RESUMEN
Populus nigra L. is a pioneer tree species of riparian ecosystems that is threatened with extinction because of the loss of its natural habitat. To evaluate the existing genetic diversity of P. nigra within ex-situ collections, we analyzed 675 P. nigra L. accessions from nine European gene banks with three amplified fragment length polymorphism (AFLP) and five microsatellite [or simple sequence repeat (SSR)] primer combinations, and 11 isozyme systems. With isozyme analysis, hybrids could be detected, and only 3% were found in the gene bank collection. AFLP and SSR analyses revealed effectively that 26% of the accessions were duplicated and that the level of clonal duplication varied from 0% in the French gene bank collection up to 78% in the Belgian gene bank collection. SSR analysis was preferred because AFLP was technically more demanding and more prone to scoring errors. To assess the genetic diversity, we grouped material from the gene banks according to topography of the location from which the accessions were originally collected (river system or regions separated by mountains). Genetic diversity was expressed in terms of the following parameters: percentage of polymorphic loci, observed and effective number of alleles, and Nei's expected heterozygosity or gene diversity (for AFLP). Genetic diversity varied from region to region and depended, to some extent, on the marker system used. The most unique alleles were identified in the Danube region (Austria), the Rhône region (France), Italy, the Rijn region (The Netherlands), and the Ebro region (Spain). In general, the diversity was largest in the material collected from the regions in Southern Europe. Dendrograms and principal component analysis resulted in a clustering according to topography. Material from the same river systems, but from different countries, clustered together. The genetic differentiation among the regions (F(st)/G(st)) was moderate.
Asunto(s)
Conservación de los Recursos Naturales/métodos , Bases de Datos Genéticas , Ambiente , Variación Genética , Populus/genética , Análisis por Conglomerados , Cartilla de ADN , Europa (Continente) , Genotipo , Geografía , Hibridación Genética , Isoenzimas , Repeticiones de Microsatélite/genética , Repeticiones de Minisatélite/genética , Polimorfismo de Longitud del Fragmento de Restricción , Análisis de Componente PrincipalRESUMEN
Two elm taxa occur naturally in the Iberian Peninsula: the Field elm (Ulmus minor) and the Wych elm (U. glabra). In addition, a third taxon, the foreign Siberian elm (U. pumila), was probably introduced in the 16th century as an ornamental tree and has spread spontaneously throughout the Peninsula. The natural hybridization between U. minor and U. pumila produced new individuals whose morphological traits appear to be mixed. Ulmus pumila, as well as its hybrids, has a high resistance to Dutch elm disease (DED). For this reason, it is commonly used in breeding programmes. Extensive hybridization and the high mortality produced by the last DED epidemic have endangered the conservation of the native elm. In this study, isozyme analyses are used to characterize the taxa U. minor and U. pumila. Siberian elms from Spain and China are compared with the native U. minor. Siberian elm produces isozyme patterns that completely differentiate it from U. minor. Three loci are completely different between the species: 6Pgd2, Mdh1 and Prx2. Isozyme markers can also be used to distinguish native elms from the hybrids that have evolved for generations.
