Genome-Wide Association Study Identifies QTL and Candidate Genes Governing Seed Mucilage Content and Hull Content in Flax (<em>Linum usitatissimum</em> L.)

New flaxseed cultivars differing in seed mucilage content (MC) with low hull content (HC) represent an attractive option to simultaneously target the food and feed markets. Here, a genome-wide association study (GWAS) was conducted for MC and HC in 200 diverse flaxseed accessions genotyped with 1.7 million SNP markers. The data obtained for MC and HC indicated a broad phenotypic variation and high (~70%) and a moderate (~49%) narrow sense heritability, respectively. MC and HC did not differ statistically between fiber and oil morphotypes, but yellow-seeded accessions had 2.7% less HC than brown-seeded ones. The genome wide linkage disequilibrium (LD) decayed to r2 = 0.1 at a physical distance of ~100 Kb. Seven and four QTL were identified for MC and HC, respectively. Promising candidate genes included Linum usitatissimum orthologs of the Arabidopsis thaliana genes TRANSPARENT TESTA 8, SUBTILISIN-LIKE SERINE PROTEASE, GALACTUROSYL TRANSFERASE-LIKE 5, MUCILAGE-MODIFIED 4, AGAMOUS-LIKE MADS-BOX PROTEIN AGL62, GLYCOSYL HYDROLASE FAMILY 17 and UDP-GLUCOSE FLAVONOL 3-O-GLUCOSYLTRANSFERASE that have been shown to play a role in mucilage synthesis and release, seed coat development and anthocyanin biosynthesis in A. thaliana were identified. The favorable alleles will be useful in flaxseed breeding towards the goal of achieving the ideal flaxseed cultivars for food and feed by genomic-based breeding.