Left – tree showing phylogenetic relationships of the 23 Fusarium species complexes and placement of F. subglutinans within the F. fujikuroi 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 – culture of F. subglutinans NRRL 66333 growing on potato dextrose agar medium. Bottom right – chemical structures of the mycotoxins beauvericin and moniliformin. 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 known as species complexes (Geiser et al. 2021). Fusarium subglutinans is a member of the Fusarium fujikuroi species complex, which consists of over 50 phylogenetically distinct species that have been further resolved into three major clades: the African Clade, American Clade and Asian Clade. Fusarium subglutinans groups within the American 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 members of later diverging complexes (4 – 7). Members of the F. fujikuroi species complex typically have 12 chromosomes, but one of them is dispensable. Fusarium subglutinans has been recovered from teosinte, the progenitor of maize, and wild grasses native to northern North America. The fungus has also been recovered from multiple crops, including banana, millet, pepper, soybean and wild rice (Leslie and Summerell, 2006). Fusarium subglutinans and its sister species F. temperatum are morphologically similar and part of a complex of species that cause ear rot, stalk rot, and seedling blight maize. Both species can produce the mycotoxin moniliformin but differ in production of the mycotoxin beauvericin. Isolates of F. temperatum tend to produce beauvericin, whereas most F. subglutinans isolates do not because of multiple mutations in the non-ribosomal peptide synthase gene required for beauvericin production (Fumero et al. 2020). Fusarium subglutinans strain NRRL 66333 was isolated from a drought-resistant variety of maize, Acoma Blue Corn, grown in the U.S. state of New Mexico.

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.

Fumero MV, Villani A, Susca A, et al. 2020. Fumonisin and beauvericin chemotypes and genotypes of the sister species Fusarium subglutinans and Fusarium temperatum. Appl Environ Microbiol 86. 10.1128/aem.00133-20.

Leslie JF, Summerell BA. 2006. The Fusarium Laboratory Manual. Ames: Blackwell Publishing. p. 388.