The Basics of Mycology & The Fungi
For educational purposes; quote cited references when available--
True Fungi (Eumycophyta) 1
Basidiomycota (Basidiomycetes, Basidiomycotina)
-- Higher fungi
The Basidiomycota include an immense variety and number of fungi in the most advanced of all fungal classes. There are several thousand species known all of which are obligately parasitic on higher plants. They include many economically important species such as the smuts, rusts, jelly fungi, mushrooms, puffballs and stinkhorns. The "shelf fungi" or bracket fungi also belong here as well as the less familiar bird's nest fungi. The higher and most familiar members of this group include the mushrooms, toadstools, puffballs and stinkhorns. The smuts, rusts and jelly fungi constitute a group that is more primitive than the higher Basidiomycota. A review of the importance of this group given by Alexopoulos (1952) remains valid to the 21st Century.
This class differs from all other fungi in that they produce their spores, called basidiospores, on the outside of a specialized, spore-producing body, the basidium. Basidiospores are usually uninucleate and haploid. Like ascospores they are the result of plasmogamy, karyogamy and meiosis, the last two of which occur in the basidium. There are usually four basidiospores produced on each basidium. The basidiospores have been considered as homologous to ascospores because both types develop comparably, and the Basidiomycota have been regarded as having originated from the Ascomycota.
This class of fungi is an important group of fungi including many harmful species as well as useful ones. The smuts and rusts are two groups of parasites causing plant diseases, which destroy a high percentage of agricultural crops annually. The most notorious are the stinking smut and black stem rust of wheat. There are many others that attack a variety of food and ornamental plants. The higher Basidiomycota are significant in causing diseases of forest and shade trees and in destroying lumber, railroad ties, etc. In tropical areas where atmospheric humidity is high it not uncommon to see old automobiles with fruiting bodies of shelf fungi growing from the skeletons of the cars.
Mushroom lovers worldwide seek many Basidiomycota for food. The cultivation of mushrooms for food has developed into an industry of considerable proportions and many of the wild species are equally good or superior in flavor.
Alexopoulos (1952) described the somatic structures of this class. The mycelium consists of well-developed septate hyphae, which penetrate into the substratum and absorb nourishment. The hyphae individuals are microscopic but they may be plainly seen in mass. The mycelium is usually white, bright yellow or orange and often spreads out in a fan-shaped growth. In some forms a number of hyphae lying parallel to one another are joined together to form thick strands of mycelium, commonly called shoestrings that technically are known as rhizomorphs. These strands are enveloped in a sheath or cortex and behave as a single unit or tissue.
The mycelium passes through three distinct stages of development before the fungus completes its life cycle. These stages are the primary, secondary and tertiary mycelia. The primary mycelium usually develops from the germination of the basidiospore. It may be multinucleate at first, the nucleus of the basidiophore dividing many times as the germ tube emerges from the spore and begins to grow. Such a multinucleate phase of the primary mycelium is short because septa are soon formed which divide the mycelium into uninucleate cells.
The secondary mycelium originates from the primary mycelium. Its cells are usually binucleate. The binucleate condition begins when the protoplasts of two uninucleate cells fuse, without karyogamy taking place after plasmogamy. The binucleate cell, which is formed, divides into two daughter cells. The two nuclei divide conjugately and the sister nuclei separate into the two daughter cells. An interesting mechanism that occurs in all major types of Basidiomycota but not in all species operates to insure that sister nuclei arising from conjugate division of the dikaryon become separated in the two daughter cells. This mechanism functions through special structures called clamp connections, which are formed during nuclear division. When a binucleate cell is ready to divide a short branch, the clamp connection, arises between the two nuclei a and b and begins to form a hook. The nuclei now divide simultaneously. The spindle of one division becomes oriented obliquely so that one daughter nucleus b forms in the clamp connection and the other b' of the first spindle, which has formed, near the other end of the cell. Meanwhile, the clamp has bent over and its free end has connected with the cell, so that the clamp forms a bridge through which one of the daughter nuclei b passes to the other end of the cell and approaches one of the daughter nuclei (a of the other spindle. A septum forms to close the clamp at the point of its origin and another septum forms vertically under the bridge to divide the parent cell into two daughter cells with nuclei a and b in one daughter cell and nuclei a' and b' in the other as shown in the following Plate 223:
Of some 26,000 species the Basidiomycota includes many plant parasites and common fleshy fungi. Their name comes from the "basidium." This structure occupies a place in the cycle of development and is homologous to the ascus in the Ascomycota. The basidium terminates a dikaryophase and is the site of nuclear fusion and the seat of meiosis. Basidiospores are primarily uninucleate, unicellular structures. The basidium is typically club-shaped and bears spores on sterigmata, which are located on the outside of the basidium. The number of spores produced is usually four (in the Ascomycota there are eight).
Two sub-classes are Heterobasidiomycetes, which includes a large number of parasitic forms and the rusts; and Homobasidiomycetes, which more the most conspicuous and commonly known, with many edible varieties.
Please refer to the following plates for characteristic structures in the Basidiomycota:
Plate 160 = Basidiomycota: Hymenium.
Plate 161 = Basidium developmental stages.
Plate 223 = Basidiomycota: Clamp Connections During Nuclear Division
Five orders of Heterobasidiomycetes are treated here, which are Uredinales, Auriculariales, Tremellales and Dacrymycetales (= frequently included in other orders). The number of known species as of the year 2010 is only about 520. Many of these are tropical and the majority is saprophytic. Fruiting bodies (basidiocarps) are produced in these orders, and in many forms are of a gelatinous texture that can dry down to a cartilaginous or horny consistency. While the basidia are in all cases mainly different from those encountered in the Autobasidiomycetes (Eubasidii), they are not uniform throughout the group. Actually it is principally on the basis of fundamental differences in basidial structure that the orders are separated. The Auriculariales, especially through Uredinella and Septobasidium, are more related to the rusts. The character of the basidium in the Dacryomycetales allies these forms to the Agaricales into which order some specialists believe that they should be incorporated.
The order Uredinales contains two families: Pucciniaceae and Melampsoraceae. A typically long-cycled rust produces Five distinct stages in its life cycle in a regular sequence as follows: Stage O = spermogonia bearing spermatia and receptive hyphae. Stage I = aecia bearing aeciospores. Stage II = uredia bearing urediospores. Stage III = telia bearing teliospores. Stage IV = promycelia bearing basidiospores.
The family Pucciniaceae generally has teliospores that are stalked and one- to many-celled. On gymnosperm hosts there is no aecial stage (Stage I). There are biological specializations where groups of individuals differ physiologically from other groups. Subspecies are common and trinomials are used to distinguish the varieties. In addition there are physiologic races and still further division of the varieties. Puccinia gramini-tritici has over 150 physiologic races.
The rusts are controlled by eliminating the secondary host (destruction of barberry in P. graminis) and by the production of resistant varieties. But because physiologic races shift from year to year, the breeding for resistance is a never-ending process. There are two main types of rusts: macrocyclic and microcyclid. The macrocyclic rusts produce one or more types of binucleate spores in addition to teliospores and they have a long cycle. In the eutype rust all spore types are present, while in democyclic rusts one spore type is absent. The microcyclic rusts have a short cycle and they are all autoecious forms. There are also no spores other than the teliospores (= Stage IV type).
The Puccinaceae is well represented by Puccinia graminis, which causes "Stem Rust of Wheat." There are hundreds of millions of bushels of wheat lost annually in North America due to this pest. The rust is heterocious, heterothallic, long-cycled or macrocyclic and of the eutype. The heteroecious habit requires the fungus to spend one portion of its development on another host (autoecious forms complete the life cycle on the same host). It produces its aecia on the leaves of members of the Berberidaceae and its uredia and telia on grasses. The species os composed of several varieties and numerous physiologic races.
European barberry is the dicot host, which produces spermatia and aeciospores. The mycelium is monokaryotic and penetrates the host, producing haustoria. There are "A" and "B" vegetative types of mycelium.
Spermogonia form on the upper surface of the host.
The spermatia ooze out in a sticky fluid that is attractive to insect vectors.
At the same time on the lower surface there are protoaecia.
Another mating type may be produced on the same leaf or another leaf; and spermatia are blown over to the sticky fluid of the other type. Flexuous hyphae (receptive hyphae) protrude from the base of the spermogonium into the sticky mass and receive the spermatia of the opposite mating type.
The nuclei eventually reach the protoecium in a process that is not clear; and the protoaecium is then changed into an aecium. Aeciospores are produced in the aecium, which is cup-like in shape. Spores are catenulate and each spore is dikaryotic with one "A" and one "B" nucleus.
The origin of aeciospores is from a single cell at the base of the aecium. It marks the beginning of the dikaryophase. Nuclei move into extensions in pairs, which is very similar to that found in ascogenous hyphae.
After indirect penetration of the germ tube of the aeciospore through the stoma of the monocot host (= wheat & other grasses), the mycelium spreads. At this time it is dikaryotic. It should be noticed that this is in contrast to the situation on a dicot host where penetration of the germ tube is direct and the mycelium is monokaryotic.
Urediospores function like conidia and constitute the vegetative stage of the rust. On the same mycelium are formed the teliospores, which are produced in the uredium that is now called a telium. The teliospore is at first dikaryotic but nuclear fusion occurs forming a diploid. Colors of the respective spores are teliospore = brown or black and urediospore = orange.
A germ tube protrudes from each cell of the teliospore, which remains attached to the telium. Each cell of the tube hs but one nucleus.
Strigmata are produced, which bear basidiospores. Basidiospores are uninucleate and either "A" or "B" (there are two of each type).
Puccinia graminis is a eutype in that all spore forms are represented in the life cycle. This species is also heteroecius, heterothallic and macrocyclic-eutype.
In other Puccinia species the teliospores are similar throughout. Most have a well-developed cupulate aecium and the life cycles differ among species. For example, Puccinia podophylli, causing Mayapple Rust, is a democyclic rust. There is no uredial stage (Stage II), and it is an autoecious form (both mono- and dikaryotic mycelium on the same host).
Uromyces spp. have one-celled teliospores.
Phragmidium sp. has a uniquely-shaped spore
Gymnosporangium juniperi-virginianae causes "Cedar-Apple Rust," and G. globosum causes "Hawthorn Rust."Both of these rusts re demicyclic and heteroecious. Red cedar serves as the alternate host for both species and conspicuous galls form on it as a response to invasion by either parasite. The telial stage develops on these galls in the spring. In life these spore horns are bright orange.
The family Melampsoraceae has sessile teliospores and is heteroecious (conifers are the alternate host). The following genera will reveal the characteristics of this family:
Melampsora spp. have teliospores formed in crusts; they are one-celled and stalkless.
Urediospores have capitate paraphyses arranged with them in the uredium. The gynnosperm host is usually larch for the aecial stage. This is a macrocyclic, eutype group.
Coleosporium spp. occur on aster in the uredo stage and on pine needles in the aecial stage. There is a peridermoid aecium (blister-like). They occur on pines that have two needles. Urediospores form chains. There is no external promycelium produced from the teliospore. Instead karyogamy and meiosis occur in the teliospore. This is a macrocyclic eutype group. Coleosporium solidaginis is a common variety in North America. It is heteroecious, producing tongue-like orange-colored aecia on the leaves of 2-needled pines. Its uredial and telial stages occur on gondenrod, asters, etc.
Cronartium spp.: C. ribicola incites White Pine Blister Rust. They are found on pines with more than two needles. They are long-cycled, heteroecious and of the eutype. Telial and uredial stages occur on Ribes and Grossularia (currant & gooseberry); aecial stages are on white pine. C. ribicola is common on white pine (Pinus strobus). The teliospores are laid side-by-side and end-to-end. C. quercuum occurs on oak where there are the uredal and telial stages. The teliospores are like C. ribicola. Cronartium quercuum is another common species in North America. This rust stimulates the production of large aecial galls on jack pine branches. The uredial and telial stages occur on various species of oak.
Please refer to the following plates for characteristic structures and Life Cycles in the Uredinales:
Basidiomycota: Heterobasidiomycetes: Uredinales
Plate 168 = Basidiospores: Uredinella coecidiophaga
Plate 169 = Rust spermogonia (2 types)
Plate 171 = Uredia: Two types
Plate 172 = Teleutospores: Uromyces, Pileolaria, Puccinia, Uropyxis, Xenodochus, Phragnidium, Nyssopsora,
Plate 173 = Life Cycle -- Puccinia graminis
Plate 174 = Telium of Cronartium ribicola
Plate 224 = Diagnostic Characters-1 -- Uredinales: Pucciniaceae
Plate 225 = Diagnostic Characters-1 -- Uredinales: Melampsoraceae
Plate 226 = Diagnostic Characters-2 -- Uredinales: Pucciniaceae
Plate 227 = Diagnostic Characters-3 -- Uredinales: Pucciniaceae
Plate 228 = Diagnostic Characters-2-- Uredinales: Melampsoraceae
The Uredinales Imperfecti is a group that contains the Imperfect Rusts. Because rusts have a polymorphic life cycle their classification is complicated. As found in the Ascomycota, but to a greater degree, imperfect stages of most rusts are more likely to be found than perfect stages in certain seasons. As the classification of the rusts is based on teleutospores, it is difficult to such structures if they are not known or not available (teleutospores are thick walled resting spores in which karyogamy occurs; they are part of the basidial apparatus). Also because in heteroecious rusts the teleutospores occur on a different host from that on which the aeciospores occur complicates the situation even more. Therefore, this has led to the creation of an artificial group, the Uredinales Imperfecti in which the aecial and uredial stages are temporarily classified until the teleutospores are discovered.. There is no perfect stage known (= telial stage). Various genera show the characteristics of these fungi in the following Fig. 385:
Please refer to the following plates for characteristic structures and Life Cycles in the Uredinales Imperfecti
Basidiomycota: Heterobasidiomycetes: Uredinales Imperfecti
Plate 170 = Aecia types: Caeoma, Aecidium, Roestelia & Peridermium.
Plate 177 = Life Cycle -- Tilletia caries.
The order Ustilaginales includes over 1,200 species in over 35 genera. These are the "smuts," which are important plant pathogens on cereal crops and vegetables. None are obligately parasitic and there is an intercellular mycelium with or without haustoria. The species have a simpler life cycle than rusts and the dikaryophase is terminated by the teliospore stage. The former order Uredinales differs by having over 6,000 species none of which are obligately parasitic; and teliospore production occurs with one or more probasidia, which bear basidiospores (sporidia). Unlike the rusts smut fungi can be cultivated on artificial media. They exhibit no trace of sex organs. Among the Heterobasidiomycetes only in smuts and rusts is no basidiocarp produced.
Teliospores in the Ustilaginales are conspicuous, dark masses (= pustules or spore masses). The usually black spores are often formed in the ovary of the host and produced in the millions. Hypertrophy is commonly induced in the host, but sometimes it is absent. In one very serious disease, "corn smut", hypertrophy occurs throughout the plant. Some smuts sporulate only in the ovaries of the host, but others form spores in other parts of the plant.
The smut spore is commonly spherical. Two nuclei fuse prior to formation of the basidium and spores are often held together in clusters, or spore balls, of they may be free and separated. Spores are retained in the host until the rupture of host tissue, and they have been given various names such as "winter spores", "smut spores", "brand spores", "teliospores" or "chlamydospores."
In the smuts conjugation may occur between compatible basidiospores. The one nucleus migrates into the other basidiospore. A basidiospore may germinate sending a hypha into the host. Growth of this hypha is weak. But if the mycelium of one basidiospore comes into contact with the mycelium of another spore, they will join together and by hyphal anastomosis set-up the dikaryophase. Some basidiospores may conjugate right on the basidium and 2N hyphae are produced right on the basidium (= "H" connections). The mycelium may have multinucleate cells within, although the nuclei always occur in pairs.
In destroying host tissue the hyphae may be very dense and profuse, and branching may occur. Eventually the hyphal cells disarticulate in defined areas with subsequent rounding up and formation of binucleate spores. Some smuts attack only the seedling stage of a host, which becomes resistant with age. Some of the smuts on cereals are like this. The corn smut fungus infects the older leaves of maize and also the tassel and stem. Attack occurs on new tissue only, however.
The teliospore lands on a style and then grows down into the host ovary and fight on through the ovary wall. Systemic infections occur in many forms. Onion smut attacks the growing points of the seedling. Some smuts enter the embryos of their hosts and then remain dormant until planting time. The maize kernel infected with corn smut may be expanded to 100-times its normal size. On smut fungus remains in the soil. Bunt, oat smut or loose smut of barley all have a terrific production of spores. Surface sterilization of seed or grain with Formalin can control these fungi. Loose smuts that attack deep within the host tissue require hot water treatment to be controlled.
The mycelium is typically dikaryotic in the host, but often there may be multinucleate cells that occur in pairs. They are predominantly heterothallic.
A tetrapolar compatibility is present: AB, Ab, aB, ab. However, only the AaBb form is compatible.
Teliospores arise when dense knots of hyphae form, each cell of which becomes definitely binucleate. The walls disappear and free the protoplasts, which round up and develop a new wall by themselves. These develop into the teliospores. Teliospores, which are diploid, form the overwintering stage.
Families in the Ustilaginales are separated on the basis of the form of the promycelium and the way in which the basidiospores (sporidia) are borne on this structure. Genera are defined primarily on teliospore characters, including such features as whether the spores occur singly, in pairs, or in spore balls. Two families presented here are Ustilaginaceae and Tilletiaceae. The principal differences are shown in Fig. 387 and Fig 388 as follows:
Genera are defined primarily on teliospore characters, including such features as whether the spores occur singly, in pairs, or in spore balls.
The number of basidiospores in the Tilletiaceae is indefinite because mitosis occurs leaving a nucleus behind in the promycelium and one in the basidiospore.
A few species of smuts produce conidia even though the principal reproductive struture is still the teliospore. The conidia are dikaryotic and give rise to new mycelia.
In the Tilletiaceae, Urocystis cepulae causes "Onion Smut." This fungus will not germinate at high temperatures, hence in warmer climatic areas the planting of onions is timed in accordance with the least prevalence of the disease. The spores occur in the soil so that a sterilizing solution is dribbled in the seed row at planting time, which remains effective through the several weeks when the onion is susceptible.
For controlling smut fungi in general it is important to understand their habits. In Tilletia caries, Ustilago hordei and U. avenae the spores occur on the surface of the grain. As the host is susceptible only at the very young stage, surface sterilization with Formalin kills the spores. When the fungus occurs in the embryo, surface sterilization will not kill the spores, but rather hot water treatment is effective. When the mycelium of a smut is localized in development in the meristematic regions, resistant varieties are the best means of control.
Please refer to the following plates for characteristic structures and Life Cycles in the Ustilaginales:
Basidiomycota: Heterobasidiomycetes: Ustilaginales
Plate 175 = Teleutospores: Ustilago levis, U. maydis, Tilletia caries, Urocystis cepulae, Tuburcinia trientalis,
Thecaphora seminis-convolvuli & Schroeteria delastrina.
Plate 176 = Life Cycle -- Ustilago maydis.
Plate 229 = Diagnostic Characters: Ustilaginales: Ustilaginaceae
Plate 230 = Diagnostic Characters: Ustilaginales: Tilletiaceae
The order Auriculariales is distinguished by having a transversely septate basidium that is comparable to the ascocarp and closely resembles that found in the Uredinales. Auricularia (Hirneola), a saprophyte on stumps, dead tree trunks, etc., is one of the commonest and best-known representatives of the order. Pilacre is also a frequently encountered saprophyte. Eocronartium musciola, on moss, is one of the few well-known Bryophyte parasites. Septobasidium parasitizes scale insects. Families of the Auriculariales that have been recognized are Auriculariaceae and Septobasidiaceae.
There is a dikaryophase established through hyphal anastomosis. The basidiocarp bears the dikaryophase and also terminates it in the basidiospores. Basidiospores germinate to produce a monokaryotic mycelium. Hyphal anastomosis then sets up the dikaryophase. The absorptive dikaryotic mycelium here is quite different than that found in the Ascomycota: Taphrinales. There are no sexual organs in all the Basidiomycota generally, and only the Uredinales have spermatia.
The family Auriculariaceae has fruiting bodies that vary from a simple weft of hyphae to well-developed, large fruiting bodies. Most are saprobic with a few being parasitic on mosses and the roots of flowering plants.
The Genus Auricularia represents this group, which is most closely related to the rusts and smuts. Ear-like fruiting bodies with a gelatinous texture are produced on the outside of wood. Sterigmata of variable length are formed, and the basidiospores that they bear are all situated on a similar plane.
The Genus Pilacre has small, mushroom-like basidiocarps, but these are not gelatinous.
The Genus Eocronartium attacks the gametophyte generation of mosses. These fungi resemble Cronartium telia on the gametophyte.
The family Septobasidiaceae includes about 165 species of which the genera Septobasidium and Uredinella re parasitic on scale insects. Members of the family resemble the Auriculariaceae in that they produce transversely septate basidia. They differ from most Auriculariaceae in that the fruiting bodies of the Septobasidiaceae are not gelatinous and in some parts of their biology. The Auriculariaceae are saprobic or parasitic on plants whereas the Septobasidiaceae are parasitic on insects. Of evolutionary significance is that in most species of Septobasidium the wall of the hypobasidium is very thick and the whole structure resembles a spore. The hypobasidium eventually emits an elongated epibasidium that soon becomes transversely septate into four cells. Each of these cells then produces a sterigma that in turn forms a basidiospore. These hypobasidia appear similar to the teleutospores of the Uredinales.
The Genus Septobasidium attacks whole colonies of scale insects. The basidiocarp is distinctively sculptured and covers the entire colony of insects. It will not attack healthy insects and infection occurs only via spores.
When the healthy scale insects mature they crawl out of their "cage" through a channel in the basidiocarp. Sporulation is timed with the emergence of the crawlers, which acquire spores as they rest on the surface of the basidiocarp.
The Genus Uredinella is similar to Septobasidium except that only one insect at a time is attacked. Basidiospores are formed from a probasidium in both species and the attacked scale insects are not severely harmed.
Please refer to the following plates for characteristic structures and Life Cycles in the Auriculariales:
Basidiomycota: Heterobasidiomycetes: Auriculariales
Plate 166 = Life Cycle -- Auricularia auricula.
Plate 167 = Structures of Septobasidium fumigatum.
Plate 231 = Example Structures -- Auriculariales, Tremellales, Dacryomycetales
The order Tremellales includes the "Jelly Fungi." Their basidiocarps vary from crust-like to stalked, and in some forms the basidiocarp is only a thin layer of gelatinous hyphae that produce the basidia. One family Tremellaceae has been recognized. The life cycle is similar to the Auriculariales except that the basidium differs. Vertical septations occur in the basidium and serigmata grow out and produce basidiospores at their apex.
Please refer to the following plates for characteristic structures and Life Cycles in the Tremellales
Basidiomycota: Heterobasidiomycetes: Tremellales:
Plate 165 = Life Cycle -- Exidia spiculosa.
Plate 231 = Example Structures -- Auriculariales, Tremellales, Dacryomycetales
The order Dacryomycetales are also Jelly Fungi whose fruiting bodies are easily recognized as small bodies, bright yellow or orange jelly-like or waxy. They occur on the branches or trunks of living or dead trees. There is a strong tendency to produce secondary basidiospores in this order, which may continue growing in a yeast-like phase if cultured. A single family the Dacryomycetaceae has been recognized.
Please refer to the following plates for characteristic structures and Life Cycles in the Dacrymycetales:
Basidiomycota: Heterobasidiomycetes: Dacrymycetales
Plate 162 = Basidiospore formation: Calocera cornea.
Plate 164 = Life Cycle -- Dacrymyces deliquescens.
Plate 231 = Example Structures -- Auriculariales, Tremellales, Dacryomycetales