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Secondary Invasion of Soybeans by Fusarium graminearum and Resulting Mycotoxin Contamination. D. T. Wicklow, USDA-ARS, Northern Regional Research Center, Peoria, IL 61604. G. A. Bennett, and O. L. Shotwell. USDA-ARS, Northern Regional Research Center, Peoria, IL 61604. Plant Dis. 71:1146. Accepted for publication 28 August 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-1146D.

Fusarium graminearum Schwabe (Gibberella zeae (Schw.) Petch) infected preharvest soybeans (Glycine max (L.) Merr.) in portions of the Midwest in 1986 and contaminated the beans with deoxynivalenol (vomitoxin) and zearalenone. The pericarps ofthese Fusarium-infected beans were commonly stained pink to red, a distinguishing feature previously unreported in lots of molded or "damaged" soybeans. F. graminearum was a secondary colonist of oospore-encrusted seeds infected by Peronospora manshurica (Naum.) Syd. ex Gaum. A period of prolonged rainy weather and mild temperatures during the fall of 1986 likely provided conditions favoring inoculum buildup and dispersal of F. graminearum after beans had matured in the field. Levels of F. graminearum mycotoxins in a pick-out sample of pink beans from northern Illinois were 2,000 ppb deoxynivalenol and 4,000 ppb zearalenone. Two representative bulk samples containing pink beans harvested near southern Michigan had less than detectable levels <50 ppb) of deoxynivalenol but 375 and 584 ppb zearalenone. F. graminearum infected 14-24% of the beans from these samples. This is the first report of F. graminearum infection and trichothecene and zearalenone contamination of soybeans sampled at harvest.