Left – tree showing phylogenetic relationships of the 23 Fusarium species complexes and placement of F. nygamai 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. nygamai NRRL 66327 growing on potato dextrose agar medium. Lower right – chemical structure of fumonisin B1, the most economically important mycotoxin produced by F. nygamai. 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 nygamai 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 nygamai is a member of the African 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 chromosome is dispensable. Fusarium nygamai can be a dominant species in native grassland soils and can occur on diverse crops, including asparagus, broad bean, cotton, maize, millet, rice and sorghum (Leslie and Summerell, 2006). Field isolates of this species often produce fumonisins, one of the mycotoxin groups of most concern to agriculture. Some strains also produce moniliformin, a mycotoxins whose effect on health is not well understood. Strain NRRL 66327 (= FRC M-7492) is a meiotic progeny from a laboratory cross of two soil isolates of F. nygamai, one from Australia and the other from South Africa (Klaasen and Nelson 1996).

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.

Klaasen JA, Nelson PE. 1996. Identification of a mating population, Gibberella nygamai sp. nov., within the Fusarium nygamai anamorph. Mycologia 88:965-969.

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