Basidiomycetes is a most advanced and largest group of higher fungi. It contains about 1100 genera and 25000 species. We generally call them rusts, smuts, mushroom, puff balls, toad stool, stink horns bracket fungi, and shelf fungi. Their fruiting body or basidiocarps are large and conspicuous, so we can find them easily in surroundings. Some puff balls and bracket fungi of Basidiomycetes can reach about 50 cm in diameter.
MAIN CHARACTERISTIC FEATURE OF BASIDIOMYCETES
- Filamentous , branched and septate hyphae form the mycelium.
- There is a barrel-shaped pore what we term as dolipore in each septum.
- The mycelia are of three types:- Primary mycelium, Secondary mycelium and Tertiary mycelium.
- The primary mycelium develops from uni nucleate haploid basidiospores. It consists of uninucleate or mono karyotic cells. It multiplies by conidia or oidia formation.
- In primary mucelium sexual fusion takes place by :- Somatogamy { fusion between two vegetative cells, between basidiospores or between two monokaryotic hyphae} AND Spermatization { fusion between a spore or spermatium and a receptive hypha}.
- The sexual reproduction involves plasmogamy, karyogamy and meiosis. Plasmogamy is achieved by somatogamy or spermatization and results the formation of a dikaryon by the process called dikaryotization. The karyogamy is delayed and the intervening phase develops from the dikaryon.
- The dikaryon or dikaryotic cells divide further to form the secondary mycelium.
- The secondary mycelium contains cells with two nuclei, so we term them as dikaryotic cells. It grows by cell division. In many basidiomycetes, the cell division is accompanied by Clamp connection ( hook like bridge between the two adjacent cells) to facilitate proper distribution of dikaryons.
- The secondary mycelium multiplies by the formation of different types of spores such as, chlamydospores, uredospores, teleutospores, aeciospores.
- Some of the reproductive cells of secondary mycelium becomes club-shaped Basidia . Fusion of nuclei along with meiotic cell division occurs in basidia. The name of the class is based after the basidia.
- Fruiting body or basidium can produce tetra basidiospores which are haploid (n) in nature. These are produced out of the body . we can find them at the beginning of tubular outgrowth which we term as sterigmata.
- Some higher fungi produces larger fruiting bodies termed basidiocarps ( as for example mushrooms, bracket fungi) . The body off basidiocarp comprises of complex secondary mycelium, called tertiary mycelium.
EXAMPLES OF BASIDIOMYCETES
Agaricus
It is the common edible mushroom. We term it also field mushroom and gilled mushroom. Some species of Agaricus are poisonous. The mycelium of fungus remains concealed in the substratum. The umbrella-shaped mushroom, which is visible from outside above the substratum, is the fruiting body or basidiocarp of the fungus.
Puccinia
This genus includes about 700 species. All are obligate parasites and cause serious disease called rusts. Symptoms of the disease appear on aerial parts of the host in the form of variously coloured rusty pustules. The disease causes a great economic loss as the plants become stunted and the yield is reduced. The fruiting body or basidiocarps are not formed. Some of the common diseases are black stem rust (Puccinia graminis tritici) yellow rust of wheat (Puccinia striformis) brown rust of wheat (Puccinia triticina).
Ustilago
The genus is economically most important as it causes destructive smut diseases in most of the cereal plants. The characteristic symptoms of the disease appear in ovaries, anthers and other floral parts replacing them completely by black colored smut spores or brand spores and reduce the productivity.
Bracket or shelf fungi
The species of Polyporus Fomes are commonly we know as Bracket fungi or shelf fungi. The basidiocarps of these genera are large, tough, leathery, corky or woody in texture and grow on roots, trunks and large branches of trees. Some species attack and destroy lumber or timber. Some of the common disease causing fungi are Polyporus sulphureus or sulphur mushroom wood-rot of apple, oak, pear etc. It produces large, sulphur yellow to orange colore shelves or brackets on tree trunk. Another fungi are Polyporus betulinus causes rots of birch wood.
Puff balls or Lycoperdon
The species of genus Lycoperdon are commonly called puff balls which grow as saprotrophs on the substratum rich in decaying organic matter. Basidiocarps are globose or pyriform in shape and attached laterally or terminally to the rhizomorphs. Young basidiocarps are edible. At maturity the fruiting bodies release puffs of spores . common species are Lycoperdon oblongisporum and Lycoperdon giganteum.
Armillaria
We term this fungi commonly as honey mushroom. The fruiting bodies are edible. The fungus grows as root parasite of hardwoods and conifers. The rhizomorphs of the fungus reach upto the phloem of the host and block the food supply.
Psilocybe
Psilocybe mexicana is commonly known as sacred mushroom as it is used by Mexican Indian for some religious ceremonies. It has hallucinating properties similar to LSD.
So this group Basidiomycetes includes diverse types of fungal members. Some parasitic forms cause destructive diseases such as smuts and rusts of cereal crops and cause severe damage ; some produce edible fruiting bodies like mushrooms; some produce hallucinogenic chemicals; and some others are extremely poisonous. Certain members of basidiomycetes are considered the best decomposers of wood material. They decompose both cellulose and lignin. The lignin is not decomposed by most other fungi and even bacteria.