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Bound Deoxynivalenol in Fusarium Head Blight Infected Barley


The objectives of the project are (1<P>) to determine the prevalence of deoxynivalenol (DON) and bound DON in barley that has been naturally infected with Fusarium Head Blight (FHB), and (2) to evaluate how timing of infection impacts the levels of total and bound DON, and (3) to establish how differences in plant resistance to FHB and DON accumulation impact the levels of total and bound DON. Bound DON includes the recently identified DON-3-glucoside, as well as non characterized forms that are released following acid solvolysis. The first objective will be accomplished on commercial barley crop samples collected during the harvest in years one and two. Greenhouse inoculations for objective 2 will be conducted in the winter of year two, and field inoculations for objective 3 will be conducted during the summers of years one and two.<P> Results of these studies will disseminated through publication in appropriate scientific journals, and presentation at the National Scab Forum of the US Wheat and Barley Scab Initiative.

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Non-Technical Summary: Fusarium Head Blight (FHB) is a fungal disease that frequently occurs on wheat and barley in the upper Midwestern USA. While it affects both grain yield and quality, the major concern with the utilization of FHB infected grain for food and feed is the presence of the fungal toxin, deoxynivalenol (DON). DON survives processing, can contaminate food, and is poisonous to animals and humans. While vigilant monitoring conducted by the grain trade has seemingly assured food and feed safety, current methods of DON analysis have been called into question by recent reports of bound DON that escapes detection during normal testing. The presence of bound DON or other mycotoxins has a number of interesting implications. While bound toxins may not be detected in raw materials by routine analytical methodology, they may be released under food processing conditions or during digestion. The objectives of this project are to determine the prevalence of bound DON in barley that has been infected with FHB, and to study how interactions between the plant and fungus influence levels of bound DON. Both objectives are needed to determine whether the presence of bound DON in grain presents a significant risk to the consumer. <P> Approach: Free deoxynivalenol (DON) is that measured by gas chromatography mass spectrometry, following extraction with acetonitrile/water and derivatization. General bound DON will be determined following solvolysis of the extract with trifluoroacetic acid prior to analysis. The DON 3 glucoside will be extracted with methanol/methylene chloride and analyzed by HPLC. Barley samples collected as part of regional crop quality surveys will be utilized to determine the prevalence of bound DON relative to free DON. In order to determine how the timing of infection impacts the levels of total and bound DON, the barley cultivars Drummond and Chevron will be inoculated with Fusarium in the greenhouse at three different growth stages. These stages include emergence from the boot, soft dough, and physiological maturity. Materials from the mist-irrigated and inoculated North American Barley Scab Evaluation Nursery (NABSEN) will be used to assess the impact of host differences in FHB resistance and DON accumulation on the levels of DON and bound DON. Relationships between the amounts of free DON, bound DON, and DON-3-glucoside will be determined using simple linear correlation. The presence of significant levels of bound DON will be of concern to plant breeders, as conjugation of toxins has been identified as a possible host resistance mechanism. Barley breeders currently assess resistance based on lower DON accumulation. However, this type of resistance would be of limited value, if it were to be shown that lower DON accumulation was offset by increased bound DON. Bound toxins have been demonstrated to be released to the free form during processing or digestion.

Schwarz, Paul
North Dakota State University
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