Genetic control of root morphological plasticity in response to nitrogen across rapeseed diversity

Abstract

Abstract Rapeseed (Brassica napus L.) is an oleaginous crop of great economic value but with considerable nitrogen requirement. Breeding for root systems efficiently taking up nitrogen from soil could be a lever to ensure genetic gains for producing rapeseed more sustainably. This study aims at identifying genomic regions regulating root morphology in response to nitrate availability. The natural variability offered by a set of 300 inbred lines was screened. Seedlings grew hydroponically with low or elevated nitrate levels. On average for the diversity panel, low nitrate level increased the root-to-shoot biomass ratio and stimulated the lateral root outgrowth. A large phenotypic variation was observed, along with important heritability values and genotypic effects, but poor genotype-by-nitrogen interactions. Genome-wide association study and bulk segregant analysis were employed to identify loci regulating traits of biomass production and root morphology. The first approach identified 1,305 SNPs, associated with 15 phenotypic traits. These SNPs clustered into 26 QTLs, with seven of them distributed on chromosome A07. Some 14 QTLs were stable across nitrate levels. The second approach was selecting segregant individuals from the tails of the phenotypic distribution of an experimental F2 population, deriving from two accessions with a contrasting lateral root development. Six genomic regions showed allele frequency differences between the two bulks above 0.15, including one significant QTL detected on A06. Some genes involved in root organogenesis coincided with QTL regions. This study provides selection targets for potentially redesigning root morphology in rapeseed.