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24.3D: Basidiomycota: The Club Fungi

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    • Contributed by Boundless
    • General Microbiology at Boundless

    The basidiomycota are mushroom-producing fungi with developing, club-shaped fruiting bodies called basidia on the gills under its cap.

    Learning Objectives

    • Describe the ecology and reproduction of the Basidiomycota

    Key Points

    • The majority of edible fungi belong to the Phylum Basidiomycota.
    • The basidiomycota includes shelf fungus, toadstools, and smuts and rusts.
    • Unlike most fungi, basidiomycota reproduce sexually as opposed to asexually.
    • Two different mating strains are required for the fusion of genetic material in the basidium which is followed by meiosis producing haploid basidiospores.
    • Mycelia of different mating strains combine to produce a secondary mycelium that contains haploid basidiospores in what is called the dikaryotic stage, where the fungi remains until a basidiocarp (mushroom) is generated with the developing basidia on the gills under its cap.

    Key Terms

    • basidiocarp: a fruiting body that protrudes from the ground, known as a mushroom, which has a developing basidia on the gills under its cap
    • basidiomycete: a fungus of the phylum Basidiomycota, which produces sexual spores on a basidium
    • Basidiomycota: a taxonomic division within the kingdom Fungi: 30,000 species of fungi that produce spores from a basidium
    • basidium: a small structure, shaped like a club, found in the Basidiomycota phylum of fungi, that bears four spores at the tips of small projections
    • basidiospore: a sexually-reproductive spore produced by fungi of the phylum Basidiomycota

    Basidiomycota: The Club Fungi

    The fungi in the Phylum Basidiomycota are easily recognizable under a light microscope by their club-shaped fruiting bodies called basidia (singular, basidium), which are the swollen terminal cell of a hypha. The basidia, which are the reproductive organs of these fungi, are often contained within the familiar mushroom, commonly seen in fields after rain, on the supermarket shelves, and growing on your lawn. These mushroom-producing basidiomyces are sometimes referred to as “gill fungi” because of the presence of gill-like structures on the underside of the cap. The “gills” are actually compacted hyphae on which the basidia are borne. This group also includes shelf fungus, which cling to the bark of trees like small shelves. In addition, the basidiomycota includes smuts and rusts, which are important plant pathogens, and toadstools. Most edible fungi belong to the Phylum Basidiomycota; however, some basidiomycetes produce deadly toxins. For example, Cryptococcus neoformans causes severe respiratory illness.

    Figure \(\PageIndex{1}\): Fruiting bodies of a basidiomycete: The fruiting bodies of a basidiomycete form a ring in a meadow, commonly called “fairy ring.” The best-known fairy ring fungus has the scientific name Marasmius oreades. The body of this fungus, its mycelium, is underground and grows outward in a circle. As it grows, the mycelium depletes the soil of nitrogen, causing the mycelia to grow away from the center, leading to the “fairy ring” of fruiting bodies where there is adequate soil nitrogen.

    The lifecycle of basidiomycetes includes alternation of generations. Spores are generally produced through sexual reproduction, rather than asexual reproduction. The club-shaped basidium carries spores called basidiospores. In the basidium, nuclei of two different mating strains fuse (karyogamy), giving rise to a diploid zygote that then undergoes meiosis. The haploid nuclei migrate into basidiospores, which germinate and generate monokaryotic hyphae. The mycelium that results is called a primary mycelium. Mycelia of different mating strains can combine and produce a secondary mycelium that contains haploid nuclei of two different mating strains. This is the dikaryotic stage of the basidiomyces lifecyle and it is the dominant stage. Eventually, the secondary mycelium generates a basidiocarp, which is a fruiting body that protrudes from the ground; this is what we think of as a mushroom. The basidiocarp bears the developing basidia on the gills under its cap.

    Figure \(\PageIndex{1}\): Lifecycle of a basidiomycete: The lifecycle of a basidiomycete alternates generation with a prolonged stage in which two nuclei (dikaryon) are present in the hyphae.
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