Expanding sugar beet's utility: genetic insights into leaf protein valorisation
Year: 2025
Type: dissertation
Abstract: Modern plant breeding has largely focused on improving crops for specific harvest organs such as fruits, seeds, or roots, while overlooking the substantial residual biomass generated during cultivation. These residues, often used for low-value purposes, contain valuable biochemicals (proteins, fibers, lipids, and bioactive compounds) that are suitable for applications in food, feed, pharmaceuticals, and bio-based materials. Adopting a whole-plant utilization approach could make agriculture more circular and resource-efficient.Sugar beet exemplifies this opportunity. Grown primarily for sugar extracted from its taproot, about one-third of its biomass consists of leaves, which are a promising source of plant-based protein. The main protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), possesses excellent functional properties for food applications, such as foaming and gelling, making it a potential alternative to egg white proteins. However, extraction yields remain too low for economic viability. Selective breeding could improve leaf protein production, but little is known about the genetic variation underlying protein yield and extractability.This thesis aimed to characterize this variation and identify genomic regions associated with protein extractability in sugar beet. High-throughput phenotyping methods were developed and applied to two panels of about 200 sugar beet hybrids evaluated in multiple field trials in the Netherlands and France (2022–2023).Chapter 2 describes the development of tools to quantify total and extractable protein, enabling the estimation of protein extractability. Studies of sampling methods showed that middle leaves from at least 25 plants per plot provided reliable estimates. A near-infrared spectroscopy (NIR) model accurately predicted total leaf protein across environments, while total nitrogen analysis correlated well with RuBisCO quantification, validating its use as a proxy for protein content.Chapter 3 explores genetic variation in leaf protein yield using a GWAS on 180 hybrids across three field trials. Traits measured included total and extractable protein, RuBisCO, dry matter content, and leaf yield. Moderate heritability was found for total protein and dry matter content, while extractable traits were less heritable. GWAS identified 45 significant marker–trait associations, with candidate genes linked to RuBisCO assembly, chloroplast development, and protein import. These results suggest that breeding for higher total protein content is more feasible than improving extractability.Chapter 4 expands the analysis to evaluate dual-purpose sugar beet varieties combining high sugar and leaf protein yields. A panel of 200 hybrids was tested for both root and leaf traits. Weak correlations between sugar and protein yields indicated no major trade-off. GWAS identified 48 QTL related to protein content, extractability, and leaf yield, some explaining over 10% of phenotypic variance. Candidate genes were associated with photosynthesis, amino acid transport, and cell wall metabolism.The general discussion integrates these findings, highlighting consistent QTL across studies and confirming the polygenic nature of protein-related traits. While improving extractability remains complex, breeding for higher total protein is a viable route to enhance leaf valorisation. Combined with process and logistic innovations, these advances position sugar beet as a potential dual-purpose crop contributing to a more sustainable and circular agricultural system.
DOI: 10.18174/681602
Author: Hugo Rijken
Institution: Wageningen University & Research
Language: English
Topic: Genetics and Plant Breeding
Subfield: Plant Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W4415613437