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

Background 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 SNP markers in 228 spring-type B. napus accessions to uncover loci associated with root vigour response to polyethylene glycol (PEG-6000)-mediated osmopriming. Results PEG-6000 osmopriming significantly enhanced root vigour traits, increasing average radicle emergence (RE) from 72.7–84.4%, 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 hours of sowing. Priming reduced trait variability and increased heritability (e.g., VI: 0.86 to 0.97), indicating enhanced genetic control. We also observed substantial phenotypic variation in relative response (e.g., 123.8% CV for RR-VI), which highlights the diversity of osmopriming responsiveness within the population. Our GWAS analysis identified 13 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, root development, cell wall remodelling, redox balance, and water transport. Notably, haplotypes RE-Hap6 on chromosome A03 and VI-Hap1 on chromosome C02 increased RR-RE and RR-VI by 44.7% and 164.9%, respectively. Conclusion Our study provides the first genomic dissection of osmopriming response in B. napus , revealing key loci and candidate genes underpinning priming-enhanced root vigour. These findings offer novel targets for marker-assisted breeding of stress-resilient rapeseed cultivars under climate-challenged environments.