Reclassification of Xanthomonas

Abstract

A comprehensive DNA-DNA hybridization study was performed by using 183 strains of the genus Xanthomonas. This genus was shown to comprise 20 DNA homology groups which are considered genomic species. Four groups corresponded to the previously described species Xanthomonas albilineans, Xanthomonas fragariae, Xanthomonas oryzae, and Xanthomonas populi. The previously described species Xanthomonas campestris was heterogeneous and was divided into 16 DNA homology groups. One of these groups exhibited a high level of DNA homology with Xanthomonas axonopodis. The 62 pathovars represented in this study were allocated to appropriate species. Our results, together with previous taxonomic data, supported a comprehensive revision of the classification of the genus Xanthomonas. The species X. albilineans, X. fragariae, X. oryzae, and X. populi are not affected. The type species of the genus, X. campestris (Pammel 1895) Dowson 1939, is emended to include only the pathovars obtained from crucifers (i.e., X. campestris pv. aberrans, X. campestris pv. armoraciae, X. campestris pv. barbareae, X. campestris pv. campestris, X. campestris pv. incanae, and X. campestris pv. raphani). X. axonopodis Starr and Garces 1950 is emended to include 34 former X. campestris pathovars. The following species names are proposed: Xanthomonas arboricola sp. nov., including X. arboricola pv. corylina, X. arboricola pv. juglandis, X. arboricola pv. poinsettiicola (type C strains of the former X. campestris pathovar), X. arboricola pv. populi, and X. arboricola pv. pruni; Xanthomonas bromi sp. nov. for strains isolated from bromegrass; Xanthomonas cassavae (ex Wiehe and Dowson 1953) sp. nov., nom. rev.; Xanthomonas codiaei sp. nov., including type B strains of the former taxon X. campestris pv. poinsettiicola; Xanthomonas cucurbitae (ex Bryan 1926) sp. nov., nom. rev.; Xanthomonas hortorum sp. nov., including X. hortorum pv. hederae, X. hortorum pv. pelargonii, and X. hortorum pv. vitians; Xanthomonas hyacinthi (ex Wakker 1883) sp. nov., nom. rev.; Xanthomonas melonis sp. nov.; Xanthomonas pisi (ex Goto and Okabe 1958) sp. nov., nom. rev.; Xanthomonas sacchari sp. nov. for strains isolated from diseased sugarcane in Guadeloupe; Xanthomonas theicola sp. nov.; Xanthomonas translucens (ex Jones, Johnson, and Reddy 1917) sp. nov., nom. rev., including X. translucens pv. arrhenatheri, X. translucens pv. cerealis, X. translucens pv. graminis, X. translucens pv. hordei, X. translucens pv. phlei, X. translucens pv. phleipratensis, X. translucens pv. poae, X. translucens pv. secalis, X. translucens pv. translucens, and X. translucens pv. undulosa; Xanthomonas vasicola sp. nov., including X. vasicola pv. holcicola and X. vasicola pv. vasculorum (type B strains of the former taxon X. campestris pv. vasculorum); and Xanthomonas vesicatoria (ex Doidge 1920) sp. nov., nom. rev., which includes the type B strains of the former taxon X. campestris pv. vesicatoria. Differentiating characteristics were determined for the new species on the basis of metabolic activity on a range of carbon substrates by using the Biolog GN microplate system.