Occurrence of Fusarium spp. on winter wheat and deoxynivalenol production in 1997

In 1997, 14 wheat samples from three sites with organic farming were investigated for the occurrence of Fusarium spp. and the contamination of grains with the mycotoxin deoxynivalenol DON. Fusarium spp. and M. nivale were isolated on selective media from grains and leaves at different growth stages. The Fusarium species were identified microscopically. DON predominantly produced by the Fusarium species F.culmorum and F.graminearum was quantified immunologically by a competitive ELISA test (R-Biopharm(R)). At GS 85 the average frequency of Fusarium spp. and M. nivale on leaves was 5-20% and 15%, respectively. Symptoms and disease intensity were low. At harvest, infection rates of grains with Fusarium spp. varied between 1 and 8,5% in organic farming and between 23 and 33% in conventional fanning. The low infestation of grains with Fusarium spp. was confirmed immunologically in a genus-specific EPS test. In contrast, the M. nivale infection rate at Hennef and Velbert was high with up to 40% compared to an average of 15% at Blankenheim. The DON content of grains varied depending on the cultivar between 40 and 410 mu g/kg with an average of 115 mu g/kg. Significant differences between cultivars could not be determined neither for Fusarium infection nor for the DON content of grains. The low incidence of Fusarium spp. as well as the comparatively low DON content are likely to result from the special conditions in the organic farming systems. In 1997, both, the infestation with Fusarium spp, as well as DON contents, were higher in grains produced in conventional farming without the use of fungicides. Fungicides applied at flowering significantly reduced the DON content of wheat.