''Fusarium oxysporum'' f. sp. ''cubense'' is a

fungal A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

plant pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

that causes

Panama disease Panama disease (or Fusarium wilt) is a plant disease that infects banana plants (''Musa'' spp.). It is a wilting disease caused by the fungus ''Fusarium oxysporum'' f. sp. ''cubense'' (Foc). The pathogen is resistant to fungicides and its cont ...

banana A banana is an elongated, edible fruit – botanically a berry – produced by several kinds of large herbaceous flowering plants in the genus ''Musa''. In some countries, bananas used for cooking may be called "plantains", distinguis ...

(''

Musa Musa may refer to: Places * Mūša, a river in Lithuania and Latvia * Musa, Azerbaijan, a village in Yardymli Rayon * Musa, Iran, a village in Ilam Province * Musa, Chaharmahal and Bakhtiari, Iran *Musa, Kerman, Iran * Musa, Bukan, West Azerbaija ...

'' spp.), also known as fusarium wilt of banana. The fungi and the related disease are responsible for widespread pressure on banana growing regions, destroying the economic viability of several commercially important banana varieties.

Description

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 ...

'' is a common inhabitant of soil and produces three types of asexual

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

s: macroconidia, microconidia and chlamydospores. The

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 nearly straight, slender and thin-walled. They usually have three or four septa, a foot-shaped basal cell and a curved and tapered apical cell. They are generally produced from

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 on

conidiophores 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 ...

basipetal This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...

division. They are important in secondary infection.Couteaudier, Y. and C. Alabouvette, 1990 Survival and inoculum potential of conidia and chlamydospores of ''Fusarium oxysporum'' f. sp. ''lini'' in soil. Can. J. Microbiol. 36:551-556 The

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 ...

are ellipsoidal and have either a single septum or none at all. They are formed from

phialides 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 Mycelium (plural mycelia) is a ...

in false heads by basipetal division. They are important in secondary infection. The chlamydospores are globose with thick walls. They are either formed from

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 or by the modification of hyphal cells. They endure in soils for long periods and act as inocula in primary infection. The macroconidia and chlamydospores are normally only formed on dead or dying host plants. Chlamydospores are the most significant survival structures of this pathogen. The

teleomorph 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 ...

or sexual reproductive stage of ''F. oxysporum'' is unknown. Four races of this pathogen have been described which attack different

banana cultivars The following is a list of banana cultivars and the groups into which they are classified. Almost all modern cultivated varieties (cultivars) of edible bananas and plantains are hybrids and polyploids of two wild, seeded banana species, '' Mus ...

: * Race 1 attacks cultivars in the ''Musa'' (AAA group) 'Gros Michel' and caused the 20th century epidemic. It also attacks ' Ducasse', '

Lady Finger Lady finger(s), ladyfinger(s), lady's finger, or ladies' fingers may refer to: Food * Ladyfinger (biscuit), a type of sponge cake * Ladyfinger, a kirsch cocktail Botany * Okra, or ladies' fingers, a pod vegetable plant * Ladyfinger cactus, a ...

', ''Musa'' (AAB group) 'Pome' and its subgroups, Musa (AAB group) 'Silk' and ''Musa'' (ABB group) 'Pisang Awak'. (See .) * Race 2 attacks ''Musa'' (ABB group) ' Bluggoe' and its close relatives. (See .) * Race 3 attacks ''

Heliconia ''Heliconia'', derived from the Greek word (), is a genus of flowering plants in the monotypic family Heliconiaceae. Most of the ca 194 known species are native to the tropical Americas, but a few are indigenous to certain islands of the we ...

'' spp. (See .) * Race 4 attacks ''Musa'' (AAA group) 'Dwarf Cavendish' as well as the hosts of races 1 and 2.Crop Protection Compendium 2005 Edition. ''Fusarium oxysporum'' f.sp. ''cubense'' (Panama disease of banana). (CAB International: Wallingford, UK). (See .)

Taxonomy

A ribosomal intergenic spacer analysis by Kurtz and Schouten 2009 failed to distinguish some ''F. oxysporum'' isolates merely

endophytic An endophyte is an endosymbiont, often a bacterium or fungus, that lives within a plant for at least part of its life cycle without causing apparent disease. Endophytes are ubiquitous and have been found in all species of plants studied to date; h ...

on ''Musa'' from pathogenic ''Foc'' strains.

Dispersal

Splash by rainfall, movement of contaminated soil, and movement of contaminated propagation materials are the major means of dispersal of ''Foc''. Dispersal by wind alone remains unproven and while animals can test positive for ''Foc'' on their outer surfaces, it remains unproven whether they can be effective

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

s. Although it is a soil-borne pathogen, it does not compete well against other soil microbes for growth on dead buried tissue. It is nonetheless able to produce infection in living ''Musa'' hosts after a complete absence of hosts for 20 years - despite a population decline of 97% within the first three years. This is thought to be due to durable

chlamydospore A chlamydospore is the thick-walled large resting spore of several kinds of fungi, including Ascomycota such as '' Candida'', Basidiomycota such as '' Panus'', and various Mortierellales species. It is the life-stage which survives in unfavourable ...

s and due to persistence as an

asymptomatic In medicine, any disease is classified asymptomatic if a patient tests as carrier for a disease or infection but experiences no symptoms. Whenever a medical condition fails to show noticeable symptoms after a diagnosis it might be considered asy ...

infection.

Infection process

Anigorufone is a

phytoalexin Phytoalexins are antimicrobial substances, some of which are antioxidative as well. They are defined, not by their having any particular chemical structure or character, but by the fact that they are defensively synthesized ''de novo'' by plants t ...

produced by ''Musa''. It is a nematicidal compound and so infection with ''Foc'' induces an anti-nematode defense. Anigorufone is the only nematicidal or nematistatic compound known among the phytoalexins. ''Foc'' rapidly invades cortical cells as do many other ''Fo f.sp.''.

Reproduction

There is some debate as to whether ''Foc'' is sexual and this is investigated by studying its history of recombination - or lack of it. One study of the

linkage disequilibrium In population genetics, linkage disequilibrium (LD) is the non-random association of alleles at different loci in a given population. Loci are said to be in linkage disequilibrium when the frequency of association of their different alleles is h ...

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s showed relatively high disequilibrium and another a high degree of correlation between independent genetic markers, both of which are diagnostic for a lack of recombination and thus a clonal population. Other post-sequencing data analysis performed by the disequilibrium study also ''failed to reject'' recombination however this could be consistent with horizontal transfer. Horizontal transfer has been experimentally induced and appears to have been proven in ''Foc''s past and so seems the more likely explanation. Both ''Fo'' mating types have been observed in ''Foc'' and protoperithecia-like structures are produced, but not the sexual structures. This does not necessarily mean that the sexual process has degenerated however, instead this may be a defect of the experiment. Spores germinate at a higher rate in the presence of ''Musa'' root secondary metabolites from

susceptible Susceptibility may refer to: Physics and engineering In physics the susceptibility is a quantification for the change of an extensive property under variation of an intensive property. The word may refer to: * In physics, the susceptibility of ...

cultivars than those from resistant cultivars. This suggests that inhibition of germination is an important part of host resistance.

Tropical Race 1/TR1

/ is also found in ''

Paspalum ''Paspalum'' is a genus of plants in the grass family. The group is widespread across much of Asia, Africa, Australia, and the Americas. Commonly known as paspalum, bahiagrasses, crowngrasses or dallis grasses, many of the species are tall pere ...

fasciculatum'', ''

Panicum ''Panicum'' (panicgrass) is a large genus of about 450 species of grasses native throughout the tropical regions of the world, with a few species extending into the northern temperate zone. They are often large, annual or perennial grasses, growi ...

purpurescens'', '' Ixophorus unisetus'', and ''

Commelina diffusa ''Commelina diffusa'', sometimes known as the climbing dayflower or spreading dayflower, is a pantropical herbaceous plant in the dayflower family. It has been introduced to the southeastern United States where it is most common in wet disturbed ...

'' in Central America. These weeds may be acting as an inoculum source.

Tropical Race 2/TR2

Tropical Race 3/TR3

/ is a pest of ''

'' ornamental flowers. Formerly reported to be a lesser pest of ''

Musa balbisiana ''Musa balbisiana'', also known simply as plantain, is a wild-type species of banana. It is one of the ancestors of modern cultivated bananas, along with ''Musa acuminata''. Description It grows lush leaves in clumps with a more upright habit th ...

'' seedlings and of

Gros Michel Gros Michel (), often translated and known as "Big Mike", is an export cultivar of banana and was, until the 1950s, the main variety grown. The physical properties of the Gros Michel make it an excellent export produce; its thick peel makes it re ...

, but that is no longer thought to be true. Now renamed ''Fusarium oxysporum'' f. sp. ''heliconiae''.

Race 4

Tropical Race 4/TR4

/ belongs to

vegetative compatibility group Vegetative describes vegetation. Vegetative may also refer to: *Vegetative reproduction, a type of asexual reproduction for plants *Persistent vegetative state, a condition of people with severe brain damage *Plant community A plant community is ...

01213/16. All

cultivars A cultivar is a type of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and when Plant propagation, propagated retain those traits. Methods used to propagate cultivars include: division, root and st ...

which are

to Race 1 and Race 2 are susceptible to TR4 (see and ). Starting in 2019 some authorities are following Maryani ''et al.'', 2019 in regarding this strain as '.

Subtropical Race 4/STR4

/ is a subtropical race and does not become symptomatic on

Cavendish Cavendish may refer to: People * The House of Cavendish, a British aristocratic family * Margaret Cavendish (1623–1673), British poet, philosopher, and scientist * Cavendish (author) (1831–1899), pen name of Henry Jones, English auth ...

until the trees are stressed by cold. Also found in ''

'' spp. and ''

Amaranthus ''Amaranthus'' is a cosmopolitan genus of annual or short-lived perennial plants collectively known as amaranths. Some amaranth species are cultivated as leaf vegetables, pseudocereals, and ornamental plants. Catkin-like cymes of densely pac ...

'' spp. in Australia. These weeds may be acting as sources of inoculum.

Research

Much research is being undertaken because of the urgency in formulating effective control methods for Panama disease and breeding resistant banana cultivars. Researchers at University Sains Malaysia are examining variability in the genome of the pathogen and its genetic variability is being studied, as are the evolutionary relationships within

s of the pathogen. Research into the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

relationships among the different strains of ''F. oxysporum'' that cause wilt of banana has been undertaken to determine whether the strains that are specific to the banana have descended from a common ancestor or have developed independently. Results of this study show that it is not

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

and appears to have multiple

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

ary origins. The largest lineages of ''F. oxysporum ''f. sp.'' cubense'' ( and ) are genetically distinct from a lineage originating from East Africa () and developed pathogenicity for bananas independently from one another. Identification, differentiation, and usage of vegetative compatibility groups is useful and valid within ''Foc'' because there are relatively few VCGs.

References

External links

Information on Fusarium wilt on Musapedia
* * * {{Taxonbar, from=Q5509901 Fungal plant pathogens and diseases Banana diseases oxysporum f.sp. cubense Forma specialis taxa Banana Wars