Left – tree showing phylogenetic relationships of the 23 Fusarium species complexes and placement of F. sulawesiensis 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 mycotoxin biosynthetic gene cluster in F. sulawesiensis. Bottom right – culture of F. sulawesiensis NRRL 66472 growing on potato dextrose agar medium. Image credit: Robert H. Proctor, Amy McGovern and Crystal Probyn.

Fusarium (family Nectriaceae) is a species-rich fungal genus that poses a dual threat to agriculture 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. Some Fusarium mycotoxins are frequent contaminants of dried distillers’ grains, coproducts of grain-based ethanol production used as a protein-rich livestock feed. In addition, some species of Fusarium are pathogens of energy crops such as corn and sugar cane. Some species can also exist as endophytes in plants, including some bioenergy crops.

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 comprised of at least 36 phylogenetically distinct species that resolve into two distinct clades, the Incarnatum clade and the Equiseti clade. Fusarium equiseti groups within the Equiseti clade. During its evolutionary diversification, Fusarium has undergone multiple chromosomal fusions. As a result, members of early diverging species complexes tend to have more chromosomes (15 – 20) than later diverging complexes (4 – 7). Although chromosome number in F. sulawesiensis has not been determined, other members of the F. incarnatum-equiseti species complex that have been examined have 9 chromosomes. Collectively, members of the complex occur in soil and on diverse crops, are geographically wide-spread, and produce trichothecenes, one of the mycotoxin groups of most concern to agriculture. However, members of the complex typically cause less severe crop disease and trichothecene contamination than members of the closely related F. sambucinum species complex. Analysis of the trichothecene biosynthetic gene cluster in F. sulawesiensis revealed how the cluster has grown by translocation of genes from other loci. Fusarium sulawesiensis NRRL 66472 was isolated from the grass (Konza sp.) growing in a native tallgrass prairie at the Konza Prairie Biological Station in the U.S. state of Kansas.

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.

Xia JW, Sandoval-Denis M, Crous PW, et al. 2019. Numbers to names - restyling the Fusarium incarnatum-equiseti species complex. Persoonia 43:186-221.