Ergosterol-based method for mapping soybean resistance to phomopsis seed decay

Overview

Phomopsis seed decay (PSD), caused by the fungal pathogen Phomopsis longicolla, is a major soybean disease that reduces seed quality and yield, particularly when harvest is delayed by adverse weather. Traditional visual assessments of infected seeds are imprecise and often fail to distinguish subtle differences in resistance among breeding lines. This research proposes a quantitative method that combines delayed harvest practices with seed ergosterol measurements to more accurately identify and map genetic loci associated with PSD resistance. Ergosterol, a sterol found in fungal cell membranes, serves as a biomarker for fungal biomass. By measuring ergosterol content in soybean seeds, breeders can achieve finer separation of resistance levels within breeding populations, enabling the discovery of minor-effect QTLs and the development of molecular markers for marker-assisted selection.

Technical specifications

• Ergosterol extraction and quantification: Ergosterol is extracted from soybean seeds and measured using high-performance liquid chromatography (HPLC), providing a reproducible and quantitative estimate of fungal biomass in infected seeds.
• Delayed harvest protocol: Soybean lines are planted late and harvested at maturity and again 15 days after maturity, with overhead irrigation applied to increase disease pressure and simulate adverse harvest conditions.
• Dual assessment strategy: Seeds are evaluated using both traditional visual disease ratings and ergosterol content analysis, allowing direct comparison of the two methods' ability to differentiate resistance levels.
• Mapping population development: Breeding lines with confirmed resistance will be used to develop mapping populations for QTL identification and molecular marker development.
• Prior validation: The ergosterol extraction and measurement technique has been previously validated for differentiating P. longicolla mutants with varying pathogenicity, demonstrating reliability and reproducibility.

Technology readiness level

This research is at an early-to-mid stage of development. The ergosterol measurement methodology has been validated in a prior published study for distinguishing pathogen strains by pathogenicity level. The current proposal extends this approach to soybean breeding populations under field conditions with delayed harvest and increased disease pressure. Future validation will involve field trials, HPLC-based ergosterol quantification, visual rating comparisons, and the development of mapping populations for marker discovery. The work is positioned to generate new molecular markers and breeding tools for PSD resistance in soybean.