
Modern Wheat Draws Mildew Resistance from the WildBy Jill Lee February 11, 1997RALEIGH, 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. U.S. Department of Agriculture | |