Report from the field: Wheat stem rust resistance screening at Njoro, Kenya

Plant breeders Peter Njau, Godwin Macharia, and Davinder Singh (from left to right) seek wheat lines that have race "non-specific" resistance to Ug99. "This type of resistance is considered effective against all races of the pathogen and is durable," explains Singh. "That is, it's hard for the pathogen to overcome."

A deadly new pathogen is carrying off wheat farmers' harvests in eastern Africa, affecting the balance of trade in countries like Kenya, and threatening vast wheat lands in other developing countries. Kenyan and Ethiopian researchers are working with CIMMYT to identify resistant wheats for the world, and new technologies are helping track the pathogen's spread.

According to Kenyan researcher Joseph Macharia, a new, highly-virulent form of the wheat disease known as stem rust is driving Kenyan wheat farmers off their land. "If farmers can't grow wheat, they just abandon the field, or some may switch to maize," says Macharia. "Wheat is a high-investment cereal, so if farmers lose their crop, they lose their investment and can't continue."

Stem rust is an age-old disease of wheat worldwide. Ug99, a new strain of stem rust, first appeared in Uganda in 1998. It was subsequently detected in Kenya in 2002 and Ethiopia in 2003, in Sudan and Yemen in 2006, and in Iran in 2007. The pathogen is expected to continue its migration to South and Central Asia, through the Middle East and North Africa, riding on the winds or by other means. Most currently-grown varieties in its path are susceptible, and the wheat areas at risk represent 20% of the global total and provide sustenance for 1 billion people.

In Kenya, Peter Njau, plant breeder and deputy director of the Kenya Agricultural Research Institute (KARI) research station at Njoro, says the loss of wheat harvests to the pathogen affect both farmers and the national economy. "Wheat is the second-most important crop in Kenya—we produce 350,000 tons every year," he says, "but we need to import 450,000 tons more to meet national consumption demands."

Finding safety in numbers
This year, Njau and his team worked with CIMMYT on the Njoro station to test 20,000 wheat lines from more than 15 countries for resistance to Ug99. Wheat scientists from most of these countries came to Kenya to evaluate their material and see first-hand the pathogen's damage. "This is a hot-spot for the disease," Njau says, referring to Nakuru District in the Central Rift Valley region of Kenya. "Disease incidence was so intense this year that 85% percent of the lines proved susceptible, and many supposedly resistant lines showed 20% greater infection than they normally would. New variants of the pathogen are appearing that overcome some of the most effective resistance genes in wheat."

But there is hope, too, according to Njau. "The experimental wheat variety Kingbird looked good under this year's conditions, and has performed well in tests elsewhere." Derived from CIMMYT germplasm, Kingbird is being used by the center to develop new varieties whose seed can be multiplied and distributed quickly to farmers in Ug99's probable path of migration. Njau has also identified an experimental wheat variety from CIMMYT's international stem rust resistance screening nursery that out-yielded the best reference variety by 27% and the average yield of varieties in the trial by 80%.

Global partners to arrest rust
Ethiopian wheat researchers are also partnering with CIMMYT to evaluate wheat germplasm from around the globe for resistance to the pathogen. "Kenya and Ethiopia are doing the world a great service by conducting these trials," says CIMMYT wheat breeder Davinder Singh, who is working in eastern Africa to combat Ug99. "The countries also benefit by having access to seed of resistant lines from international sources."

Efforts in both countries form part of the Borlaug Global Rust Initiative, led by Cornell University and supported by a growing number of donors, including the Bill & Melinda Gates Foundation, the USAID-seed project, USDA-ARS, ICAR-India, China, Arab Funds for Agricultural Development, FAO-training, and a northwestern Mexican farmer association known as the Patronato. GRDC-Australia also supports selected activities at CIMMYT and KARI relating to stem rust resistance screening and breeding, and Peter Njau receives funding from the Swiss Agency for Development and Cooperation (SDC) for his PhD thesis research on stem rust.

Google Earth tracking system
To provide timely, reliable information to scientists and decision makers in at-risk countries, scientists in CIMMYT’s Geographical Information Systems (GIS) laboratory have used the popular satellite-image virtual globe "Google Earth" to create a program that tracks Ug99 occurrences, models wind trajectories and potential dispersion paths for the pathogen, and summarizes information on wheat production and susceptibility for countries in Ug99's pathway. Called "RustMapper," the program is automatically updated twice weekly.

RustMapper is another component of the Borlaug Global Rust Initiative, undertaken by CIMMYT, in collaboration with the International Center for Agricultural Research in the Dry Areas (ICARDA) and FAO, to fight the spread of wheat rust fungal diseases.

For more information: Ravi Singh, head, irrigated bread wheat improvement and rust research (r.singh@cgiar.org)