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Rôle de la migration dans la gestion dynamique des ressources génétiques végétales

Abstract : Dynamic management (DM) of genetic ressources is a strategy for the conservation of genetic diversity in which heterogenous populations evolve in contrasted environements under natural selection pressure and other evolutionary forces. The aim of the DM is to let individual populations become locally adapted while maintaining the initial diversity over the whole system. In order to study this approach, DM experimental wheat populations were developed by INRA starting in 1984. These populations beacame differentiated for flowering time and disease resistance, thereby showing indices of local adaptation. Selection and drift led to a decrease of within-population genetic diversity, which could lead to a decrease of fitness or evolutionary potential in the mid to long term. Genetic rescue by migration can limit this phenomenon by increasing within-population genetic variability. However, outbreeding depression can counteract the positive effects of genetic rescue. The aim of this thesis is to answer to the question: "What is the best strategy to manage migration in a DM system in order to maintain evolutionary potential without compromising local adaptation within each population?" We have analysed within and between-population cross progeny over two generations. The second generation was evaluated in the three sites of origin of the parental populations of the crosses (reciprocal transplants). In the transplant experiment, we have shown that local adaptation occured in the populations for plant height ans thousand-kernel weight. Using an analysis of covariance of this trait with flowering time, we showed that late genotypes were selected against in the South because of their low thousand-kernel weight. We then showed that VRN1 gene was involved in flowerinf time in the DM populations and that its structuration and the evolution of its diversity could be linked to selective pressures related to climatic adaptation. Analysis of the 1st and 2nd progeny generations allowed us to show that there was inbreeding depression within populations but only small genetic loads (small betweenpopulation components of heterosis). We did not find outbreeding depression for any type of cross. This last result could be explained by two hypotheses: (i) there were no co-adapted genes complexes broken by outcrossing and local adaptation had only weak effects on the cross progeny values or (ii) the positive effects of heterosis and the negative effects of outbreeding depression compensated for each other which lead to weak betweenpopulations component of heterosis.
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Yves Rousselle. Rôle de la migration dans la gestion dynamique des ressources génétiques végétales. Génétique. Université Paris Sud 11, 2010. Français. ⟨tel-02969719⟩

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