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East African Stem Rust: Research Needs and
Challenges
Brian Steffenson
Department of Plant PathologyUniversity of Minnesota
St. Paul
38th Barley Improvement ConferenceJanuary 13, 2011
One of the most devastating plant diseases
Can cause complete crop loss over wide area
Stem Rust of BarleyStem Rust of Barley
Durable resistance achieved using gene Rpg1
Has protected barley from losses since 1942
Is present in all Midwest cultivars, but is ineffective against some stem rust races
Durable Stem Rust Resistance in BarleyRpg1
Rpg1 rpg1
Virulent stem rust isolate found attacking wheats carrying gene Sr31 in Uganda
In 1999, characterization of isolate Ug99: keyed to race TTKS later TTKSK
New Threat to WheatEast African stem rust
Zack Pretorius
TTKSK possesses a dangerous combination of virulences
Can attack 70% and 90% of world’s wheat and barley varieties, respectively!!
This includes most of the US & Canadian varieties
New Threat to Wheat and BarleyRace TTKSK
Isolates with Sr24 virulence
Isolates with Sr36 virulence
New Threat to Wheat and BarleyVariation for virulence
LcSr24Ag (Sr24)
Sr31/6*LMPG
RL 6081(Sr38)
McNair701 (SrMcN)
TTKST
TTKSK on Sisson (Sr31+36)TTTSK on Sisson
TTKSK
New Threat to Wheat and BarleyTTKSK and variants
Should We Fear East African Stem Rust?
Potential for severe or complete crop loss
Ease of spread by wind or travelers
Wide virulence on wheats & barley varieties
Potential for virulence changes
Greenhouse studies have identified resistance in cultivated, landrace, and wild barley
Adult plant resistance also identified in Africa
TTKSK Resistance Exists in Hordeum
Cultivated Landrace Wild Susceptible
Breeding varieties for resistance is the best means for stem rust control
Fungicides can also control stem rust, but are costly
Control of Stem Rust
Research NeedsField Testing
Kenya Agr. Res. Inst. (KARI) at Njoro:
Excellent staff & fairly reliable disease pressure
Two screening times: “main” season (Jun-Oct) and “off” season (Dec to Apr)
Cost: $10/line—subsidized by USDA and BGRI
Limitations on lines: 30 per breeding program + 300
Research NeedsField Testing
University of Orange Free State & Pannar Seed Company, Greytown, South Africa
Can include larger numbers of lines including segregating populations
One screening season per year (June-Oct)
Reputed to be a reliable stem rust site
Cost: $13/line
Research NeedsSeedling Screening Tests: BSL-3
Seedling tests are done in the Bio-Safety Level (BSL-3) Containment Facility (Nov to Mar)
Agreement between seedling and adult plant reactions is generally poor
Yet in some cases, seedling tests may prove valuable & also for testing to different variants
Space and $
Research NeedsSNP Genotyping and MAS
SNP markers provide great advantages for efficiently mapping and tagging resistance genes
Pipeline and funding for high throughput genotyping, Marker Assisted Selection (MAS), & validation must be maintained
Research NeedsCoordination
Coordination among research groups
Gene deployment schemes: using different resistance sources in NE and MN/ND germplasm
“Puccinia Pathway”
Research NeedsData on Fungicide Efficacy
Recovery Plan for Stem Rust of Wheat: March 2010