Durable Rust Resistance in Wheat

Objective 5: Breeding (Conventional and Molecular) to Produce Rust

A small group of improved breeding lines of wheat with diverse sources of both race-specific (major-gene-based) and complex adult-plant (minor-gene-based) resistance to the Ug99 race of stem rust, identified recently through rigorous field and greenhouse testing, is currently available and can now be employed in developing and delivering wheat cultivars with durable resistance and other desired characteristics.

The following two strategic approaches will be used to combat the threat of stem rust: 1) breeding wheat cultivars that have minor-gene adult plant resistance for high risk areas of East Africa and for production areas in the Ug99 migration path to avoid further breakdown of resistance through the accumulation of additional virulences for race-specific genes and 2) breeding race-specific resistance major genes into targeted varieties and promising new wheat materials in secondary risk areas. The race-specific resistance major genes will be used in combinations of two or more to enhance their longevity. This strategy can be applied for genes that have not been used previously. The above two approaches are necessary due to the current status of resistance in the adapted germplasm and cultivars that will be used for breeding. This approach will also enhance the level of genetic diversity for resistance within and between different epidemiologic zones.

Approach 1 will be accomplished through an accelerated shuttle breeding program to grow wheat breeding materials twice per year at key field sites; this enables intense selection pressure for all three rusts and other important diseases and pests together with adaptation related traits (photoperiod and vernalization response, days to maturity, etc), yield potential, and tolerance to drought and heat stress. Some of the early segregating generations will be exposed to high stem rust pressure at critical field sites in East Africa to enhance the frequency of Ug99 resistant advanced lines. Final confirmation of resistance will be made by testing advanced lines at least twice in East Africa while characterizing the yield potential and determining tolerance to other abiotic stresses. For Approach 2, marker-assisted selection will be employed to transfer currently effective resistance genes with known markers in important cultivars and new elite wheat lines that have potential to become cultivars in the future. Once new genes become available, they will be incorporated in combinations.

Races of stem rust, different from Ug99, with virulence for resistance genes in durum wheats occur principally in Ethiopia, where durum wheat is grown in marginal areas by mostly resource poor farmers especially to avoid the risk of major stem rust epidemics that are more common in areas with moderate to high rainfall or irrigation. Knowledge of resistance to stem rust in durum wheat is limited at present and resistance to Ethiopian races is known to be present in few land races, old tall and semi-dwarf varieties.

Considering the diverse ecology and type of wheats grown in the principal risk areas along the migration path of Ug99 and secondary risk areas of developing countries, the objective will be met by eight breeding activities to focus each target environment. Breeding and testing will be done by CIMMYT and ICARDA in collaboration with various National Programs that are close collaborators.

Objective Activities will be targeted to address the needs of developing countries under immediate risk along the predicted migration path of Ug99, as well as other secondary risk areas where the unpredicted introduction of Ug99 may cause severe losses affecting local as well as global food security and livelihoods.

Outcomes (near and longer term)

Local, national, regional and global food security ensured.
Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties.
Negative impacts on livelihoods of resource poor farmers from rust epidemics thwarted.
Excessive use of agrochemicals (fungicides) with negative impacts on environment and human health avoided.
Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, stress tolerance and improved end use quality characteristics.
New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and International Centers will help sustain long-term productivity of wheat based cropping systems.

The breeding program will be a large multi-national and multi-institutional effort that will take advantage of all of the outputs developed by the other proposed objectives. It is also the most expensive single activity, taking up almost 25% of the proposed project budget. Success of the program will be a function of this team working closely with all the other teams. It will likely be year two before the first new rust resistant varieties will be available and probably five years before the varieties are widely adopted by growers. During this time frame, efforts will be made to assure that a workable seed multiplication and distribution system is place in all the affected countries. This will be important for quick adoption of the new varieties.

Objective 5: Breeding (Conventional and Molecular) to Produce Rust Resistant Wheat Varieties
Activities	Outputs	Outcomes (Short- and Long-Term)
Activity 5.1 Spring bread wheat varieties for irrigated and high production environments of Africa, Middle East, West, Central and South Asia developed by the Irrigated Spring Bread Wheat Improvement Program, CIMMYT, Mexico.	30–50 high yielding, rust resistant potential replacement varieties tested annually in replicated yield trials in various countries at 50+ field sites. 100–150 additional high yielding, multiple rust resistant lines distributed annually for evaluation and selection as small plots at over 100 sites worldwide. About 10 new multiple rust resistant varieties with >5% higher yield potential than current cultivars released officially in various countries by years 3 and 4. Application of appropriate breeding methodology and use of germplasm with durable resistance promoted for NARS breeding program. Strong partnerships built for a fast release and promotion of new stem rust resistant cultivars.	Food security in spring wheat irrigated and high production environments of Africa, Middle East and Asia ensured. Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Reduced use of agrochemicals (fungicides) with associated negative impacts on environmental and human health avoided. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end-use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.
Activity 5.2 Spring bread wheat varieties for drought-stressed and low production environments of Africa, Middle East, West, Central and South Asia developed by the Rainfed Spring Wheat Improvement Program, CIMMYT, Mexico.	At least 5–10 lines sent every year (from year 1) to NARS coming from rainfed international trials and screening nurseries with good yield potential, tolerance to drought and resistance to yellow rust, leaf rust and Ug99 stem rust. At least 70 lines sent to NARS at the end of year 6 with good yield potential, tolerance to drought, resistance to yellow rust, leaf rust and Ug99 stem rust, and resistance to biotic and abiotic soil stresses. 3–4 stem rust resistant varieties selected for release by NARS by year 4	Food security in spring wheat low production environments of Africa, Middle East and Asia ensured. Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. heat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.
Activity 5.3 Spring bread wheat varieties for diverse production environments of CWANA region developed by Spring Bread Wheat Improvement Program, ICARDA, Syria.	4–5 new varieties released by NARS by year 3 from existing resistant materials ex CIMMYT/ICARDA. About 30 high yielding lines with resistance to stem rust distributed to NARS in CWANA region in year 6 as replicated yield trials. About 100 high yielding lines with resistance to stem rust distributed to NARS in CWANA region in year 6 as screening nurseries.	Food security in diverse spring wheat production environments of CWANA region ensured. Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Excessive use of agrochemicals (fungicides) with negative impacts on environment and human health avoided. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.
Activity 5.4 Developing and delivering stem rust resistant facultative and winter bread wheat varieties for CWANA region.	At least 30 winter and facultative wheat lines combining resistance to Ug99 and other diseases targeted to irrigated and rainfed conditions of CWANA are sent to cooperators in NARS 2-3 new varieties submitted for official testing by the NARS to replace the varieties susceptible to Ug99	Food security in diverse facultative and winter wheat production environments of CWANA region ensured. Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Excessive use of agrochemicals (fungicides) with negative impacts on environment and human health avoided. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and International Centers help sustain long-term productivity of wheat based cropping systems.
Activity 5.5 Developing and delivering stem rust resistant photosensitive spring bread wheat varieties for Central Asia.	100–200 lines available at the end of year 4 with resistance to Ug99 based on major genes, resistance to leaf rust, good adaptation to Northern Kazakhstan, available to local breeding programs for testing and use in crossing. 2–5 varieties identified at the end of year 7 with resistance to Ug99, and potential to replace current varieties in Northern Kazakhstan.	Food security in photosensitive wheat production environments of Central Asia ensured. Serious losses from Ug99 race of stem rust pathogen and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and International Centers help sustain long-term productivity of wheat based cropping systems.
Activity 5.6 Developing and delivering stem rust resistant spring, facultative and winter bread wheat varieties for China.	30–40 advanced lines with high yield potential, resistance to Ug99 and other diseases will be developed. 5–8 varieties with high yield potential, good quality, and resistance to UG99 will be released at provincial levels.	Food security in diverse wheat production environments of China ensured. Serious losses from Ug99 race of stem rust and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Use of agrochemicals (fungicides) with negative impacts on environment and human health avoided. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.
Activity 5.7 Durum wheat varieties for Africa, Middle East, Asia and Latin America by Durum Wheat Improvement Program, CIMMYT, Mexico.	2–3 stem rust resistant varieties for release in Ethiopia by year 5. 20–30 stem rust resistant durum lines with >5% higher yields than current varieties distributed worldwide in year 5 for yield testing. About 50 additional high yielding, stem rust resistant durum lines distributed worldwide in CIMMYT screening nurseries.	Food security in durum wheat production environments of Africa, Middle East, Asia and Latin America ensured. Serious losses from Ug99 race of stem rust and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.
Activity 5.8 Durum wheat varieties for CWANA by Durum Wheat Improvement Program, ICARDA, Syria.	20–30 potential stem rust resistant varieties with >5% higher yield potential than current cultivars in year 4 and 5 distributed for testing by NARS in replicated yield trials. About 100 additional stem rust resistant durum lines developed and distributed in small seed quantities by year 4 and 5. At least 2 stem rust resistant durum varieties identified for release in Ethiopia by year 5.	Food security in durum wheat production environments of CWANA region assured. Serious losses from Ug99 race of stem rust and other rust diseases averted through the cultivation of genetically resistant wheat varieties. Negative impacts on livelihoods of farmers, especially the resource poor, from rust epidemics thwarted. Wheat productivity and income enhanced by growing new wheat varieties that have higher yield potential, better stress tolerance and improved end use quality characteristics. New wheat germplasm with enhanced genetic diversity and breeding methodologies used by National Programs and IARCs help sustain long-term productivity of wheat based cropping systems.