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Basidiomycetes in lab tomorrowBasidiomycetes in lab tomorrow• Quiz (Lab manual pages 7-13 Isolation of fungal pathogens

and 51-57 Ascos III, and intro pages for Basidiomycetes (pp. 59-61) and Race I.D. of Wheat Stem Rust (p. 109).

• Look at Basidiomycete diseases – signs and symptoms –emphasis is understanding disease cycles and knowingthe types of spores present on the host tissues

• Inoculate wheat cultivars with rust isolates

Basidiomycetes (the club fungi)

• Septate hyphae• Dikaryotic (paired haploid) nuclei (n + n)• Cell wall made of chitin• Sexual reproduction: basidiospores

produced externally on a club-like one or four celled basidium

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Diseases caused by Basidiomycetes

Four major pathogen groups• Root rots & web blights (‘sterile fungi’) • Root and heart rots of forest and

fruit trees• Smuts of cereals • Rusts of grasses, pines, rose family,

coffee, etc

1st Group: Root rot and web blight pathogens(Facultative parasites)

• In herbaceous plants, diseases caused by “sterile” fungi --- (some produce a teliomorph, but only rarely)

• Produce sclerotia (or other vegetative survival structure) but generally no asexual spores

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Damping-off of alfalfacaused by RhizoctoniaRhizoctonia

Lesion caused by Lesion caused by RhizoctoniaRhizoctonia spp.spp.

Group 1 pathogen:Group 1 pathogen:

RhizoctoniaRhizoctonia-causes many, many diseases-mostly soilborne

Black-coloredsclerotia ofRhizoctoniasolanion a potato

RhizoctoniaRhizoctoniaHyphae branch at right anglesHyphae branch at right angles

No asexual sporesNo asexual spores

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Other diseases of Group 1 basidiomycetes:

Red thread

Graysnowmold

Turf diseases:

22ndnd Group: Rots of treesGroup: Rots of trees(Facultative parasites)(Facultative parasites)

• Life strategy: Facultative parasite• Fruiting body (basidiocarp) is a mushroom• Fungus spreads from tree to tree via root-to-

root contact or rhizomorphs• Large host range: oak, grape, pine ,fruit trees• Aggressive colonizer of dead wood

Example: Armillaria root rot

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Mushrooms of

Armellaria

basidium from a mushroom or conk

basidiospores

In the gills of the mushroom:

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Rhi

Rhizomophs

Rhizomorphsare aggregated,mycelium strandsused by Armilleriato grow along rootsand from root to root.

Mushroom ‘fairy ring’ in golf green.

In the woods, Armillaria

fairy rings can have diameters of many miles, giving this

pathogen the nickname, “Humungous

Fungus”.

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Another Example: Heart rots

• In living trees, decay of older, central wood (heartwood)

• Caused by large fleshy fungi• Basidia are produced on basidiocarps

(conks or mushrooms)

Ken’s housein grad school

The tree fellon Ken’s bedroom

He narrowly escaped the work of aplant pathogen

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The fallen poplar tree had ‘heartrot’

Fruiting bodies (conks) of the heartrot pathogen

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Pore of conk producing basidiomycete

Basidium with basidiospores

Billion spores per day

Number of basidiospores produced in a conk

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3rd group: Smuts • Obligate parasites – known as ‘replacement

diseases’ because fungal teliospores replace normal seeds of plant

• Two kinds of spores: 1) teliospores(overwintering) that germinates to form a 2) basidium bearing basidiospores (infective)

• Host tissue infected initially helps to understand disease cycles of smut fungi:seed via flowers - leading to systemic infectionemerging coleoptiles in soil -systemic infectionvery young, growing tissues -local infections

Loose smut of barleyLoose smut of barley--Seed infection via Seed infection via

flowerflowerSpores from diseased heads infect healthy flowers

Healthy appearing butinfected seed leads to diseased plants in next crop

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Common bunt (covered Common bunt (covered smut) of wheatsmut) of wheat-- Infection of Infection of emerging coleoptiles emerging coleoptiles via soil infestation or via soil infestation or contaminated seedcontaminated seed

cloud of smut spores

Spores on Spores on healthy seed (or healthy seed (or in soil) infect in soil) infect next crop after next crop after seed is plantedseed is planted

Common corn smutCommon corn smut-- Local infectionLocal infection

In Mexico,immature smut balls are considereda delicacy

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Teliospores of Smut Fungi

Long-livedResting spores

Germination of teliospores (n+n) of smut fungi to produce basidiospores (n)

Two basidiospores (n) must fuseto form an infective hyphae (n+n)

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4th group: Rusts • Obligate parasites• Attack leaves and stems• Produce pustules (masses of

yellow, orange or rusty spores that erupt through the epidermis)

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Rusts cont’d • Many rust fungi produce 5 types

of fruiting structures and 5 types of spores (= macrocyclic rusts)

• Other rusts, like smuts, produce only teliospores and basidiospores (= microcyclic rusts)

• Some rust produce only urediniospores (= asexual rust)

teliospores

basidiospores

spermatia

aeciospores

urediniospores

teliospores

basidium

spermagonium

aecium

uredium

telium

Repeatingstage

Overwinteringstage

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Rusts cont’d. • Some rusts complete their life cycle on a single

host = autoecious e.g. rose rust

• Other rust fungi require two different plant hosts to complete their life cycle = heteroecious

e.g. stem rust of wheat (polycyclic on wheat)uredia and telia on wheatspermagonia and aecia on barberry

e.g. cedar-apple rust (monocyclic)telia on cedar (no uredial stage)

spermagonia and aecia on apple

basidium

teliospore

basidiosporesof a rust fungus

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Spermagonia (n) and aecia (n+n)Upper surface or lesion center Lower surface or lesion edge

Infection by basidiosporeleads to spermagonium

aecium

Aecia onapplefruit

Pustule with uredia and urediniospores repeating stage/ summer spore

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telia and uredia(black) (orange)

For many rusts, late in the season, the uredium converts to a telium

TeliosporesTelial gallsbearing teliospores

Telia on whichbasidiosporeswere produced

cedar apple rust

rose rust

Germinate to produce basidiospores in spring

Telia are produced en mass on the fleshy galls