Fusarium Link, 1809

Fusarium (; Audio:) is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. The name of Fusarium comes from Latin fusus, meaning a spindle. Most species in Genus Fusarium are harmless saprobes found in relative abundance in the soil microbial community, and some exist as commensal members of the skin microbiome.

Some species produce mycotoxins in cereal crops that can affect human and animal health if they enter the food chain; the main toxins produced by Fusarium species are the fumonisin and trichothecene families, and zearalenone. Despite most species being harmless, some Fusarium species and subspecific groups are among the most important fungal pathogens of plants and animals.

Taxonomy

The taxonomy of the genus is complex. Phylogenetic studies show seven major clades within the genus. A number of different taxnomic schemes have been used, and up to 1,000 species have been identified, with approaches varying between wide and narrow concepts of speciation (lumpers and splitters).

One proposal with wide specialist subscription maintains the genus as singular, including all agriculturally significant Fusaria species; A counterproposal—unrelated to Watanabe 2011—divides the one into seven entirely separate genera.

Subdivision

Various schemes have subdivided the genus into subgenera and sections. There is a poor correlation between sections and phylogenetic clades.

Pathogen

The genus includes a number of economically important plant pathogenic species.

Fusarium graminearum commonly infects barley if there is rain late in the season. It is of economic impact to the malting and brewing industries, as well as feed barley. Fusarium contamination in barley can result in head blight, and in extreme contaminations, the barley can appear pink. The genome of this wheat and maize pathogen has been sequenced. F. graminearum can also cause root rot and seedling blight. The total losses in the US of barley and wheat crops between 1991 and 1996 have been estimated at $3 billion.

Fusarium oxysporum f.sp. cubense is a fungal plant pathogen that causes Panama disease of banana (Musa spp.), also known as fusarium wilt of banana. Panama disease affects a wide range of banana cultivars, which are propagated asexually from offshoots and therefore have very little genetic diversity. Panama disease is one of the most destructive plant diseases of modern times, and caused the commercial disappearance of the once dominant Gros Michel cultivar. A more recent strain also affects the Cavendish cultivars which commercially replaced Gros Michel. It is considered inevitable that this susceptibility will spread globally and commercially wipe out the Cavendish cultivar, for which there are currently no acceptable replacements. Fusarium oxysporum has also been known to infect a variety of other fruit, vegetable and field crops. The rate of infection of these crops has led to economic losses worldwide .

Fusarium oxysporum f. sp. narcissi causes rotting of the bulbs (basal rot) and yellowing of the leaves of daffodils (Narcissi).

Fusarium xyrophilum was able to hijack a South American species of yellow-eyed Xyris grass, creating "pseudoflowers", fooling bees and other pollinating insects into visiting them, taking fungal spores to other plants. (For this phenomenon, see also Puccinia monoica.)

In humans

Some species may cause a range of opportunistic infections in humans. In humans with normal immune systems, fusarial infections may occur in the nails (onychomycosis) and in the cornea (keratomycosis or mycotic keratitis). In humans whose immune systems are weakened in a particular way, (neutropenia, i.e., very low neutrophils count), aggressive fusarial infections penetrating the entire body and bloodstream (disseminated infections) may be caused by members of the Fusarium solani complex, Fusarium oxysporum, Fusarium verticillioides, Fusarium proliferatum and, rarely, other fusarial species. In order to properly treat these infections, it is important, but often difficult, to identify the specific species causing the infection. These species are resistant to most antifungal drugs.

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