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 aw and at 20, 25, and 30 °C on wheat-based media. Then, F. graminearum was treated with rac-tebuconazole and its enantiomers at the EC10, EC50, and EC90 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 EC50 doses of rac-tebuconazole and its enantiomers for 4, 8, and 14 days at 30 °C and aw 0.997. The results showed that the fungicidal activity of tebuconazole was strongly influenced by temperature, aw, 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 aw is the most suitable for DON production by F. graminearum. The test strains of F. graminearum treated with the EC10 dose of (-)-tebuconazole produced the greatest amounts of DON.
Keywords: TRI5; TRI6; biological activity; deoxynivalenol; stereoisomers.