May 4, 2005 AMARILLO – 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.
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