Characterization of the association between post-anthesis infection and deoxynivalenol accumulation in asymptomatic wheat spikes using quantitative real-time PCR

Fusarium head blight (FHB), caused by Fusarium graminearum, is a destructive disease of wheat that reduces yield and contaminates grain with the mycotoxin deoxynivalenol (DON), which is harmful to humans and livestock. Wheat is most susceptible to infection at anthesis, but infections can occur at later growth stages, leading to DON contamination of asymptomatic spikes. This study was conducted to characterize the association between infection and DON accumulation in grain from asymptomatic spikes. Three soft red winter wheat cultivars (Cooper, susceptible; Hopewell, moderately susceptible; and Truman, moderately resistant) were inoculated at anthesis, 1, 2 and 3 wk after anthesis with different spore concentrations of F. graminearum. FHB index was rated at soft dough, and asymptomatic spikes were tagged at hard dough and harvested at physiological maturity. Milled grain samples from these spikes were tested for DON and F. graminearum biomass was quantified in each sample by amplifying Tri5 DNA using quantitative RT-PCR. DON values from asymptomatic spikes inoculated after anthesis ranged from not detectable (