Basidiomycete Plant Pathogens

Rusts!

Smuts &

Bunts!

Wood & Root Rots!

Rots & Damping-Off!

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

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

Basidio Sexual Reproduction

Sexual reproduction structure:

Basidium - “club”

Basidiospores (1n)

4 per basidium

www.apsnet.org

n

Basidiomycota

•HymenomycetesMushroo

ms

•UrediniomycetesRusts

•UstilaginomycetesSmuts

Tom Volk

apsnet.org

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

Wheat RustPuccinia graminis

Urediospores erupting from uredinia on wheat stem.

a.k.a. Stem Rust, Black Rust

USDA, ARS

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

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.

Lifecycle of Puccinia graminis

Basidiospores

Spermatia and receptive hyphae

Urediospore

Teliospore

AeciosporeBarberry

Wheat

1

5

4

3

2

Barberry Barberry infected by Basidiospore (n) in

spring (primary inoculum)

Overwinters as Teliospore (n+n)

in crop debris

Wheat

Dikaryotic hyphae (n+n)

form on Barberry.

Direct penetration of barberry leaf

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

Puccinia graminis infection of barberry showing aecia on lower leaf surface

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

Puccinia graminis uredia erupting from upper

epidermis of wheat leaf.

Urediospores

Barberry

Wheat

Teliosporesn+n

Urediosporesn+n

Wheat hosts senesce and dry at end of season

In Teliosporen+n 2n 4 (1n)Meiosis occurs

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

Life cycle of Puccinia graminis

Basidiospores

Spermatia and receptive hyphae

UrediosporeTeliospore

AeciosporeBarberry

WheatA

MACROCYCLIC RUST

Control of Wheat Rust Resistant varieties

Fungicides Many applications required = $$$ Scouting and Forecasting

Barberry Eradication

Spread of P. graminis in 1923

E.C.Stakeman and J.G.Harrar. 1957

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

Stomate architecture influences penetration.

Wynn, W. 1976. Phytopathology 66: 136-146Urediospores Bean rust fungus - Uromyces phaseoli

Bean rust fungus (Uromyces phaseoli) penetrating stomate in bean leaf host.

guard cells

stomate

urediospore

appressorium

Host Specificity

Rust does not recognize non-host

stomata:

No penetration, no infection

Host topography affects appressorium formation

Allen et al., Phytopathology, 1991

Uromyces

Puccinia

Polystyrene membranes with

6.7um ridges

thigmotropism

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.

USDA-ARS Foreign Disease Containment GreenhouseFort Detrick, Frederick, MD

“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.