FUSARIUM HEAD BLIGHT DISEASE DEVELOPMENT AND MYCOTOXIN ACCUMULATION IN WHEAT
Open Access
- Author:
- Willyerd, Katelyn Tilley
- Graduate Program:
- Plant Pathology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 15, 2009
- Committee Members:
- Gretchen Anna Kuldau, Dissertation Advisor/Co-Advisor
Gretchen Anna Kuldau, Committee Chair/Co-Chair
Douglas D Archibald, Committee Member
Erick D De Wolf, Committee Member
Maria Del Mar Jimenez Gasco, Committee Member
Gary William Moorman, Committee Member
Henry K Ngugi, Committee Member - Keywords:
- electron capture detection
masked mycotoxin
gas chromatography
deoxynivalenol-3-glucoside
ergosterol
vomitoxin
DON
deoxynivalenol
Fusarium damaged kernels
disease severity
infection-timing
Fusarium graminearum
plant pathology
epidemiology
mycotoxicology - Abstract:
- Fusarium graminearum, causal agent of Fusarium Head Blight (FHB) of wheat, causes yield losses and contaminates grain with mycotoxins, most commonly deoxynivalenol (DON). FHB is one of the most destructive and economically important plant diseases and is found in all wheat-growing regions of the world. DON is the most widely encountered mycotoxin by humans in the world. This toxin binds to eukaryotic ribosomes and inhibits protein synthesis in wheat, humans and animals. During acute exposure DON can cause cell death, vomiting and suppress the immune system. Annual FHB epidemics and DON levels are extremely influenced by the environment. The effects of environment on the relationships between fungal growth, disease development and DON accumulation are not fully understood. Without this basic knowledge, FHB and DON prevention, control and mitigation will continue to be a problem for all involved in the wheat industry and consumers. The purpose of this dissertation was to characterize FHB disease development and mycotoxin accumulation during the grain development stages in wheat. A two-year field experiment was designed to study the effects of infection-timing and cultivar on disease severity, kernel damage and accumulation of DON. Three winter wheat cultivars, with different degrees of susceptibility to FHB, were planted in a split-plot design. Misting treatments were designed to facilitate infections during anthesis and/or late-milk stages. All plots were inoculated with F. graminearum macroconidia prior to each misting treatment to ensure the presence of the pathogen. Disease severity of each subplot was assessed during the dough stages, while Fusarium-damaged kernels (FDK) and DON accumulation were measured post-harvest. Misting treatment, cultivar and their interactions were significant factors for severity, FDK and DON. This study confirmed that infections during both anthesis and grain-fill contributed to symptoms and DON levels. Infections during grain-fill alone contributed to DON accumulation (> 2ppm) and had little effect on symptoms. Response to infection-timing was found to be cultivar-specific. Infection-timing and host genotype interactions play significant roles in disease development and mycotoxin contamination of wheat. Future work should incorporate a wider range of wheat cultivars so as to gain more information on the effect of infection-timing. The second objective of this work was to develop a method to simultaneously detect DON and fungal biomass in wheat heads, as the relationship between toxin production and fungal growth is not fully understood. By analyzing single wheat florets from infected wheat heads, infection and toxin accumulation patterns could be studied. Deoxynivalenol was extracted from FHB-affected single florets with acetonitrile-water. Ergosterol, a fungal-specific sterol found in the cell membrane, was used as a biomarker for fungal biomass. Ergosterol was removed from the same wheat florets through saponification and extraction with hexane. Toxin and ergosterol extracts were combined and analyzed via gas chromatography with electron capture detection (GC-ECD). This method was also designed to detect deoxynivalenol-3-glucoside (DON-gluc), a conjugated mycotoxin, which forms in planta. Retention times were confirmed with analytical standards and standard curves were created to estimate concentrations of these in floret samples. The limits of quantification were 0.005, 0.050 and 0.100ng/µl for DON, ergosterol and DON-gluc, respectively. The extraction protocols and GC-ECD method are tools with the potential to study trichothecene accumulation and fungal colonization of many important agricultural commodities.