Chemotype and aggressiveness of isolates of Fusarium graminearum causing head blight of wheat in Nebraska

Fusarium head blight (FHB) or scab of wheat (Triticum aestivum L.) and its associated mycotoxin deoxynivalenol (DON) can cause devastating economic losses. In North America, FHB of wheat is caused mainly by Fusarium graminearum Schwabe [sexual stage Gibberella zeae (Schwein.) Petch]. In this study, the chemotype of 73 single-spore isolates of F. graminearum obtained from wheat kernels collected from 2007 to 2010 from FHB-Affected fields and grain elevators in Nebraska was determined to be 15-ADON. Eight selected isolates were evaluated for aggressiveness on spikes and DON production in grain using the FHB-susceptible spring wheat cultivar Wheaton. Aggressiveness was quantified as disease severity and area under the disease progress curve (AUDPC). Disease severity at 21 days after inoculation ranged from 40.9% to 99.5% and AUDPC ranged from 284%-days to 1279%-days. DON production in grain, measured by enzyme-linked immunosorbent assay (ELISA), ranged from 0.2 to 11.0 g g^-1. Aggressiveness as measured using AUDPC was positively and linearly related to DON production in grain (R² = 0.98; P < 0.0001). Isolates that produced the most DON were also the most aggressive. These results confirmed previous findings that the predominant F. graminearum chemotype in North America is 15-ADON and suggest that in Nebraska, there are highly aggressive populations of F. graminearum with high DON production capacity that have potential to cause severe losses due to reduction in yield and grain quality. This information will enhance farmers preparedness and willingness to apply management measures in years with a high risk for FHB outbreaks and will help researchers better understand FHB.