Fusarium is a large genus of filamentous fungi widely distributed in soil and in association with plants. Most species are harmless saprobes and are relatively abundant members of the soil microbial community. 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 these Fusarium species are fumonisins and trichothecenes.
The genus includes a number of economically important plant pathogenic species. The genome of the wheat and maize pathogen, Fusarium graminearum, has been sequenced. In addition, 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 count of the white blood cell type called neutrophils), 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. The neutropenia in such cases is almost always the result of chemotherapy against certain kinds of leukemia or else heavy use of immunosuppressive drugs in problematic cases of major organ transplant surgery.
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. 
Fusarium 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. 
Use as human food
Mass casualties occurred in the Soviet Union in the 1930s and 1940s when Fusarium-contaminated wheat flour was baked into bread, causing alimentary toxic aleukia with a 60% mortality rate. Symptoms began with abdominal pain, diarrhea, vomiting, and prostration. Within days fever, chills, myalgias and bone marrow depression with granulocytopenia and secondary sepsis. Further symptoms included pharyngeal or laryngeal ulceration and diffuse bleeding into the skin (petechiae and ecchymoses), melena, bloody diarrhea, hematuria, hematemesis, epistaxis, vaginal bleeding, Pancytopenia and gastrointestinal ulceration. Fusarium sporotrichoides contamination was found in affected grain in 1932, spurring research for medical purposes and for use in biological warfare. The active ingredient was found to be trichothecene T-2 mycotoxin, and was produced in quantity and weaponized prior to the passage of the Biological Weapons Convention in 1972. The Soviets were accused of using the agent, dubbed "yellow rain", to cause 6,300 deaths in Laos, Kampuchea, and Afghanistan between 1975 and 1981.
Following an outbreak of Fusarium oxysporum that affected coca plantations in Peru, and other crops planted in the area, the United States has proposed the use of the agent as a mycoherbicide in drug eradication. In 2000, a proposal was passed to use the agent as part of Plan Colombia. In response to concerns that use of the fungus could be perceived as biological warfare, the Clinton Administration "waived" this use of Fusarium. A subsequent law passed in 2006 has mandated the testing of mycoherbicide agents - either Fusarium oxysporum or Pleospora papaveracea - in field trials in U.S. territory. Use of Fusarium oxysporum for these tests has raised concerns because resistant coca from the previous outbreak has been widely cultivated, and the fungus has been implicated in the birth of 31 anencephalic children in the Rio Grande region of Texas in 1991, the loss of palm trees in Los Angeles, and eye infections from contact lens solutions. The alternative Pleospora papaveracea is less well-known; despite decades of study in the Soviet biowarfare lab in Tashkent, Uzbekistan, the relevant mycotoxins reportedly have not yet been isolated, named, or studied.
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 Brewing Microbiology 3rd Edition Priest and Campbell, ISBN0-306-47288-0
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