The Fungicidal Activity of Tebuconazole Enantiomers against Fusarium graminearum and Its Selective Effect on DON Production under Different Conditions

Tebuconazole, which consists of a pair of enantiomers with different fungicidal activities, is one of the most common fungicides used in the control of Fusarium graminearum . In this study, the fungicidal activity of rac -tebuconazole and its enantiomers against F. graminearum was determined at 0.997, 0.975, and 0.950 a w and at 20, 25, and 30 °C on wheat-based media. Then, F. graminearum was treated with rac -tebuconazole and its enantiomers at the EC 10, EC 50, and EC 90 levels under different culture conditions, and DON production was measured. Finally, expression of the DON biosynthetic genes ( TRI5 and TRI6 ) was quantified by real-time RT-PCR after incubation with EC 50 doses of rac -tebuconazole and its enantiomers for 4, 8, and 14 days at 30 °C and a w 0.997. The results showed that the fungicidal activity of tebuconazole was strongly influenced by temperature, a w, and the combined factors. (−)-Tebuconazole is higher in fungicidal activity than (+)-tebuconazole and rac -tebuconazole with 24–99-fold and 1.8–6.7-fold, respectively. However, (−)-tebuconazole was generally more favorable for DON production than (+)-tebuconazole under the same conditions. Additionally, (−)-tebuconazole and rac -tebuconazole induced significantly increased expression of the DON biosynthetic genes ( TRI5 and TRI6 ) compared to the control by the 14th day of treatment. In this research, the combination condition of 30 °C and 0.997 a w is the most suitable for DON production by F. graminearum. The test strains of F. graminearum treated with the EC 10 dose of (−)-tebuconazole produced the greatest amounts of DON.