Basidiomycota

Mushroom Growing 4 You

Growing Mushrooms at Home

Get Instant Access

This large group of some 25 000 species contains the true mushrooms and toadstools as well as other familiar fungi such as puffballs and bracket fungi. In fact the great majority of the fungi that we see in fields and woodlands belong to the Basidiomycota. They are of great economic importance in the breakdown of wood and other plant material (Chapter 16). The group derives its common name of the club fungi from the way that the spore-bearing hyphae involved in reproduction are swollen at the tips, resembling clubs (the basidia: Figure 8.7).

Figure 8.7 Different forms of basidia. The club-like appearance of basidia gives the Basid-iomycota their common name of 'club Fungi'. From Langer, E: Die Gattung Botryobasidium DONK (Corticiaceae, Basidiomycetes). Bibl Mycol 158, 1-459. Reproduced by permission of Schweizerbart Science Publishers (http://schweizerbart.de)

Figure 8.7 Different forms of basidia. The club-like appearance of basidia gives the Basid-iomycota their common name of 'club Fungi'. From Langer, E: Die Gattung Botryobasidium DONK (Corticiaceae, Basidiomycetes). Bibl Mycol 158, 1-459. Reproduced by permission of Schweizerbart Science Publishers (http://schweizerbart.de)

Asexual reproduction occurs much less frequently in basidiomycetes than in the other types of fungi. When it does occur, it is generally by means of conidia, although some types are capable of fragmenting their hyphae into individual cells, each of which then acts like a spore and germinates to form a new mycelium.

Sexual reproduction in a typical mushroom involves the fusion of haploid hyphae belonging to two compatible mating types to produce a dicaryotic mycelium in which each cell has two haploid nuclei (Figure 8.8). The most striking feature of this secondary mycelium is the clamp connection; this is unique to the Basidiomycota and is a device for ensuring that as growth continues, each new cell has one nucleus from each of the

Haploid ff^Cif-"---- basidiospores cS

Meiosis n

Germination

Haploid ff^Cif-"---- basidiospores

Meiosis n

Germination

Aerial 182 Jpg

Basidia on gills

Haploid mycelium

Dicaryotic mycelium

Fusion of hyphae from compatible mating types

Figure 8.8 Life cycle of the Basidiomycota. Most of the fungus exists as a mycelial mass underground. The mushroom is an aerial fruiting body that facilitates the dispersal of spores

Basidia on gills

Asexual reproduction by fragmentation

Asexual reproduction by fragmentation

Haploid mycelium

Dicaryotic mycelium n+n

Fusion of hyphae from compatible mating types

Figure 8.8 Life cycle of the Basidiomycota. Most of the fungus exists as a mycelial mass underground. The mushroom is an aerial fruiting body that facilitates the dispersal of spores

Box 8.1 Clamp connections

Imagine the situation in a dicaryotic cell when mitosis took place. The most likely outcome would be that as the two nuclei divided, both of one type would end up in one daughter cell and both of the other type in the other. As growth and cell division proceeds in the secondary mycelium, it is therefore necessary to ensure that the dicaryotic state is maintained, i.e. that each new cell inherits one nucleus of each type from its parent. This is achieved by means of clamp connections.

a)

o

• :>

b)

o

o

r^i

c)

o

o o

d)

o

As the terminal hyphal cell elongates (b), a tube-like clamp connection grows out backwards (c). As this happens, one nucleus enters the clamp and mitosis occurs simultaneously in both parental nuclei. A septum is formed to separate the first pair of nuclei (d), then, as the loop of the clamp connection is completed, a second septum separates the second pair (e). The result is two new daughter cells, each with one copy of each nuclear type.

parent mating strains (see Box 8.1). This dicaryotic secondary mycelium continues to grow, overwhelming any remaining haploid hyphae from the parent fungi.

When the secondary mycelium has been developing for some time, it forms a dense compact ball or button, which pushes up just above the surface and expands into a basidiocarp; this is the mushroom itself. Stalk formation and upward growth is extremely rapid; a stalk or stipe of 10 cm can be formed in only about 6-9 hours. The growth is initially towards light (positive phototropism) and then upward (negative geotropism). As the cap expands, fleshy flaps radiating from the centre of its underside open up. These are the gills, made up of compacted hyphae with numerous basidia arranged at right angles. As each basidium matures, its two nuclei finally fuse, and then undergo meiosis to produce four haploid basidiospores. A single large mushroom can produce millions of basidiospores in the space of a few days. They are discharged from the end of the basidia and then fall by gravity from the gills. Air currents then carry them away for dispersal. Upon finding a suitable substratum, the spores germinate into a haploid mycelium just below the surface of the soil, thus completing the life cycle.

THE FUNGI Table 8.1 Some fungal diseases of humans

Disease

Histoplasmosis Blastoplasmosis Cryptococcosis Cutaneous mycoses Pneumocystis pneumonia Candidiasis ('thrush') Aspergillosis

Fungus

Histoplasma capsulatum Blastomyces dermatitidis Cryptococcus neoformans Trichophyton spp. Pneumocystis carinii Candida albicans Aspergillus fumigatus

Was this article helpful?

0 0
Cure Your Yeast Infection For Good

Cure Your Yeast Infection For Good

The term vaginitis is one that is applied to any inflammation or infection of the vagina, and there are many different conditions that are categorized together under this ‘broad’ heading, including bacterial vaginosis, trichomoniasis and non-infectious vaginitis.

Get My Free Ebook


Post a comment