Mycelial cord

Last updated
The mycelial cords found under a rotting log Hyphae.JPG
The mycelial cords found under a rotting log

Mycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae. Cords may look similar to plant roots, and also frequently have similar functions; hence they are also called rhizomorphs (literally, "root-forms"). As well as growing underground or on the surface of trees and other plants, some fungi make mycelial cords which hang in the air from vegetation. [1]

Contents

Mycelial cords are capable of conducting nutrients over long distances. For instance, they can transfer nutrients to a developing fruiting body, or enable wood-rotting fungi to grow through soil from an established food base in search of new food sources. For parasitic fungi, they can help spread infection by growing from established clusters to uninfected parts. The cords of some wood-rotting fungi (like Serpula lacrymans ) may be capable of penetrating masonry.

The mechanism of the cord formation is not yet precisely understood. Mathematical models suggest that some fields or gradients of signalling chemicals, parallel to the cord axis, may be involved.

Rhizomorphs can grow up to 9 m (30 ft) in length and 5 mm (0.20 in) in diameter. [2]

Rhizomorph

Unmelanized rhizomorphs of Desarmillaria tabescens in Malt yeast extract medium Desarmillaria.png
Unmelanized rhizomorphs of Desarmillaria tabescens in Malt yeast extract medium

Rhizomorphs are a special morphological adaptation root-like structures found in fungi. These root-like structures are composed of parallel-oriented hyphae that can be found in several species of wood-decay and ectomycorrhizal basidiomycete as well as ascomycete fungi. [3] Rhizomorphs can facilitate the colonization of some dry-rot fungi such as Serpula lacrymans and Meruliporia incrassata and cause damage to homes in Europe and North America, respectively, by decaying wood. [4] Another genus that is very well studied for their abundance of rhizomorphs production is Armillaria , with some species being pathogens and others saprotrophs of trees and shrubs. [5]

Known for their role in facilitating the spread and colonization of fungi in the environment, rhizomorphs are the most complex organs produced by fungi. They are made up of highly specialized hyphae that are different in size, orientation, and function. [6] Fungi that possess these structures can compete and grow in harsh conditions. [7]

Rhizomorphs are sometimes called mycelial cords, although they are structurally different; mycelial cords are less complex and have a loose network of hyphae giving an appearance of a fan-like mat. [6] While rhizomorphs are more complex organs that have apically dominant growth tips. [4] water-resistant surfaces and can transport oxygen. Rhizomorphs and mycelial cords both function in nutrient transport, water absorption, translocation and colonization of substrates. [6]

Development and morphology of rhizomorphs

The development of rhizomorphs begins with a submerged thallus that produces mycelium (hyphae biomass) that when deprived of nutrients and exposed to increasing oxygen, morphogenesis occurs giving rise to pseudo or microsclerotia (survival structures of some fungi), which precede rhizomorph development. [8] Concentrations of oxygen play an important role in the production of rhizomorphs. When there is a high concentration of oxygen in the atmosphere, soil moisture, temperature and pH, rhizomorph production increases. [9]

Rhizomorphs contain four differentiated types of tissues:

  1. The outer layers are a compact growing point that make up the mucilage
  2. The melanized wall that serves as protection against colonization by another microorganisms (bacteria or fungi)
  3. The medulla that serves for conduction of water and dissolved nutrients
  4. The central line used as an air conducting channel. [7]

Rhizomorphs can be of a cylindrical or flat type, and melanized or unmelanized, respectively. [3] The flat unmelanized type is more common under the bark of trees and the cylindrical melanized rhizomorph can be found in the root systems of trees. [3] For example, species of Armillaria form melanized (dark or brown due to the formation of melanin) rhizomorphs in nature with the exception of Desarmillaria tabescens (formerly, Armillaria tabescens ) which produces unmelanized rhizomorphs in culture. [10]

Function

Rhizomorphs act as a system of underground absorption and growth structures that invade and decay roots and wood, [11] as well as sometimes propagating through the air. [1] They can access places where food resources are not available, [7] giving certain advantages to the fungi that produce them in terms of competition. [11] They act as an extension of the fungal body and allow the fungus to infect, disseminate and survive for long periods of time. [7] Rhizomorphs are composed of a medulla and central line which are responsible for water, nutrient, and gas transportation. [7] The transportation of oxygen occurs from the base of rhizomorphs to the terminal growing part (tips). Rhizomorphs that live under free oxygen conditions are able to absorb and transport nutrients. [7]

Example taxa

Armillaria cords Rhizomorph Armillaria.jpg
Armillaria cords
Aerial rhizomorphs of Brunneocorticium corynecarpon Brunneocorticium corynecarpon 580927.jpg
Aerial rhizomorphs of Brunneocorticium corynecarpon

Evolution of rhizomorphs in Armillaria species

The genus Armillaria is a well-studied and widely distributed mushroom-forming genus with rhizomorph production abundant in most species. One of the more common morphological characteristics for the genus is the presence of an annulus, which is a ring-like structure in the stem of the fruiting body with exception of the species Desarmillaria tabescens. [8] This species is known to produce unmelanized rhizomorphs in-vitro, but it does not produce them in nature. [12] In a controlled environment study with high levels of oxygen and saturated soil moisture content, Desarmillaria species produces melanized rhizomorphs [13] However, these two conditions are difficult to find in the climate of today and could explain the lack of melanized rhizomorphs in nature and could be a carryover from previous evolutionary periods. [8]

Rhizomorph traits can be found in all species of the Armillaria as well as other fungi but it appears that the most recently diverged species are adapted to form melanized rhizomorphs. Melanin in rhizomorphs are known for the absorption of metal ions from the soil and can be found in different structures such as spores and cell walls of fungi among others. Functions of melanin also include protecting against UV radiation and moisture stress. [14] Thus melanin production aids in longevity and survival of rhizomorphs in the soil. [14]

Aerial rhizomorphs in the Marasmiaceae

Brunneocorticium corynecarpon is a fungus known only from its branched white aerial rhizomorphs which grow in tropical forest canopies. DNA analysis has shown it to belong in the Marasmiaceae (normally a mushroom-forming family), but no fruiting bodies or other fertile structures of it have been found. [1]

Marasmius crinis-equi ("Horse-hair fungus") is another species which generates aerial rhizomorphs, but these often have tiny mushrooms branching out from them. [1]

Related Research Articles

<span class="mw-page-title-main">Mycelium</span> Vegetative part of a fungus

Mycelium is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates into a monokaryotic mycelium, which cannot reproduce sexually; when two compatible monokaryotic mycelia join and form a dikaryotic mycelium, that mycelium may form fruiting bodies such as mushrooms. A mycelium may be minute, forming a colony that is too small to see, or may grow to span thousands of acres as in Armillaria. The network of mycelium acts similar to human brains, in the way that mycelium is used to send electrical signals to the fruiting bodies of mushrooms. These electrical signals can be used to convey information or warn about incoming danger.

<span class="mw-page-title-main">Hypha</span> Long, filamentous structure in fungi and Actinobacteria

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.

<i>Armillaria</i> Genus of fungi

Armillaria is a genus of fungi that includes the A. mellea species known as honey fungi that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as A. mellea. Armillarias are long-lived and form the largest living fungi in the world. The largest known organism covers more than 3.4 square miles (8.8 km2) in Oregon's Malheur National Forest and is estimated to be 2,500 years old. Some species of Armillaria display bioluminescence, resulting in foxfire.

<i>Armillaria mellea</i> Species of fungus

Armillaria mellea, commonly known as honey fungus, is an edible basidiomycete fungus in the genus Armillaria. It is a plant pathogen and part of a cryptic species complex of closely related and morphologically similar species. It causes Armillaria root rot in many plant species and produces mushrooms around the base of trees it has infected. The symptoms of infection appear in the crowns of infected trees as discoloured foliage, reduced growth, dieback of the branches and death. The mushrooms are edible but some people may be intolerant to them. This species is capable of producing light via bioluminescence in its mycelium.

<i>Armillaria luteobubalina</i> Species of fungus in the family Physalacriaceae.

Armillaria luteobubalina, commonly known as the Australian honey fungus, is a species of mushroom in the family Physalacriaceae. Widely distributed in southern Australia, the fungus is responsible for a disease known as Armillaria root rot, a primary cause of Eucalyptus tree death and forest dieback. It is the most pathogenic and widespread of the six Armillaria species found in Australia. The fungus has also been collected in Argentina and Chile. Fruit bodies have cream- to tan-coloured caps that grow up to 10 cm (4 in) in diameter and stems that measure up to 20 cm (8 in) long by 1.5 cm (1 in) thick. The fruit bodies, which appear at the base of infected trees and other woody plants in autumn (March–April), are edible, but require cooking to remove the bitter taste. The fungus is dispersed through spores produced on gills on the underside of the caps, and also by growing vegetatively through the root systems of host trees. The ability of the fungus to spread vegetatively is facilitated by an aerating system that allows it to efficiently diffuse oxygen through rhizomorphs—rootlike structures made of dense masses of hyphae.

<i>Armillaria tabescens</i> Species of fungus

Armillaria tabescens is a species of fungus in the family Physalacriaceae. It is a plant pathogen. The mycelium of the fungus is bioluminescent.

<span class="mw-page-title-main">Radiotrophic fungus</span> Fungus that is claimed to use ionizing radiation as an energy source

Radiotrophic fungi are fungi that can perform the hypothetical biological process called radiosynthesis, which means using ionizing radiation as an energy source to drive metabolism. It has been claimed that radiotrophic fungi have been found in extreme environments such as in the Chernobyl Nuclear Power Plant.

<i>Armillaria fuscipes</i> Species of fungus

Armillaria fuscipes is a plant pathogen that causes Armillaria root rot on Pinus, coffee plants, tea and various hardwood trees. It is common in South Africa. The mycelium of the fungus is bioluminescent.

<i>Armillaria novae-zelandiae</i> Species of fungus

Armillaria novae-zelandiae is a species of mushroom-forming fungus in the family Physalacriaceae. This plant pathogen species is one of three Armillaria species that have been identified in New Zealand.

<i>Armillaria gallica</i> Species of fungus in the family Physalacriaceae

Armillaria gallica is a species of honey mushroom in the family Physalacriaceae of the order Agaricales. The species is a common and ecologically important wood-decay fungus that can live as a saprobe, or as an opportunistic parasite in weakened tree hosts to cause root or butt rot. It is found in temperate regions of Asia, North America, and Europe. The species forms fruit bodies singly or in groups in soil or rotting wood. The fungus has been inadvertently introduced to South Africa. Armillaria gallica has had a confusing taxonomy, due in part to historical difficulties encountered in distinguishing between similar Armillaria species. The fungus received international attention in the early 1990s when an individual colony living in a Michigan forest was reported to cover an area of 15 hectares, weigh at least 9.5 tonnes, and be 1,500 years old. This individual is popularly known as the "humongous fungus", and is a tourist attraction and inspiration for an annual mushroom-themed festival in Crystal Falls. Recent studies have revised the fungus's age to 2,500 years and its size to about 400 tonnes, four times the original estimate.

<i>Armillaria</i> root rot Fungal tree disease

Armillaria root rot is a fungal root rot caused by several different members of the genus Armillaria. The symptoms are variable depending on the host infected, ranging from stunted leaves to chlorotic needles and dieback of twigs and branches. However, all infected hosts display symptoms characteristic of being infected by a white rotting fungus. The most effective ways of management focus on limiting the spread of the fungus, planting resistant species, and removing infected material. This disease poses a threat to the lumber industry as well as affecting recreational areas.

<i>Armillaria ostoyae</i> Species of fungus

Armillaria ostoyae is a species of fungus (mushroom), pathogenic to trees, in the family Physalacriaceae. In the western United States, it is the most common variant of the group of species under the name Armillaria mellea. A. ostoyae is common on both hardwood and conifer wood in forests west of the Cascade Range in Oregon, United States. It has decurrent gills and the stipe has a ring. The mycelium invades the sapwood and is able to disseminate over great distances under the bark or between trees in the form of black rhizomorphs ("shoestrings"). In most areas of North America, Armillaria ostoyae can be separated from other species by its physical features: cream-brown colors, prominent cap scales, and a well-developed stem ring distinguish it from other Armillaria. Like several other Armillaria, the mycelium of Armillaria ostoyae can display bioluminescence, resulting in foxfire.

<span class="mw-page-title-main">Nidulariaceae</span> Family of fungi

The Nidulariaceae are a family of fungi in the order Agaricales. Commonly known as the bird's nest fungi, their fruiting bodies resemble tiny egg-filled birds' nests. As they are saprobic, feeding on decomposing organic matter, they are often seen growing on decaying wood and in soils enriched with wood chips or bark mulch; they have a widespread distribution in most ecological regions. The five genera within the family, namely, Crucibulum, Cyathus, Mycocalia, Nidula, and Nidularia, are distinguished from each other by differences in morphology and peridiole structure; more recently, phylogenetic analysis and comparison of DNA sequences is guiding new decisions in the taxonomic organization of this family.

<span class="mw-page-title-main">Ectomycorrhiza</span> Non-penetrative symbiotic association between a fungus and the roots of a vascular plant

An ectomycorrhiza is a form of symbiotic relationship that occurs between a fungal symbiont, or mycobiont, and the roots of various plant species. The mycobiont is often from the phyla Basidiomycota and Ascomycota, and more rarely from the Zygomycota. Ectomycorrhizas form on the roots of around 2% of plant species, usually woody plants, including species from the birch, dipterocarp, myrtle, beech, willow, pine and rose families. Research on ectomycorrhizas is increasingly important in areas such as ecosystem management and restoration, forestry and agriculture.

<span class="mw-page-title-main">Ectomycorrhizal extramatrical mycelium</span>

Ectomycorrhizal extramatrical mycelium is the collection of filamentous fungal hyphae emanating from ectomycorrhizas. It may be composed of fine, hydrophilic hypha which branches frequently to explore and exploit the soil matrix or may aggregate to form rhizomorphs; highly differentiated, hydrophobic, enduring, transport structures.

Dark septate endophytes (DSE) are a group of endophytic fungi characterized by their morphology of melanized, septate, hyphae. This group is likely paraphyletic, and contain conidial as well as sterile fungi that colonize roots intracellularly or intercellularly. Very little is known about the number of fungal taxa within this group, but all are in the Ascomycota. They are found in over 600 plant species and across 114 families of angiosperms and gymnosperms and co-occur with other types of mycorrhizal fungi. They have a wide global distribution and can be more abundant in stressed environments. Much of their taxonomy, physiology, and ecology are unknown.

<i>Cladophialophora carrionii</i> Species of fungus

Cladophialophora carrionii is a melanized fungus in the genus Cladophialophora that is associated with decaying plant material like cacti and wood. It is one of the most frequent species of Cladophialophora implicated in human disease. Cladophialophora carrionii is a causative agent of chromoblastomycosis, a subcutaneous infection that occurs in sub-tropical areas such as Madagascar, Australia and northwestern Venezuela. Transmission occurs through traumatic implantation of plant material colonized by C. carrionii, mainly infecting rural workers. When C. carrionii infects its host, it transforms from a mycelial state to a muriform state to better tolerate the extreme conditions in the host's body.

<i>Cladosporium sphaerospermum</i> Species of fungus

Cladosporium sphaerospermum is a radiotrophic fungus belonging to the genus Cladosporium and was described in 1886 by Albert Julius Otto Penzig from the decaying leaves and branches of Citrus. It is a dematiaceous (darkly-pigmented) fungus characterized by slow growth and largely asexual reproduction. Cladosporium sphaerospermum consists of a complex of poorly morphologically differentiated, "cryptic" species that share many physiological and ecological attributes. In older literature, all of these sibling species were classified as C. sphaerospermum despite their unique nature. Accordingly, there is confusion in older literature reports on the physiological and habitat regularities of C. sphaerospermum in the strict sense. This fungus is most phylogenetically similar to C. fusiforme. According to modern phylogenetic analyses, the previously synonymized species, Cladosporium langeroni, is a distinct species.

<i>Rhizomorpha</i> Genus of fungi

Rhizomorpha is a genus of fungi that was created for species known only by their mycelial cords ("rhizomorphs") and so impossible to classify within the normal taxonomic system, which is based on reproductive structures.

References

  1. 1 2 3 4 Koch RA, Lodge DJ, Sourell S, Nakasone K, McCoy AG, Aime MC (2018). "Tying up loose threads: revised taxonomy and phylogeny of an avian-dispersed Neotropical rhizomorph-forming fungus". Mycological Progress. 17 (9): 989–998. doi: 10.1007/s11557-018-1411-8 .
  2. ↑ Isaac S (May 1995). "What are fungal cords, strands and rhizomorphs and how are they of benefit to the fungus?" (PDF). Mycologist. 9 (2): 90–91. doi:10.1016/S0269-915X(09)80223-1. Archived from the original (PDF) on 2 April 2015.
  3. 1 2 3 Webster J, Weber R (2007). Introduction to Fungi. Cambridge: Cambridge University Press. doi:10.1017/cbo9780511809026. ISBN   9780511809026.
  4. 1 2 Yafetto L, Davis DJ, Money NP (September 2009). "Biomechanics of invasive growth by Armillaria rhizomorphs". Fungal Genetics and Biology. 46 (9): 688–94. doi:10.1016/j.fgb.2009.04.005. PMID   19427390.
  5. ↑ Sinclair WA, Lyon HH (2005). Diseases of Trees and Shrubs (2nd ed.). Comstock Publishing Associates (Verlag). doi:10.1111/j.1365-3059.2006.01404.x. ISBN   978-0-8014-4371-8.
  6. 1 2 3 Yafetto L (January 2018). "The structure of mycelial cords and rhizomorphs of fungi: A mini-review" (PDF). Mycosphere. 9 (5): 984–98. doi: 10.5943/mycosphere/9/5/3 .
  7. 1 2 3 4 5 6 Shaw CG, Kile GA (1991). "Armillaria Root Disease". Mycologia. Agriculture Handbook. Washington, D.C.: Forest Service, U.S. Dept. of Agriculture. 691 (2): 270–271. doi:10.2307/3760266. JSTOR   3760266.
  8. 1 2 3 Lopez-Real JM, Swift MJ (1977). "Formation of pseudosclerotia ('zone lines') in wood decayed by Armillaria mellea and Stereum hirsutum". Transactions of the British Mycological Society. 68 (3): 321–325. doi:10.1016/s0007-1536(77)80183-6.
  9. ↑ Rishbeth J (1978). "Effects of soil temperature and atmosphere on growth of Armillaria rhizomorphs". Transactions of the British Mycological Society. 70 (2): 213–220. doi:10.1016/s0007-1536(78)80033-3.
  10. ↑ Koch RA, Wilson AW, Séné O, Henkel TW, Aime MC (January 2017). "Resolved phylogeny and biogeography of the root pathogen Armillaria and its gasteroid relative, Guyanagaster". BMC Evolutionary Biology. 17 (1): 33. doi: 10.1186/s12862-017-0877-3 . PMC   5264464 . PMID   28122504.
  11. 1 2 Townsend BB (1954). "Morphology and development of fungal Rhizomorphs". Transactions of the British Mycological Society. 37 (3): 222–233. doi:10.1016/s0007-1536(54)80004-0.
  12. ↑ Henkel TW, Smith ME, Aime MC (September 2010). "Guyanagaster, a new wood-decaying sequestrate fungal genus related to Armillaria (Physalacriaceae, Agaricales, Basidiomycota)". American Journal of Botany. 97 (9): 1474–84. doi:10.3732/ajb.1000097. hdl: 10161/4195 . PMID   21616901.
  13. ↑ Mihail JD, Bruhn JN, Leininger TD (June 2002). "The effects of moisture and oxygen availability on rhizomorph generation by Armillaria tabescens in comparison with A. gallica and A. mellea". Mycological Research. 106 (6): 697–704. doi:10.1017/s0953756202005920.
  14. 1 2 Rizzo DM, Blanchette RA, Palmer MA (August 1992). "Biosorption of metal ions by Armillaria rhizomorphs". Canadian Journal of Botany. 70 (8): 1515–1520. doi:10.1139/b92-190.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.