Analysis of the Fusarium graminearum Species Complex in Wheat-Maize and Wheat-Rice Rotation Fields in Henan, China

The Fusarium graminearum species complex (FGSC) causes multiple cereal diseases. This study aimed to investigate the specific effects of different cropping systems on the population composition and trichothecene chemotypes of the FGSC under the same climatic conditions within a single region. From 2013 to 2023, we performed isolation and identification of the FGSC population in adjacent wheat-maize and wheat-rice rotation fields in Kaifeng, Henan, China; 1,586 FGSC isolates were obtained. The results showed that the 15-acetyldeoxynivalenol genotype of F. graminearum sensu stricto (F. graminearum-15ADON) was predominant in both rotation fields (93.6%), followed by the 3ADON genotype of F. asiaticum (F. asiaticum-3ADON) (5.7%). There were significant differences in the isolation frequencies of the two species from Fusarium head blight samples. The isolation frequency of F. asiaticum-3ADON was the highest in wheat, followed by that in rice and rice residues; no F. asiaticum isolates were obtained from maize and maize residues. Rotation systems, isolation source, and annual climatic conditions all have a significant effect on the isolation frequencies of F. graminearum-15ADON and F. asiaticum-3ADON. Cross-pathogenicity tests showed that F. graminearum-15ADON was more pathogenic to wheat and maize than F. asiaticum-3ADON. Interspecific competition assays revealed that the pathogenicity following mixed inoculation with the two species was lower than that of F. graminearum-15ADON alone. Meanwhile, F. graminearum-15ADON displayed strong competitive dominance in hosts, with its re-isolation frequency consistently exceeding 98%. This likely explains the dominance of F. graminearum-15ADON in the two rotation fields.