Fusarium head blight, caused by members of the Fusarium graminearum species complex (FGSC), is among the most destructive and economically important diseases of small grain crops, including wheat. To determine the phylogenetic species and mycotoxin (trichothecene) chemotypes of the FGSC in the major winter-wheat-producing areas of China, 530 isolates were collected from diseased wheat during the years 2008, 2009, and 2010, and typed using a polymerase chain reaction-based trichothecene genotype assay. Virulence of isolates with different chemotypes was also compared. Of the 530 isolates typed, 348 were F. asiaticum and 182 were F. graminearum. Subdividing the 530 isolates by the trichothecene predicted to be expressed, 482 were of the deoxynivalenol (DON) chemotype and 48 were nivalenol (NIV). Acetylated derivatives of DON included 3-acetyldeoxynivalenol (3-AcDON; 300 isolates), and 15-acetyldeoxynivalenol (15-AcDON; 182 isolates). Chemotypes of the F. asiaticum isolates were either 3-AcDON or NIV, with 3-AcDON being predominant. F. graminearum isolates were all of the 15-AcDON chemotype. F. asiaticum was the predominant phylogenetic species in the Yangtze River Basin and F. graminearum was dominant in the north of China. Two areas of co-occurrence of trichothecene chemotypes were found. The 3-AcDON and 15-AcDON isolates had similar levels of virulence. The DON isolates were significantly more virulent than those of the NIV. The 3-AcDON and 15-AcDON chemotypes were predominant in the Yangtze River Basin and areas north of the Yangtze River Basin, respectively, and it is suggested that geographic distribution is associated with differences in temperature as well as crop rotation systems.

Cyclobutrifluram (TYMIRIUM® technology), a new succinate dehydrogenase inhibitor (SDHI) fungicide, is currently being registered by SYNGENTA for controlling Fusarium crown rot (FCR) of wheat in China. The application of 15 or 30 g of active ingredient/100 kg seed of cyclobutrifluram significantly reduced pre-emergence damping-off, discoloration on the stem base and formation of whiteheads caused by FCR. The EC₅₀ values of cyclobutrifluram for 60 isolates of F. pseudograminearum, 30 isolates of F. asiaticum and 30 isolates of F. graminearum ranged from 0.016 to 0.142 mg L^-1, 0.010 to 0.041 mg L^-1 and 0.012 to 0.059 mg L^-1, respectively. One hundred and seven cyclobutrifluram-resistant (CR) mutants were obtained from three Fusarium species isolates, with ten types of mutations identified in Sdh genes. Three Fusarium species isolates exhibited similar resistance mechanisms, with the most prevalent mutations, SdhC₁^A83V and SdhC₁^R86K, accounting for 61.68% of mutants. The CR mutants possessed comparable or slightly impaired fitness compared to the corresponding parental isolates. The CR mutants carrying FpSdhB^H248Y/Q/D exhibited increased sensitivity to fluopyram. An overall moderate risk of resistance development in three Fusarium species was recommended for cyclobutrifluram.