Basidiomycetes

Basidiomycetes 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 knowing
the types of spores present on the host tissues
• Inoculate wheat cultivars with rust isolates
Basidiomycetes
(the club fungi)
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•
•
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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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Blackcolored
sclerotia of
Rhizoctonia
solani
on a potato
Damping-off of alfalfa
caused by Rhizoctonia
Group 1 pathogen:
Rhizoctonia
-causes many, many diseases
-mostly soilborne
Lesion caused by
Rhizoctonia spp.
Rhizoctonia
Hyphae branch at right angles
No asexual spores
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Other diseases of Group 1 basidiomycetes:
Turf diseases:
Gray
snow
mold
Red
thread
2nd Group: Rots of trees
(Facultative parasites)
Example: Armillaria root rot
• Life strategy: Facultative parasite
• Fruiting body (basidiocarp) is a mushroom
• Fungus spreads from tree to tree via root-toroot contact or rhizomorphs
• Large host range: oak, grape, pine ,fruit trees
• Aggressive colonizer of dead wood
4
Mushrooms
of
Armellaria
In the gills of the mushroom:
basidiospores
basidium from
a mushroom
or conk
5
Rhizomorphs
are aggregated,
mycelium strands
used by Armilleria
to grow along roots
and from root to root.
Rhizomophs
R
h
i
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 house
in grad school
The tree fell
on Ken’s
bedroom
He narrowly
escaped the
work of a
plant
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
Number of basidiospores produced in a conk
Billion spores per day
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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 infection
emerging coleoptiles in soil -systemic infection
very young, growing tissues -local infections
Loose smut of barley
-Seed infection via
flower
Spores from diseased
Healthy appearing but
heads infect healthy flowers
infected seed leads to
diseased plants in next crop
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Common bunt (covered
smut) of wheat
- Infection of
emerging coleoptiles
via soil infestation or
contaminated seed
cloud of smut spores
Spores on
healthy seed (or
in soil) infect
next crop after
seed is planted
Common corn smut
- Local infection
In Mexico,
immature
smut balls
are considered
a delicacy
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Long-lived
Resting spores
Teliospores of Smut Fungi
Germination of teliospores (n+n)
of smut fungi to produce
basidiospores (n)
Two basidiospores (n) must fuse
to 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
basidium
basidiospores
spermagonium
spermatia
aecium
aeciospores
uredium
urediniospores
telium
teliospores
Overwintering
stage
Repeating
stage
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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 wheat
spermagonia and aecia on barberry
e.g. cedar-apple rust (monocyclic)
telia on cedar (no uredial stage)
spermagonia and aecia on apple
basidiospores
of a rust
fungus
basidium
teliospore
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Spermagonia (n) and aecia (n+n)
Upper surface or lesion center
Lower surface or lesion edge
Infection by basidiospore
leads to spermagonium
Aecia on
apple
fruit
aecium
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
Telial galls
bearing teliospores
cedar apple rust
Teliospores
Germinate to
produce
basidiospores
in spring
Telia on which
basidiospores
were produced
Telia are
produced en
mass on the
fleshy galls
rose rust
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