Initial characterization of a Xanthomonas sp. causing bacterial spot of shrub rose (Rosa spp.)
G. VALLAD (1), C. Summers (1), H. Adkison (1), E. Margenthaler (1)
(1) University of Florida, Wimauma, FL, U.S.A.
Phytopathology 100:S129

A severe bacterial spot of shrub rose (Rosa spp.) caused by a xanthomonad was observed during summer production in Florida. Foliar symptoms consisted of small black lesions with defined margins that were fairly vein delimited and often located along leaf margins. Based on fatty acid composition and 16S rRNA sequence, the strain was most closely related to several pathovars of Xanthomonas axonopodis. The 16S-23S rRNA intergenic spacer (ITS) and flanking portions of the 16S and 23S rRNA genes were sequenced and compared among three rose strains and those of several characterized strains of X. citrumelo, X. euvesicatoria, X. dieffenbachiae, X. manihotis, and X. perforans. Sequence identity within the nearly 2 kb region was greater than 98.3% among all strains with 100% identity among the rose strains. The rose strains exhibited 99.9% identity with X. perforans. Phylogenetic analyses of the ITS region consistently grouped rose strains closest to X. perforans. Rose strains caused few symptoms when infiltrated at 10⁶ cfu/ml into leaves of citrus, tomato, pepper, or several members of the Euphorbiaceae or Araceae. However, strains were clearly pathogenic on rose and another Rosaceae, Indian Hawthorne (Rhaphiolepis indica). Results suggest that the rose strains may represent a new species or subspecies of Xanthomonas. Further characterization of rose strains through multi-locus sequence typing and host testing is in progress. This is the first pathogenic Xanthomonas sp. associated with rose.