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Déterminisme génétique et écophysiologique de la variabilité des masses de grains individuels chez le blé tendre (Triticum aestivum).

Abstract : Wheat breeding faces the dual challenge of climate change and changes in agricultural practices. In this context, new breeding strategies based on the search for yield stability in future genetic material are being developed. Wheat grain yield is usually decomposed into yield components: number of spikes/m², number of grains/spike, number of grains/m² and thousand kernel weight (TKW). These components are correlated one with another due to compensations that exist between the different scales of the canopy (m2, plant, spike, grain). Until now, the yield gains achieved by wheat breeders in recent decades mainly occured through increases in grain number per m². However, with increasing occurrences of post-flowering abiotic stress associated with climate change, TKW may become severely limiting and hence a target for breeding. TKW is usually studied at the plot scale as it represents the average mass of a grain. However, this view disregards the large intra-genotypic variance of individual grain mass that exists between- and within spikes. The identification of such intra-genotypic variability and its implication in TKW setting as well as in the response of TKW to post-flowering abiotic stresses remains unexplored. This work therefore aims to evaluate the interest of taking into account explicitly intra-genotypic variability in improving yield through breeding for TKW under post-flowering abiotic stress.The results show that there is a genetic variability of the correlation between the individual grain mass and TKW, i.e. genotypes may have similar TKW from distributions of individual grain masses with different intra-genotypic variability. This intra-genotypic variability is mainly driven by canopy structure (number of grains per m²) but has also a specific genetic determinism. Moreover, considering the single grain scale allowed to refine our understanding of the physiological basis of the genetic variability of TKW by highlighting constitutive genotypic differences in individual grain masses; these differences are independent from the number of grains per m², and vary according to the position of the grain within the spike. This single grain scale also reveals differential responses of individual grains to post-flowering heat stress depending on their position within the spike. These results demonstrate the relevance of considering not only the mean value of the target trait (TKW) but also its variance and offer new perspectives for the search for future genetic material tolerant to post-flowering abiotic stress. To do this, genotypic strategies of grain number establishment and/or the specific genetic variability of the intra-genotypic variance could be targeted. More generally, this thesis is part of a conceptual framework developed in ecology with the aim to understand the role of intra-genotypic variability of traits on the stability of plant canopy performance.
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Aurore Beral. Déterminisme génétique et écophysiologique de la variabilité des masses de grains individuels chez le blé tendre (Triticum aestivum).. Biologie végétale. Université Clermont Auvergne, 2020. Français. ⟨NNT : 2020CLFAC039⟩. ⟨tel-03156382⟩

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