Wheat for making pasta, couscous and semolina is bred for resistance to leaf rust and also for the quality traits that the market demands.

Dr. Karim Ammar, a durum wheat breeder, is proud of his new wheat lines growing green and disease-free in the Yaqui Valley of northern Mexico. It took 6 years to get this far. This despite the efficiency of a shuttle system between the Yaqui Valley and the highland research station of the International Maize and Wheat Improvement Center (CIMMYT by its Spanish abbreviation) at Toluca, Mexico, which allows wheat breeders to plant and select wheat twice a year.

"Between preliminary yield trials and elite yield trials we've got about 2,500 lines," Ammar says. "And they're all resistant to leaf rust."

This is good news for the durum wheat farmers of the world. Durum is the kind of wheat used for pasta, couscous and semolina. Today, 85% of spring durum wheat grown in developing countries traces its origins to the durum wheat program at CIMMYT. This agricultural research Center supported by the Consultative Group on International Agricultural Research regularly sends out seed samples to national breeding programs around the developing world. The most suitable in each region are used to breed local varieties. When mutations in the leaf rust fungus allowed it to bypass the resistance mechanisms in durum wheat, the breeding team at CIMMYT faced a serious problem.

"We had to rebuild the program, because you can no longer use something that becomes susceptible to a disease," says Ammar. "That's no service to the national programs or farmers in developing countries."

Ammar, a Tunisian, is acutely aware that his work will have a major impact in the developing countries where durum wheat is grown.

Looking at this as a single problem - producing disease-resistant plants or plants that can produce more grain - would have been easy, but the team realized that the challenge was much more complicated. To improve their livelihood, farmers in developing countries need high-quality grain for which there is a market.

Breeding itself is a process of combination and then elimination - selecting potentially good parent seeds with desirable characteristics and crossing them, then eliminating the offspring that do not measure up. The process is repeated until the breeder is satisfied that all required characteristics have been incorporated into the new plants.

Leaf rust harms yields enough to make growing susceptible varieties a losing proposition for farmers. Their needs were at the heart of the breeding strategy devised by the breeding team.

"So their priority becomes ours," Ammar says. "And once objectives are defined with our clients and their respective markets in mind, then I start thinking about the plants - how a plant or a certain cross or combination of genes would achieve that objective in the most efficient, fastest way possible."

The breeders knew that disease resistance was vital, but quality that was acceptable to farmers and their markets was equally essential. At the same time, they thought they could enhance the performance of wheat under drought stress and incorporate resistance to other diseases. In the beginning they had to sacrifice yield and other key characteristics to be sure they had resistance to leaf rust, the biggest problem durum wheat growers faced. But, once that was done, the team focused on making the best possible wheat from all other perspectives.

"Now we're back to the point where we can address yield, drought tolerance and quality very effectively because we know we have enough variability for rust resistance," says Ammar. "It's no longer the critical trait."

The most critical trait now may well be the color or the quality of the gluten in durum wheat grains. Last year farmers in the Yaqui Valley grew close to 150,000 hectares of a durum wheat variety that yielded well and stood up to leaf rust. Unfortunately, because its grain did not have enough of the yellow pigment desired by the export market, there was little market for the wheat except as pig feed. Many of the 2,500 new lines that Ammar is testing outperform that variety in yield and in the most important quality traits.

The program in Mexico has been supported by the government of Spain and by several agencies in Mexico. The best of the lines at the CIMMYT breeding station will be sent to national programs for evaluation. Mexico has already begun to evaluate in parallel, so it will be ready as soon as possible to release new varieties based on the CIMMYT lines to farmers.

For more information Karim Ammar at k.ammar@cgiar.org.