In this article we will discuss about:- 1. Meaning of Basidiomycetes 2. Salient Features of Basidiomycetes 3. Significance.
Meaning of Basidiomycetes:
Basidiomycetes are fairly a large group of fungi represented by about 1100 genera consisting of 16,000 species and classified under the sub-division Basidiomycotina. Many of the Basidiomycetes are the familiar larger fleshy fungi such as mushrooms, toadstools, puffballs, geasters, stinkhorns, earth stars, bird’s nest fungi, jelly fungi bracket fungi, rusts, and smuts.
Majority of the Basidiomycetes are saprophytes causing decay of litter, wood or dung. A few forms are found as symbionts forming mycorrhizae in trees, whereas some ones are destructive parasites destroying a wide range of woody and herbaceous plants. Rusts and smuts are pathogenic to plants causing important diseases and are restricted to live tissues of their respective host plants.
Salient Features of Basidiomycetes:
(i) Thallus is usually mycelial (some are yeasts called basidiomycetous yeasts). Hyphae are septate. In some cases, a number of hyphae lying parallel to one another are joined together to form thick strands enveloped in a sheath or cortex and behave as a unit or tissue. This modified hyphal form is called rhizomorph.
(ii) The mycelium of most of the Basidiomycetes passes through three distinct stages of development, which are called primary mycelium (monokaryotic and develops from the germination of sexual spore called basidiospore), secondary mycelium (dikaryotic and develops from primary mycelium after the process of plasmogamy during sexual reproduction), and tertiary mycelium (represented by well-matured secondary mycelia that compose the fruiting bodies called basidiomata of complex Basidiomycetes).
(iii) Septa in hyphae are simple or characteristic dolipore. The dolipore septum flares sharply and broadly in the middle portion forming a barrel-shaped structure with open ends, which is covered by membranous structure called paranthesome or septal pore cap.
(iv) Cell wall is made up of chitin and glucans.
(v) In all the Basidiomycetes, except the rusts, a specialized structure called clamp-connection is formed on the secondary mycelium. Clamp-connection is a device for the perpetuation of dikaryophase in the secondary mycelia in Basidiomycetes.
(vi) The asexual reproduction takes place by oidia, conidia, or chlamydospore formation. Out of the several types of spores developed in the life cycle of rusts and smuts, some (e.g., uredospore) function as asexual spores. The higher taxa of this class lack asexual reproduction.
(vii) No specialized sex organs develop in Basidiomycetes and sexual reproduction takes place by conjugation of nuclei of two different strains.
(viii) During sexual reproduction, the dikaryotic cell is formed by spermatization, somatogamy, clamp- connection, or Buller phenomenon.
(ix) Karyogamy does not occur just after plasmogamy because there exists a prolonged dikaryophase between plasmogamy and karyogamy. The fusion of nuclei of two different strains occurs within the basidial mother cell.
(x) Meiosis takes place just after karyogamy resulting in haploid daughter nuclei that are used in the formation of basidiospores.
(xi) Basidiospores are the characteristic haploid sexual spores of basidiomycetous fungi, which are produced exogenously on the surface of basidia after karyogamy and meiosis within nuclei lying inside basidia. If the sexual spore of a fungus is a basidiospore, the fungus is a Basidiomycete regardless of any other character. This one character distinguishes Basidiomycetes from all other fungi.
(xii) Except rusts and smuts, the Basidiomycetes usually produce fruiting bodies called basidiomata (sing. basidioma), which were earlier called basidiocarps.
Significance of Basidiomycetes:
(i) Rusts and smuts cause many diseases of cereals and other economically important plants resulting in great loss in production that brings famine in certain parts of the world.
(ii) Mushrooms are edible and are enjoyed by mycophagists for food and flavour. Agaricus, Pleurotus, and Volvoriella are cultivated on large scale throughout the world. Mushroom cultivation industry is growing fastly.
(iii) Some mushrooms (called toadstools) such as Amanita spp. are deadly poisonous, while others such as Psilocybe spp. produce hellucinogenic chemical substances.
(iv) The polypores cause enormous damage to forest trees as parasites and to timber as saprophytes.
(v) Mycelia of basidiomycetous fungi play significant role in decomposition of organic matter and recycling of nutrients. It is because they bear ability to produce various extracellular enzymes which break down complex chemicals like cellulose and lignin.