Entre code-barres génétiques et reconnaisance phylogénétique, clarification de la systématique des espèces responsables de la rouille du peuplier (Melampsora spp)

Authors: Vialle, Agathe
Advisor: Bernier, LouisHamelin, Richard C.
Abstract: Poplar rust species, belonging to the genus Melampsora, are considered the most important poplar disease. In case of introduction and/or propagation of these pathogens, species definition and recognition are critical steps in determining rapid and efficient management options. First, this thesis work reviewed 170 years of taxonomical descriptions for Melampsora species identified on poplar. This analysis of peer-reviewed publications showed uncertainties in the Melampsora species concept and difficulties in species and formae speciales recognition using traditional taxonomical criteria. Despite the development of molecular tools, recognition at the species level and evolutionary relationships among poplar Melampsora taxa remain obscure. Thus, 14 mitochondrial genes were evaluated as potential DNA barcodes, a recent popular molecular taxonomic tool proposed to identify species. Assessed in silico, only 3 out of the 14 genes showed all characteristics for an optimal DNA barcode. Moreover, biological validation indicated that no single mitochondrial gene gave a better taxonomic resolution than ribosomal loci, regions already widely used in fungal molecular taxonomy. A molecular approach, applied to Melampsora species identified on poplars from the botanical section Populus, confirms these previous results. A DNA barcode obtained from the ribosomal internal transcribed spacer (ITS) sequence provided the most accurate results for identifying and resolving taxa among Melampsora populnea, a taxonomical challenging species complex found on white poplars. Moreover, this DNA barcode approach provided evidence for genetic distance between two different species considered as synonymous and highlighted species misidentifications in specimens from Canadian national herbaria. These results confirmed the need for a molecular approach, in complement to previous taxonomical descriptions, to achieve a robust species definition among the poplar rusts. Finally, phylogenetic species boundaries were defined using genealogical concordance of four independent gene regions (ribosomal DNA, mitochondrial DNA, and 2 nuclear coding genes). The phylogenetic relationships revealed a potential co-evolution between Melampsora species and their alternate host (aecial host) and confirmed the importance of this criterion in natural poplar rust species delineation.
Document Type: Thèse de doctorat
Issue Date: 2011
Open Access Date: 18 April 2018
Permalink: http://hdl.handle.net/20.500.11794/22959
Grantor: Université Laval
Collection:Thèses et mémoires

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