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
ARS plant geneticist Gina Brown-Guedira is combining leaf rust resistance found
in two ancestors of modern wheatAegilops tauschii (also known as
goatgrass), a weedy wheat relative found from Afghanistan to Syria, and
Triticum timopheevii from Iran, Iraq, and Turkeyinto "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
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
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)
"Tagging New Leaf Rust Resistance Genes in
Wheat" was published in the
issue of Agricultural Research magazine.