Louis Bernier

Affiliation : U.Laval

Spécialité : Pathologie forestière

Courriel : louis.bernier@rsvs.ulaval.ca

Implication :

• Membre du comité scientifique

Projets dont Louis Bernier est Responsable :

• Revue bibliographique des problèmes pathologiques et entomologiques chez les essences à croissance rapide.

• Développement et utilisation de marqueurs phénotypiques et moléculaires pour l’amélioration de la résistance aux maladies chez les peupliers hybrides.

• Développement et utilisation d’outils moléculaires pour l’étude de la phylogénie et des populations chez le Mycosphaerella populorum, agent de la tache des feuilles et du chancre septorien chez les peupliers hybrides.

Projets dont Louis Bernier est Collaborateur :

• Veille pathologique et entomologique annuelle.

Publications :

• Nicolas Feau, Richard C. Hamelin, Louis Bernier. 2007. Variability of Nuclear SSU-rDNA Group Introns Within Septoria Species: Incongruence with Host Sequence Phylogenies. Journal of Molecular Evolution. 64:489-499 doi:10.1007/s00239-005-0309-7. Cet article est réalisé dans le cadre du Volet 3 TP 4

  (Résumé)

  We report structural features and distribution patterns of 26 different group I introns located at three distinct nucleotide positions in nuclear small subunit ribosomal DNA (SSU-rDNA) of 10 Septoria and 4 other anamorphic species related to the teleomorphic genus Mycosphaerella. Secondary structure and sequence characteristics assigned the introns to the common IC1 and IE groups. Intron distribution patterns and phylogenetic relationships strongly suggested that some horizontal transfer events have occurred among the closely related fungal species sampled. To test this hypothesis, we used a comparative approach of intron- and rDNA-based phylogenies through MP- and ML-based topology tests. Our results showed two statistically well-supported major incongruences between the intron and the equivalent internal transcribed spacer (ITS) tree comparisons made. Such absence of a co-evolutive history between group I introns and host sequences is discussed relatively to the intron structures, the mechanisms of intron movement, and the biology of the Mycosphaerella pathogenic fungi. © Springer

• Nicolas Feau, Richard C. Hamelin, Louis Bernier. 2006. Attributes and congruence of three molecular data sets: inferring phylogenies among Septoria-related species from woody perennials. Molecular Phylogenetics and Evolution. 40(3):808-829 doi:10.1016/j.ympev.2006.03.029. Cet article est réalisé dans le cadre du Volet 3 TP 4

  (Résumé)

  To improve our understanding of phylogenetic relationships within the anamorphic genus Septoria, three molecular data sets representing 2417 bp of nuclear and mitochondrial genes were evaluated. Separate gene analyses and combined analyses were performed using first, the maximum parsimony criterion and second, a Bayesian framework. The homogeneity of data partitions was evaluated via a combination of homogeneity partition tests and tree topology incongruence tests before conducting combined analyses. A last incongruence re-evaluation using partitioned Bremer support was performed on the combined tree, which corroborated the previous estimates. After each separate data set attributes were examined, simple explanations were advocated as the causes of the significant incongruences detected. The analysis of multiple gene partitions showed unprecedented phylogenetic resolution within the genus Septoria that supported the results from previously published single gene phylogenies. Specifically, we have delimited distinct but closely related species representing monophyletic groups that frequently correlated with their respective host families. Conversely, the occurrence of well-supported groups including closely related but distinct molecular taxa sampled on unrelated host-plants allowed us to reject, in these particular cases, the co-evolutionary concept expected between a parasite and its host and to discuss alternative evolutionary models recently proposed for these pathogens. Copyright © 2009 Elsevier B.V.

• Nicolas Feau, Volker Jacobi, Richard C. Hamelin, Louis Bernier. 2006. Screening of ESTs from Septoria musiva (teleomorph Mycosphaerella populorum) for detection of SSR and PCR-RFLP markers. Molecular Ecology Notes. 6(2):356-358 doi:10.1111/j.1471-8286.2006.01230.x. Cet article est réalisé dans le cadre du Volet 3 TP 4

  (Résumé)

  The development of an expressed sequence tag (EST) collection for the poplar pathogen Septoria musiva presented an opportunity for the development of locus-specific polymorphic markers. Five microsatellites simple sequence repeat (SSR) and six polymerase chain reaction (PCR)–restriction fragment length polymorphism (RFLP) markers were identified and tested on three S. musiva populations collected in the north-central and northeastern regions of North America. The results obtained support previously published random amplified polymorphic DNA (RAPD) data.

• Nicolas Feau, J. Weiland, Glen R. Stanosz, Louis Bernier. 2005. Specific and sensitive PCR based detection of Septoria musiva, S. populicola and S. populi, the causes of leaf spot and stem canker on poplars. Mycology Research. 109(9):1015-1028 doi:10.1017/S0953756205003242. Cet article est réalisé dans le cadre du Volet 3 TP 7

  (Résumé)

  The development of a PCR assay for the detection of the poplar pathogenic fungi Septoria musiva (teleomorph Mycosphaerella populorum), S. populicola (M. populicola) and S. populi (M. populi) is described. Three pairs of speciesspecific PCR primers were designed using interspecific polymorphisms in the internal transcribed spacer (ITS) of nuclear ribosomal RNA gene (rDNA) repeats. The specificity of the three primer pairs was successfully tested on a collection of 40 S. musiva, 39 S. populicola and six S. populi isolates. Using stringent PCR conditions, no cross-reaction was observed with any of the isolates tested. The specificity of the PCR assay was further confirmed with DNA extracted from 12 additional Septoria species and 17 other fungal species obtained from stems or leaves of poplars. Specific amplification of the fragments for S. musiva and S. populicola was sensitive relatively to the technique used, detecting as low as 1 pg template DNA, and 10 pg of DNA of the target species in a background of 1 ng of DNA of the other species. Moreover, using DNA purified directly from disrupted conidia, it was possible to detect with a probability of 90%, using one unique PCR assay, the DNA equivalent of 166 conidia per ìl of S. musiva and 156 conidia per ìl of S. populicola. The procedures developed in this work can thus be applied for rapid and accurate detection and identification of Septoria species from poplars. Copyright © 2009 Elsevier B.V.

• Nicolas Feau, Richard C. Hamelin, C. Vandecasteele, Glen R. Stanosz, Louis Bernier. 2005. Genetic structure of Mycosphaerella populorum (anamorph Septoria musiva) populations in north central and northeastern North America. Phytopathology. 95:608-616 doi:10.1094/PHYTO-95-0608. Cet article est réalisé dans le cadre du Volet 3 TP 7

  (Résumé)

  In order to characterize the genetic variation of the poplar pathogen Mycosphaerella populorum (anamorph Septoria musiva), we have studied seven North American populations using the polymerase chain reaction random amplified polymorphic DNA (RAPD) technique. The fungal populations were sampled in 2001 and 2002 by obtaining 352 isolates from cankers and leaf spots in hybrid poplar plantations and adjacent eastern cottonwood (Populus deltoides). A total of 21 polymorphic RAPD markers were obtained with the six RAPD primers used. A fine-level scale analysis of the genetic structure within the populations revealed that subpopulations sampled on P. deltoides and on hybrid trees were not significantly differentiated. In contrast, analyses performed on the entire data set showed high levels of haplotypic diversity and moderate to high genetic differentiation, with 20% of the expected genetic diversity found at the interpopulation level. Moreover, a high and significant correlation between genetic and geographic distances among populations was found, suggesting isolation by distance of the sampled populations. Although the occurrence of the sexual stage of this fungus remained unclear in field populations, five of the six populations were at gametic equilibrium for RAPD loci, suggesting the occurrence of recombination episodes in Septoria musiva populations. Overall, S. musiva appears to consist of differentiated subpopulations, with both asexual and sexual recombination contributing to the local level of genetic structure.

• Christian Messier, Brigitte Bigué, Louis Bernier. 2003. Using fast-growing plantations to promote forest ecosystem protection in Canada. Unasylva. 54(214-215):59-63 doi:FAO