Fusarium sporotrichioides

Fusarium sporotrichioides is a fungal plant pathogen, one of various Fusarium species responsible for damaging crops, in particular causing a condition known as Fusarium head blight in wheat, consequently being of notable agricultural and economic importance. The species is ecologically widespread, being found across tropical and temperate regions, and is a significant producer of mycotoxins, particularly trichothecenes. Although mainly infecting crops, F. sporotrichioides-derived mycotoxins can have repercussions for human health in the case of the ingestion of infected cereals. One such example includes the outbreak of alimentary toxic aleukia (ATA) in Russia, of which F. sporotrichioides-infected crop was suspected to be the cause. Although current studies on F. sporotrichioides are somewhat limited in comparison to other species in the genus, Fusarium sporotrichioides has found several applications as a model system for experimentation in molecular biology. The genus Fusarium was first characterised by the German botanist Johann Link in 1809, prior to the recognition of fungal involvement in plant disease. Over a thousand different species of Fusarium were identified by the 1930s, however, upon further analysis, these were narrowed down to 65 different species. Despite this reduction in the recognised number of species, differentiating one from the other remained difficult and unclear. Lacking a satisfactory system of classification and identification with which to organise these many, seemingly similar Fusarium species, the mycologists Snyder and Hansen collected samples of various fusaria from laboratories worldwide, isolated single spores and cultured them for subsequent analysis of their genetic variation. Their work indicated the existence of 9 distinct species of Fusarium, but there have since been several different classification systems that reach different conclusions, and consensus around this has been difficult to establish, perhaps in part because research focuses predominantly on the agriculturally or botanically more significant fusaria. F. sporotrichioides exemplifies these classification difficulties, as it is usually designated as belonging to the section Sporotrichiella, along with other similar species such as the more well-studied F. poae and F. tricinctum, although other classification systems have placed F. sporotrichioides in the Arthrosporiella section, based on the similarity of its conidial morphology to other species in the section. More currently, the taxonomy of the genus Fusarium is studied using high-performance liquid chromatography, with each of the peaks on the resulting chromatograph being detected by a photodiode array and grouped into chromophore families. As each species produces a different pattern of peaks, this technique allows accurate species identification, and has successfully been applied to several fusaria, including F. sporotrichioides. For larger samples, thin-layer chromatography is usually used as a less expensive alternative. Fusarium sporotrichioides are found in many tropical and temperate regions, usually in the soil or on wheat. Several members of the genus Fusarium are often found colonising the same area, with the proportion of the total Fusarium population each species constitutes fluctuating depending on extant weather conditions, as for example, colder weather hinders the growth of dominant species such as F. avenaceum, allowing others such as F. culmorum to dominate. In contrast to other taxonomically-related fusaria that are mainly found on cereal crops, F. sporotrichioides is often soil-dwelling. Furthermore, other non-pathogenic or opportunistic Fusarium species are frequently found alongside F. sporotrichioides as part of a phylogenetically similar species complex. Fusarium sporotrichioides is usually white in early growth, but syellow, brownish, red, pink, or purple later on. The hyphae are usually trinucleated, but can have up to eight nuclei. F. sportotrichioides usually has many aerial mycelia, and may form reddish- or yellow-brown clusters of hyphae, called sporodochia. Yellow sporodochia turn purple upon addition of alkaline substances such as ammonia, whilst reddish-brown clusters turn yellow under acidic conditions. Members of this species have irregularly shaped, almost globular microconidia (referred to as subglobose), that are usually 5-7 μm in diameter, whilst their macroconidia are slightly curved and usually have three to five septa. Many have numerous brown, globose chlamydospores that are 7 to 15 μm in diameter, and serve as an important feature for their distinction from other fusaria. Fusarium sporotrichioides carries out both sexual and asexual mechanisms of reproduction, with its teleomorphs including Nectria and Gibberella. It is a fast-growing fungus, usually able to grow up to 8-8.8 cm in diameter within four days. Its optimal growth temperature ranges from 22.5–27.5 °C (72.5–81.5 °F), with the minimum and maximum temperatures required for growth being 2.5–7 °C (36.5–44.6 °F) and 35 °C (95 °F), respectively. The minimum humidity level required for vegetative growth is 88%.