Genetic determinants of leaf protein content and extractability in sugar beet: Opportunities for leaf biomass valorisation

Sugar beet (Beta vulgaris L.) leaves represent an underutilized agricultural byproduct with potential for valorisation through leaf protein extraction. However, current extraction yields are too low to render this protein source economically viable. To date, variation in leaf protein yield among sugar beet germplasm remains largely unexplored. To assess this variation and unravel the genetic architecture underlying relevant traits, we conducted a genome-wide association study (GWAS). A panel of 180 sugar beet accessions was evaluated across three field trials in the Netherlands. Phenotyping included total and extractable leaf protein content, extractable RuBisCO, protein extractability, dry matter content, and leaf yield. Moderate heritability was observed for total protein content and dry matter content, while the extractable protein fractions, protein extractability and leaf yield exhibited low heritability. The GWAS identified 45 significant marker–trait associations and underlying quantitative trait loci (QTLs) related to key traits influencing leaf protein extraction. Candidate gene analysis revealed several genes with putative roles in RuBisCO assembly, chloroplast development, and chloroplast protein import. Our findings indicate that breeding for higher total leaf protein content is feasible, while gains through enhanced extractability may be limited. This study lays the foundation for the genetic improvement of sugar beet leaf protein traits. However, further functional validation of the identified QTLs and candidate genes is essential to confirm their practical utility. • Sugar beet leaves offer potential for protein extraction but are not yet economically viable. • GWAS reveals genetic variation in sugar beet leaf protein traits. • Leaf dry matter and protein show moderate heritability; environment affects yield and extractability. • 45 marker-trait associations found for sugar beet protein extraction traits. • Candidate genes linked to RuBisCO assembly, chloroplast development, and protein import. • Provides genetic basis to boost protein yield in beet leaves and guide future gene validation.