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
Sexual reproduction structure: Basidium - “club” Basidiospores (1n) 4 per basidium n
Hymenomycetes Mushrooms Urediniomycetes Rusts Ustilaginomycetes Smuts Tom Volk apsnet.org
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
Urediospores erupting from uredinia on wheat stem. a.k.a. Stem Rust, Black Rust USDA, ARS
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
Obligate biotroph – no saprophytic stage. Heteroecious – 2 hosts required for lifecycle: Grass species (monocot) Barberry (dicot) Polycyclic pathogen Aerial urediospores spread 100s of miles.
Basidiospores Spermatia and receptive hyphae Urediospore Teliospore Aeciospore BarberryWheat
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
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
BarberryWheat Teliospores n+n Urediospores n+n Wheat hosts senesce and dry at end of season In Teliospore n+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
Basidiospores Spermatia and receptive hyphae Urediospore Teliospore Aeciospore BarberryWheat A MACROCYCLIC RUST
Resistant varieties Fungicides Many applications required = $$$ Scouting and Forecasting Barberry Eradication
E.C.Stakeman and J.G.Harrar. 1957
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
Allen et al., Phytopathology, 1991 Uromyces Puccinia Polystyrene membranes with 6.7um ridges thigmotropism
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 Greenhouse Fort Detrick, Frederick, MD
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.