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