title: Strong genetic differentiation between North American and European populations of Phytophthora alni subsp. uniformis.
abstract: Alder decline caused by Phytophthora alni has been one of the most important diseases of natural ecosystems in Europe during the last 20 years. The emergence of P. alni subsp. alni -the pathogen responsible for the epidemic-is linked to an interspecific hybridization event between two parental species: P. alni subsp. multiformis and P. alni subsp. uniformis. One of the parental species, P. alni subsp. uniformis, has been isolated in several European countries and, recently, in North America. The objective of this work was to assess the level of genetic diversity, the population genetic structure, and the putative reproduction mode and mating system of P. alni subsp. uniformis. Five new polymorphic microsatellite markers were used to contrast both geographical populations. The study comprised 71 isolates of P. alni subsp. uniformis collected from eight European countries and 10 locations in North America. Our results revealed strong differences between continental populations (Fst = 0.88; Rst = 0.74), with no evidence for gene flow. European isolates showed extremely low genetic diversity compared with the North American collection. Selfing appears to be the predominant mating system in both continental collections. The results suggest that the European P. alni subsp. uniformis population is most likely alien and derives from the introduction of a few individuals, whereas the North American population probably is an indigenous population.
authors.affiliation: INRA, UMR1136, INRA, Université de Lorraine, Interactions Arbres- Micro- organismes, IFR110 EFABA, Centre INRA de Nancy, 54280 Champenoux, France.
authors.forename: Jaime
authors.initials: J
authors.lastname: Aguayo
authors.forename: Gerard C
authors.initials: GC
authors.lastname: Adams
authors.forename: Fabien
authors.initials: F
authors.lastname: Halkett
authors.forename: Mursel
authors.initials: M
authors.lastname: Catal
authors.forename: Claude
authors.initials: C
authors.lastname: Husson
authors.forename: Zoltán Á
authors.initials: ZÁ
authors.lastname: Nagy
authors.forename: Everett M
authors.initials: EM
authors.lastname: Hansen
authors.forename: Benoît
authors.initials: B
authors.lastname: Marçais
authors.forename: Pascal
authors.initials: P
authors.lastname: Frey
mesh_terms: D000483:Alleles; D029661:Alnus / Q000469:parasitology*; D005060:Europe; D005787:Gene Frequency; D040961:Genetic Drift; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D005843:Geography; D018895:Microsatellite Repeats / Q000235:genetics*; D060885:Multiplex Polymerase Chain Reaction; D009656:North America; D010838:Phytophthora / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification; D010935:Plant Diseases / Q000469:parasitology*; D011110:Polymorphism, Genetic; D012098:Reproduction