Left – tree showing phylogenetic relationships of the 23 Fusarium species complexes and placement of F. lateritium within the F. lateritium 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). Upper right – culture of F. lateritium NRRL 13622 growing on potato dextrose agar medium. Lower right – karyotype of F. lateritium NRRL 13622.

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, which are coproducts of grain-based ethanol production and used as protein-rich livestock feed. In addition, some species of Fusarium are pathogens of bioenergy 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 (Geiser et al. 2021). Fusarium lateritium is a member of the Fusarium lateritium species complex (FLSC), which consists of at least five phylogenetically distinct species: F. citri-sinensis, F. lateritium, F. massalimae, F. sarcochroum and F. stilboides (Zhao et al. 2022). Interest in FLSC stems in part from its position near the middle of Fusarium species trees. 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). The one member of FLSC that has been examined (F. stilboides NRRL 13622) has 15 chromosomes (Waalwijk et al. 2018).

Collectively, members of FLSC have a worldwide distribution and tend to occur as pathogens or endophytes on woody plants, including citrus, coffee, and mulberry. At least one species is a pathogen of sweet potato. There are no confirmed reports that members of the complex produce major Fusarium mycotoxins (i.e., fumonisins, trichothecenes or zearalenone). However, F. lateritium and F. sarcochroum have the gene cluster required for production of fusarins, a family of mycotoxins whose health effects are poorly understood. In addition, F. sarcochroum has a gene cluster that likely confers production of a metabolite(s) that is similar in structure to fumonisins (Kim et al. 2020). Fusarium lateritium NRRL 13622 was isolated from an elm tree (Ulmus sp.) growing in the U.S. state of Louisiana.

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.

Kim HS, Lohmar JM, Busman M, et al. 2020. Identification and distribution of gene clusters required for synthesis of sphingolipid metabolism inhibitors in diverse species of the filamentous fungus Fusarium. BMC Genomics 21:510.

Waalwijk C, Taga M, Zheng S-L, et al. 2018. Karyotype evolution in Fusarium. IMA Fungus 9:13-26. 10.5598/imafungus.2018.09.01.02

Zhao L, Wei X, Huang CX, Yi JP, Deng JX, Cui MJ. 2022. Fusarium citri-sinensis sp. nov. (Ascomycota: Nectriaceae) isolated from fruit of Citrus sinensis in China. Phytotaxa 555:259-266. 10.11646/phytotaxa.555.3.5