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Architecture génétique des traits de croissance et de ramification du chêne

Abstract : Epicormics may seriously impair the wood quality of oaks which are the most important hardwoods in French forestry. Successive projects have been carried out to understand the ontogenic and silviculture effects on sequential and epicormic branching. Effects of environment and genetics have been reported in the literature, but the knowledge about the genetic architecture of branching on oak and on epicormics in general is still limited. This last project quantifies this genetic architecture on growth, branching and especially epicormics traits. It takes advantage of observations from computed tomography (CT) or externally recorded, the genetic map of oak being built and a full-sib progeny installed in two experimental designs. The aim was to analyze and localize the Quantitative Trait Locus (QTLs) of the growth and branching traits on the genetic map of pedunculate oak, in order to contribute to characterize the genetic architecture of the sequential and epicormic branching on oak. A full-sibs offspring from an interspecific crossing of Quercus robur was planted at two sites in north-eastern France (CH) and south-western France (BR) with quite different environments and silvicultural intervention. In a first study, 1m-long logs from BR were scanned by CT; wood quality and branching traits were deduced on which a QTL analysis was performed. In a second study, QTL analysis was performed with traits deduced from external observation made on standing trees at the two sites. The QTL stability in two sites was evaluated. Finally, we questioned the impact of the tree growth on the branching through the QTLs detected. The QTL analysis revealed a moderate genetic control for latent bud production mainly. The interaction between the QTLs and the sites was highlighted especially concerning the development of epicormic branches. An independent genetic control was assumed for the sequential branches. Several “hot-spots” were identified on the genetic map of oak for the epicormic and growth traits. We suggest that some genetic controls of these regions are related to the axillary meristem initiation and that some genetic controls of the epicormic branching are probably involved also in the control of the tree growth. These results showed that the genetic control of epicormic branching is moderate and that the environment effect is likely involved more in the fate of these latent buds in interaction with the genetic effect. Since the oak genome was recently sequenced, a bioinformatics analysis is being performed on these regions for testing whether the candidate genes involved in plant hormones could explain the genetic mechanisms underlying these genomic regions related to the epicormic branching traits of the oak.
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Jialin Song. Architecture génétique des traits de croissance et de ramification du chêne. Biologie végétale. AgroParisTech, 2017. Français. ⟨NNT : 2017AGPT0010⟩. ⟨tel-02900570⟩

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