Gary E. Vallad,
Elaina Margenthaler, and
Christina Schneider, Gulf Coast Research and Education Center, University of Florida, IFAS, Wimauma 33598;
Jason Hong and
Jeffrey B. Jones, Department of Plant Pathology, University of Florida, Gainesville 32611;
Kevin Ong, Texas Plant Disease Diagnostic Lab, Texas A&M University, College Station 77845; and
David J. Norman, Mid-Florida Research and Education Center, University of Florida, IFAS, Apopka 32703
A bacterial spot of rose (Rosa spp.) caused by a xanthomonad was observed in Florida and Texas. Ten representative strains collected from the two states between 2004 and 2010 were used to determine the taxonomic position of this rose pathogen. Fatty acid methyl ester analysis was performed and a nearly 2-kb 16S-23S rRNA intergenic spacer along with flanking portions of the 16S and 23S rRNA genes were sequenced for selected strains, showing that they were members of the genus Xanthomonas. Multilocus sequence typing and analysis (MLST/MLSA) and pathogenicity tests were conducted to further characterize the Xanthomonas strains. The MLSA, based on six gene fragments—fusA, gapA, gltA, gyrB, lacF, and lepA—showed that the rose strains fell into Xanthomonas axonopodis subgroup 9.2 and shared the highest similarity values (98.8 to 99.7%) with X. alfalfae subsp. citrumelonis of the subgroup. However, principal coordinate analysis grouped the rose strains into a unique cluster distinct from other members of the subgroup according to virulence phenotypes on 11 plant species belonging to five plant families (Araceae, Euphorbiaceae, Rosaceae, Rutaceae, and Solanaceae). Moreover, the rose strains were aggressive on rose and Indian Hawthorn (Rhaphiolepsis indica). On the basis of the MLSA and virulence phenotypes, the pathovar epithet rosa is proposed.