Impact of three sterol-biosynthesis inhibitors on growth of Fusarium langsethiae and on T-2 and HT-2 toxin production in oat grain under different ecological conditions

The health-beneficial properties of oats have led to an increase in the consumption of oats and oat-based food products in recent years. Fusarium langsethiae grows on small grain cereals, especially oats and can result in contamination with type A trichothecenes (T-2 toxin (T-2) and HT-2 toxin (HT-2)) in crops pre- and post-harvest. The aim of this work was to assess the efficacy of three fungicides (fenpropimorph, prochloraz and tebuconazole) on temporal growth of two F. langsethiae strains and the accumulation of T-2 and HT-2 in oat grains, under different water activities (aw; 0.95 and 0.98) and temperatures (15 and 25 °C). All the antifungal agents reduced growth rates when compared to controls, and this increased with increasing fungicide dose. The ranges of ED50 values (mg/kg) were 65–270 for fenpropimorph, 0.25–4.2 for prochloraz, and 0.3–14 for tebuconazole. The ED90 values (mg/kg) ranged from 170 to > 800, 0.5 to > 10 and 0.5 to > 15 for these three fungicides respectively. The ED50 values were not statistically significantly affected by the factors aw, temperature or strain. However, there were significant differences among the fungicides. Fenpropimorph proved less efficient that the two azoles, which do not differ significantly. In general, levels of HT-2 were higher than T-2 in all cultures regardless of environmental conditions. Overall, HT-2 concentration was always higher at 25 than 15 °C and increased from day 14 to day 21. Levels of both toxins generally decreased with increasing fungicide dose regardless of fungicide type, strain and incubation time. No toxins were detected in cultures at 0.95 aw in the presence of any of the three fungicides. Also under wetter conditions at 0.98 aw neither mycotoxin was found in cultures treated with prochloraz at doses >1 mg/kg (15 °C) or >3 mg/kg (25 °C) or tebuconazole at doses >6 mg/kg (15 or 25 °C). ANOVA showed that in treatments with each fungicide the factors dose, time and temperature significantly affected toxin production while there was no difference between the strains.