I. Introduction.

    This group includes most of the mushrooms, "toadstools",rusts and smuts that are so well known as food, poisonous fungi, and agricultural pests. Cell walls are usually chitinous. Asexual spores are various types of conidiospores.

II. Sexual Reproduction.

    The sexual spores are basidiospores, borne on basidia, usually located on a basidiocarp. Basidiomycota differ from Ascomycota in that there is an extensive dikaryotic (n+n) mycelium beginning shortly after germination of the haploid spores, not just resulting from fusion at the antheridium and ascogonium. The developing mycelia soon locate one another, and undergo plasmogamy, to establish the dikaryon. Many hyphae are characterized by clamp connections, which allow nuclei to pass one another in the narrow hyphae as cell division occurs. Since each cell of the dikaryon has a paternal and a maternal nucleus, it is necessary that when they divide, one be able to pass by one of the others, to maintain the maternal/paternal nuclear presence in each daughter cell. The clamp connection begins as a pocket in the wall of the ultimate cell, into which on of the nuclei enters. The pocket grows beyond the point where the new septum will form, and joins with the penultimate cell. After the nucleus in the pocket divides, one passes back to the penultimate cell, and one returns to the ultimate cell.

    Most of the dikaryons result from fusion of heterothallic hyphae of different mating types, (-) and (+) for example. However there are homothallic forms where fusion is between any two cells on any hyphae - even the same hypha.

    As the mycelium matures, basidiocarps are produced. The typical basidiocarp begins as a "button" stage as it emerges from the soil. It is covered with a veil, which will rupture as the mushroom grows. In some forms such as Amanita, there is another veil covering the entire button. This is the universal veil, which when ruptured during growth, leaves the characteristic volva or "death cup" at the base of the stipe, and which will also fragment on the upper surface of the pileus as it enlarges, leaving the characteristic flecking on the upper surface of the pileus. Most forms, however, do not show these structures. The common feature to all mushrooms include the stipe or stalk, the pileus,or cap, and an annulus on the stipe where the veil was attached at the button stage. Then there will be either lamellae, or gills, or pores, with hymenial layers bearing the basidia.

    Eventually karyogamy will occur, establishing a diploid cell. This normally occurs in the basidiocarp in the cells which will become basidia. Meiosis occurs promptly, and the 4 nuclei migrate to the stalk-like sterigmata, where the will form the haploid basidiospores. These basidia are usually in a layer known as the hymenial layer. Some basidia are entirely enclosed within the basidiocarp. Such a fruiting body is a gleba, characteristic of the Gasteromycetes.

    Basidia occur in 4 forms. They include:

A. Tuning-fork type - this form has only 2 basidiospores
B. Cruciate type
C. Transversely septate type - as in rusts
D. Homobasidium - the "typical" basidium as in Agaricus.

III. Representative forms.

A. Agaricus
    This is the common edible mushroom, consisting of a stipe, pileus and lamellae. This is actually only the terminus of an extensive underground mycelium. When a spore print is done, brown spores will be seen.
B. Amanita
    This genus includes some of the most deadly organisms, and yet also some quite edible forms. Obviously an intimate knowledge of Amanita taxonomy is essential if one plans to indulge in mycophagy of Amanita! This genus is characterized by white spores, a universal veil resulting in a volva and pileal flecks. A. muscaria - the Fly Amanita or Fly Mushroom is rather toxic. Its pileus is a reddish-orange color with pale flecks. Its name comes from the fact that it has been used to mix with milk to poison flies. A. phalloides - the Destroying Angel, is one of the most deadly mushrooms.  Numerous other Amanita species are known.
C. Pore fungi
    There are many genera of fungi whose pilei have vertical tubes lined with hymenium, rather than the lamellae of the common mushroom. Two common genera include Boletus and Polyporus. These are two huge genera with hundreds of species. In addition, there are many groups known as bracket fungi, shelf fungi, and conks, which grow on dead or dying trees.
D. Lycoperdon
    These are the puffballs. This genus of sometimes very large fungi are all edible, if collected while young and solid. They are enclosed basidiocarps known as glebas. When ripe, they discharge incredible numbers of spores, often through an ostiole, and usually in response to a touch or kick from a passing animal, or in other cases, from the impact of super-drops of water during or following rains.
E. Geastrum
    Earth stars are similar to puffballs, but have an outer layer to the gleba which splits into several hygroscopic arms, which open an close, depending on the humidity, and expose the spores when they are best able to be dispersed.
F. Cyathus
    Bird's nest fungi are one of the more interesting fungi, with the basidiocarp arranged into a splash cup containing several peridioles.
G. Clavaria
    Coral fungi are named because of their resemblance to certain forms of corals. They are common inhabitants of the forest floor.
H. Exidia glandulosa
    Jelly fungus
I. Rusts.
    Rusts are divided into two groups based on details of their life cycles. Autoecious rusts are those which completing their life cycles on a single host, while heteroecious rusts require at least two different species of hosts. All are serious pests of plants, but the heteroecious forms include some of the most devastating agricultural crops.
1. Heteroecious rusts
a. Puccinia graminis
    Wheat rust (Also known as red stem rust and black stem rust). This is the most notorious of the genus, inflicting massive damage on wheat crops. Its complex life history includes five types of spores and involves two hosts - Wheat, Triticum and barberry, Berberis vulgaris. We will begin with the summer red rust stage.
i. Red rust stage.
    This is a dikaryotic mycelium which in the spring, grows from an aeciospore which has arrived from the barberry. The mycelium weakens the stem and reduces viability and productivity, and may result in the head breaking the stem and hanging downward, thus often missing the harvester, and being wasted. The mycelium erupts from the stem and leaves as reddish pustules known as uredia. The uredia produce uredospores, which are unicellular dikaryotic cells with rather thin walls. They are not very resistant, and occur only in the spring and summer, in the cooler areas, but may occur year round in the warmer parts. These spores infect only wheat, but because of the large number produces, allow for rapid dispersal of the rust. In the cooler regions, the next stage is initiated in the late summer or fall.
ii. Black rust stage
    Usually in the mid to late summer, a new type of black pustule is seen on the wheat. These are telia containing teliospores. They are bicellular spores with a thick resistant wall. They are dikaryotic initially, but later in the fall, or in the following spring, each cell will experience karyogamy, thus beginning the diploid stage, and then meiosis to initiate the haploid stage. The meiotic nuclei will enter the basidium.
iii. Basidiospore stage
    Each cell of the teliospore will develop a transversely septate basidium, and the 4 nuclei resulting from meiosis will ascend into the basidium and onto the sterigmata. From here, wind will carry the basidiospores until they contact a barberry plant, where they will germinate and establish the next stage.
iv. Spermagonium or pycnium stage
    Each basidiospore germinates into a short hypha which enters the leaf of the barberry, and establishes a haploid mycelium of the mating type carried by the basidiospore. The mycelium will form flask-shaped structures on the upper surface of the leaf. These are the spermagonia or pycnia, within which conidia-like chains of spermatia or pycniospores will form. There are also receptive hyphae emerging from the spermagonia. The spermatia emerge from the spermagonia into a nectar-like drop of fluid, which attracts insects. These insects aid in the dispersal of the spermatia to receptive hyphae from spermagonia of the opposite mating type. When a spermatium contacts the appropriate receptive hypha, plasmogamy occurs, and a dikaryotic mycelium begins. This cross-fertilization allows for the genetic recombination which can result in new strains of rust.
v. Aecial Stage
    The dikaryotic mycelium laid down from the plasmogamy of spermatia works its way through the leaf, and usually masses on the lower surface, where aecia or "cluster cups" form. Conidia-like chains of dikaryotic aeciospores are formed, and these, when released are carried by the wind back to wheat plants, where they will germinate into the mycelium which will eventually form uredia.
b. Cronartium ribicola
    White pine blister rust. This has been a scourge of the eastern pine forests, causing the loss of large numbers of this important lumber tree. Its life cycle is similar to Puccinia, with gooseberries and currants (Ribes) being the alternate hosts.
c. Gymnosporangium juniperi-virginianum
    Apple-cedar rust. This harmful rust affects apple trees, and uses the red cedar Juniperus as its alternate host. Large fruiting bodies with jelly-like extrusions are formed on the cedars, and are termed cedar apples.
2. Autoecious rusts
    These rusts require only one host species. Included are:
a. Hollyhock rust
b. Asparagus rust
J. Smuts
1. Local smuts. Ex, Ustilago maydis (=zeae)
    In these smuts, the infection remains localized, producing pustules or tumors. These may be on nodes or ears, and result in hypertrophy of the affected parts. The kernels enlarge because of the presence of the mycelium which eventually gives rise to the masses teliospores seen in the lab slides. (Note - the mycelium is dikaryotic.) The teliospores over-winter. Karyogamy takes place at this time, and in the springtime, meiosis and basidiospore formation occurs. Basidiospores may infect new corn plants, or may form sporidia which bud, and the resulting cells infect corn plants.
    Once infection of the new corn plant occurs, a small haploid mycelium develops, and soon plasmogamizes with a mycelium of opposite mating strain, thus establishing the dikaryon. Once more, a tumor or pustule forms - these may be up to the size of a baseball - and teliospores once more form.
2. Blossom-infecting smuts. Ex. U. tritici, U. avenae
    Basidiospores only infect the pistils of the flowers of wheat or oats respectively. These cause the loose smuts of wheat or oats.
    Teliospores mature in the ears of diseased plants at the same time that healthy plants blossom. Teliospores are transferred by wind to the pistils where they germinate. The first two divisions are meiotic - there is no basidium produced. The succeeding mitotic divisions produce a small mycelium in the embryo of the kernel. The mycelium may be heterothallic or homothallic, and undergoes plasmogamy. This new dikaryotic mycelium does not affect the kernel. The following season, when the infected kernel germinates, the mycelium becomes active, especially near the meristematic tissues, so that it grows at the same pace as the seedling. The mycelium affects the developing plant, causing it to grow faster and mature earlier than the uninfected plants. In the flower head of the infected plant, the mycelium enters and totally replaces the developing embryo, so that the ear eventually consists of a mass of black teliospores which are blown away by the wind, leaving only the bare spike axes.
    By this time, the healthy plants are just flowering, so that the wind-borne teliospores can infect the pistils of these flowers, and thus prepare another generation of infected grain, ready to be grown the next season.
3. Seedling infecting smuts. Ex. Tilletia tritici.
    Bunt, or stinking smut. In this disease the kernels are replaced by teliospores, as in the blossom-infecting type, , but the seed coat remains intact, so that the spores are not released. Instead, the kernel coat and its spores are harvested with the normal kernels, but during the harvest process, are broken open. This releases the sticky teliospores, which attach to uninfected grains.
    These spores have a putrid odor, rendering the entire harvest unfit for man or beast. Also, as the spores dry, they disperse as a fine dust in grain silos, and allow for fires and explosions due to the quantity of fine dust in the enclosed space.
    The next season finds grains with attached spores being sown. Meiosis now occurs and may be followed by mitotic divisions to give several haploid nuclei. A mycelium develops which in turn gives rise to sporidia. Sporidia undergo plasmogamy to reestablish the dikaryon, from which conidia will be produced. These conidia infect the seedling wheat plants, growing with them near the meristems, until the heads begin to form. Once the ovaries are formed, the hyphae penetrate the grains, and replace most or all of the structure, except the seed coats. Teliospores are produced, and the cycle will continue.   To Top of Page   To Plant Diversity Page    To Tony Futcher's Home Page