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Tagging New Leaf Rust Resistance Genes in Wheat

  Like the Egyptians who built pyramids to immortalize their best citizens, ARS researchers in Manhattan, Kansas, are building pyramids of genes to provide better-lasting resistance to wheat leaf rust. ARS plant geneticist Gina 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—into "gene pyramids." Once built, these gene complexes can be moved into wheat germplasm. Ultimately, varieties having more durable resistance can be developed, which could help farmers gain ground against leaf rust throughout the Great Plains. Leaf rust is caused by a fungal pathogen called Puccinia triticinia. In the 1990s, crop yield losses from leaf rust averaged 5.7 percent in the hard winter wheat growing area of the Great Plains. This translates into average yearly losses of 50 million bushels. Over the decade, the price of wheat averaged $3 a bushel, so leaf rust costs Great Plains farmers about $150 million each year. Not only does leaf rust lessen on-farm yields, it also seriously affects the milling and baking qualities of wheat flour. In the past, wheat-breeding programs have released resistant varieties, but these wheats possessed only a single leaf rust resistance gene. A few years after release, these varieties usually begin to lose their effectiveness against the rapidly changing P. triticinia. The result is a boom-and-bust cycle of disease for farmers in the major wheat-growing areas of the world. In wheat, Brown-Guedira has identified DNA markers, small pieces of DNA that can be visualized on a gel and are known to be linked to resistance genes. These markers offer a faster way to identify the presence of wheat leaf rust resistance because they can be seen at any stage of plant growth without infecting plants with the fungus. Scientists currently must use time-consuming classical genetic studies to determine whether a plant has more than one resistance gene. In contrast, Brown-Guedira can test a plant for the presence of several DNA markers. Because the markers are closely linked to the resistance genes, there is a good chance the resistance genes are also present. This work can speed up the task of developing germplasm and varieties with multiple resistance genes.—By Linda McGraw, Agricultural Research Service Information Staff. Gina Brown-Guedira is in the USDA-ARS Plant Science and Entomology Unit, Kansas State University, Manhattan, KS 66501; phone (785) 532-7260, fax (785) 532-6167.

"Tagging New Leaf Rust Resistance Genes in Wheat" was published in the May 2001 issue of Agricultural Research magazine.



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