Building Wheats with Multiple Resistance to Leaf Rust

By Linda McGraw
May 21, 2001

Genetic markers—tools of modern biotechnology—are being used by Agricultural Research Service scientists to fortify wheat with longer-lasting resistance to leaf rust, a disease that costs Great Plains wheat farmers about $150 million annually.

ARS plant geneticist Gina Brown-Guedira in Manhattan, Kan., is building gene complexes using markers closely linked to leaf rust resistance. The markers are made of genetic material called DNA.

Brown-Guedira is combining leaf rust resistance found in two ancestors of modern wheat: Aegilops tauschii (also known as goatgrass), a weedy wheat relative found from Afghanistan to Syria, and Triticum timopheevii from Iran, Iraq and Turkey. Ultimately, genes from these ancestors can be combined and moved into germplasm from which new resistant wheat varieties can be developed.

Leaf rust is caused by a fungal pathogen called Puccinia triticinia. In the 1990s, crop yield losses from leaf rust in the hard winter wheat growing area of the Great Plains averaged 5.7 percent. In addition, leaf rust seriously affects the milling and baking qualities of wheat flour.

In the past, wheat breeding programs have released resistant varieties with only a single leaf rust resistance gene. A few years later, these varieties usually begin to lose their effectiveness against the rapidly changing fungus.

The result is a boom and bust cycle of wheat disease for farmers in the major wheat growing areas of the world.

Scientists currently must use time-consuming classical genetic studies to determine if a plant has more than one resistance gene. In contrast, Brown-Guedira can look for the DNA markers at any stage of plant growth without having to infect plants with the fungus. Because the markers are closely linked to the resistance genes, there is a good chance those genes are also present.

This work, which can speed up the task of developing germplasm with multiple resistance genes, is reported in the May issue of Agricultural Research magazine and is available online.

ARS is the chief scientific research agency for the U.S. Department of Agriculture.

Scientific contact: Gina Brown-Guedira, ARS Plant Science and Entomology Unit, Kansas State University, Manhattan, Kan., phone (785) 532-7260, fax (785) 532-6167, gbg@ksu.edu.