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Master thesis

Evolution de la taille des spores au cours de la dispersion de Melampsora larici-populina, agent de la rouille du peuplier

Abstract : A classical trade-off in the evolution of dispersal is the relative ability to colonize empty sites versus the ability to compete with relatives in a satured site. In this study, the poplar rust fungi Melampsora larici-populina has served as model to test this paradigm focusing on the evolution of fungal spores during dispersal. An ecological corridor, the Durance River valley, permits us to monitor each year a rust epidemic that spreads downstream. Ninety isolates were randomly sampled in 2008 and 2009 among three populations each year: an "initial" population sampled upstream the valley at the beginning of the epidemic, a "resident" population sampled at the same place at the end of the epidemic and a "migrant" population collected at the end of the epidemic downstream the valley. We first characterize the neutral genetic differentiation between populations, using 25 microsatellites markers, before characterizing the phenotypic differentiation based on two spore traits involved in the dispersal capacity of the fungus: "spore volume" and "length over width ratio". Our goal was to decipher the nature of evolutionary forces acting during the epidemic. Genetic analyses showed that "migrants" populations differentiated through drift (strong genetic differentiation with the other populations and independent evolution of allele frequencies between years). Concerning phenotypic evolution, we observed a consistent pattern of "spore volume" evolution across populations between years. Evolution pattern for the "length over ratio" trait was less obvious. Comparisons of neutral genetic and phenotypic differentiations proved that selection occurred on "spore volume" during dispersal of the fungus along the Durance River valley. Here, we thus provide some pieces of evidence that natural selection is acting in the time curse of a single epidemic. Studying other traits involved in the aggressiveness of the fungi, (e.g. latent period, infection efficiency, sporulation capacity) could provide us with additional insights into the selection processes acting during dispersal of this plant-pathogenic fungi.
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Master thesis
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Submitted on : Wednesday, May 9, 2018 - 10:50:59 AM
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Michaël Pernaci. Evolution de la taille des spores au cours de la dispersion de Melampsora larici-populina, agent de la rouille du peuplier. Sciences de l'environnement. 2011. ⟨hal-01788549⟩



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