Mycota (Fungi)

Fungi form the kingdom Mycota. They are eukaryotic, mostly multicellular, heterotrophic organisms that live as the major decomposers of the ecosystem. This chapter covers their general characteristics, classification, representative genera (Mucor, yeast and mushrooms), and their economic importance.

General Characteristics of Fungi

• Fungi are eukaryotic, multicellular and heterotrophic organisms.
• The body is a thallus (not differentiated into root, stem and leaves).
• The thallus is made up of thread-like hyphae (singular: hypha).
• They occur in different habitats.
• They are the major decomposers of the ecosystem.
• They are achlorophyllous (lack chlorophyll).
• The cell wall is made up of chitin.
• The sex organs are usually unicellular.

Classification

According to Alexopoulos (1962), on the basis of the organization of the vegetative thallus, the morphology of the reproductive structures, the way spores are produced and the particular life cycle involved, the kingdom Mycota is classified as follows.

1) Oomycetes

• They range from a primitive unicellular thallus to a profusely branched filamentous mycelium.
• Most of them are terrestrial and obligate parasites.
• Sexual reproduction takes place by the formation of oospores and asexual reproduction by biflagellate zoospores.
• Example: Phytophthora infestans.

2) Zygomycetes

• They are mostly saprophytic and some are parasitic.
• Sexual reproduction occurs by conjugation of gametangia, resulting in the formation of a zygospore.
• Examples: Rhizopus, Mucor.

3) Ascomycetes

• They are mostly terrestrial, occurring as saprophytes or parasites.
• Asexual reproduction is by non-motile spores: conidia, oidia or chlamydospores.
• Examples: Saccharomyces cerevisiae, Aspergillus.

4) Basidiomycetes

• The mycelium is highly developed, profusely branched and septate.
• They are saprophytic or parasitic.
• Asexual reproduction takes place by fragmentation, budding, oidia and conidia.
• Examples: mushrooms, Puccinia.

5) Deuteromycetes

• These fungi are saprophytes as well as parasites.
• The mycelium consists of well-developed, septate, profusely branched hyphae without haustoria.
• The sexual (perfect) stage is absent in the life cycle, so they are called fungi imperfecti.
• Examples: Alternaria, Helminthosporium.

Classification outline

The kingdom Mycota is grouped as:

• Myxomycotina (slime moulds)
• Eumycotina (true fungi)
  • Lower true fungi (aseptate mycelium): Oomycetes (water moulds), Zygomycetes (conjugation fungi)
  • Higher true fungi (septate mycelium): Ascomycetes (sac fungi), Basidiomycetes (club fungi), Deuteromycetes (imperfect fungi)

Difference between Ascomycetes and Basidiomycetes