Lecture #16

Pyrenomycetes and Plectomycetes

Pyrenomycetes- perithecial; 2 definitions 1) flask-shaped ascoma with a true perithecial wall, or 2) asci produced from well developed hymenium

Plectomycetes- cleistothecial; 2 definitions 1) closed ascoma with a true perithecial wall, or 2) scattered production of asci

"Pyrenomycetes"

Large group, consisting primarily of perithecial ascomycetes; all ascomycetes that form perithecia are not pyrenomycetes

Perithecial, or occasionally, cleistothecial ascocarps that may be formed in a stroma, immersed in a subiculum or be unassociated with specialized stromatic structures,
Ovoid to cylindrical unitunicate asci, usually formed from ascogenous hyphae and croziers in a hymenium or becoming secondarily scattered throughout the ascocarp,
Persistent asci that have forcible discharge of ascospores through an ascal tip apparatus or evanescent asci with passive discharge,
Hamathecia that may consist of one or more types of sterile hyphae and pseudoparenchymatous tissue,
One- to several-celled ascospores of various shapes, and
Diverse and often complex anamorphs and related conidial species, some of which do not reproduce sexually

Ecology

I.Endophytes - Members of several orders are endophytes of living plants

Endophytes restricted to grasses and sedges are found in one group of Hypocreales. These include species of Epichloë, Balansia, and conidial forms in Acremonium. Many of these endophytes become systemic in above ground plant parts and may be seed dispersed. These endophytes produce a variety of secondary products, notably alkaloids, that affect other organisms.
Other pyrenomycetous endophytes generally have broad host ranges in a variety of dicotyledonous angiosperms and conifers. Example, in temperate and tropical regions mycologists generally encounter species of Xylariales on decaying wood; many now are recognized as endophytes of trees in many regions of the world, and it even has been suggested that the group is basically one of endophytic life style

II.Plant Pathogens

Diaporthales (Diaporthe, Chryphonectria, Annisogramma)
Hypocreales (Nectria, Gibberella, and Claviceps)
Ophiostomatales (Ophiostoma)
Microascales (Ceratocystis)

In some cases the plant pathogen is better known by its anamorph because it is the form more commonly encountered during the growing season.

III.Arthropod associates

IV.Mycoparasites

Large number of hypocrealean species, some of which may be host specific 30 species known to parasitize the plant pathogen Rhizoctonia solani; of these well over half are hypocrealean anamorphs, including five species of Trichoderma.
Hypomyces lactiflorum the lobster mushroom
Many fungi on highly decayed wood are parasites of initial wood decay fungi
Researchers are actively pursuing the use of parasitic fungi as agents of biological control

Hypocreales

Pale to brightly colored, fleshy stromata
Perithecial ascocarps in most species
Ovoid to cylindrical asci with an apical pore in a more or less thickened apex
Ascospores sphaerical to needle-like, one to several celled, breaking into part spores in some species
Ascospores forcibly discharged, and
Conidia produced enteroblastically from phialidic conidiophores

Centrum development & families

Nectriaceae -Nectria centrum type: characterized by a basal cluster of asci with evanescent apical paraphyses arising from the apical region of the ascocarp and extending downward to become interspersed among the asci.

Hypocreaceae -Hypomyces centrum type:Hypomyces and Hypocrea have a varient of the Nectria centrum, paraphyses arise centripetaly from the innermost layer of the perithecium rather than only apically. The paraphyses at the upper part of the perithecium elongate greatly and are homologous with apical paraphyses; they then grow downward to help form the cavity of the perithecium .

Clavicipitaceae -Claviceps centrum type: basal cluster of asci with evanescent paraphyses that arise from the lateral walls of the perithecium outside the ascus cluster; thus, the paraphyses and asci are usually not interspersed. Paraphyses of Nectriaceae & Hypocreaceae are considered to be homologous to the lateral paraphyses of Clavicipitaceae

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Species of Hypocreales are remarkable for their diversity of biotrophic and necrotrophic interactions. They are endophytes and parasites of animals, plants, and other fungi

Hypocreaceae

Hypocrea is a commonly encountered genus

Cushion-shaped or effused stromata can be found on the surface of decaying wood, bark, and leaves

Asci are narrowly cylindric, containing eight two-celled ascospores in a single series

Spores are constricted at the septum and break into part spores so that the ascus appears to have sixteen spores at maturity

Several types of anamorphs are found within Hypocrea, including Trichoderma and Gliocladium.

Hypomyces produce soft, hyaline to brightly colored perithecia sunken in a subiculum, a loose, thick, cottony, hyphal weft

Ascospores are one or two celled

Most species are parasitic on fleshy fungi

Nectriaceae

Nectria produces its perithecia on the surface of a cushion-shaped stroma

Ascocarps are brightly colored shades of orange and red

N. haematococca produces large crescent-shaped, multiseptate conidia of the Fusarium type

N. cinnabarina produces minute, one-celled conidia of the Tubercularia type;

causes disease is known as dieback on many species including maple
Tuberculariaanamorph with bright, orange-pink sporodochia, appears on the surface of the bark over the infected area.
as the season progresses, small dark-red perithecia begin to form superficially at the base of the same stromata that bore conidiophores earlier
asci arising from croziers at the base of the perithecium among apical paraphyses.
each ascus contains eight two-celled, boat-shaped ascospores

Clavicipitaceae

Bright or darkly pigmented fleshy stromata often in shades of orange and yellow or a subiculum,

Long, narrowly cylindrical asci with thickened, dome-like caps perforated by long cylindrical pores,

Paraphyses formed on the lateral walls of the ascocarp

Ascospores are thread-like and extend the length of the ascus; in some species the septate ascospores break into fragments at the septa that are called part spores

Anamorphs are phialidic

Members of Clavicipitaceae are well known for their associations with arthropods and plants. For example Claviceps, is parasitic on grasses;

Cordyceps, pathogenic on insects and on hypogeous ascocarps of Elaphomyces;Torrubiella on spiders;Epichloe endophyte of grasses.

Claviceps purpurea, is the cause of ergot of rye; alkaloid-containing sclerotia in the production of the disease,ergotism, was not suspected, and ergots were harvested and milled with rye grain for flour.

The disease became well-known in the Middle Ages when it was known as St. Anthony's Fire due to the fact that a religious order dedicated to St. Anthony cared for those with severe symptoms. Some of the alkaloids produce vaso-constriction which results in insufficient blood flow to legs and arms, a condition that produces an extreme burning sensation, blackening, and may result in loss of the limb. Many died, particularly in countries where the consumption of rye bread, primarily by the poor, was high.

Although earlier suggestions of the involvement of ergotism in the infamous witch trials and hangings of 1692 in Salem, Massachusetts, were disclaimed, interpretation of new evidence makes a strong case for ergotism (Matossian, 1989). Matossian documents historical climatic conditions, food consumption patterns, sociology, and symptoms to suggest that ergotism has had profound effects on large numbers of people throughout history.

Sclerotia of C. purpurea contain three families of alkaloids: secoergolenes, ergolines, and lysergic acid derivitives. Together, the toxic alkaloids are psychoactive and produce vasoconstriction; however, these same effects may be medicinally useful when administered in the correct dosage to induce labor, prevent post partum hemorrhage, and treat migraine

Cordyceps- parasites of Elaphomyces and many arthropods

Endophytes of Monocots - Species of Epichloe and their close relatives,Balansia, Atkinsonella, and Myriogenospora are endophytes that live their lives between the cells or on the surface of grasses and sedges.

Xylariales

Diverse group of pyrenomycetes with dark, leathery, woody, or carbonaceous perithecial or, occassionally, cleistothecial ascocarps, sometimes embedded in a stroma.

Asci form a persistent peripheral or basal layer, and are subglobose, club-shaped, or, most frequently, cylindrical, usually with an apical ring. The ring may become blue (amyloid) in iodine. Asci within a perithecium mature at different times, so that ascospores of different ages can be found in the same ascocarp over a long period of time.

Ascospores are hyaline or dark, one or few-celled and may have germination slits or pores.

Paraphyses grow upward from the base and inward from the sides of the ascocarp wall interspersed among the asci, and the pressure they exert is thought to function in expanding the ascocarp and creating a central cavity; they are lysed to a greater or lesser extent by developing asci.

Periphyses typically are present in the neck of perithecial forms

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Anamorphs mostly show holoblastic conidiogenesis with the conidiogenous cell proliferating sympodially or percurrently.

3-10 families

Xylariaceae

Perithecial ascocarps bearing paraphyses and periphyses that are embedded in a stroma
Asci of most species bear a ring at the apex that is evident when examined in unstained preparations, and characteristically appears as an amyloid ascal plug when stained with iodine
Often dark-colored ascospores typically bear a longitudinal slit that may be elongated, elongated-spiral, or poroid; however, germ slits are absent in some genera and species
Many species are characterized by conidia with sympodial proliferation of the conidiogenous cell that are produced singly and seceed schizolytically, leaving a distinctive thickened scar. Conidia often are formed on the surface of the stroma well before perithecia develop

Many species of Xylariaceae decay wood of living or dead angiosperms and are considered to be saprobic; however, several saprobic species are known from gymnosperms, dung, and soil. Some are severe pathogens

Xylaria is a large genus (Rogers et al, 1988; San Martín Gonzales and Rogers, 1989).

Xylaria species are mostly saprobic or weak parasites on woody plants and usually have erect elongated stromata

Common species:X. hypoxylon, with tall, slender, subcylindrical or flattened stromata that are forked, and X. polymorpha, commonly called "dead man's fingers" with club-shaped, clustered stromata, up to 8 x 2.5 cm, X. filiformis, with long filiform stromata

Daldinia

Genus that forms large, black, hemispherical stromata, with a zonate inner stromatal tissue. Daldinia concentrica is the most common and widespread species. The concentric semicircles, easily visible when the stroma is cut vertically

Rosellinia

Characterized by a subiculum from which the anamorph, and later, the stroma, develops. Each stroma usually contains one or only a few perithecia

Ascospores may bear appendages with slimey sheaths

Monograph of the genus Petrini (1993) discussed a number of common characters among Rosellinia and some species of Hypoxylon and Astrocystis.

The genus is well represented in temperate regions

"Pyrenomycetes"

Hypocreales