Deoxynivalenol and nivalenol production by Fusarium culmorum isolates differing in aggressiveness toward winter rye

A susceptible synthetic winter rye population was inoculated with 42 isolates of Fusarium culmorum, originating from nine European countries and Australia, at two field locations in Germany. Significant (P = 0.01) genetic variation in aggressiveness of isolates of F. culmorum was observed across both field locations. Field samples were used to determine deoxynivalenol (DON), nivalenol (NIV), and ergosterol (ERG) contents. The 42 isolates also were incubated on rye grain in vitro, and DON and NIV contents were analyzed. Thirty-four isolates produced DON, and seven isolates produced NIV at both field locations and in vitro. Mean DON contents ranged from 0.5 to 64.6 mg/kg in grain from field trials and from 0.3 to 376.3 mg/kg in grain incubated in vitro; mean NIV contents ranged from 17.6 to 30.4 mg/kg in grain from field trials and from 0.8 to 381.0 mg/kg in grain incubated in vitro. No correlation was found between the DON content of field-grown grain and grain incubated in vitro. NIV-producing isolates originated from the Netherlands, Germany, Italy, and Australia. More aggressive isolates produced higher mean DON contents in grain in field trials (r = 0.69; P = 0.01). However, DON production rate per unit of fungal biomass, estimated as the DON/ERG ratio at harvest, was not correlated with aggressiveness. Toxin production seemed to be a common feature in F. culmorum. In vitro assays reliably distinguished DON- and NIV-producing types of F. culmorum; however, these assays could not predict production of DON by these isolates in the field