Environmental conditions after fusarium head blight visual symptom development affect contamination of wheat grain with deoxynivalenol and deoxynivalenol-3- glucoside

Authors: MORAES, WANDERSON - The Ohio State University; Baik, Byung-Kee; MADDEN, LAURENCE - The Ohio State University; PAUL, PIERCE - The Ohio State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2022
Publication Date: 3/5/2023
Citation: Moraes, W.B., Baik, B.V., Madden, L.V., Paul, P.A. 2023. Environmental conditions after fusarium head blight visual symptom development affect contamination of wheat grain with deoxynivalenol and deoxynivalenol-3- glucoside. Phytopathology. 113(2): 206-224. https://doi.org/10.1094/phyto-06-22-0199-r.
DOI: https://doi.org/10.1094/phyto-06-22-0199-r

Interpretive Summary: Wheat grain contaminated with a harmful mycotoxin called deoxynivalenol (DON) is known to cause vomiting, feed refusal, reproductive disorders, impaired immune function, reduced weight gain, and growth retardation upon consumption in animals and humans. Wheat grain containing DON at a level higher than 2 ppm is often rejected at grain elevators or subjected to price discounts in the United States. Accordingly, the accurate determination of the DON level of wheat grain is very important in making decisions regarding grain utilization, handling, and marketing. Fusarium head blight (FHB) is a fungal disease that is responsible for the production of DON. FHB infection leads to bleaching of the spikes, floret sterility, and the production of small, shriveled, lightweight kernels containing DON; therefore, it is commonly used as a practical and inexpensive indicator of possible grain contamination with DON. The relationship between FHB disease intensity and wheat grain DON level is, however, often too weak to use the former for the estimation of the latter. The relationship between FHB and DON breaks down in many instances under certain climatic conditions, as it is fairly complex and not fully understood. Conversion of DON to DON-3-glucoside (D3G) is assumed to be responsible for the poor relationship between FHB disease severity and DON level of wheat grain, as only free DON is detected with most conventional testing methods. Failure to detect DON as well as D3G is a food safety concern because as the latter is exposed to stomach acids, the glucose radical may be cleaved, releasing the original and more toxic DON after ingestion. Therefore, the conversion of DON to D3G may mask the toxic effects of DON in food and feed rather than promote its detoxification. This study provides evidence that rainfall after FHB visual symptom development, which tends to induce pre-harvest sprouting of grain and increase DON-to-D3G conversion, lowers the estimated level of DON and weakens the relationship between FHB severity and DON level. This information could ultimately be used to develop and refine mycotoxin risk assessment tools to influence grain handling and marketing decisions.

Technical Abstract: Fusarium head blight (FHB) of wheat, caused by the fungus Fusarium graminearum, leads to grain contamination with mycotoxins such as deoxynivalenol (DON). Although FHB is often positively correlated with DON, this relationship may break down under certain conditions. One possible explanation for this could be the conversion of DON to DON-3-glucoside (D3G), which is typically missed by common DON testing methods. The objective of this study was to quantify the effects of temperature, relative humidity, and pre-harvest rainfall patterns on DON, D3G, and their relationship in grain from wheat spikes with different levels of FHB index (IND). D3G levels were higher in grain from spikes exposed to 100% RH than to 70, 80, or 90% RH at 20 and 25 Degree Celsius across all tested IND levels. Mean D3G contamination was higher at 20 Degree Celsius than at 25 or 30 Degree Celsius. There were significantly positive linear relationships between DON and D3G. Rainfall treatments resulted in significantly higher mean D3G than the rain-free check and induced pre-harvest sprouting, as indicated by low falling numbers (FN). There were significant positive relationships between the rate of increase in D3G per unit increase in DON (a measure of conversion) and sprouting. As FN decreased, the rate of D3G conversion increased, and this rate of conversion per unit decrease in FN was greater at relatively low than at high mean DON levels. These results provide strong evidence that moisture after FHB visual symptom development influenced DON-to-D3G conversion and constitute valuable new information for understanding this complex disease-toxin system.