The 2022 Fusarium head blight outbreak in Ethiopia: Emerging pathogens, mixed mycotoxins, and interspecies interactions.

As Ethiopia pushes towards self-sufficiency in wheat production, it has escaped large outbreaks of Fusarium head blight (FHB), a disease that threatens wheat production globally. However, in 2022, FHB incidences in Ethiopia rose to 80%, with some areas experiencing 100% disease severity. Here we provide insights into the etiology of this disease outbreak and point towards future directions to mitigate the emerging threat of FHB on a global scale. While most wheat samples from 2022 exhibited low trichothecene levels, 26% exceeded recommended thresholds and several contained multiple trichothecene variants. We obtained 64 isolates from the outbreak and identified diverse members of the Fusarium graminearum species complex (FGSC) and many Epicoccum species. The FGSC species contributing to the outbreak are rare on a global scale. Genomic analyses reveal that Fusarium aethiopicum has persisted in Ethiopia for decades and shares ancient ancestry with a newly emerged novel species in the FGSC that we formally described as Fusarium kistleri. SNP-based analyses suggest high clonal fraction among FGSC isolates in Ethiopia, raising questions about a recent population expansion. Our findings reveal that while Epicoccum alone causes minimal disease on wheat, its presence can have a small but synergistic impact on disease symptoms when F. graminearum has already infected. The unique diversity and species composition of the 2022 Ethiopian outbreak underscores the importance of addressing emerging threats in a globalized agricultural economy to secure food safety, food security, and global food equity.