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 degrees 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 (TRIS and TRIO 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 degrees 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 ractebuconazole 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 degrees 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 EC10 dose of (-)-tebuconazole produced the greatest amounts of DON.