Chapter 23
The Fungi
The Fungi
Outline
Characteristics
Structure
Reproduction
Evolution
Sac Fungi
Yeasts
Club Fungi
Smuts and Rusts
Imperfect Fungi
Symbiotic Relationships
2
The Fungi
3
Characteristics of the Fungi
Kingdom Fungi contains 80,000 spp
Mostly multicellular eukaryotes that share a
common mode of nutrition
Heterotrophic
Cells release digestive enzymes and then absorb
resultant nutrient molecules
Some are parasitic
Several have mutualistic relationship
The Fungi
Structure of Fungi
Body (thallus) of most fungi is multicellular
mycelium (yeasts are unicellular)
Consists of a vast network of thread-like hyphae
- Septate fungi have hyphae with cross walls
- Nonseptate fungi are multinucleated
- Hyphae grow from tip
Give the mycelium a large surface area per unit
volume
Cell walls of chitin, like insect exoskeleton
Excess food stored as glycogen as in animals
Possibly evolved from red algae - both lack
flagella
4
Mycelia and Hyphae of Fungi
5
The Fungi
Reproduction of Fungi
Both sexual (in most) and asexual reproduction
Sexual reproduction involves three stages:
Haploid Hyphae
Dikaryotic Stage
Diploid Zygote
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The Fungi
7
Reproduction of Fungi
During sexual reproduction, hyphae from two different
mating types fuse
Hyphae that contain paired haploid nuclei are said to be
dikaryotic
Nuclear fusion produces diploid nucleus, which produces
haploid windblown spores by meiosis
Spores germinate directly into haploid hyphae without
embryological development
Asexual reproduction usually involves the production of
windblown spores
Unicellular yeasts reproduce by budding
Dispersal of Spores
8
Diversity of Fungi:
Zygomycota
The Fungi
Zygospore Fungi
Phylum Zygomycota
Mainly saprotrophs decomposing animal
and plant remains
Black bread mold - Rhizopus stolonifer
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Black Bread Mold,
Rhizopus stolonifer
10
Diversity of Fungi:
Zygomycota
The Fungi
11
Life cycle
Hyphae of opposite mating types grow toward each other
Hyphae swell at tips; cross walls develop behind each end;
form gametangia
Gametangia merge resulting in a large multi-nucleate cell
- Nuclei of the two mating types pair and then fuse
- A thick wall develops around the zygospore
The zygospore becomes dormant for period
Sporangiophore(s) then sporangia develop, spores
released
Spores dispersed by air currents; germinate into mycelia
Diversity of Fungi:
Sac Fungi
The Fungi
12
Phylum Ascomycota - about 60,000 species of sac fungi
Most are saprotrophs that digest resistant materials
containing cellulose, lignin, or collagen
Most are composed of septate hyphae
Neurospora, experimental organism for the one-geneone-enzyme studies
Morels and truffles, famous gourmet delicacies revered
throughout the world
Many plant diseases: Powdery mildews; leaf curl fungi;
ergot of rye; chestnut blight and Dutch elm disease
Aspergillus and Candida cause serious human
infections
Talaromyces (formerly Penicillium) is source of penicillin
Sac Fungi:
Reproduction - Asexual
The Fungi
13
Life cycle
Asexual reproduction is the norm
Yeasts usually reproduce by budding
- A small bulge forms on side of cell
- Receives a nucleus and gets pinched off and becomes full
size
The other ascomycetes produce spores called conidia or
conidiospores
Vary in size and shape and may be multicellular
 Conidia usually develop at the tips of conidiophores

- Conidiophores differ in appearance and are diagnostic
- Conidia are windblown
- Conidia of Cladosporium cause allergies - concentrations of
more than 35,000 conidia/m3 over Leiden (Germany)
Asexual Reproduction in Sac Fungi
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Sac Fungi:
Reproduction - Sexual
The Fungi
15
Life cycle, cont.
Sexual reproduction
Ascus refers to the fingerlike sac that develops
during sexual reproduction
Asci usually surrounded and protected by sterile
hyphae within an ascocarp
- In cup fungi, ascocarps are cup-shaped
- In morels they are stalked and are pitted like the
surface of the moon
Haploid hyphae fuse to make diploid nucleus
Mitosis and then meiosis produces 8 ascospores
Sexual Reproduction in Sac Fungi
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Black Mold
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Tineas
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Sac Fungi:
Reproduction - Yeasts
The Fungi
19
Term “yeasts” is loosely applied to unicellular
fungi, many of which are ascomycetes
Budding is common form of asexual reproduction
Sexual reproduction results in the formation of
asci and ascospores
When some yeasts ferment, they produce ethanol
and carbon dioxide
Diversity of Fungi:
The Club Fungi
The Fungi
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Phylum Basidomycota – 22,000 spp
Familiar toadstools, mushrooms, bracket fungi,
puffballs, stinkhorns – some deadly poisonous
Also plant diseases such as the smuts and rusts
Mycelium composed of septate hyphae
The Club Fungi:
Reproduction
The Fungi
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Usually reproduce sexually
Haploid hyphae fuse, forming a dikaryotic (n + n)
mycelium
Dikaryotic mycelium forms fruiting bodies called
basidiocarps
Contain club-shaped structures called basidia
Nuclear fusion followed by meiosis produces
basidiospores (up to 40,000,000 per hour)
Club Fungi
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Club Fungi
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The Club Fungi:
Smuts and Rusts
The Fungi
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Smuts and rusts are club fungi that parasitize cereal
crops
Great economic importance because of annual crop
losses
- Do not form basidiocarps
Life cycle of rusts often requires two different plant host
species
Black stem rust of wheat uses barberry bushes
Blister rust of white pine uses currant and gooseberry
bushes
Eliminating these bushes in crop areas keeps rusts in
check
Wheat rust
- Controlled by breeding new resistant strains of wheat
- Requires continuous development, because rust can mutate
Smuts & Rusts
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Symbiotic Relationships:
Lichens
The Fungi
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Symbiotic association between a fungus and a
cyanobacterium or green alga
Specialized fungal hyphae penetrate
photosynthetic symbiont
Transfer nutrients directly to the fungus
Possibly mutualistic, but fungal symbiont
probably a parasite of photosynthetic symbiont
Photosynthetic symbiont independent
Fungal symbiont usually can’t grow alone
Symbiotic Relationships:
Lichens
The Fungi
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Three morphological types
Compact crustose lichens - seen on bare rocks or
on tree bark
Fruticose lichens – shrub-like
Foliose lichens - leaf-like
Can live in areas of extreme conditions and
contribute to soil formation
Sensitive indicators of air pollution
Lichen Morphology
28
Symbiotic Relationships:
Mycorrhizae
The Fungi
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Mutualistic relationships between soil fungi and the roots
of most familiar plants
Give plant greater absorptive surface
Help plants acquire mineral nutrients in poor soil
Fungal symbiont usually a sac fungus
Hyphae may enter cortex of root, but not cytoplasm
- Ectomycorrhizae form a mantle that is exterior to the root,
and they grow between cell walls.
- Endomycorrhizae penetrate only the cell walls
Earliest fossil plants have mycorrhizae associated with
them
Plant Growth Experiment
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The Fungi
Review
Characteristics
Structure
Reproduction
Evolution
Sac Fungi
Yeasts
Club Fungi
Smuts and Rusts
Imperfect Fungi
Symbiotic Relationships
31
Ending Slide Chapter 23
The Fungi