Fusarium solani

The genus Fusarium was described in 1809 by Link.[3] In the 1930s, Wollenweber and Reinking organized the genus Fusarium into sections, including Martiella and Ventricosum,[3] which were collapsed together by Snyder and Hansen in the 1940s to form a single species, Fusarium solani;[3] one of nine Fusarium species they recognized based on morphological features.[2] The current concept of F. solani is as a species complex consisting of multiple, closely related and morphologically poorly distinguishable, "cryptic" species with characteristic genetic differences.[4] There is a proposed concept for the entire genus - widely subscribed by specialists - that would include this complex.[5][6] However, there is a smaller counterproposal that radically refiles the genus including making this complex into a genus Neocosmospora.[7] The fungus is allied with the sexual species, Nectria haematococca, in the family Nectriaceae (phylum Ascomycota).[1]

Like other species in its genus, Fusarium solani produces colonies that are white and cottony. However, instead of developing a pink or violet centre like most Fusarium species,[8] F. solani becomes blue-green or bluish brown.[1][8][9] On the underside, they may be pale, tea-with-milk-brown, or red-brown.[1] However, some clinical isolates have been blue-green or ink-blue on the underside.[1] F. solani colonies are low-floccose, loose, slimy, and sporadic.[1] When grown on potato dextrose agar (PDA), this fungus grows rapidly, but not as rapidly as Fusarium oxysporum.[9] In PDA, F. solani colonies reach a diameter of 64–70 mm in 7 days.[1]

F. solani has aerial hyphae that give rise to conidiophores laterally.[1] The conidiophores branch into thin, elongated monophialides that produce conidia.[1][9] Phialides that produce macroconidia are shorter than those that produce microconidia.[1] The macroconidia produced by F. solani are slightly curved, hyaline, and broad,[1] often aggregating in fascicles.[10] Typically the macroconidia of this species have 3 septa but may have as many as 4–5.[1][10] Microconidia have thickened basal cells and tapered, rounded apical cells.[1] However, some F. solani isolates have pointed, rather than rounded, macroconidia.[1] Microconidia are oval or cylindrical, hyaline, and smooth.[1] Some microconidia may be curved.[1] Microconidia typically lack septa, but occasionally they may have up to two.[1] Fusarium solani also forms chlamydospores most commonly under suboptimal growth conditions.[10] These may be produced in pairs or individually.[9][10] They are abundant, have rough walls, and are 6-11 μm.[1] F. solani chlamydospores are also brown and round.[11]

F. solani is found in soil worldwide.[2] However, a given species within the complex may not be as widespread[2] and may not have the same ecology as others in the complex.[10] In general, as a soil fungus, F. solani is associated with the roots of plants[1] and may be found as deep in the ground as 80 cm.[10] It is frequently isolated in tropic, subtropic, and temperate locations, and less frequently isolated from alpine habitats.[10] The pH of soil does not have a significant effect on F. solani, however, soil fumigation causes an increase in occurrence.[10] F. solani is typically sensitive to soil fungicides.[10] F. solani has been found in ponds, rivers, sewage facilities, and water pipes.[1] It has also been found in larvae and adults of the picnic beetle, is a symbiote of the ambrosia beetle.[10]

F. solani can be found in soils worldwide, where its chlamydospores overwinter on plant tissue/seed or as mycelium in the soil.[12] The pathogen enters hosts through developing roots, where it can infect the host. After infection, F. solani produces asexual macro and microconidia which are dispersed through wind and rain.[13] The pathogen can persist in the soil for a decade, and if left unchecked can cause complete crop loss.

F. solani have 5-13 chromosomes,[3][10] with a genome size of about 40 Mb.[3] The GC-content of its DNA is 50%.[10] Mycelium of F. solani is rich in the amino acid alanine, as well as a range of fatty acids including δ-aminobutyric-, palmitic-, oleic-, and linolenic acids.[10] Fusarium solani requires potassium for growth,[10] and develops a feathery pattern when potassium levels are below 3 mM.[3] In culture the following disaccharides are utilized (from most- to least preferential): mannose, rhamnose and sorbose.[10] This species can decompose cellulose at an optimal pH of 6.5 and temperature of 30 °C.[10] It can also metabolise steroids and lignin,[3] and reduce Fe³⁺ to Fe²⁺.[10] Fusarium solani produces mycotoxins like Fusaric acid and naphthoquinones.[1][14] Other toxins have also been isolated from F. solani, including:

• Fusarubin[10]
• Javanicin[10]
• Marticin[10]
• Isomarticin[10] - causes chlorosis in citrus[3]
• Solaniol[10]
• Neosolaniol[10]
• T-2 toxin[10]
• HT-2 toxin[10]
• Diacetoxyscirpenol[10]

F. solani has been investigated as a biological control for certain plants including leafy spurge, morning glory, striga, gourd, and water hyacinth.[3]