Genome-wide association mapping reveals genetic loci underlying phenotypic variation in early root vigour improvement induced by osmopriming in Brassica napus L

Seed osmopriming is an effective pre-sowing treatment that enhances early seedling vigour and promotes robust root development in Brassica napus L., thereby contributing to improved establishment during the early growth stages. However, the genetic basis of variation in osmopriming responsiveness remains poorly understood. This study employed genome-wide association studies (GWAS) using 15,311 single-nucleotide polymorphisms (SNPs) in 228 spring-type B. napus accessions to uncover loci associated with root vigour response to polyethylene glycol (PEG-6000)-mediated osmopriming. PEG-6000 osmopriming significantly enhanced root vigour traits, increasing average radicle emergence (RE) from 72.7% to 84.4%, root length (RL) by 64.6% (18.2 mm to 29.9 mm), root growth rate (RGR) by 97.8% (1.37 mm/h to 2.71 mm/h), and vigour index (VI) by 88.6% (1355 to 2556) after 72 h of sowing. We also observed substantial phenotypic variation in relative response (e.g., 99.69% CV for RR-VI), which highlights the diversity of osmopriming responsiveness within the population. Our GWAS analysis identified 11 significant SNPs across seven chromosomes (A03, A04, A07, C01, C02, C03, C08), associated with relative responses in four root vigour traits (RR-RE, RR-RL, RR-RGR, and RR-VI). Candidate genes within these loci include regulators of osmotic stress adaptation, water transport, root development, redox balance, and cell wall remodelling. Notably, haplotypes RR-RE-Hap6 on chromosome A03 and RR-VI-Hap1 on chromosome C02 were identified as favourable haplotypes for RR-RE and RR-VI, respectively. Our study provides the first genomic dissection of osmopriming response in B. napus, identifying key loci and candidate genes associated with priming-enhanced root vigour. These findings highlight novel targets that could be leveraged in marker-assisted breeding to develop rapeseed cultivars with improved early root growth, which is crucial for robust seedling establishment.