title: Ribosomal and Mitochondrial DNA Analyses of Xiphinema americanum-Group Populations.
abstract: The 18S ribosomal DNA (rDNA) and cytochrome oxidase I region of mitochondrial DNA (mtDNA) were sequenced for 24 Xiphinema americanum-group populations sourced from a number of geographically disparate locations. Sequences were subjected to phylogenetic analysis and compared. 18S rDNA strongly suggested that only X. pachtaicum, X. simile (two populations) and a X. americanum s.l. population from Portugal were different from the other 20 populations studied, whereas mtDNA indicated some heterogeneity between populations. Phylogenetically, based on mtDNA, an apparent dichotomy existed amongst X. americanum-group populations from North America and those from Asia, South America and Oceania. Analyses of 18S rDNA and mtDNA sequences underpin the classical taxonomic issues of the X. americanum-group and cast doubt on the degree of speciation within the X. americanum-group.
authors.affiliation: Central Laboratory of General Ecology, 2 Gargarin Street, 1113 Sofia, Bulgaria Scottish Crop Research Institute, Dundee, DD2 5DA, Scotland, UK Instituto Biológico, P.O. Box 70, 13001-970, Campinas, SP, Brazil Laboratoire National de Santé, 20A, rue Auguste Lumière, L-1950, Luxembourg.
authors.forename: Stela S
authors.initials: SS
authors.lastname: Lazarova
authors.forename: Gaynor
authors.initials: G
authors.lastname: Malloch
authors.forename: Claudio M G
authors.initials: CM
authors.lastname: Oliveira
authors.forename: Judith
authors.initials: J
authors.lastname: Hübschen
authors.forename: Roy
authors.initials: R
authors.lastname: Neilson