Filamentous fungi a background
Lecture 1 and 2
What are they?
What are they doing?
Fungi are important in nature
As decomposers
As pathogens of plants, animals
and humans, and in food spoilage
As producers of secondary
metabolites, e. g. penicillin
In cheese, bread and wine making
Fly agaric
(flugsvamp)
Ergot of rye
• Caused by Claviceps
purpurea.
• Cause of ergotism:
“Holy Fire” or “St.
Anthony’s Fire”.
• Sclerotia are
dangerous.
• Witch hunts.
• Caused low fertility
and death in 14th-18th
century Europe.
Other toxins made by fungi
• Endophytic fungi (Acremonium) in grasses
can be toxic to cattle (fescue toxicosis)
• Other mycotoxins:
– Ochratoxins
– Aflatoxins - carcinogenic
– Fumonosins - blind stagger of horses
– Patulin - bleeding in lungs and brain,
kidney damage, cancer
Medicines that come from fungi
• Penicillin. Penicillium chrysogenum.
Alexander Fleming, 1928.
• Cephalosporin
• Cyclosporin
Fungal diseases of humans - mycoses
• Trichophyton rubrum. Causal agent of athlete’s
foot. Came from tropics.
• Candida albicans. Causes candidiasis = yeast
infections.
– Around genitalia.
– Disease of mouth and throat.
• Blastomycosis, Cryptococcosis, Histoplasmosis,
Aspergillosis are other diseases.
Smut infection of a wheat field in
Eastern Washington (1956)
Ustilago maydis - the corn smut fungus
Ustilago maydis
is a popular food
delicacy in Mexico
Examples of symptoms
caused by fungi:
Cankers
Storage rots of fruits and
vegetables
Rust, mildews
Leaf spots
Pathogen life styles
Necrotrophs - kill
host cells with
toxins and
hydrolytic enzymes.
Ex: Botrytis cinerea.
Biotrophs - specialize
on a living host.
Ex. Powdery
mildews and rusts.
Hemibiotrophs - start out
biotrophic. Then, they kill the host
cells. Ex. Phytophthora infestans.
Botrytis cinerea - a fungus -causes
grey mold
Grey mould of strawberries
Characteristics of grey mold
• B. cinerea is a necrotroph, entering the plant through dead
or dying tissue.
• It is a pathogen that attacks almost any known plant
species. It invades healthy tissue through dead petals or
leaves or dying wood.
Botrytis cinerea causes rots on
fruits and vegetables, blossom
blights, damping off, stem
cankers, leaf spots and bulb rots.
scleriotia
In the field, blossom blight often
precede the fruit rots
The fungus enters the fruit
through the dead flower petals.
The fungus Botrytis cinerea
Develops grey
mycelium with long,
branched
conidiophores with
clusters of one-celled,
ovoid conidia.
The conidiophores and
conidia resemble a
grapelike cluster.
Botrytis cinerea of tomato
Botrytis cinerea of tomato
Spots on fruits are from spores that have landed
Attack on fruit originated in the flower
Grey mould - continued
•B. cinerea overwinters as mycelium in
decaying plant debris or as sclerotia black, hard resting structures.
•It also attacks fruit and vegetables
during storage. The fruits rot internally
(often from the flower end) and a soft
mycelial mat develops on the surface.
The fungus does most damage when it is
very humid and damp.
Life cycle of Botrytis cinerea
Powdery mildew on rose
• Sphaerotheca pannosa
is the causal agent of
powdery mildew on
roses. It is an example
of a biotroph: It grows
only in living plant
tissue.
• The white, powdery
appearance is due to
conidiophores/conidia
Powdery mildew on Poinsettia
Powdery mildew on squash
Powdery mildew on cucumber
Life cycle of powdery mildew
Rust of roen (rönn)
Rust of raspberry
Rust of rose
Four phyla of fungi
o Chytridiomycota - no sexual spore
o Zygomycota - zygospore
o Ascomycota - ascospore
o Basidiomycota - basidiospore
Characteristics of fungi
Fungi have hyphae. A mass
of hyphae is a mycelium.
The hyphae may be septate
or aseptate.
Specialized hyphae,
haustoria are feeding
structures.
Fungal reproduction
Asexually, by forming conidia
Sexually (three steps):
•Plasmogami (dikaryon)
•Karyogami (zygote forms)
•Meiosis (sexual spore forms):
•Zygospore
•Ascospore
•Basidiospore
Incompatibility systems
Fungi (ascomycetes) have mating types.
They are designated MATa and MATa
(yeast), MATA and MATa (Neurospora)
or MAT1-1 and MAT1-2.
Sexual reproduction in a heterothallic
ascomycete requires the participation of
different mating types. In a homothallic
strain the fusing individuals are of the
same mating type. The inability of two
individuals of the same mating type to
fuse is called vegetative incompatibility.
Chytridiomycota
Zygomycota
Gametangia fuse to produce a
zygospore (Rhizopus stolonifer)
Ascomycota
Penicillium and Aspergillus
Examples of
conidiophores of other
imperfect fungi or
Deuteromycetes