Amarillo, Texas
May 3, 2005
Getting resistance to the latest biotype of
greenbug or rust in wheat may require some bridge building.
Dr. Jackie Rudd, associate professor at the
Texas A&M University System
Agricultural Research and Extension Center and state wheat
breeder, is looking at wild grass species and synthetic wheats
for possible solutions.
"We're looking for new unique sources of resistance to various
biotic and abiotic stresses," Rudd said. "I'm being forced to
find broader gene pools to bring in the genetic variability I
believe is necessary for the gene pool here."
Karnal bunt, new races of Hessian fly, new leaf rust, stripe
rust and Russian wheat aphid, as well as the need for more
drought tolerance present challenges, he said. Progress in
traditional breeding has been slow due to limited genetic
variability for these traits.
Two projects growing in the Texas Agricultural Experiment
Station greenhouses in Vernon and Bushland are designed to
increase the genetic variability. These projects are being
funded by the Texas Wheat Producers Board.
"My preference is to cross wheat with wheat," Rudd said. "The
best chance for success is to cross High Plains wheat with High
Plains wheat. But to get genetic variability, you cross state
lines or even into other countries. The next step would be to
cross species, if the desired traits can't be obtained in a
wheat-to-wheat cross."
A wild grass collection being mined for its genetics has 716
lines of wheat relative species. The grasses originated in
Turkey and were collected in 1992 as a joint project between
Texas A&M University and Centro Internacional de Mejoramiento de
Maiz y Trigo, (The International Maise and Wheat Improvement
Center) better known as CIMMYT.
"This is a gold mine of untapped genetics," Rudd said. "They can
be tapped directly through laboratory crosses, but it is
difficult."
The researcher must pollinate from a wild species to a hexaploid
wheat and then rescue and nurture the developing embryo to get a
plant, he said. Hexaploid wheat has three genomes or sets of
chromosomes. This is the makeup of the typical bread wheat.
After such a cross, the initial plant will have genetic
abnormalities. A series of crosses back to the hexaploid wheat
is necessary before the desired trait from the wild species is
expressed without any genetic abnormalities.
The second part of Rudd's research, working with synthetic or
man-made hexaploid wheats, provides a more accessible bridge to
the wild species, he said.
Most synthetic hexaploid wheats are crosses between Durum
(pasta-type) wheat, which has two genomes or sets of
chromosomes, and Aegilops Tauchii or goat grass, Rudd said.
The synthetic hexaploid made from this initial cross is
generally wild and unuseable, except as a bridge to the wild
species, he said.
"Valuable genetics are lost in the direct cross with the wild
grass due to genetic abnormalities," Rudd said. "With synthetic
hexaploids, the full compliment of wild relative genes is
available for selection."
Researchers in Bushland and Vernon are studying synthetic
hexaploids already developed through CIMMYT. Crosses between
Texas winter wheat and 117 CIMMYT synthetics have already been
made and another 1,100 crosses are expected to be made available
to U.S. researchers, he said.
"We want to look at them for the forage characteristics they may
offer, which have not been evaluated," Rudd said. "They have
been shown to have large, strong seed for rapid stand
establishment and early growth in the fall."
These synthetic spring wheat varieties must be backcrossed to
make them winter wheats, he said. Then they can be looked at for
other characteristics.
"If we find something useful in the wild, we may make a
synthetic hexaploid from it, or directly cross into wheat," Rudd
said.
"Through traditional genetic variability we've been able to gain
1 percent a year in grain yield," he said. "Can we double our
genetic gain by doubling our variability?"
CIMMYT predicted that within a few years, more than one-half of
its advance lines of wheat will trace back to a synthetic wheat.
And that's from a project started less than 20 years ago, in a
world where breeders spend up to 15 years trying to get a
desired trait in a line of wheat. |