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Genetic mechanisms involved in climatic adaptation of experimentally evolving populations of bread wheat

Abstract : Local adaptation resulting from selection pressure acts on heritable characters and is a major force shaping the phenotypic diversity of natural populations. Currently, numerous questions exist surrounding the impact of selection on the evolution of genes involved in the structure of adaptive traits, which are often complex characters involving many interacting genes. The objective of this thesis is to identify certain genetic mechanisms which are activated during the adaptation of experimental wheat populations to different climactic contexts. The adaptive trait studied was flowering time, which permits the plant to synchronize reproduction with favorable seasonal conditions. The experimental populations considered had a common genetic origin and have evolved independently since 1984 in different sites in France, without conscious human selection or migration, but subject to the influence of natural selection and genetic drift. Using a base of knowledge on genes implicated in flowering in Arabidopsis thaliana and rice, and recent publications on wheat, the evolution of nucleotide polymorphisms in candidate genes was followed during 12 generations (2, 7 and 12) in three experimental populations (Vervins in the north of France, Le Moulon in the Parisian region and Tolouse in the South). These populations were also characterized for precocity of flowering time measured under different day length and vernalization regimes (duration of exposure to low temperatures) and for diversity of microsatellite loci sampled from throughout the genome. The comparison of levels of genetic differentiation among populations for these three measures of genetic diversity showed that precocity was subject to divergent selection from the first generations. However, it appears that this selection was not directly for flowering time, but instead achieved through indirect selection on correlated traits in the different environments, such as plant height or grain weight. Selection for precocity can be related to climactic characteristics of the experimental locations, with the northern populations flowering later than the southern population. This rapid evolution of the trait accompanied significant changes in allele frequencies for major genes involved in flowering time, and the development of specific multi-locus allelic combinations in the different climatic contexts considered. This evolution did not diminish the existing within-population genetic diversity because multiple combinations were favored in the different populations. The work presented in this thesis is an important contribution to our understanding of the maintenance of evolutionary potential in cultivated species.
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Submitted on : Monday, December 1, 2008 - 8:00:00 AM
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Bénédicte Rhoné. Genetic mechanisms involved in climatic adaptation of experimentally evolving populations of bread wheat. Sciences of the Universe [physics]. AgroParisTech, 2008. English. ⟨NNT : 2008AGPT0018⟩. ⟨pastel-00003822⟩

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