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Genetic bases of root morphology in response to nitrate supply in rapeseed

par Haelterman, Loïc
Président du jury Hardy, Olivier J.
Promoteur Hermans, Christian
Publication Non publié, 2024-09-30

Thèse de doctorat

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Résumé :

For decades, nitrogen inorganic fertilization has been used to increase crop yields. However, excessive nitrate levels are harmful to the environment. Rapeseed (Brassica napus L.) is an oil-containing crop of great economic value with considerable nitrogen requirement. One promising approach to reduce nitrogen fertilizer use is breeding crops for root attributes. This doctoral dissertation brings insights into the genetic bases of rapeseed root morphology in response to nitrate supply. The phenotypic variability offered by a large diversity panel and by existing or newly created experimental populations was screened. Seedlings grew hydroponically with low or elevated nitrate levels. Fifteen traits related to biomass production and root morphology were measured. Overall, the low nitrate level increased the root-to-shoot biomass ratio and promoted the primary and lateral root growth. A large phenotypic variation was observed, suggesting a polygenic nature for the measured traits. Moderate to elevated heritability values were observed, with a predominant genotypic effect over genotype-by-nitrate interaction. Three different mapping approaches (genome-wide association, bulk segregant analysis and linkage analysis) uncovered 80, 1 and 26 quantitative trait loci, respectively. Some loci were consistently identified under both nitrate levels. The concomitant detection of loci across different nitrate supplies or different analyses nominated candidate genes putatively regulating root morphology. The structural organisation of gene copies was investigated, revealing duplicated candidates. Finally, a root global transcriptomic analysis, carried on rapeseed genotypes with contrasting root morphologies, revealed genes differentially expressed in response to nitrate. In conclusion, this work delivers genetic resources that hold promise for genomic improvement approaches aimed at optimizing root morphology.