Fusarium solani (257 25) Cultured and stained deuteromycetes

''Fusarium solani'' is a species complex of at least 26 closely related filamentous fungi in the division

Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...

, family

Nectriaceae The Nectriaceae comprise a family of fungi in the order Hypocreales. It was circumscribed by brothers Charles and Louis René Tulasne Louis René Étienne Tulasne, a.k.a. Edmond Tulasne (12 September 1815 – 22 December 1885) was a French b ...

. It is the

anamorph In mycology, the terms teleomorph, anamorph, and holomorph apply to portions of the life cycles of fungi in the phyla Ascomycota and Basidiomycota: *Teleomorph: the sexual reproductive stage (morph), typically a fruiting body. *Anamorph: an ase ...

of ''

Nectria haematococca ''Fusarium solani'' is a species complex of at least 26 closely related filamentous fungi in the division Ascomycota, family Nectriaceae. It is the anamorph of '' Nectria haematococca''. It is a common soil fungus and colonist of plant mater ...

''. It is a common soil fungus and colonist of plant materials. ''Fusarium solani'' is implicated in plant disease as well as human disease notably infection of the cornea of the eye.

History and taxonomy

The genus ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' was described in 1809 by Link. In the 1930s, Wollenweber and Reinking organized the genus ''Fusarium'' into sections, including ''Martiella'' and ''Ventricosum,'' which were collapsed together by Snyder and Hansen in the 1940s to form a single species, ''Fusarium solani;'' one of nine ''Fusarium'' species they recognized based on morphological features. The current concept of ''F. solani'' is as a

species complex In biology, a species complex is a group of closely related organisms that are so similar in appearance and other features that the boundaries between them are often unclear. The taxa in the complex may be able to hybridize readily with each oth ...

consisting of multiple, closely related and morphologically poorly distinguishable, "cryptic" species with characteristic genetic differences. There is a proposed concept for the entire genus - widely subscribed by specialists - that would include this complex. However there is a smaller counterproposal that radically refiles the genus including making this complex into a genus ''Neocosmospora''. The fungus is allied with the sexual species, ''Nectria haematococca'', in the family Nectriaceae (phylum Ascomycota).

Growth and morphology

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, ''F. solani'' becomes blue-green or bluish brown. On the underside, they may be pale, tea-with-milk-brown, or red-brown. However, some clinical isolates have been blue-green or ink-blue on the underside. ''F. solani'' colonies are low-floccose, loose, slimy, and sporadic. When grown on

potato dextrose agar Potato dextrose agar (BAM Media M127
from the U.S.

(PDA), this fungus grows rapidly, but not as rapidly as ''

Fusarium oxysporum ''Fusarium oxysporum'' (Schlecht as emended by Snyder and Hansen), an ascomycete fungus, comprises all the species, varieties and forms recognized by Wollenweber and Reinking within an infrageneric grouping called section Elegans. It is part of ...

''. In PDA, ''F. solani'' colonies reach a diameter of 64–70 mm in 7 days. ''F. solani'' has aerial

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e that give rise to

conidiophore A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...

s laterally. The conidiophores branch into thin, elongated monophialides that produce

conidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to the ...

Phialide The phialide ( ; el, phialis, diminutive of phiale, a broad, flat vessel) is a flask-shaped projection from the vesicle (dilated part of the top of conidiophore) of certain fungi. It projects from the mycelium without increasing in length unless ...

s that produce

macroconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an Asexual reproduction, asexual, non-motility, motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are al ...

are shorter than those that produce

microconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to th ...

. The macroconidia produced by ''F. solani'' are slightly curved, hyaline, and broad, often aggregating in fascicles. Typically the macroconidia of this species have 3 septa but may have as many as 4–5. Microconidia have thickened basal cells and tapered, rounded apical cells. However, some ''F. solani'' isolates have pointed, rather than rounded, macroconidia. Microconidia are oval or cylindrical, hyaline, and smooth. Some microconidia may be curved. Microconidia typically lack septa, but occasionally they may have up to two. ''Fusarium solani'' also forms chlamydospores most commonly under suboptimal growth conditions. These may be produced in pairs or individually. They are abundant, have rough walls, and are 6-11 μm. ''F. solani'' chlamydospores are also brown and round.

Host and symptoms

''F. solani'' is a very generalistic fungal specie and has been known to infect peas, beans, potatoes, and many types of cucurbits. There has been increasing evidence that ''F. solani'' can also act as a causal agent of mycoses in humans. ''F. solani'' can also cause damping off, corn rot, and root rot, as well as sudden death of soybeans(SDS). Symptoms include general plant decline, wilting, and large necrotic spots on tap roots. Recently the pathogen has also done serious damage to olive trees throughout the mediterranean. F. ''solani'' has been and remains a serious economic disease in North and South America.

Ecology

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

ambrosia beetle Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae ( Coleoptera, Curculionidae), which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead, stressed, and healthy trees in wh ...

Life cycle

''F. solani'' can be found in soils worldwide, where its chlamydospores overwinter on plant tissue/seed or as mycelium in the soil. 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. The pathogen can persist in the soil for a decade, and if left unchecked can cause complete crop loss.

Management

The ubiquitous nature of ''F. solani'' gives rise to a plethora of management practices developed independently. One particular method is the use of the bacterial complex ''Burkholderia cepacia,'' which is a registered control method. This bacterial complex has been shown to produce several types of antibiotics (depending on the strain), and can act as a substitute for chemical pesticides. Precautionary methods include planting during warm/dry weather, 3 plus years of crop rotation of non host species, and avoiding dense seed planting.

Physiology and biochemistry

''F. solani'' have 5-13 chromosomes, with a genome size of about 40 Mb. The

GC-content In molecular biology and genetics, GC-content (or guanine-cytosine content) is the percentage of nitrogenous bases in a DNA or RNA molecule that are either guanine (G) or cytosine (C). This measure indicates the proportion of G and C bases out o ...

of its DNA is 50%. Mycelium of ''F. solani'' is rich in the amino acid

alanine Alanine (symbol Ala or A), or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group side c ...

, as well as a range of fatty acids including δ-aminobutyric-, palmitic-, oleic-, and

linolenic acid Linolenic acid is a type of naturally-occurring fatty acid. It can refer to either of two octadecatrienoic acids (i.e. with an 18-carbon chain and three double bonds, which are found in the '' cis'' configuration), or a mixture of the two. Lino ...

s. ''Fusarium solani'' requires

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

for growth, and develops a feathery pattern when potassium levels are below 3 mM. In culture the following disaccharides are utilized (from most- to least preferential):

mannose Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation ...

, rhamnose and

sorbose Sorbose is a ketose belonging to the group of sugars known as monosaccharides. It has a sweetness that is equivalent to sucrose (table sugar). The commercial production of vitamin C Vitamin C (also known as ascorbic acid and ascorbate) ...

. This species can decompose

cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

at an optimal pH of 6.5 and temperature of 30 °C. It can also metabolise

steroid A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and a ...

s and

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...

, and reduce Fe³⁺ to Fe²⁺. ''Fusarium solani'' produces

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...

s like Fusaric acid and

naphthoquinone Naphthoquinones constitute a class of organic compounds structurally related to naphthalene. Two isomers are common for the parent naphthoquinones: * 1,2-Naphthoquinone * 1,4-Naphthoquinone Natural products * Alkannin * Hexahydroxy-1,4-napht ...

s. Other toxins have also been isolated from ''F. solani'', including: * Fusarubin * Javanicin * Marticin * Isomarticin - causes

chlorosis In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

in citrus * Solaniol * Neosolaniol *

T-2 toxin T-2 Mycotoxin (pronounced as 'Tee-Two') is a trichothecene mycotoxin. It is a naturally occurring mold byproduct of ''Fusarium'' spp. fungus which is toxic to humans and animals. The clinical condition it causes is ''alimentary toxic aleukia'' ...

* HT-2 toxin *

Diacetoxyscirpenol Diacetoxyscirpenol (DAS), also called anguidine, is a mycotoxin from the group of type A trichothecenes. It is a secondary metabolite product of fungi of the genus ''Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a grou ...

Pathology

Humans

Half of human disease involving ''Fusarium'' is caused by ''F. solani'' and it is involved in most cases of systemic fusariosis and corneal infections. ''F. solani'' has been implicated in the following diseases:

disseminated disease Disseminated disease refers to a diffuse disease-process, generally either infectious or neoplastic. The term may sometimes also characterize connective tissue disease. A disseminated infection, for example, has extended beyond its origin or nidus ...

osteomyelitis Osteomyelitis (OM) is an infection of bone. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. The long bones of the arms and legs are most commonly involved in children e.g. the femur and humerus, while the ...

skin infection A skin infection is an infection of the skin in humans and other animals, that can also affect the associated soft tissues such as loose connective tissue and mucous membranes. They comprise a category of infections termed skin and skin structure ...

fungemia Fungemia is the presence of fungi or yeasts in the blood. The most common type, also known as candidemia, candedemia, or systemic candidiasis, is caused by '' Candida'' species; candidemia is also among the most common bloodstream infections of a ...

, and

endophthalmitis Endophthalmitis is inflammation of the interior cavity of the eye, usually caused by infection. It is a possible complication of all intraocular surgeries, particularly cataract surgery, and can result in loss of vision or loss of the eye itself ...

. In immunocompromised patients, ''F. solani'' is one of the most common agents in disseminated and cutaneous infections. Fungal keratitis in the southern USA is most commonly caused by ''F. solani'', as well as ''F. oxysporum''. Cases of fungal keratitis occur most frequently during harvest season as a result of corneal trauma from dust or plant material. Fungal spores come into contact with the damaged cornea and grow. Without treatment, the hyphae can grow into the cornea and into the anterior chamber of the eye. ''F. solani'' is also a major cause of fungal keratitis in HIV positive patients in Africa. ''F. solani'' was implicated in cases of fungal keratitis involving the Bausch and Lomb ReNu contact lens solution. Some strains of ''F. solani'' can produce a biofilm on soft contact lenses. However, when lenses are cleaned correctly with solution, these biofilms are prevented. Prevention also includes leaving lenses in polyhexanide biguanide solution overnight to inhibit ''F. solani''. Other risk factors of contact lens-related ''Fusarium'' keratitis include use of daily-wear lenses beyond the recommended timeline and overnight wear. ''F. solani'' is largely resistant to typical antifungal agents. The most effective antifungals in treating ''F. solani'' infections are

amphotericin B Amphotericin B is an antifungal medication used for serious mycosis, fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candida infections, candidiasis, coccidioidomy ...

and

natamycin Natamycin, also known as pimaricin, is an antifungal medication used to treat fungal infections around the eye. This includes infections of the eyelids, conjunctiva, and cornea. It is used as eyedrops. Natamycin is also used in the food indust ...

; however, these agents have only modest success in the treatment of serious systemic infection.

Other animals

''F. solani'' is implicated in cutaneous infections of young turtles as well as infections of turtle egg shells. It has also caused infections in Australian crocodile farms, sea lions and grey seals. ''F. solani'' is a facultative pathogen of the

castor bean tick ''Ixodes ricinus'', the castor bean tick, is a chiefly European species of hard-bodied tick. It may reach a length of when engorged with a blood meal, and can transmit both bacterial and viral pathogens such as the causative agents of Lyme disea ...

. It is also lethal to southern pine beetles.

Plants

''F. solani'' rots the roots of its host plant. It also causes soft rot of plant tissues by penetrating plant cell walls and destroying the

torus In geometry, a torus (plural tori, colloquially donut or doughnut) is a surface of revolution generated by revolving a circle in three-dimensional space about an axis that is coplanar with the circle. If the axis of revolution does not tou ...

. It is implicated, along with ''

Pythium myriotylum ''Pythium myriotylum'' is a soil-borne oomycete necrotroph that has a broad host range, this means that it can infect a wide range of plants. Hosts and symptoms ''Pythium myriotylum'' is a causal agent of soft root rot in economically important ...

'', in pod rot of the pods of groundnuts. Virulence of this agent in plants is controlled by the

cutinase The enzyme cutinase (systematic name: cutin hydrolase,''EC 3.1.1.74 is a member of the hydrolase family. It catalyzes the following reaction: R1COOR2 + H2O -> R1COOH + R2OH In biological systems, the reactant carboxylic ester is a constituent of ...

genes ''cut1'' and ''cut2''. These genes are upregulated by exposure to the plant’s cutin monomers. ''F. solani'' is known to cause sudden death syndrome in soybeans, and it is also known to cause disease in other economically important crops such as avocado, citrus, orchids,

passion fruit ''Passiflora edulis,'' commonly known as passion fruit, is a vine species of passion flower native to southern Brazil through Paraguay and northern Argentina. It is cultivated commercially in tropical and subtropical areas for its sweet, seedy ...

, peas, peppers, potato, and squash.

Biotechnology

''F. solani'' has been investigated as a biological control for certain plants including leafy spurge,

morning glory Morning glory (also written as morning-glory) is the common name for over 1,000 species of flowering plants in the family Convolvulaceae, whose current taxonomy and systematics are in flux. Morning glory species belong to many genera, some of ...

striga ''Striga'', commonly known as witchweed, is a genus of parasitic plants that occur naturally in parts of Africa, Asia, and Australia. It is currently classified in the family Orobanchaceae, although older classifications place it in the Scrophul ...

gourd Gourds include the fruits of some flowering plant species in the family Cucurbitaceae, particularly ''Cucurbita'' and ''Lagenaria''. The term refers to a number of species and subspecies, many with hard shells, and some without. One of the earli ...

, and

water hyacinth ''Pontederia crassipes'' (formerly ''Eichhornia crassipes''), commonly known as common water hyacinth is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range.solani Fungi described in 1881 Fungal plant pathogens and diseases