title: Phytophthora alni sp. nov. and its variants: designation of emerging heteroploid hybrid pathogens spreading on Alnus trees.
abstract: In 1993 a destructive new Phytophthora pathogen of riparian Alnus trees was discovered in the UK and subsequently shown to be present in other parts of Europe. The new Phytophthora comprised a group of emergent heteroploid hybrids, probably between P. cambivora and a species related to P. fragariae. These included a common, near tetraploid standard hybrid, the presumptive allopolyploid; and four scarcer major variant types with chromosome numbers intermediate between diploid and tetraploid, named the Swedish, Dutch, German and UK variants. The standard hybrid type is formally designated here as Phytophthora alni subsp. alni. The Swedish variant is designated as P. alni subsp. uniformis; and the Dutch, German and UK variants collectively as P. alni subsp. multiformis. The properties of the Dutch, German and UK variants within subsp. multiformis are informally described. The problems of designating emergent species hybrids under the International Code of Botanical Nomenclature and the reasons for the taxonomic choices made are discussed.
authors.affiliation: Forest Research Agency (FRA), Farnham, Surrey GU10 4LH, UK. clive.brasier@forestry.gsi.gov.uk
authors.forename: Clive M
authors.initials: CM
authors.lastname: Brasier
authors.forename: Susan A
authors.initials: SA
authors.lastname: Kirk
authors.forename: Jose
authors.initials: J
authors.lastname: Delcan
authors.forename: David E L
authors.initials: DE
authors.lastname: Cooke
authors.forename: Thomas
authors.initials: T
authors.lastname: Jung
authors.forename: Willem A
authors.initials: WA
authors.lastname: Man in't Veld
mesh_terms: D029661:Alnus; D001483:Base Sequence; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D021901:DNA, Intergenic / Q000737:chemistry / Q000235:genetics; D005060:Europe; D008969:Molecular Sequence Data; D010802:Phylogeny; D010838:Phytophthora / Q000145:classification* / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D010935:Plant Diseases / Q000382:microbiology*; D017422:Sequence Analysis, DNA
chemical_list: D004271:DNA, Fungal; D021901:DNA, Intergenic