Download - Basidiomycete Plant Pathogens
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Basidiomycete Plant Pathogens
Rusts!
Smuts &
Bunts!
Wood & Root Rots!
Rots & Damping-Off!
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Review: Pathogen Characteristics
Somatic ploidy
2n
n
n+n
Chitin wallMotile
zoospores
yes
no
no
Septate hyphae
no
yes
yes
Sexual spore
noOomycota
Ascomycota
Basidiomycota
yes
yes
Oospore
Asco-spore
Basidio-spore
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Basidiomycota Mushrooms
Agaricus Lentinula (shitake) Aminita (destroying angel)
Mycorrhizal fungi – forest ecosystems Wood decay fungi Pathogens on major crops:
Rusts of grains, soybean, coffee, ornamentals Smuts of small grains and corn
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Basidio Sexual Reproduction
Sexual reproduction structure:
Basidium - “club”
Basidiospores (1n)
4 per basidium
www.apsnet.org
n
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Basidiomycota
•HymenomycetesMushroo
ms
•UrediniomycetesRusts
•UstilaginomycetesSmuts
Tom Volk
apsnet.org
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Uredinales - Rusts Puccinia – grass and cereal rusts Phakopsora – Soybean Rust Gymnosporangium – Cedar-Apple Rust Hemileia – Coffee Rust Cronartium – White Pine Blister Rust Uromyces – carnation and bean rusts Phregmidium – Orange rust of blackberry
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Wheat RustPuccinia graminis
Urediospores erupting from uredinia on wheat stem.
a.k.a. Stem Rust, Black Rust
USDA, ARS
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Rusts in History Described in Bible and Broadway:
Famine in Joseph and Amazing Technicolor Dreamcoat story
In writings of Theophrastus (“Father of Botany”)
Robigus – Roman rust god Honored by Robigalia – sacrificed
reddish-colored animals
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Puccinia graminis Obligate biotroph – no saprophytic stage.
Heteroecious – 2 hosts required for lifecycle: Grass species (monocot) Barberry (dicot)
Polycyclic pathogen Aerial urediospores spread 100s of miles.
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Lifecycle of Puccinia graminis
Basidiospores
Spermatia and receptive hyphae
Urediospore
Teliospore
AeciosporeBarberry
Wheat
1
5
4
3
2
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Barberry Barberry infected by Basidiospore (n) in
spring (primary inoculum)
Overwinters as Teliospore (n+n)
in crop debris
Wheat
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Dikaryotic hyphae (n+n)
form on Barberry.
Direct penetration of barberry leaf
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Puccinia graminis
Spermagonia (upper) and aecia (lower) on leaf of barberry seen in cross section by light
microscopy
Aecia form from (n+n) hyphae created by fusion of receptive hyphae with spermatia of
opposite mating type
Aeciospores (n+n) on underside of barberry leaf.
Infect only wheat plants
Spermacia (n-) and (n+) Receptive Hyphae on upper barberry leaf surface
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Puccinia graminis infection of barberry showing aecia on lower leaf surface
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Aeciospores (n+n) wind blown to wheat host plants and infect leaves by
penetrating stomates.
Urediospores ( n+n) erupt from upper leaf surface.
Repeating stage.
Aeciospores(n+n)
Stomate
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Puccinia graminis uredia erupting from upper
epidermis of wheat leaf.
Urediospores
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Barberry
Wheat
Teliosporesn+n
Urediosporesn+n
Wheat hosts senesce and dry at end of season
In Teliosporen+n 2n 4 (1n)Meiosis occurs
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Puccinia graminis Teliospore produced at end of season when
grain plants begin to senesce and dry down
Uredia shift production to thick-walled dark colored 2-celled Teliospores (n+n)
that overwinter in debris
Rusty Urediospores
Dark Teliospores
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Life cycle of Puccinia graminis
Basidiospores
Spermatia and receptive hyphae
UrediosporeTeliospore
AeciosporeBarberry
WheatA
MACROCYCLIC RUST
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Control of Wheat Rust Resistant varieties
Fungicides Many applications required = $$$ Scouting and Forecasting
Barberry Eradication
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Spread of P. graminis in 1923
E.C.Stakeman and J.G.Harrar. 1957
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Rusts are very specific Formae speciales (f.sp.) – “special forms”
Puccinia graminis f.sp. tritici - wheat Puccinia graminis f.sp. secalis – barley
Pathogen recognizes host morphology – only then will it penetrate and infect. Guard cells of stomata Leaf topography
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Stomate architecture influences penetration.
Wynn, W. 1976. Phytopathology 66: 136-146Urediospores Bean rust fungus - Uromyces phaseoli
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Bean rust fungus (Uromyces phaseoli) penetrating stomate in bean leaf host.
guard cells
stomate
urediospore
appressorium
Host Specificity
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Rust does not recognize non-host stomata:
No penetration, no infection
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Host topography affects appressorium formation
Allen et al., Phytopathology, 1991
Uromyces
Puccinia
Polystyrene membranes with
6.7um ridges
thigmotropism
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P. graminis as biological weapon
Rapidly spreading (aerial), polycyclic pathogen capable of destroying an economically important crop.
Potential use in bio-terrorism/warfare: Rust pandemic would have negative economic, food
security and psychological effects.
Has been weaponized in the past by USSR and US Army Biological Weapons lab at Fort Detrick, MD.
1970 – USSR & USA signed Biological Weapons Treaty banning development and testing of biological warfare weapons.
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USDA-ARS Foreign Disease Containment GreenhouseFort Detrick, Frederick, MD
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“New” race of P. graminis:
UG99 Uganda, 1999
Defeats more of the known resistance genes than any other known strain. Could infect 90% of world’s wheat varieties.
$26.8 million grant from the Bill & Melinda Gates Foundation.