Basidiomycota is one of two large
phylaIn biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
that, together with the
AscomycotaThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...
, comprise the subkingdom
DikaryaDikarya is a subkingdom of Fungi that includes the phyla Ascomycota and Basidiomycota, both of which in general produce dikaryons, may be filamentous or unicellular, but are always without flagella. The Dikarya are most of the so called "higher fungi", but also include many anamorphic species that...
(often referred to as the
"higher fungi") within the Kingdom Fungi. More specifically the Basidiomycota include these groups:
mushroomA mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
s,
puffballA puffball is a member of any of several groups of fungus in the division Basidiomycota. The puffballs were previously treated as a taxonomic group called the Gasteromycetes or Gasteromycetidae, but they are now known to be a polyphyletic assemblage. The distinguishing feature of all puffballs is...
s, stinkhorns,
bracket fungiBracket fungi, or shelf fungi, among many groups of the fungi in the phylum Basidiomycota. Characteristically, they produce shelf- or bracket-shaped fruiting bodies called conks that lie in a close planar grouping of separate or interconnected horizontal rows...
, other
polyporePolypores are a group of tough, leathery poroid mushrooms similar to boletes, but typically lacking a distinct stalk. The technical distinction between the two types of mushrooms is that polypores do not have the spore-bearing tissue continuous along the entire underside of the mushroom. Many...
s, jelly fungi,
boleteA bolete is a type of fungal fruiting body characterized by the presence of a pileus that is clearly differentiated from the stipe, with a spongy surface of pores on the underside of the pileus...
s,
chanterellesCantharellus is a genus of popular edible mushrooms, commonly known as chanterelles . They are mycorrhizal fungi, meaning they form symbiotic associations with plants, making them very difficult to cultivate...
,
earth starsThe earthstars are the family Geastraceae of gasterocarpic basidiomycetes . It includes the genera Geastrum and Myriostoma. About sixty-four species are classified in this family, divided among eight genera....
,
smutsThe smuts are multicellular fungi, that are characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease...
,
buntsCommon bunt, also known as stinking smut and covered smut is a disease of both spring and winter wheats. It is caused by two very closely related fungi, Tilletia tritici and T. laevis Common bunt, also known as stinking smut and covered smut is a disease of both spring and winter wheats. It is...
,
rustsRusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing...
, mirror yeasts, and the human pathogenic yeast
CryptococcusCryptococcus is a genus of fungus. Species grow in culture as yeasts. The perfect forms or teleomorphs of Cryptococcus species are filamentous fungi in the genus Filobasidiella...
. Basically, Basidiomycota are filamentous fungi composed of
hyphaA hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
e (except for yeasts), and reproducing sexually via the formation of specialized club-shaped end
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s called
basidiathumb|right|500px|Schematic showing a basidiomycete mushroom, gill structure, and spore-bearing basidia on the gill margins.A basidium is a microscopic, spore-producing structure found on the hymenophore of fruiting bodies of basidiomycete fungi. The presence of basidia is one of the main...
that normally bear external
meiosporeMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
s (usually four). These specialized
sporeIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s are called
basidiosporeA basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. In grills under a cap of one common species in the phylum of...
s. However, some Basidiomycota reproduce asexually in addition or exclusively. Basidiomycota that reproduce asexually (discussed below) can be recognized as members of this phylum by gross similarity to others, by the formation of a distinctive anatomical feature (the
clamp connectionA clamp connection is a structure formed by growing hyphal cells of certain fungi. It is created to ensure each septum, or segment of hypha separated by crossed walls, receives a set of differing nuclei, which are obtained through mating of hyphae of differing sexual types...
- see below),
cell wallThe cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
components, and definitively by phylogenetic molecular analysis of
DNA sequenceThe sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
data.
Classification
The most recent classification adopted by a coalition of 67 mycologists recognizes three subphyla (
PucciniomycotinaPucciniomycotina is a subdivision of fungus within the division Basidiomycota. According to the Dictionary of the Fungi, the subdivision contains 8 classes, 18 orders, and 36 families.-References:...
,
UstilaginomycotinaUstilaginomycotina refers to a subphylum within the phylum Basidiomycota of the kingdom Fungi, consisting of the classes Entorrhizomycetes, Ustilaginomycetes, Exobasidiomycetes and the order Malassezia.-External links:*...
,
AgaricomycotinaThe subphylum Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota . The Agaricomycotina contain some 20,000 species, and about 98% of these are in the class Agaricomycetes: most of the fungi known as mushrooms, including the bracket fungi and...
) and two other class level taxa (
WallemiomycetesThe Wallemiomycetes are a class of fungi in the Basidiomycota division. It consists of the single order Wallemiales, containing the single family Wallemiaceae, which in turn contains the single genus Wallemia...
,
EntorrhizomycetesThe Entorrhizomycetes are a class of fungi in the Basidiomycota phylum. It contains the single order Entorrhizales, which in turn contains the single family Entorhizaceae, a small group of teliosporic root parasites that form galls on plants in the Juncaceae and Cyperaceae families....
) outside of these, among the Basidiomycota. As now classified, the subphyla join and also cut across various obsolete taxonomic groups (see below) previously commonly used to describe Basidiomycota. According to a 2008 estimate, Basidiomycota comprise three subphyla (including six unassigned classes) 16 classes, 52 orders, 177 families, 1,589 genera, and 31,515 species.
Traditionally, the Basidiomycota were divided into two classes, now obsolete:
- Homobasidiomycetes
Agaricomycetes is a class of fungi. The taxon is roughly identical to that defined for the Homobasidiomycetes by Hibbett & Thorn, with the inclusion of Auriculariales and Sebacinales. It includes not only mushrooms but also most species placed in the deprecated taxa Gasteromycetes and...
, including true mushroomA mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
s
- Heterobasidiomycetes, including the jelly, rust
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing...
and smutThe smuts are multicellular fungi, that are characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease...
fungi
Previously the entire Basidiomycota were called
Basidiomycetes, an invalid class level name coined in 1959 as a counterpart to the
AscomycetesThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...
, when neither of these taxa were recognized as phyla. The terms basidiomycetes and ascomycetes are frequently used loosely to refer to Basidiomycota and Ascomycota. They are often abbreviated to "basidios" and "ascos" as mycological slang.
Agaricomycotina
The
AgaricomycotinaThe subphylum Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota . The Agaricomycotina contain some 20,000 species, and about 98% of these are in the class Agaricomycetes: most of the fungi known as mushrooms, including the bracket fungi and...
include what had previously been called the Hymenomycetes (an obsolete morphological based class of Basidiomycota that formed hymenial layers on their fruitbodies), the Gasteromycetes (another obsolete class that included species mostly lacking hymenia and mostly forming spores in enclosed fruitbodies), as well as most of the
jelly fungiThe class Heterobasidiomycetes or jelly fungi is a paraphyletic group of several fungal orders: Tremellales, Auriculariales, Dacrymycetales. These fungi are so named because their foliose to irregularly branched fruiting body is, or appears to be, the consistency of jelly. Actually, many are...
. The three classes in the Agaricomycotina are the
AgaricomycetesAgaricomycetes is a class of fungi. The taxon is roughly identical to that defined for the Homobasidiomycetes by Hibbett & Thorn, with the inclusion of Auriculariales and Sebacinales. It includes not only mushrooms but also most species placed in the deprecated taxa Gasteromycetes and...
, the
DacrymycetesThe Dacrymycetes are a class consisting of only one family of jelly fungi, which has imperforate parenthesomes and basidia that are usually branched. There are 9 genera and 101 species in the Dacrymycetaceae family.-References:...
, and the
TremellomycetesThe Tremellomycetes are a class of dimorphic fungi. Some species have a gelatinous fruiting body or a sacculate parenthesome. There are 3 orders, 11 families, 50 genera, and 377 species in the Tremellomycetes....
.
Pucciniomycotina
The
PucciniomycotinaPucciniomycotina is a subdivision of fungus within the division Basidiomycota. According to the Dictionary of the Fungi, the subdivision contains 8 classes, 18 orders, and 36 families.-References:...
includes the rust fungi, the insect parasitic/symbiotic genus
SeptobasidiumSeptobasidium is a genus of Basidiomycota fungi. Septobasidium species are known as plant pathogens.-External links:*...
, a former group of smut fungi (in the
MicrobotryomycetesThe Microbotryomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains four orders: the Heterogastridiales, the Leucosporidiales, the Microbotryales, and the Sporidiobolales. In these orders are a total of 4 families, 25 genera, and 208 species....
, which includes mirror yeasts), and a mixture of odd, infrequently seen or seldom recognized fungi, often parasitic on plants. The eight classes in the Pucciniomycotina are
AgaricostilbomycetesThe Agaricostilbomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class consists of 2 orders, 3 families, 10 genera, and 47 species....
,
AtractiellomycetesThe Atractiellomycetes are class of fungi in the Pucciniomycotina subdivision of the Basidiomycota. The class consists of a single order, the Atractiellales, which contains 3 families, 10 genera, and 34 species....
,
ClassiculomycetesThe Classiculomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains a single order, the Classiculales, which in turn contains the single family Classiculaceae. The family contains two monotypic genera....
,
CryptomycocolacomycetesThe Cryptomycocolacomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains a single order, the Cryptomycocolacales, which in turn contains the single family Cryptomycocolacaceae. The family has two monotypic genera....
,
CystobasidiomycetesThe Cystobasidiomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains three orders: the Cystobasidiales, the Erythrobasidiales, and the Naohideales....
,
MicrobotryomycetesThe Microbotryomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains four orders: the Heterogastridiales, the Leucosporidiales, the Microbotryales, and the Sporidiobolales. In these orders are a total of 4 families, 25 genera, and 208 species....
,
MixiomycetesThe Mixiomycetes are class of fungi in the Pucciniomycotina subphylum of the Basidiomycota. The class contains a single order, the Mixiales, which in turn contains a single family, the Mixiaceae that circumscribes the monotypic genus Mixia...
, and
PucciniomycetesThe Pucciniomycetes are a class of fungi in the Pucciniomycotina subdivision of the Basidiomycota. The class contains 5 orders, 21 families, 190 genera, and 8016 species...
.
Ustilaginomycotina
The
UstilaginomycotinaUstilaginomycotina refers to a subphylum within the phylum Basidiomycota of the kingdom Fungi, consisting of the classes Entorrhizomycetes, Ustilaginomycetes, Exobasidiomycetes and the order Malassezia.-External links:*...
are most (but not all) of the former smut fungi and along with the
ExobasidialesThe Exobasidiales are an order of fungi in the class Exobasidiomycetes. The order consists of four families as well as one genus, Cladosterigma, not assigned to any family....
. The classes of the Ustilaginomycotina are the
ExobasidiomycetesThe Exobasidiomycetes are a class of fungi sometimes associated with the abnormal outgrowths of plant tissues known as galls. The class includes Exobasidium camelliae Shirai, the camellia leaf gall and Exobasidium vaccinii Erikss, the leaf and flower gall...
, the Entorrhizomycetes, and the
UstilaginomycetesUstilaginomycetes is the class of true smut fungi. They are plant parasites with about 1400 recognised species in 70 genera....
.
The class
WallemiomycetesThe Wallemiomycetes are a class of fungi in the Basidiomycota division. It consists of the single order Wallemiales, containing the single family Wallemiaceae, which in turn contains the single genus Wallemia...
is not yet placed in a subphylum.
Typical life-cycle
Unlike higher animals and plants which have readily recognizable male and female counterparts, Basidiomycota (except for the
RustRusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing...
(Pucciniales)) tend to have mutually indistinguishable, compatible haploids which are usually mycelia being composed of filamentous hyphae. Typically haploid Basidiomycota mycelia fuse via
plasmogamyPlasmogamy is a stage in the sexual reproduction of fungi. In this stage, the cytoplasm of two parent mycelia fuse together without the fusion of nuclei, as occurs in higher terrestrial fungi. After plasmogamy occurs, the secondary mycelium forms. The secondary mycelium consists of dikaryotic...
and then the compatible nuclei migrate into each other's mycelia and pair up with the resident nuclei.
KaryogamyKaryogamy is the fusion of pronuclei of two cells, as part of syngamy, fertilization, or true bacterial conjugation.It is one of the two major modes of reproduction in fungi...
is delayed, so that the compatible nuclei remain in pairs, called a
dikaryonDikaryon is from Greek, di meaning 2 and karyon meaning nut, referring to the cell nucleus.The dikaryon is a nuclear feature which is unique to some fungi, in which after plasmogamy the two compatible nuclei of two cells pair off and cohabit without karyogamy within the cells of the hyphae,...
. The hyphae are then said to be
dikaryotic. Conversely, the haploid mycelia are called
monokaryons. Often, the dikaryotic mycelium is more vigorous than the individual
monokaryotic mycelia, and proceeds to take over the substrate in which they are growing. The dikaryons can be long-lived, lasting years, decades, or centuries.
The monokaryons are neither male nor female. They have either a
bipolar (
unifactorial) or a
tetrapolar (
bifactorial) mating system. This results in the fact that following
meiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
, the resulting haploid
basidiosporeA basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. In grills under a cap of one common species in the phylum of...
s and resultant monokaryons, have nuclei that are compatible with 50% (if bipolar) or 25% (if tetrapolar) of their sister basidiospores (and their resultant monokaryons) because the mating genes must differ for them to be compatible. However, there are many variations of these genes in the population, and therefore, over 90% of monokaryons are compatible with each other. It is as if there were multiple sexes.
The maintenance of the dikaryotic status in dikaryons in many Basidiomycota is facilitated by the formation of
clamp connectionA clamp connection is a structure formed by growing hyphal cells of certain fungi. It is created to ensure each septum, or segment of hypha separated by crossed walls, receives a set of differing nuclei, which are obtained through mating of hyphae of differing sexual types...
s that physically appear to help coordinate and re-establish pairs of compatible nuclei following synchronous mitotic nuclear divisions. Variations are frequent and multiple. In a typical Basidiomycota lifecycle the long lasting dikaryons periodically (seasonally or occasionally) produce basidia, the specialized usually club-shaped end cells, in which a pair of compatible nuclei fuse (
karyogamyKaryogamy is the fusion of pronuclei of two cells, as part of syngamy, fertilization, or true bacterial conjugation.It is one of the two major modes of reproduction in fungi...
) to form a diploid cell.
MeiosisMeiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
follows shortly with the production of 4 haploid nuclei that migrate into 4 external, usually apical
basidiosporeA basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. In grills under a cap of one common species in the phylum of...
s. Variations occur, however. Typically the basidiospores are
ballisticBallistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.A ballistic body is a body which is...
, hence they are sometimes also called
ballistosporeA spore that is shot off. In fungi most types of basidiospores, formed on basidia are discharged into the air from the tips of sterigmata. These actively discharged spores are a type of ballistospore....
s. In most species, the basidiospores disperse and each can start a new haploid mycelium, continuing the lifecycle. Basidia are microscopic but they are often produced on or in multicelled large fructifications called
basidiocarpIn fungi, a basidiocarp, basidiome or basidioma , is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do not produce such structures...
s or basidiomes, or
fruitbodiesIn fungi, the sporocarp is a multicellular structure on which spore-producing structures, such as basidia or asci, are borne...
), variously called
mushroomA mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
s,
puffballA puffball is a member of any of several groups of fungus in the division Basidiomycota. The puffballs were previously treated as a taxonomic group called the Gasteromycetes or Gasteromycetidae, but they are now known to be a polyphyletic assemblage. The distinguishing feature of all puffballs is...
s, etc. Ballistic basidiospores are formed on
sterigmata which are tapered spine-like projections on basidia, and are typically curved, like the horns of a bull. In some Basidiomycota the spores are not ballistic, and the sterigmata may be straight, reduced to stubbs, or absent. The basidiospores of these non-ballistosporic basidia may either bud off, or be released via dissolution or disintegration of the basidia.
In summary, meiosis takes place in a diploid basidium. Each one of the four haploid nuclei migrates into its own basidiospore. The basidiospores are ballistically discharged and start new haploid mycelia called monokaryons. There are no males or females, rather there are compatible thalli with multiple compatibility factors. Plasmogamy between compatible individuals leads to delayed karyogamy leading to establishment of a dikaryon. The dikaryon is long lasting but ultimately gives rise to either fruitbodies with basidia or directly to basidia without fruitbodies. The paired dikaryon in the basidium fuse (i.e. karyogamy takes place). The diploid basidium begins the cycle again.
Variations in life-cycles
Many variations occur. Some are self compatible and spontaneously form dikaryons without a separate compatible thallus being involved. These fungi are said to be
homothallic, versus the normal
heterothallic species with mating types. Others are
secondarily homothallic, in that two compatible nuclei following meiosis migrate into each basidiospore, which is then dispersed as a pre-existing dikaryon. Often such species form only two spores per basidium, but that too varies. Following meiosis, mitotic divisions can occur in the basidium. Multiple numbers of basidiospores can result, including odd numbers via degeneration of nuclei, or pairing up of nuclei, or lack of migration of nuclei. For example, the chanterelle genus
CraterellusCraterellus is a genus of generally edible fungi similar to the closely related chanterelles, with some species recently reassigned to this genus. They are distinguished by their lack of gill-like structures on the underside of their caps....
often has 6-spored basidia, while some corticioid
SistotremaSistotrema is a genus of fungi in the Hydnaceae family. The widespread genus contains 46 species. Phylogenetic analyses show that Sistotrema is a polyphyletic genus.-Species:*Sistotrema adnatum*Sistotrema alboluteum...
species can have 2-, 4-, 6-, or 8-spored basidia, and the cultivated button mushroom,
Agaricus bisporus. can have 1-, 2-, 3- or 4-spored basidia under some circumstances. Occasionally monokaryons of some taxa can form morphologically fully formed basidiomes and anatomically correct basidia and ballistic basidiospores in the absence of dikaryon formation, diploid nuclei, and meiosis. A rare few number of taxa have extended diploid life-cycles, but can be common species. Examples exist in the mushroom genera
Armillaria and
XerulaXerula is a genus of gilled mushrooms in the Physalacriaceae family.-Species:*Xerula americana*Xerula amygdaliformis*Xerula asprata*Xerula aureocystidiata*Xerula australis*Xerula caussei*Xerula chiangmaiae...
, both in the
PhysalacriaceaePhysalacriaceae are a family of fungi in the order Agaricales. Species in the genus have a widespread distribution, but most are found in the tropics, particularly in South-East Asia and Australasia. Molecular studies suggested that Physalacria, formerly the sole genus in this family, is related to...
. Occasionally basidiospores are not formed and parts of the "basidia" act as the dispersal agents, e.g. the peculiar mycoparasitic jelly fungus,
Tetragoniomyces or the entire "basidium" acts as a "spore", e.g. in some false puffballs (
SclerodermaScleroderma is a genus of fungi, commonly known as earth balls, now known to belong to the Boletales order, in suborder Sclerodermatineae.. The best known species are S. citrinum and S. verrucosum...
). In the human pathogenic genus
CryptococcusCryptococcus is a genus of fungus. Species grow in culture as yeasts. The perfect forms or teleomorphs of Cryptococcus species are filamentous fungi in the genus Filobasidiella...
, 4 nuclei following meiosis remain in the basidium but continually divide mitotically, each nucleus migrating into synchronously forming nonballistic basidiospores that are then pushed upwards by another set forming below them, resulting in 4 parallel chains of dry "basidiospores".
Other variations occur, some as standard life-cycles (that themselves have variations within variations) within specific orders.
Rusts
RustsRusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing...
(Pucciniales, previously known as Uredinales) at their greatest complexity produce five different types of spores on two different hosts in two unrelated host families. Such rusts are heteroecious (requiring 2 hosts) and macrocyclic (producing all 5 spores types). Wheat
stem rustThe stem, black or cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. An epidemic of stem rust on wheat caused by race Ug99 is currently spreading across Africa, Asia and most recently into Middle East and is causing major concern due to...
is an example. By convention the stages and spore states are numbered by
Roman numeralsThe numeral system of ancient Rome, or Roman numerals, uses combinations of letters from the Latin alphabet to signify values. The numbers 1 to 10 can be expressed in Roman numerals as:...
. Typically, basidiospores infect host one, also known as the alternate or sexual host, the mycelium forms pycnidia, which are miniature, flask-shaped, hollow, submicroscopic bodies embedded in host tissue (such as a leaf). This stage, numbered "0", produces single-celled spores that ooze out in a sweet liquid and that act as nonmotile spermatia, and also protruding receptive hyphae.
InsectInsects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s and probably other vectors such as rain carry the spermatia from spermagonia to spermagonia, cross inoculating the mating types. Neither thallus is male or female. Once crossed, the dikaryons are established and a second spore stage is formed, numbered "I" and called aecia, which form dikaryotic aeciospores in dry chains in inverted cup-shaped bodies embedded in host tissue. These aeciospores then infect the second host, known as the primary or asexual host (in macrocyclic rusts). On the primary host a repeating spore stage is formed, numbered "II", the urediospores in dry pustules called uredinia. Urediospores are dikaryotic and can infect the same host that produced them. They repeatedly infect this host over the growing season. At the end of the season, a fourth spore type, the
teliosporeTeliospore is the thick-walled resting spore of some fungi , from which the basidium arises.-Development:They develop in telia ....
, is formed. It is thicker-walled and serves to overwinter or to survive other harsh conditions. It does not continue the infection process, rather it remains dormant for a period and then germinates to form basidia (stage "IV"), sometimes called a promycelium. In the Pucciniales, the basidia are cylindrical and become 3-
septateIn anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
after meiosis, with each of the 4 cells bearing one basidiospore each. The basidospores disperse and start the infection process on host 1 again. Autoecious rusts complete their life-cycles on one host instead of two, and
microcyclic rusts cut out one or more stages.
Smuts
The characteristic part of the life-cycle of
smutsThe smuts are multicellular fungi, that are characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease...
is the thick-walled, often darkly pigmented, ornate, teliospore that serves to survive harsh conditions such as overwintering and also serves to help disperse the fungus as dry
diasporesIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
. The teliospores are initially dikaryotic but become diploid via karyogamy. Meiosis takes place at the time of germination. A promycelium is formed that consists of a short hypha (equated to a basidium). In some smuts such as
Ustilago maydis the nuclei migrate into the promycelium that becomes septate, and haploid yeast-like conidia/basidiospores sometimes called sporidia, bud off laterally from each cell. In various smuts, the yeast phase may proliferate, or they may fuse, or they may infect plant tissue and become hyphal. In other smuts, such as
Tilletia cariesTilletia tritici is the causal agent of common bunt of wheat.The tilletia was named after French agronomist Mathieu Tillet .-Use as a biological weapon:...
, the elongated haploid basidiospores form apically, often in compatible pairs that fuse centrally resulting in "H"-shaped diaspores which are by then dikaryotic. Dikaryotic conidia may then form. Eventually the host is infected by infectious hyphae. Teliospores form in host tissue. Many variations on these general themes occur.
Smuts with both a yeast phase and an infectious hyphal state are examples of
dimorphicPolymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
Basidiomycota. In plant parasitic taxa, the saprotrophic phase is normally the yeast while the infectious stage is hyphal. However, there are examples of animal and human parasites where the species are dimorphic but it is the yeast-like state that is infectious. The genus
FilobasidiellaFilobasidiella is a genus of fungi in the family Tremellaceae. Species are parasitic on other fungi and do not produce distinct basidiocarps . The genus is the teleomorphic state of the yeast genus Cryptococcus, some species of which are human pathogens.-History:The genus was first described in...
forms basidia on hyphae but the main infectious stage is more commonly known by the anamorphic yeast name
CryptococcusCryptococcus is a genus of fungus. Species grow in culture as yeasts. The perfect forms or teleomorphs of Cryptococcus species are filamentous fungi in the genus Filobasidiella...
, e.g.
Cryptococcus neoformansCryptococcus neoformans is an encapsulated yeast that can live in both plants and animals. Its teleomorph is Filobasidiella neoformans, a filamentous fungus belonging to the class Tremellomycetes. It is often found in pigeon excrement....
and
Cryptococcus gattiiCryptococcus gattii, formerly known as Cryptococcus neoformans var gattii, is an encapsulated yeast found primarily in tropical and subtropical climates...
.
The dimorphic Basidiomycota with yeast stages and the pleiomorphic rusts are examples of fungi with anamorphs, which are the asexual stages. Some Basidiomycota are only known as anamorphs. Many are yeasts, collectively called basidiomycetous yeasts to differentiate them from ascomycetous yeasts in the
AscomycotaThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac fungi. They are the largest phylum of Fungi, with over 64,000 species...
. Aside from yeast anamorphs, and uredinia, aecia and pycnidia, some Basidiomycota form other distinctive anamorphs as parts of their life-cycles. Examples are
Collybia tuberosaCollybia tuberosa, commonly known as the lentil shanklet or the appleseed coincap, is an inedible species of fungus in the Tricholomataceae family, and the type species of the genus Collybia. Like the two other members of its genus, it lives on the decomposing remains of other fleshy mushrooms...
with its apple-seed-shaped and coloured
sclerotiumA sclerotium is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until a favorable opportunity for growth. Other fungi that produce...
,
Dendrocollybia racemosa with its sclerotium and its
Tilachlidiopsis racemosa conidia,
Armillaria with their
rhizomorphsMycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae...
,
HohenbueheliaHohenbuehelia is a genus of fungi in the Pleurotaceae family. The genus has a widespread distribution and contains about 50 species.- Species :thumb|right|Hohenbuehelia mastrucata* H. abietina* H. aciculospora* H. amazonica...
with their
NematoctonusNematoctonus is a genus of fungi in the Pleurotaceae family. The genus—an anamorphic form of Hohenbuehelia—has a widespread distribution and contains 16 species.-Species:*Nematoctonus angustatus*Nematoctonus brevisporus...
nematodeThe nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
infectious, state and the coffee leaf parasite,
Mycena citricolorMycena citricolor is a plant pathogen....
and its
Decapitatus flavidus propaguleIn horticulture, a propagule is any plant material used for the purpose of plant propagation. In asexual reproduction, a propagule may be a woody, semi-hardwood, or softwood cutting, leaf section, or any number of other plant parts. In sexual reproduction, a propagule is a seed or spore...
s called gemmae.
See also
External links