Leaf protein extractability in sugar beet: Genetic control and breeding potential for dual-purpose cultivars

Sugar beet ( Beta vulgaris ssp. vulgaris ) is primarily cultivated for sugar, but its abundant leafy biomass also represents a promising source of plant protein. Achieving high protein extraction yields without compromising sugar yield is a key to economic viability. This study evaluated the genetic potential of sugar beet for leaf protein production and identified genomic regions associated with traits relevant to leaf protein extractability. Across four field trials, 200 sugar beet hybrids were evaluated for traits related to leaf protein extraction (leaf protein content, extractable protein content, extractable RuBisCO, protein extractability, and leaf yield), alongside root yield and sugar content. Correlations between leaf and sugar traits were assessed, and a genome-wide association study (GWAS) was conducted to identify associated genetic markers. Sugar yield showed only a week correlation with leaf protein yield, suggesting that leaf protein can be enhanced without a significant trade-off in sugar yield. The GWAS identified 48 quantitative trait loci (QTL) regions associated with leaf protein content and related traits, with several markers explaining over 10 % of the phenotypic variance, suggesting promising selection targets. Candidate genes were linked to photosynthesis, amino acid transport, and cell wall metabolism, providing insights into the genetic control of leaf protein content and extractability in sugar beet. These findings highlight the potential to breed sugar beet cultivars that combine high sugar yield with improved leaf protein extractability. The identified genetic markers provide useful tools to accelerate the development of dual-purpose cultivars, supporting the sustainable valorization of sugar beet biomass.