English: Sac fungi; Ascomycetes.
Botany: 64000 species; the ascus, meaning "sac" or "wineskin", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed, though some are asexual without asci.
IntroductionAscomycota are characterized by a saclike structure, the ascus, which contains anything from four to eight ascospores in the sexual stage. The sac fungi are separated into subgroups based on whether asci arise singly or are borne in one of several types of fruiting structures, or ascocarps, and on the method of discharge of the ascospores. Many ascomycetes are plant pathogens, some are animal pathogens, a few are edible mushrooms, and many live on dead organic matte, as saprobes. The largest and most commonly known ascomycetes include the morel and the truffle, however,
TaxonomyThe classification of
Fungi has been difficult. But 2 main groups have been recognised for a long time
Ascomycota and
Basidiomycota. The classification of
Ascomycota has been more diffcult.
The
Ascomycota can be grouped in several ways. One is in:
1. Hemiascomycetes = Saccharomycotina
They are mostly the
Saccharomycetales, the first diverging lineage of
Ascomycota.
2. Protomycetes = Taphrinomycotina
They are mostly the
Saccharomycetales, the second diverging lineage of
Ascomycota.
3. Euasocomycetes = Pezizomycotina
The majority of
Ascomycota. ik can be split in 4 clades
1.
Plectomycetidae, also named Eurotiomycetes
2.
Pyrenomycetidae1. Taphrinomycetidae = Protomycetes = Taphrinomycotina2. Eurotiomycetes =
Plectomycetidae = Prototunicatae = Onygenidae
3. Sordariomycetes =
Pyrenomycetidae = Unitunicatae inoperculatae 1
4.
Leotiomycetes =
Pyrenomycetidae = Unitunicatae inoperculatae 2
5. Pezizetidae = Unitunicatae operculatae
Characteristics1. Vegetative body is unicellular or commonly well developed, branched septate mycelium with uni- or multinucleate cells having perforated septa.
2. Mostly, the cell wall is composed of chitin and glucans, but in unicellular form, it is composed of glucans and mannans.
3. Vegetative reproduction takes place by fragmentation (in filamentous form), fission and budding (in unicellular form).
4. Asexual reproduction takes place by non-motile spores, such as conidia, oidia and chlamydospores.
5. Sexual reproduction takes place by gametangial copulation (Saccharomyces), gametangial contact (Penicillium), somatogamy (Morchella) or spermatiza- tion (Polystigma).
6. Complete absence of motile structures.
7. The product of sexual reproduction is the ascospores grown inside a small specialised sac-like structure, called ascus.
8. The fruit bodies (inside which ascus developed) are the ascocarps. The asco- carps may be cleistothecium (Penicilliumi), apothecium (Ascobolus), perithecium (Daldenia) or ascostroma (Elsinoe veneta).
CharacteristicsAscomycota are morphologically diverse. The group includes organisms from unicellular yeasts to complex cup fungi.
98% of lichens have an
Ascomycota as the fungal part of the lichen.
There are 2000 identified genera and 30,000 species of
Ascomycota.
The unifying characteristic among these diverse groups is the presence of a reproductive structure known as the ascus, though in some cases it has a reduced role in the life cycle.
Many ascomycetes are of commercial importance. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies.
Many of them cause tree diseases, such as Dutch elm disease and apple blights.
Some of the plant pathogenic ascomycetes are apple scab, rice blast, the ergot fungi, black knot, and the powdery mildews.
The yeasts are used to produce alcoholic beverages and breads. The mold Penicillium is used to produce the antibiotic penicillin.
Almost half of all members of the phylum
Ascomycota form symbiotic associations with algae to form lichens.
Others, such as morels (a highly prized edible fungi), form important mycorrhizal relationships with plants, thereby providing enhanced water and nutrient uptake and, in some cases, protection from insects.
Almost all ascomycetes are terrestrial or parasitic. However, a few have adapted to marine or freshwater environments.
The cell walls of the hyphae are variably composed of chitin and β-glucans, just as in
Basidiomycota. However, these fibers are set in a matrix of glycoprotein containing the sugars galactose and mannose.
The mycelium of ascomycetes is usually made up of septate hyphae. However, there is not necessarily any fixed number of nuclei in each of the divisions.
The septal walls have septal pores which provide cytoplasmic continuity throughout the individual hyphae. Under appropriate conditions, nuclei may also migrate between septal compartments through the septal pores.
A unique character of the
Ascomycota (but not present in all ascomycetes) is the presence of Woronin bodies on each side of the septa separating the hyphal segments which control the septal pores. If an adjoining hypha is ruptured, the Woronin bodies block the pores to prevent loss of cytoplasm into the ruptured compartment. The Woronin bodies are spherical, hexagonal, or rectangular membrane bound structures with a crystalline protein matrix.
Subclasses Pezizomycotina
Arthoniomycetes
Coniocybomycetes
Dothideomycetes
Eurotiomycetes
Geoglossomycetes
Laboulbeniomycetes
Lecanoromycetes
LeotiomycetesLichinomycetes
Orbiliomycetes
Pezizomycetes
Sordariomycetes
Xylonomycetes
"Unplaced orders"Lahmiales
Itchiclahmadion
Triblidiales
Saccharomycotina
SaccharomycetesTaphrinomycotina
Archaeorhizomyces
Neolectomycetes
Pneumocystidomycetes
Schizosaccharomycetes
Taphrinomycetes