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Genetic Analyses of Xanthomonas axonopodis pv. dieffenbachiae Strains Reveal Distinct Phylogenetic Groups

First author: University of Florida, SWFREC, Immokalee, FL 34142; second author: University of Florida, Department of Plant Pathology, Gainesville, FL 32611; third and fourth authors: Virginia Polytechnic Institute & State University, Department of Plant Pathology, Physiology, and Weed Science, Blacksburg, VA 24061; and fifth author: University of Florida, MFREC, Apopka, FL 32703.

A comprehensive analysis of 175 Xanthomonas axonopodis pv. dieffenbachiae strains isolated from 10 Araceae hosts was done to identify pathogen variation. The strains were subjected to repetitive extragenic palindromic sequence polymerase chain reaction and four major phylogenetic clusters were generated. A subset of 40 strains isolated from Anthurium, Dieffenbachia, and Syngonium was further defined by amplified fragment length polymorphism and fatty acid methyl ester analysis and the same four phylogenetic clusters were observed. Comparison of representative strains in the first three clusters using DNA-DNA hybridization and multilocus sequence analysis supports the previous reclassification of strains in cluster I, including the X. axonopodis pv. dieffenbachiae pathovar reference strain (LMG695), to X. citri. Our research findings indicate that strains in cluster I, isolated primarily from anthurium, probably represent an undescribed pathovar. Other phylogenetic subclusters consisting primarily of strains isolated from xanthosoma and philodendron in clusters III and IV, respectively, may yet represent other undescribed species or pathovars of Xanthomonas.