New Zealand strains of plant pathogenic bacteria classified by multi‐locus sequence analysis; proposal of Xanthomonas dyei sp. nov.

Abstract

Strains of Xanthomonas isolated in New Zealand from diseased endemic and introduced plants, investigated in a multi‐locus sequence analysis (MLSA), were distributed primarily in two species. Strains from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia were members of Xanthomonas arboricola. Strains of Xanthomonas campestris pv. laureliae, X. campestris pv. eucalypti and strains from Aralia, Diospyros, Dysoxylum, Eriostemon, Eucalyptus, Metrosideros and Olea formed a population distinct from all known Xanthomonas spp. These latter strains have a unique fatty acid methyl ester profile and are considered to be members of a new Xanthomonas species, for which the name Xanthomonas dyei is proposed. Xanthomonas campestris pv. eucalypti and X. campestris pv. laureliae are considered to be pathovars of the new species and their reclassification as X. dyei pv. eucalypti and X. dyei pv. laureliae, respectively, is proposed. Strains previously identified as Pseudomonas syringae pv. dysoxyli from Dysoxylum spectabile, including the pathotype strain, were examined and found not to represent the pathogen originally described as P. dysoxyli. Other strains (proved to be pathogenic) from diseased D. spectabile, corresponding to the original description of P. dysoxyli, are members of X. dyei and the new combination X. dyei pv. dysoxyli is proposed. The geographic and evolutionary origins of X. dyei, apparently endemic to Australasia, and the adaptation of strains to the introduced host plants Aralia, Diospyros, Eriostemon, Metrosideros and Olea, are discussed. The origins of the X. arboricola strains isolated from Dysoxylum, Hardenbergia, Liquidambar, Magnolia and Mahonia pose a conundrum.