-A*, represent a variant of #X. axonopodis# pv. #citri# pathotype-A with pathogenicity limited to #C. aurantifolia#. The existence of extensive genotypic and phenotypic variation within pathotype A of #X. axonopodis# pv. #citri# was unexpected and further complicates the systematics of this species. (Résumé d'auteur