''Amylostereum'' is the single

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

in the fungal

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Amylostereaceae. The genus currently comprises four

saprotrophic Saprotrophic nutrition or lysotrophic nutrition is a process of chemoheterotrophic extracellular digestion involved in the processing of decayed (dead or waste) organic matter. It occurs in saprotrophs, and is most often associated with fungi ...

and

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

species, which live off living or dead wood. The Amylostereaceae cause

white rot A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as ''Serpula lacrymans'', and some, such as '' Armillaria'' (honey fungus), are par ...

in the wood by disintegrating the tissue component

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 rigidit ...

. They produce crust-like, partially wavy

fruit bodies The sporocarp (also known as fruiting body, fruit body or fruitbody) of fungi is a multicellular structure on which spore-producing structures, such as basidia or asci, are borne. The fruitbody is part of the sexual phase of a fungal life cyc ...

on the surface of infested trees, which are similar to those produced by ''

Stereum ''Stereum'' is the type genus of the Stereaceae family of fungi, in the Russulales order. Common names for species of this genus include leaf fungus, wax fungus, and shelf fungus. Fungi having a shape similar to a ''Stereum'' are said to have a s ...

'' species. There are four described species in the Amylostereaceae: '' A. chailletii'' (the

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

), '' A. areolatum'', '' A. ferreum'' and '' A. laevigatum''. The species were initially considered part of ''Stereum'' until

mycologist Mycology is the branch of biology concerned with the study of fungi, including their taxonomy, genetics, biochemical properties, and use by humans. Fungi can be a source of tinder, food, traditional medicine, as well as entheogens, poison, and ...

Jacques Boidin found atypical microscopic differences between them. Forty years after his extensive researches from 1958, Boidin

reclassified ''Reclassified'' is the reissue of Australian rapper Iggy Azalea's debut studio album, '' The New Classic'' (2014). It was released internationally on 21 November 2014 by Virgin EMI Records, and in the United States on 24 November 2014 by Gran ...

''Amylostereum'' into its own family. Three ''Amylostereum'' species are

symbiont Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biological interaction, between two organisms of different species. The two organisms, termed symbionts, can fo ...

s of

wood wasp Sawflies are wasp-like insects that are in the suborder Symphyta within the order Hymenoptera, alongside ants, bees, and wasps. The common name comes from the saw-like appearance of the ovipositor, which the females use to cut into the plan ...

s in the genera ''

Sirex ''Sirex'' is a genus of sawfly in the family horntail, Siricidae, the horntails or wood wasps. Their bodies are black with a dark blue or green metallic reflection with some species having reddish-brown portions. They inject eggs with fungal e ...

'', ''

Urocerus ''Urocerus'' is a genus of horntails in the family Siricidae. There are about eight described species in ''Urocerus''. Species These species belong to the genus ''Urocerus'': * '' Urocerus albicornis'' ( Fabricius, 1781) (white horned horntail) ...

'', and ''

Xoanon A xoanon (, ; plural: , from the verb , , to carve or scrape ood was a wooden cult image from Archaic Greece. Classical Greeks associated such cult objects, whether aniconic or effigy, with the legendary Daedalus. Many such cult images were p ...

'', which infest

conifer Conifers () are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a sin ...

s. The female wood wasps deposit their eggs together with fungal

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s and mucus in trees, and the fungus is eaten by the wasp's

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

as food. The fungus propagates

vegetatively Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment or Cutting (plant), cutting of the parent pl ...

through the formation of asexual spores in newly emerged females that are stored in special structures adapted for the transport of symbiotic fungi. The ''A. areolatum''–''

Sirex noctilio ''Sirex noctilio'', known as the Midnight woodwasp, European woodwasp, European horntail woodwasp, or sirex woodwasp, is a species of horntail, woodwasp, native to Europe, Asia, and northern Africa.New York State Department of Environmental Cons ...

'' symbiont complex has been studied extensively because of its potential to cause substantial economic losses in the forestry industry, particularly in non-native regions.

Taxonomy and history of research

Amylostereaceae species were for a long time classified in the genus ''

'', based primary on the layered structure of the fruit body and the similar physiological activity. Mycologist

Jacques Boidin Jacques or Jacq are believed to originate from the Middle Ages in the historic northwest Brittany region in France, and have since spread around the world over the centuries. To date, there are over one hundred identified noble families related t ...

separated ''Amylosterum'' from ''Stereum'' in 1958, justifying this decision by explaining that microscopic differences such as

amyloid Amyloids are aggregates of proteins characterised by a fibrillar morphology of typically 7–13 nm in diameter, a β-sheet secondary structure (known as cross-β) and ability to be stained by particular dyes, such as Congo red. In the human ...

spores and encrusted

cystidia A cystidium (: cystidia) is a relatively large cell found on the sporocarp of a basidiomycete (for example, on the surface of a mushroom gill), often between clusters of basidia. Since cystidia have highly varied and distinct shapes that are o ...

were sufficiently distinct to warrant recognition as a new genus. Although the

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

of the genus (today called '' A. chailletii'') was initially named ''Trichocarpus ambiguus'', the name ''Trichocarpus'' had already been used for a genus in the flowering plant family

Malvaceae Malvaceae (), or the mallows, is a family of flowering plants estimated to contain 244 genera with 4225 known species. Well-known members of economic importance include Theobroma cacao, cacao, Cola (plant), cola, cotton, okra, Hibiscus sabdariffa, ...

. Boidin thus chose the genus name ''Amylostereum'', referring to the amyloid spores. Based on

DNA analysis Genetic testing, also known as DNA testing, is used to identify changes in DNA sequence or chromosome structure. Genetic testing can also include measuring the results of genetic changes, such as RNA analysis as an output of gene expression, or ...

, Boidin in 1998 moved ''Amylostereum'' into a new,

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

family, the Amylostereaceae, which he attributed to the Hericiales order. Later studies, however, supported the initial classification in the

Russulales The Russulales are an order of the Agaricomycetes, (which include the agaric genera '' Russula'' and ''Lactarius'' and their polyporoid and corticioid relatives). According to the ''Dictionary of the Fungi'' (10th edition, 2008), the order con ...

Classification

The

classification Classification is the activity of assigning objects to some pre-existing classes or categories. This is distinct from the task of establishing the classes themselves (for example through cluster analysis). Examples include diagnostic tests, identif ...

of the Amylostereaceae is not completely resolved. The next closest relatives might be – depending on the research – either '' Echinodontium tinctorium'' and most other species of the genus '' Echinodontium'', or '' Artomyces pyxidatus''. Most of the previous DNA analysis results suggest a narrow relation to ''Echinodontium'', but several results of studies partially contradict this conclusion. Only the classification to the

is regarded as correct. Some authors have suggested that ''Amylostereum'' should be placed in the family

Echinodontiaceae The Echinodontiaceae are a family of crust fungi in the order Russulales. Species of this family, divided amongst two genera—'' Echinodontium'' and '' Laurilia''—have a widespread distribution, although they are especially predominant in nort ...

. The similarities between ''A. chailletii'' and ''A. areolatum'' have caused some confusion regarding their placement in the genus. As only the size of their fruit bodies differ from each other in appearance, researcher German Josef Krieglsteiner assumed that both are the same species in different age stages. Experiments with

pure culture A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diag ...

s of the fungi, however, showed that the mycelia of ''A. chailletii'', ''A. laevigatum'' and ''A. ferreum'' were partially compatible to each other, but the mycelium of ''A. areolatum'' was incompatible to other species. Boidin believes that the common ancestor of all ''Amylostereum'' fungi used yellowwoods as a host. This genus of conifers was native in Europe until the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

and

Neogene The Neogene ( ,) is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period million years ago. It is the second period of th ...

Periods (66 million to 2.6 million years ago), but became extinct there, so the ''Amylostereum'' fungi specialized on other conifers and differentiated into several species. Only ''A. ferreum'' specialized on yellowwoods in South America. Compatibility tests as well as

molecular A molecule is a group of two or more atoms that are held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemistry, ...

analysis indicated that ''A. areolatum'' separated very early from other ''Amylostereum'' fungi. The other three species separated later from each other and are thus partially compatible to each other. ''A. ferreum'' and ''A. laevigatum'' produced in 59% of all cases a common mycelium, ''A. ferreum'' and ''A. chailletii'' only in 44%. There is an undescribed species in ''Amylostereum''; according to DNA analysis, it stands between ''A. laevigatum'' and ''A. ferreum''. This is remarkable, as these fungi originated from Mycetangae (storing organs of

Platypodinae Platypodinae is a weevil subfamily in the family Curculionidae. They are important early decomposers of dead woody plant material in wet tropics; all but two species are ambrosia beetles that cultivate fungi in tunnels excavated in dead wood as t ...

) of a North American wood wasp, while ''A. laevigatum'' has never been seen as symbiont of wood wasps, neither in North American nor in Europe. The fungus possibly represents a separated species or a sub

taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

of ''A. laevigatum''. As ''A. areolatum'' and ''A. chailletii'' mainly reproduce asexually through the symbiosis of wood wasps, the

genetic variability Genetic variability is either the presence of, or the generation of, genetic differences. It is defined as "the formation of individuals differing in genotype, or the presence of genotypically different individuals, in contrast to environmentally ...

within these species is relatively low.

Description

Macroscopic

The Amylostereaceae produce crust-like, dry and leathery-corky fruit bodies on the bark of infested trees. The fruit bodies are thick, irregularly shaped and are able to cover a large surface on the bark or otherwise can appear as small spots. They lie directly on the bark. The ochrous, grey or brownish fruit body (

hymenium The hymenium is the tissue layer on the hymenophore of a fungal fruiting body where the cells develop into basidia or asci, which produce spores. In some species all of the cells of the hymenium develop into basidia or asci, while in oth ...

) has a smooth to warty surface texture and is turned outwards. It is bordered by a highly bent and wavy (effuso-reflex) edge on all species except ''A. laevigatum'', which has a churlish surface (a

tomentum {{Short pages monitor ''A. ferreum'' is the only ''Amylosterum'' species that has not been associated with any woodwasps.

Host spectrum

The

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

spectrum of the Amylostereaceae comprises several, partially very different genera of Coniferae. ''A. chailletii'' usually infests

Pinaceae The Pinaceae (), or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as Cedrus, cedars, firs, Tsuga, hemlocks, Pinyon_pine, piñons, larches, pines and spruces. The family is incl ...

such as

fir Firs are evergreen coniferous trees belonging to the genus ''Abies'' () in the family Pinaceae. There are approximately 48–65 extant species, found on mountains throughout much of North and Central America, Eurasia, and North Africa. The genu ...

s (''Abies'') and

spruce A spruce is a tree of the genus ''Picea'' ( ), a genus of about 40 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Northern hemisphere. ''Picea'' ...

s (''Picea''), but also cedars (''Cedrus'') and

Douglas fir The Douglas fir (''Pseudotsuga menziesii'') is an evergreen conifer species in the pine family, Pinaceae. It is the tallest tree in the Pinaceae family. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Or ...

s (''Pseudotsuga''). ''A. areolatum'' has a similar host spectrum, which uses mainly firs,

Japanese cedar ''Cryptomeria'' (literally "hidden parts") is a monotypic genus of conifer in the cypress family Cupressaceae. It includes only one species, ''Cryptomeria japonica'' ( syn. ''Cupressus japonica'' L.f.). It is considered to be endemic to Japan, ...

s (''Cryptomeria''),

larch Larches are deciduous conifers in the genus ''Larix'', of the family Pinaceae (subfamily Laricoideae). Growing from tall, they are native to the cooler regions of the northern hemisphere, where they are found in lowland forests in the high la ...

es (''Larix''), spruces,

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. ''World Flora Online'' accepts 134 species-rank taxa (119 species and 15 nothospecies) of pines as cu ...

s (''Pinus'') and Douglas firs as hosts. While spruces dominate as hosts in the native habitat, this species is more common in pines on other locations. The host spectrum of ''A. laevigatum'' comprises

Cupressaceae Cupressaceae or the cypress family is a family of conifers. The family includes 27–30 genera (17 monotypic), which include the junipers and redwoods, with about 130–140 species in total. They are monoecious, subdioecious or (rarely) dioecio ...

such as

juniper Junipers are coniferous trees and shrubs in the genus ''Juniperus'' ( ) of the cypress family Cupressaceae. Depending on the taxonomy, between 50 and 67 species of junipers are widely distributed throughout the Northern Hemisphere as far south ...

s (''Juniperus'') or

cypress Cypress is a common name for various coniferous trees or shrubs from the ''Cupressus'' genus of the '' Cupressaceae'' family, typically found in temperate climates and subtropical regions of Asia, Europe, and North America. The word ''cypress'' ...

es (''Cupressus'') and the English yew (''Taxus baccata''). ''A. ferreum'' is, however, only common on neotropic yellowwoods (''Podocarpus'').

Symptoms of infestation

The Amylostereaceae are

pathogens. They disintegrate the

of the host wood, whereby the infested wood parts become less stable and take a fibrous structure. The wood bleaches as fungal enzymes break down and remove the brown-

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

ed lignin. The distribution in wood takes place mainly along the transport channels in the

xylem Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...

. If the wood is crosscut, the

red rot Red rot is a degradation process found in vegetable-tanned leather. Red rot is caused by prolonged storage or exposure to high relative humidity, environmental pollution, and high temperature. In particular, red rot occurs at pH values of 4.2 ...

is vertically positioned, on which bleached, infested areas contrast with intact wood. Symptoms of infestion by the symbiotic partner—wood wasps—include circular exit holes in the crust and acute stress through dryness, common in hanging, falling or tanning needles.

Ecological and economical importance

In their native habitat, all ''Amylostereum'' species have a minor importance as forest pests. The infestation through wood wasps does not assume greater dimensions and is, compared with other pests, almost insignificant. The infection rates are even lower during sexual reproduction via fruit bodies, as the wasps do not play a part in the process. Furthermore, the ''Amylostereum'' fungi are alone often incapable of infesting healthy trees. They thus mostly act as

saprobiontic Saprobionts are organisms that digest their food externally and then absorb the products. This process is called saprotrophic nutrition. Fungi are examples of saprobiontic organisms, which are a type of decomposer. Saprobiontic organisms feed off ...

s. Pine monocultures in Australia, New Zealand, Africa and South America were shown to be susceptible to the Sirex woodwasp (''

''), which was introduced there and which is associated with ''A. areolatum''. The wasp's phytotoxic secretion, its larvae and the fungus combine very effectively with each other and contribute to forest decline rates of up to 80%. This is mainly owing to the poor water and nutrient supply of the trees, which can poorly reconcile the

drought stress In botany, drought tolerance is the ability by which a plant maintains its biomass production during arid or drought conditions. Some plants are naturally adapted to dry conditions'','' surviving with protection mechanisms such as desiccation tole ...

caused by infestation. ''S. noctilio'' was detected in North America in the 2000s (decade); in Canada alone, the total economic loss to the forestry industry caused by the ''Sirex''–''Amylostereum'' symbiosis could be as high as $254 million per year for the next 20 years. As a countermeasure, cultures of the

nematode The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (h ...

'' Deladenus siricidicola'' have been used as

biological control Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or o ...

to protect trees since the 1980s. This

parasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

feeds on the mycelia of ''A. areolatum'' and is therefore a food competitor of wood wasp larvae. Where ''S. noctilio'' larvae are present, the parasite infects and sterilizes the eggs of female wasps, causing them to be

infertile In biology, infertility is the inability of a male and female organism to reproduce. It is usually not the natural state of a healthy organism that has reached sexual maturity, so children who have not undergone puberty, which is the body's sta ...

. These infertile females lay infected eggs into new trees and thus spread the nematode. This control method has proven to be relatively successful to combat the ''Sirex''–''Amylostereum'' complex. In the Southern Hemisphere, where the technique has been widely employed, reductions of parasitism levels of 70%–100% have been achieved.

References

;Further reading * * *

External links

{{Authority control Parasitic fungi Russulales Russulales genera