It is a unique kingdom of heterotrophic organisms.

• They show a great diversity in morphology and habitat.

• Fungi are cosmopolitan and occur in air, water, soil, and on animals and plants.

  • They prefer to grow in warm and humid places.

  • Fungi are filamentous (Except Yeast).

    • Their bodies consist of long, slender thread-like structures called hyphae and their network is known as mycelium.

    • Some hyphae are continuous tubes filled with multinucleated cytoplasm known as coenocytic hyphae.

• The cell walls of fungi are composed of chitin and polysaccharides.

Examples:

• The common mushroom and toadstools.

• White spots seen on mustard leaves are due to a parasitic fungus.

• Yeast is used to make bread and beer. (unicellular fungi)

• Puccinia causes rusting in wheat.

• Penicillin is a source of antibiotics.

Saprophytes:

Most fungi are heterotrophic and absorb soluble organic matter from dead substrates.

Parasites:

• The fungi are heterotrophic and depend on living plants and animals.

• They can also live as symbionts – in association with algae as lichens and with roots of higher plants as mycorrhiza.

Reproduction:

• Vegetative means – fragmentation, fission, and budding.

• Asexual reproduction is by spores called conidia or sporangiospores or zoospores.

• Sexual reproduction is by oospores, ascospores, and basidiospores****.

  • The various spores are produced in distinct structures called fruiting bodies.

  • The fusion of protoplasms between two motile or non-motile gametes is called plasmogamy.

    • Fusion of two nuclei called karyogamy.

    • Meiosis in zygotes results in haploid spores.

    • When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse.

Exception: In Ascomycetes and Basidiomycetes, an intervening dikaryotic stage (two nuclei per cell) occurs which is called a dikaryon and the phase is called dikaryophase of fungus.

Phycomycetes:

• Members of Phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants.

• The mycelium is aseptate and coenocytic.

  • Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile).

    • These spores are endogenously produced in sporangium.

  • A zygospore is formed by the fusion of two gametes.

    • These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).

Examples: Mucor, Rhizopus (the bread mold), and Albugo (the parasitic fungi on mustard).

Ascomycetes:

• They are mostly multicellular. (Exception: yeast or Saccharomyces)

• They are saprophytic, decomposers, parasitic or coprophilous.

• Mycelium is branched and septate.

  • The asexual spores are conidia produced exogenously on the special mycelium called conidiophores.

    • Conidia on germination produce mycelium.

  • Sexual spores are called ascospores which are produced endogenously in sac-like asci.

    • These asci are arranged in different types of fruiting bodies called ascocarps.

Examples: Aspergillus, Claviceps, and Neurospora.

Note: Many members like morels and truffles are edible and are considered delicacies.

Basidiomycetes:

• They grow in soil, on logs and tree stumps, and in living plant bodies as parasites.

• The mycelium is branched and septate.

  • The asexual spores are generally not found, but vegetative reproduction by fragmentation is common.

    • The sex organs are absent, but plasmogamy is brought about by the fusion of two vegetative or somatic cells of different strains or genotypes.

      • The resultant structure is dikaryotic which ultimately gives rise to basidium.

    • Karyogamy and meiosis take place in the basidium producing four basidiospores.

• The basidiospores are exogenously produced on the basidium.

  • The basidia are arranged in fruiting bodies called basidiocarps.

Examples: Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).

Deuteromycetes:

• They are commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are found.

• Once perfect (sexual) stages of members of Deuteromycetes were discovered they were often moved to ascomycetes and basidiomycetes.

  • The Deuteromycetes reproduce only by asexual spores known as conidia.

    • The mycelium is septate and branched.

  • Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in mineral cycling.

Examples: Alternaria, Colletotrichum, and Trichoderma.