Left – tree showing phylogenetic relationships of the 23 Fusarium species complexes and placement of F. equiseti within the F. incarnatum-equiseti species complex. In the tree, species complex names are abbreviated using specific epithets of the species after which the complexes are named (e.g., the F. sambucinum species complex is abbreviated as sambucinum). Middle right – trichothecene toxin biosynthetic gene cluster in F. equiseti. Lower left – culture of F. equiseti NRRL 66338 growing on potato dextrose agar medium. Lower right – chemical structure of diacetoxyscirpenol, the most economically important trichothecene mycotoxin produced by F. equiseti.
Image Credit: Robert Proctor, Amy McGovern and Crystal Probyn.

Fusarium equiseti NRRL 66338

Fusarium (family Nectriaceae) is a species-rich genus that poses a dual threat to agriculture production because many species cause destructive crop diseases and/or contaminate infected crops with toxic secondary metabolites (mycotoxins) that are health hazards to humans and other animals. Fusarium mycotoxins are frequent contaminants of dried distillers grains (DDGs), a coproduct of grain-based ethanol production that is used as protein-rich livestock feed. Some Fusarium species can also exist in plants as endophytes (i.e., without causing disease).

DNA-based phylogenetic analyses have resolved Fusarium into 23 multi-species lineages, or species complexes. Fusarium equiseti is a member of the Fusarium incarnatum-equiseti species complex, which is composed of at least 36 phylogenetically distinct species. Collectively, members of this complex occur on diverse crops, are geographically widespread, and produce trichothecenes, one of the mycotoxin groups of most concern to food and feed safety. However, the contributions of members of the complex to crop diseases and mycotoxin contamination are considered to be less than those caused by members of the closely related lineage, the F. sambucinum species complex. The geographic distribution and host range of F. equiseti are unclear because, prior to the recent resolution of the F. incarnatum-equiseti complex into its constituent species, the name “F. equiseti” was applied to multiple phylogenetically distinct species. Strain NRRL 66338 was isolated from an oat plant (Avena sativa) grown in Canada and its identity as F.  equiseti has been confirmed by DNA sequence analysis.

References:

• Geiser DM, Al-Hatmi A, Aoki et al. 2021. Phylogenomic analysis of a 55.1 kb 19-gene dataset resolves a monophyletic Fusarium that includes the Fusarium solani Species Complex. Phytopathology 111: 1064-1079.
• Villani A, Proctor RH, Kim HS, Brown DW, Logrieco AF, Amatulli MT, Moretti A, Susca A. 2019. Variation in secondary metabolite production potential in the Fusarium incarnatum-equiseti species complex revealed by comparative analysis of 13 genomes. BMC Genomics. 20: 314.