BASIDIOMYCETES: CHARACTERISTICS, NUTRITION, HABITAT AND REPRODUCTION - BIOLOGY - 2025

The Basidiomycetes are fungi that make the phylum Basidiomycota within the sub-kingdom dikarya. It presents some 30,000 species distributed in various habitats throughout the planet. In this group of fungi we find edible mushrooms, rusts, charcoals, gelatinous fungi and some yeasts.

The main characteristic of basidiomycetes is the presence of basidiospores (sexual spores) that are produced in basidia. The body of basidiomycetes consists of a short-lived haploid primary mycelium, followed by a diploid secondary mycelium. The hyphae are septate and the septa are called dolípores.

Diversity of fungi of the phylum Basidiomycota

The basidiocarpals constitute the tertiary mycelium. This basidiocarp is the fruiting body (where the basidia are formed) that we see with the naked eye as mushrooms, stick ears or the so-called gelatinous fungi.

Reproduction of basidiomycetes can be asexual or sexual. Asexual reproduction can occur by budding in yeast, by fragmentation of mycelium and in some groups (carbons and rusts) by the formation of various types of asexual spores.

In sexual reproduction, layers called hymeniums are formed on the basidiocarp, where the terminal hyphae undergo a process of fusion of nuclei (karyogamy) to form the basidium. After meiosis, the basidiospores are formed on the basidium.

These fungi are heterotrophic, with saprophytic species, parasites and symbionts. Saprophytes are important elements in forest ecology, as some species can degrade lignin.

Many species form mycorrhizae (usually mushrooms) with tree roots. Other species are symbiotic with ants from the Attini tribe. Parasitic species are abundant, being responsible for various plant diseases, such as rusts and smut.

The Basidiomycetes are monophyletic, being a sister group to the Ascomycetes. It has been subdivided into three sub-phyla: Pucciniomycotina, where the rusts are found, Ustilaginomycotina, which includes coals, and Agaricomycotina, the group of mushrooms.

General characteristics

Most basidiomycetes are multicellular, but some species are unicellular (yeast) or have a unicellular and a multicellular phase (dimorphic).

Multicellular species start when a basidiospore germinates that forms a haploid (homokaryotic) primary mycelium. Mycelia are made up of septate hyphae, where the septa have a central, barrel-shaped pore called a dolippore.

During the development of the fungus, two haploid mycelia fuse and form the secondary (dikaryotic) mycelium which is diploid.

The nuclei of binucleated cells divide by mitosis. Just before the start of division, a projection (fibula) forms between the two nuclei, allowing the daughter cells to present a nucleus from each fused mycelium.

The characteristic shared by all basidiomycetes is the presence of basidiospores (sex spores) that form from specialized structures called basidia.

Basidia develop on fruiting bodies (basidiocarps) that originate from the union of numerous mycelia, forming the tertiary mycelium. The basidiocarp is macroscopic in several groups of basidiomycetes and in the case of mushrooms, it is what is consumed.

Phylogeny and taxonomy

The Basidiomycetes constitute a monophyletic group that is the brother of the Ascomycetes, forming the Dikarya sub-kingdom. This phyllum has traditionally been divided into three sub-phyllum: Agaricomycotina, Pucciniomycotina, and Ustilaginomycotina.

Agaricomycotina is the largest group of the Basidiomycetes. It is characterized by presenting a macroscopic basidiocarp and is divided into three classes (Agaricomycetes, Dacrymycetes and Tremellomycetes). In this group are edible and poisonous mushrooms, gelatinous mushrooms and species of yeast.

Pucciniomycotina contains about 7,000 species and does not have a dolíporeal septum. It includes rusts and symbiotic groups with insects.

There are approximately 1,000 species in Ustilaginomycotina, the majority being obligate plant pathogens, such as charcoal. These are dimorphic, with a haploid unicellular phase and a diploid multicellular phase.

Nutrition

Basidiomycetes are heterotrophs, presenting saprophytic groups, parasites and symbionts.

Saprophytic groups

These species decompose different compounds from dead organic matter in forests. Some species (Schizophyllum commune, Trametes versicolor, among others) are capable of degrading lignin (a compound that gives hardness to wood) and play an important role in the dynamics of forest ecosystems.

Strobilurus tenacellus, is a species of interest since it decomposes cones of various species of Pinus. This species produces a chemical compound called strobilurin that has been found to be effective in the control of phytopathogenic fungi and bacteria.

Another prominent saprophytic species is Ganoderma lucidum, which has been used as an antiviral, antitumor and antioxidant due to the chemical compounds it produces.

Parasite groups

Parasitic groups within the Basidiomycetes are abundant. These are the cause of various diseases in plants and some animals.

Various species of Pucciniomycotina are obligate plant pathogens, being known as rusts. You are causing severe damage to numerous crops such as cereals, coffee and fruit trees among others, reducing their productivity. They can form galls or abnormal growths on the plant, known as a witch's broom.

Rusts were known since Roman times. The goddess Robigus was invoked at the end of April to prevent this disease from causing damage to the ears of wheat.

Coals or smuts are diseases caused by Ustilaginomycotina species. They receive this name because masses of teliospores (asexual spores) of black color are formed. These fungi mainly attack the reproductive structures of their host, totally damaging cereal production.

Species of the genus Malassezia (Ustilaginomycotina) are the cause of dandruff and skin diseases in humans.

Some Basidiomycetes can parasitize other fungi through special structures that allow them to penetrate the host and use it to disperse their spores.

Symbiote groups

Within the groups that form mutualistic associations, there are those that form mycorrhizae with various species of trees. In the case of basidiomycetes, ectomycorrhizae (external mycorrhizae) occur.

The hyphae of the fungus spread in the soil increasing the absorption surface of water and minerals that are used by the plant, while it provides sugars produced by photosynthesis.

The mycorrhizal groups are of great economic and ecological value, since there are edible mushrooms, among which the mushroom (Agaricus bisporicus) as well as hallucinogenic mushrooms (Amanita muscaria) stand out.

The mycorrhizae of the basidiomycetes form a very wide network with the roots of trees in the forests, which maintain the dynamics of these ecosystems.

Species of the order Agaricales are closely related to ants of the Attine tribe. The ants grow the fungus in their nests and feed on it. Fungi decompose accumulated organic matter in nests, and ants disperse their spores when they move to other nests.

Habitat

Basidiomycetes are distributed throughout the world and can be found in terrestrial or aquatic environments. Approximately 60 species live in fresh water bodies or marine ecosystems, in mangroves, sea grasses, algae, or free-living beings. They are found in both temperate and tropical zones.

The terrestrial groups are distributed in different environments. They are frequent in both temperate and tropical forests, where they form extensive mycorrhizal structures. Parasites are associated with the distribution of their hosts.

Reproduction

Basidiomycota have both sexual and asexual reproduction.

Asexual reproduction

In groups with a yeast phase, they reproduce by budding.

Fragmentation is common in many species. This consists of the separation of a piece of mycelium that follows its growth independently.

Four types of asexual spores are produced in the rust group. In pycnidial-type conidia, pycniospores are produced that invade the primary host and are haploid.

Then the diploid eiospores are formed, being dispersed by the wind until they reach a secondary host. They are generally located on the underside of the leaf.

The production of uredospores is known as the replication phase of rusts. They are produced in large quantities and are dispersed by the wind. This constitutes the mechanism of spread of the disease in the parasitized crop.

The last type of asexual spores are teliospores which have a very tough wall and can remain dormant during adverse periods.

Sexual reproduction

This occurs differently in groups of Basidiomycetes.

In Agaricomycotina the fruiting body (basidiocarp) is generally macroscopic. This is formed by the union of a large number of hyphae that form the tertiary mycelium. The basidiocarp can have very varied textures (fleshy, woody, gelatinous among others).

In mushrooms (Agaricales) the basidiocarp is made up of a foot and the cap (pileus). Under the hat a layer called hymenium is formed, where the basidia will develop.

In the basidia, meiosis occurs and four cells are generally formed that develop thinning called sterigmas, which are located on the basidium and on which the basidiospores (sexual spores) are formed.

Basiodiospores are generally globose, being colorless or pigmented. When they mature, they are violently expelled by a mechanism called ballistosporous.

In rusts and blights a basidiocarp is not produced, but an elongated structure (metabasidium) with a diploid nucleus is formed from the germination of teliospores. This nucleus divides by meiosis, forming four cells that produce sterigmas on which the basiodiospores are located.

References

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