KINGDOM FUNGI
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KINGDOM FUNGI
(General Characteristics)
• They show a great diversity in morphology and habitat.
• Fungi are cosmopolitan; occur in air, water, soil, and on animals and plants. They prefer to grow in warm and humid
places.
•
Fungi are filamentous & multicellular except yeasts, which are unicellular.
• Their body consists of long, slender thread-like structures called hyphae.
• The network of hyphae is known as mycelium. Some hyphae are continuous tube filled with multinucleated cytoplasm
these are called coenocytic hyphae. Others have septa or cross walls in their hyphae.
• The cell walls of fungi are composed of chitin and polysaccharides.
• Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes.
Some are called parasites. Many also live as symbionts – in association with algae as lichens and with roots of higher
plants as mycorrhiza.
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• Reproduction in fungi can take place by 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 sexual cycle involves the following three steps:
(i) Plasmogamy : Fusion of protoplasms between two motile or
non-motile gametes.
(ii) Karyogamy : Fusion of two nuclei.
(iii)Meiosis in zygote resulting in haploid spores.
When a fungus reproduces sexually, two haploid hyphae of compatible
mating types come together and fuse.
In some fungi the fusion of two haploid cells immediately results in
diploid cells (2n). However, in other fungi an intervening dikaryotic
stage (n + n i.e. two nuclei per cell) occurs; such a condition is called a
dikaryon and the phase is called dikaryophase of fungus.
Later, the parental nuclei fuse and the cells become diploid. The fungi
forms fruiting bodies in which reduction division occurs, leading to
formation of haploid spores.
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CLASSIFICATION OF KINGDOM FUNGI
The morphology of the mycelium, mode of spore formation and fruiting bodies, form
the basis for division of the kingdom into various classes.
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I) PHYCOMYCETES (LOWER OR ALGAL FUNGI)
•
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.
Fig: Rhizopus
•
Fig: Mucor
Fig: Albugo
Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These
spores are endogenously produced in sporangia.
•
Zygospores are formed by fusion of two gametes. These gametes are similar in morphology
(isogamous) or dissimilar (anisogamous or oogamous). Some common examples are Mucor, Rhizopus
(the bread mould) and Albugo (parasitic on mustard).
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ECONOMIC IMPORTANCE OF PHYCOMYCETES
ü Rhizopus and Mucor grow on fruits and vegetables and cause spoilage.
ü Cause diseases in plants
• Phytophthora infestans - Late blight of potato
• Albugo candida – White rust of crucifers
• Pythium – damping off disease in many crucifers
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II) ASCOMYCETES (SAC-FUNGI)
•
Unicellular, e.g., Yeast (Sacharomyces) or multicellular, e.g., Penicillium.
•
Saprophytic, decomposers, parasitic or coprophilous (growing on dung).
•
Mycelium is branched and septate and septa are porous.
•
The asexual spores are conidia produced exogenously on the special
mycelium called conidiophores. Conidia on germination produce mycelium.
•
Sexual reproduction involves plasmogamy leading to a dikaryotic stage. This
is followed by karyogamy and meiosis in the dikaryon, which becomes an
ascus (pl: asci). The 4 nuclei formed by meiosis undergo mitosis to form 8
spores called the ascospores. These are produced endogenously. The asci are
arranged in fruiting bodies called ascocarps.
Penicillium
Aspergillus
Yeast
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ECONOMIC IMPORTANCE OF
ASCOMYCETES
ü Saccharomyces cerevisae (baker’s yeast) is
employed in bakeries and breweries for alcohol
formation.
ü Penicillium notatum and P. chrysogenum are
employed in the production of penicillin, an
antibiotic.
ü Morel (Morchella) and truffles are edible
delicacies.
ü Penicillium roqueforti is used for flavoring
roquefort cheese.
ü Neurospora crassa is widely used for biochemical
and genetic researches.
ü Claviceps purpurea causes the disease ergot of
rye.
III)
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BASIDIOMYCETES (CLUB FUNGI)
Most advanced and most commonly seen fungi as their fructification are often large and conspicuous. e.g.
mushrooms, bracket fungi or puffballs.
•
They grow in soil, on logs and tree stumps and in living plant bodies as parasites, e.g., rusts and smuts.
•
The mycelium is branched and septate and septa are porous. The asexual spores are generally not found,
but vegetative reproduction by fragmentation is common.
•
Sex organs are absent, but plasmogamy is brought about by 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 (pl: basidia). The basidia are arranged in fruiting bodies called
basidiocarps.
•
Some common example are Agaricus (mushroom) , Ustilago (smut) and Puccinia (rust fungus).
Agaricus
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ECONOMIC IMPORTANCE OF BASIDIOMYCETES
ü Ustilago tritici causes smut disease in wheat.
ü Puccinia causes rust of wheat and other cereals.
ü Polyporus decomposes wood.
ü Agaricus ( mushroom) is edible.
SMUT OF WHEAT
RUST OF WHEAT
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IV) DEUTEROMYCETES (IMPERFECT FUNGI)
•
An artificial class of fungi, includes all those fungi in which sexual stage is either absent or not known.
•
Commonly known as imperfect fungi because only the asexual or vegetative phases of these fungi are
known.
•
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.
•
e.g. Alternaria, Colletotrichum and Trichoderma.
Trichoderma
Leaf infection due to Alternaria
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ECONOMIC IMPORTANCE OF DEUTEROMYCETES
ü Alternaria solani causes early blight of potato.
ü Colletotrichum falcatum causes red rot of sugar cane.
ü Arthrobotrys is a predatory fungus, that feeds on living nematodes.
ü Trichoderma polysporum is a source of immunosuppressive drug called
cyclosporin A.
ü Trichoderma also serves as a bio-control agent for management soil born
diseases.
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