Modern Wheat Draws Mildew Resistance from the Wild

RALEIGH, N.C., Feb. 11--Weeds with old family ties to today's wheat could help save U.S. farmers as much as $20 million now lost every year to a crop disease called powdery mildew, a U.S. Department of Agriculture scientist says.

Certain weeds that grow wild in Armenia and Iran can be crossed with modern wheat to produce hybrids with stronger disease resistance, according to plant pathologist Steven Leath, with USDA's Agricultural Research Service.

"Iran, Iraq and Armenia are part of the epicenter of wheat evolution," Leath said. "Wheat is actually a combination of three plant ancestors. By borrowing the right genes from some of them, we're giving red winter wheat added protection against powdery mildew."

Leath and Paul Murphy, a North Carolina State University plant breeder, have already developed three new hybrids--NC96BGTD-1, 2, and 3--that are available to scientists and plant breeders seeking to boost the disease resistance of commercial wheat lines. In three years of field tests, the new hybrids demonstrated consistent resistance to all strains of powdery mildew, even the most exotic strains.

"Domestic wheat has genes to fight powdery mildew, but over time they became less and less effective against this microbial pest," Leath said. "The genetic reserves of U.S. wheat began to run out, so we turned to germplasm collections at ARS and the Wheat Genetic Resource Center at Kansas State University to enhance resistance." The wild varieties came to the U.S. collections through Japanese researchers traveling in the Middle East.

Hard red winter wheat, grown mainly in Midwestern states, is the principal ingredient in commercially-made bread. Soft red winter wheat, grown in the Southeast, is used in cookies, cakes and other snack foods. All-purpose flour is usually made from a combination of both.

Powdery mildew can strike in the Midwest, but prefers the humid climate of the Southeast, so the soft red winter wheat crop is especially vulnerable. Powdery mildew claims 1 to 3 percent of the southeastern wheat crop every year, translating to losses of $6.5 million to $20 million.

Breeding for resistance makes sense, Leath said, because growers often find chemical treatments for powdery mildew too costly at an average of $20 per acre.

To create the new hybrids, Leath and his colleagues at Raleigh, N.C., pollinated domestic female plants with wild males. The plants were so genetically different that the resulting embryo couldn't survive and develop inside the female, and instead had to be grown in a tissue culture solution. The resultant offspring must be bred with another wild male.

"By using this method, we can retain many of the traits the growers want in their wheat," said Leath. "With traditional crosses, the genetic exchange is roughly 50/50, but with this method we only alter one-third of the genetic make-up."

Scientific contact: Steven Leath, Plant Science Research Unit, Agricultural Research Service, USDA, Raleigh, N.C. 27695-7614. Telephone (919) 515-6819; fax (919) 515-7716.