Filamentous fungi -a background

Lecture 2

Fungi are important in natureFungi are important in nature

As decomposersAs pathogens of plants, animals and humans, and in food spoilageAs producers of secondary metabolites, e. g. penicillinIn cheese, bread and wine making

Four phyla of fungiFour phyla of fungi

o Chytridiomycota - no sexual sporeo Zygomycota - zygosporeo Ascomycota - ascosporeo Basidiomycota - basidiospore

Fungal reproductionFungal reproductionAsexually, by forming conidia

Sexually (three steps):•Plasmogami (dikaryon)•Karyogami (zygote forms)•Meiosis (sexual spore forms):

•ZygosporeZygospore•AscosporeAscospore•BasidiosporeBasidiospore

ChytridiomycotaChytridiomycota

ZygomycotaZygomycota

Gametangia fuse to produce a Gametangia fuse to produce a zygospore (zygospore (Rhizopus stoloniferRhizopus stolonifer))

AscomycotaAscomycota

Ascomycota -32 300 described species

• Powdery mildews

• Nectria cankers of trees (Nectria galligena)

• Brown rot of stone fruit (Monilia fructicola)

• Chestnut blight (Cryphonectria parasitica)

• Dutch elm disease (Ophiostoma ulmi)

• Most yeasts

• Morels and truffles

Characteristics of Ascomycota• Septate hyphae• Uninucleate or multinucleate hyphae• Heterothallic or homothallic• Sexual spore = ascospore, produced in sac

called ascus. Usually 8 ascospores per ascus.

• Ascocarp (fruiting body) can be of three different types: cleistothecium, perithecium or apothecium.

Botrytis cinereaBotrytis cinerea - a fungus -causes - a fungus -causes grey moldgrey mold

Powdery mildew of cucumber

Cleistothecia of powdery mildew

Anthracnose of cucurbits

Anthracnose of Anthracnose of melon caused by melon caused by Colletotrichum Colletotrichum orbiculareorbiculare

Eye spot disease of strawberryRamularia grevilleana,

Mycosphaerella fragariae

Canker, Nectria galligena

Perithecium of Nectria galligena

PenicilliumPenicillium and and AspergillusAspergillus

Examples of Examples of

conidiophores of other conidiophores of other

imperfect fungi or imperfect fungi or

DeuteromycetesDeuteromycetes

Wilts caused by Fusarium oxysporum

Wilt of field grown melon Wilt of field grown melon caused by caused by F. ox.F. ox. formae formae speciales speciales melonismelonis

Darkened vascular Darkened vascular tissue of cucumber tissue of cucumber caused by caused by F. ox.F. ox. f.sp. f.sp. cucumerinumcucumerinum

Life cycles of fusarium wilts

Basidiomycota -22 300 described species

• Mushrooms, stinkhorns, puffballs (Basidiomycetes)

• Rusts (Teliomycetes)

• Smuts (Ustomycetes)

Basidiospores (sexual spore) made on club-Basidiospores (sexual spore) made on club-like structure, called basidium.like structure, called basidium.

BasidiomycotaBasidiomycota

Characteristics of Basidiomycota• Mycelium is septate• Septa are perforated - sometimes with

dolipore (doughnut shaped)

Characteristics of Basidiomycota• Mycelium passes two phases -

monokaryotic and dikaryotic.• Two hyphal ends of the monokaryotic

mycelium (of different mating types) fuse and produce the dikaryotic mycelium.

• The dikaryotic mycelium can divide at the apical cell and form clamp connections.

Basidiomycetes have clamp Basidiomycetes have clamp connectionsconnections

““Fairy ring”Fairy ring”

Fruiting bodies

Fly agaricFly agaric(flugsvamp)(flugsvamp)

Hallocinogenic fungi

• Mushrooms are part of many religious ceremonies in Mexico and Central America. Psilocybe mexicana is a fungus that contains the hallucinogenic drug psilocybin, which is related to LSD and mescaline.

Psilocybe mexicanaPsilocybe mexicana PsilocybinPsilocybin

Rhizoctonia solani• It is a basidiomycete;

teliomorph (Thanatephorus cucumeris) is rare.

• Has very characteristic mycelium; typical of basidiomycete.

• Differentiated into anastomosisanastomosis groups (AGAG) (fusion of hyphae only occur if same anastomosis group)

The disease cycle of Rhizoctonia solani

Characteristics of the rusts (Teliomycetes)

• Sori, in which uredospores are formed.• Were thought to be obligate parasites, but some can

be grown in the laboratory.• Can live on one host - autoecious, or two hosts -

heteroecious.• New races appear constantly; difficult to control.• Spore forms: basidiospore (n), aeciospore (n+n),

uredospore (n+n) and teliospore (2n).

Rusts

Wheat stem rustWheat stem rust ( (Puccinia Puccinia graminisgraminis))

Stem rust of wheat

Rust of roen (rönn)

Rust of raspberry

Disease cycle of cedar-apple rust

Rust of rose

Uredospores of rose rust

Teleutospores, rose rust

Corn smutCorn smut

Corn smut

Teliospores (2N)

MeiosisInfection

Mating Budding cells (1N)FilamentousDikaryon (N+N)

Chlamydospores (1N)The life cycle of smut fungiThe life cycle of smut fungi

(sexual spores)

(asexual spores)