Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2006
Publication Date: 10/15/2006
Citation: Xue, H., Upchurch, R.G., Kwanyuen, P. 2006. Ergosterol as a quantifiable biomass marker for diaporthe phaseolorum and cercospora kikuchii. Plant Disease, Vol. 90:1395-1398. Interpretive Summary: We developed and assay to measure the extent of seed colonization by two fungal pathogens that cause substantial economic loss to soybean growers. The assay detects and quantifies the fungi-specific lipid molecule called ergosterol. Both seed pathogens, Diaporthe phaseolorum (Dp) and Cercospora kikuchii (Ck) produce this molecule. Ergosterol was shown to be a biomass marker for both fungi since it was found to be highly linearly correlated with fungal dry mass. We determined that ergosterol content was positively correlated to the amount of pathogen colonizing the infected seed. Using the ergosterol assay, we found that soybean varieties differ with respect to the extent of seed colonization by these fungi. Our results show that ergosterol content can be used to quantify Dp and Ck colonization of soybean seed and that the method has the potential to detect variety differences in seed susceptibility to these two pathogens.
Technical Abstract: The relationship between ergosterol content and biomass was determined for the soybean fungal pathogens Diaporthe phaseolorum (Cooke & Ellis) Sacc. var. sojae [Dp] causative agent of Phomopsis Seed Decay and Cercospora kikuchii (Matsumoto & Tomoyasu) [Ck] causative agent of leaf blight and purple seed stain. Biomass was manipulated by varying incubation period and ergosterol was quantified by high-pressure liquid chromatography. Fungal dry mass was linearly correlated with ergosterol content (r2= 0.90, p<0.05 for Dp and r2= 0.95, p<0.01 for Ck). Ergosterol content in free-living fungi was 3.16 ug/mg for Dp and 2.85 ug/mg for Ck. Ergosterol content of inoculated seed was qualitatively correlated with observed seed colonization by Dp and Ck. Soybean variety had a significant effect on fungal colonization and ergosterol content by Dp. Our results show that ergosterol content can be used to quantify Dp and Ck colonization of soybean seed and that the method has the potential to detect variety differences in seed susceptibility to these two pathogens.