These sterile structures either form the main part of the ascocarp or the system of ascogenous hyphae may simply give rise to a structure of sterile hyphae below the sexual structures, which is still an ascocarp, however.
Three types of ascocarps are found in the three respective groups of the Euascomycetes, or series Fig The order Plectascales is characterized by the families Gymnoascaceae, Aspergillaceae and Elaphomycetaceae. They are similar to Dermophytes in the Deuteromycota, and they can produce a mild skin disease in humans that is not as serious as in the Deuteromyccota.
They have a Racquet mycelium where the hyphae are racquet-shaped. Two kinds of vegetative reproduction are by conidia or chlamydospores. The conidia occur in long chains at the ends of branched or unbranched conidiophores. The Deuteromycota have a genus Paescilomyces that produces conidia in the same manner. During sexual reproduction antheridia and ascogonia fuse.
Ascogenous hyphae branch out from the ascogonium and the ascus forms as a result of crozier formation from the ascogenous hyphae. Many asci are produced, which are typically naked, each with 8 ascospores. There is no real ascocarp although there may be a weak suggestion of one.
In the Genus Gymnoascus a sexual process initiates the building the building up of a weak wall, and spines occur on the tips of swelled hyphae. These are considered to be a "weft of specialized hyphae. Principal Characteristics of Euascomycetes. Asci are clustered and borne in a fructification ascocarp. The asci are formed in connection with an ascogenous hyphal system. Ascogenous hyphae arise as outgrowths of an ascogonium. Nuclei pass from an antheridium to an ascogonium but do not fuse. Instead, conjugate nuclear division increases each nucleus respective to set up a dikaryotic phase in the ascogenous hyphal system.
The dikaryophase is ended when the asci form, which involves a crozier. Classification of the groups series is based on the form of the ascocarp, the form of the asci and the distribution of asci in the ascocarp.
The Plectomycetes have a closed fructification cleistothecium , scattered asci and globular asci. The Pyrenomycetes have a flask-shaped fructification perithecium , asci occur in a definite layer hymenium and they are elongated. The Discomycetes have an open fructification apothecium , asci occur in a definite layer and they are also elongated.
The order Plectascales is the most characteristic order in the group. Most ascocarps are very small although the family Elaphomycetaceae is an exception some doubt about its classification.
The family Gymnoascaceae has poorly developed ascocarps thin wefts of hyphae , but all other typical features of Euascomycetes are present. A scattered group of more or less globular asci each containing from spores is formed. The genus Byssochlamys has relatively undeveloped ascocarps. The family also has karytinophilis forms. It is related to a group of Fungi Imperfecti Dermatophytes ecause of the peculiarity of the racquet mycelium.
The family Aspergillaceae has very small ascocarps with well-defined peridial walls and a well-developed cleistothecium. The asci are globular, scattered in the ascocarp with 8 ascospores per ascus, and thus are similar to the Gymnoascaceae. The Genus Aspergillus has a characteristic pattern in the conidial stage. Sterigmata are formed, and conidia are produced in chains at the ends of the sterigmata.
Sometimes there are secondary sterigmata also. Similar forms in the Fungi Imperfecti bear the name Aspergillus , but they never possess the added names of Eurotium , Emericella , and Sartorya.
Members of the genus possess the ability to grow where there is a high osmotic concentration high sugar, salt, etc. Species that best represent the genus are Aspergillus ametelodami , with both sexual and asexual stages; and Aspergillus niger , A.
The Genus Penicillium is a companion genus of Aspergillus , both occurring in the soil. However, Penicillium exceeds Aspergillus in abundance. The ascocarpic stage is similar to Aspergillus , but the conidial stage differs. Here conidiophores do not form a vesicle, instead a penicillus of where there are three types Fig The structure bearing the chains of conidia are called sterigmata.
The abundance of Penicillium spp. In nature is extensive. They are primarily saprophytic forms and plan an important role in the breakdown of organic matter.
They also may spoil many foodstuffs. There is no perfect stage. Penicillium chrysogenum secretes penicillin. It acts on gram-positive organisms, which are very common in nature. Although other species also produce antibiotics, P. Other species are P. Thielavia basicola occurs in the soil and was once erroneously thought to be pathogenic on tobacco. The disease "Thielaviopsis" was actually caused by one of the Fungi Imperfecti.
Ascocarps are similar to Aspergillus and Penicillium, but they are dark and football shaped. The ascospores spill out into the cavity of the cleistothecium and the ascus is evanescent. Monascus spp. Cause the disease " Purple silage mold. The family Elaphomycetaceae has ascocarps far different from any previous form. They are the size of a hickory nut and hypogenous. They are associated with tree roots and believed to be a mycorrhizal fungus by occurring on tree roots.
The Genus Elaphom yces may actually be a highly modified Discomycete. Ascomycota: Euascomycetes: Plectascales. The order Myriangiales has short and wide asci, which are scattered. There is no typical cleistothecium. Species in the genus Myriangium are parasitic on scale insects. They build a dense mass of compacted hyphae stroma , which flatten out to form capsules. The whole structure is stromatic. The asci are borne scattered in the capsules. The ascospores are muriform where multicellular spores appear as bricks in a wall.
The Genus Elsinoe also has a stromatic form. Ascospores are scattered through an undifferentiated stromatic layer. The genus includes pathogens of cultivated plants and causes " Spot Anthracnose " especially in tropical regions. The imperfect stages is referred to as " Sphaceloma. A stroma appears as a layer on or under the host epidermis. Ascospores are not muriform but are simply divided by a few crosswalls. Ascomycota: Euascomycetes: Myriangiales.
Byssochlamys nivea, carpenteles, P. The order Erysiphales , which is almost equivalent to the group formerly known as "Perisporiales", contains several families, the members of which are usually found growing on leaves, stems and fruits of seed plants.
The mycelium is largely, if not entirely, confined to the surface of the suscept organ involved and may be either white or dark colored. There are both obligate parasites, as in the Erysiphaceae, or forms merely growing as saprophytes on honeydew that is deposited by insects. The ascocarps are mostly cleistothecia. The family Erysiphaceae includes the Powdery Mildews.
All are common parasites. The mycelium is primarily superficial on leaves, stems and even fruit, but may be internal also. Haustoria anchor the mycelium to epithelial cells, which forms a whitish powdery mass with profusion of conidia. The mycelium is composed of short, uninucleate cells, and the haustoria are bulbous usually with a single nucleus. They may be elongated or they may even occur uncommonly in the subepidermal layer.
The Meliolaceae and Capnodiaceae have a dark superficial mycelium, and these forms are common in the tropics. The Erysiphaceae incite a great variety of diseases of cultivated and wild plants. The grape industry in France was threatened before with the surge of the Downy Mildews Zygomycota. Dusting with sulfur onto the vines successfully controlled the infection that was the first successful use of a fungicide.
But in humid areas the powdery mildews may be reduced by moisture on the leaf surfaces. The Genus Phyllactinia is only one of the six common genera in North America. It has both a superficial and an internal mycelium.
There is no form with only an internal mycelium. There is an Oidium Imperfect Stage , where the fungus bears unbranched, upright conidiophores with catenulate conidia. The conidiophore typically has only one nucleus. The nucleus keeps dividing in the conidiophore and migrates to the terminus to form a new conidium with an indefinite number of conidia.
In some species the conidia are seldom found in long chains e. Spores are carried by wind to a new host where they may germinate without water being present.
This explains why powdery mildews thrive under dry conditions. Spraying with water may even control these fungi. The Ascocarpic Stage has a diagrammatic cleistothecia with a well-defined wall of interwoven hyphae. The color is usually dark. Appendages grow out from the outside layer. A delicate inner layer is present and there is usually only one ascus inside the ascocarp with less than 8 ascospores. Although there were originally also 8 nuclei the others disintegrate.
Alternatively there may be several asci in a hymenium. Ascocarps are the overwintering structures and they are produced in abundance toward the end of the growing season of plants. The cleistohecium may explode in the spring followed by an explosion of the asci, which aides in scattering the spores. Taxonomy is based on appendages and the number of asci per ascocarp as is shown in Fig :. The Genus Spaerotheca has a Perfect Stage with distinctive characteristics. Many species are heterothallic; and an ascogonium and antheridium are each produced on separate hyphae.
Each possesses a single nucleus. The male nucleus passes into the ascogonium through a pore to form the dikaryophase. The ascocarpic wall begins to form by sterile hyphae moving out from either adjacent cells, the ascogonium or even the antheridium. This process begins before fusion of nuclei karyogamy.
As the cell grows it digests the hyphae that are in the interior of the fructification. These hyphae are the sertoli layer. There are eight nuclei in the ascospore, but not all may develop into ascospores.
When more than one ascus is delimited, the ascogonium has previously sent out a system of ascogenous hyphae. The families Meliolaceae and Capnodiaceae include the " Sooty Molds.
Information about them is scanty. The mycelium is largely superficial but there may be a partial internal mycelium that produces haustoria. The mycelium is always dark in color. There are no obligate parasites and some species even grow as saprophytes on insect honeydew. When on fruit they can disfigure the surface. Meliolaceae is the most important family of sooty molds and is one of the most common maladies in tropical areas. The term "Sooty Molds" may also be applied to other fungal groups as well.
Plate Ascomycota: Euascomycetes: Erysiphales. In the Sub-Class Euascomycetes , the Series Pyrenomycetes is a large group with few stable, ordinal characteristics. Their classification has been in a continuous state of flux with various new alignments being proposed.
The changes which have been suggested from time to time originate from the continuing attempt to make classification of the fungi as natural as possible. They produce perithecia or perithecia-like hyphae. A perithecium possesses a peridium while the "perithecium-like" forms are without such a peridium. The ostiole is an opening in the perithecium. Among the gametes the female is the ascogonium and the male the antheridium or spermogonium. The spermogonium produces small, uninucleate cells at its base, which are termed spermatia.
These will generally not germinate but act rather as non-motile male gametes. Inside the perithecium there may occur two kinds of elongated asci. Most asci are initiated by crozier formation, and they are always formed at the base of the perithecium as a hymenium. Sterile hyphae will often project between the asci on the hymenium.
They may vary in shape and length. Others may occur just under the ostiole and project into the opening. The basal structures are termed paraphyses and the apical ones periphyses. Pseudoparaphyses are sterile hyphae that are joined to the perithecial wall basally and apically.
Two stages that occur generally in the Pyrenomycetes are a perfect one that allows for a recombination of characteristics, and an imperfect one, which does not allow for character combination. Two orders in the Pyrenomycetes , Huypoceales and Sphaeriales , constitute the "core" of the Pyrenomycetes. Previously the genera of both of these orders have been classified on the basis of the color of their ascocarps, and so they will be treated here:. In the order Hypocreales the Genus Neocosmospora is a typical representative.
This is an old order that some authorities have contended should be merged with the Sphaeriales. Generally the members of these two groups are basically much alike. They have been segregated primarily on the basis of what some feel are unimportant characters: principally differences in the color and texture of the ascocarps.
The Sphaerailes as traditionally defined have ascocarps that are brown to black and carbonaceous to leathery in texture. Morphologically similar forms with softer, bright-colored fructifications have been assigned to the Hypocreales.
In both orders the ascocarp is an ostiolate perithecium and in either the perithecia may be borne singly on the mycelium or they may be produced in dense clusters, seated upon or imbedded within a stroma. In the latter case the color and texture of the stroma are usually similar to that of the perithecial walls. Whatever the groupings are there is in the large assemblage of forms producing dark and bright-colored true perithecia the core group of the Pyrenomycetes. The perithecium is typically flask-shaped with a well-developed peridium.
These are found grouped or distributed over the mycelium. Elongated asci are usually cylindrical, which at maturity contain 8 ascospores arranged linearly inside the asci.
At maturity of the ascospores the neck of the perithecium becomes dark. There is a Cephalosporium Imperfect Stage. Here there are simple conidiophores and the conidia are suspended in a drop of slime at the apex of the conidiophore:. Perithecia may be borne singly on the mycelium or in a stroma. The family Nectriaceae is distinguished by producing their perithecia superficially either on a well-developed stroma or without a stroma.
Species of the Genus Nectria are saprophytes on twigs and branches although some are also parasitic. The mycelium is distributed over the host bark and small patches of stroma form under the bark surface.
The bark ruptures, exposing orange, cushion-shaped stroma. The Fusarium Imperfect Stage forms on top of the stroma. Perithecia develop on the stroma at the end of summer, with the youngest perithecia appearing at the apex.
They completely cover the stroma. Pseudoparaphyses occur in the perithecium. Asci contain 8, two-celled ascospores with a shape similar to Hypomyces. The family Hypocreaceae has their perithecia either completely or partially buried in a well-developed stroma. But the existence of intermediate forms makes separation on this basis difficult. The Genus Hypomyces contain species that are parasites of gill fungi Agaricales.
The host gills fail to develop and there is a distortion of tissue. A stroma completely covers the host with a thin, orange-colored layer. Perithecia are embedded in the stroma with their necks projecting.
The ascospores are two-celled. The conidia that are produced by the Fusarium Imperfect Stage show much variation in size, shape, number of nuclei, etc.
The family Clavicipitaceae is characterized by asci that are elongated at maturity and they have a width that approaches that of the bacteria. A fascile, or bundle, of filamentous ascospores is produced.
In many species crosswalls may come in so that each ascospore may contain up to cells. Paraphyses disintegrate before the ascospores mature. The Genus Cordyceps has over species most of them parasitic on insects. Coremia are usually found in the Imperfect Stage Isaria Stage. Erect, clavate or stalked perithecial stromata also grow out from the mummified insect. When parasitic on Elaphomyces an easy to locate the hypogenal ascocarps is to view the brightly colored stromata that appear on the ground surface.
Perithecia occur on the periphery of the stroma. The larvae of the June beetle are attacked and mummification ensues. Perithecia develop on the periphery of an apical club sent up from the host, but not all stroma are club shaped here. In the Isaria Imperfect Stage a pyramid of hyphae with condiiophores branch off. Claviceps purpurea causes Ergot or Spur Disease of rye, wheat and wild grasses.
Thousands of asci fill a fruiting body called the ascocarp. The diploid nucleus in each ascus gives rise to haploid nuclei by meiosis, and spore walls form around each nucleus. The spores in each ascus contain the meiotic products of a single diploid nucleus.
The ascospores are then released, germinate, and form hyphae that are disseminated in the environment and start new mycelia Figure 2. Improve this page Learn More.
Skip to main content. Module 6: Fungi. Search for:. Practice Question Which of the following statements is true? A dikaryotic ascus that forms in the ascocarp undergoes karyogamy, meiosis, and mitosis to form eight ascospores. A diploid ascus that forms in the ascocarp undergoes karyogamy, meiosis, and mitosis to form eight ascospores. A haploid zygote that forms in the ascocarp undergoes karyogamy, meiosis, and mitosis to form eight ascospores.
A dikaryotic ascus that forms in the ascocarp undergoes plasmogamy, meiosis, and mitosis to form eight ascospores. Show Answer Statement a is true. Try It. Did you have an idea for improving this content? Licenses and Attributions.
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