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Étude des ressources génétiques du noyer en vue de la mise en œuvre d'une sélection assistée par marqueurs

Abstract : The present work carried out on walnut consisted in exploiting the rich genetic resources available at the INRAE of Nouvelle-Aquitaine-Bordeaux, in order to provide the tools that can be used in a new breeding program conducted by the CTIFL, centre opérationnel de Lanxade. In fact, in view of the walnut's significant economic development, the choice of varieties in France does not seem to be sufficient to meet future new constraints such as global competition and climate change. The prospecting work carried out mainly by Éric Germain's team has made it possible to gather most of the species of the genus Juglans and numerous accessions of cultivated walnut, Juglans regia L, at the UEA of Toulenne. The use of his archives accumulated over 30 years permitted to make public important chronological phenotyping data concerning this collection. These data showed the advance of the phenology of the two control varieties 'Lara' and 'Franquette' in relation to climate change. Using a set of 13 SSR markers, alleles specific to Juglans species were identified and the structure of the collection was studied. This structure shows two main subgroups, one comprising accessions from Eastern Europe and Asia and the other from Western Europe and the USA. Also, a core collection was defined to carry out GWAS studies on the main traits of agronomic interest, from flower to fruit, using a 600,000 SNP chip developed by the University of Davis in California. Associations between SNPs and several phenology-related traits were identified using archives and newly acquired data. A SNP strongly related to the budbreak date of leaves and female flowers was identified on chromosome 1 and co-localized with a QTL detected in parallel on a F1 progeny. A KASP marker was validated with plant material from the University of Davis. Other associations were also identified for dichogamy and bearing habit, a trait directly affecting yield, and led to the definition of candidate genes. Further GWAS analyses were conducted on fruit-related traits such as nut size, weight, breaking yield and force required to break the shell. In parallel, methods using robust phenotyping techniques have been developed, such as the use of X-ray microtomography to measure all morphological traits without breaking the nut. Finally, work was carried out to compare the efficiency of the two types of markers used in this work, SSR and SNP. The results show that the 13 SSR markers give similar results to several thousands of SNPs with regard to structure determination and construction of core collections, which are essential in the management of genetic resources. In the long term, the results of this work will make it possible to initiate marker-assisted selection for the creation of new varieties, within the framework of a new improvement program to be carried out by the CTIFL. These new varieties will be able to meet the criteria sought in the coming years, taking into account climate change.
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Submitted on : Friday, January 22, 2021 - 2:28:28 PM
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Anthony Bernard. Étude des ressources génétiques du noyer en vue de la mise en œuvre d'une sélection assistée par marqueurs. Biologie végétale. Université de Bordeaux, 2020. Français. ⟨NNT : 2020BORD0128⟩. ⟨tel-03118714⟩

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