Varying stem rust epidemics on wheat stems (Photo: Evans Lagudah & Zakkie Pretorius)
WASHINGTON - Scientists have isolated two genes that protect wheat plants from a disease that threatens the crop worldwide.
At its worst, stem rust can wipe out nearly an entire wheat field. After a 1953 outbreak destroyed 40 percent of the U.S. spring wheat harvest, scientists bred new varieties with resistance to the disease.
That solved the problem for several decades.
Out of Africa
“But then, just in 1999, a new race evolved in Africa," says Kansas State University plant disease expert Eduard Akhunov. "And they found that it overcomes all these resistance genes.”
First found in Uganda, this new "race" - a strain called Ug99 - has spread from South Africa to Iran.
But experts are worried the fungus won’t stop there. Nearly all of the world’s commercial wheat varieties are susceptible to it.
A global effort is under way to create new, Ug99-proof varieties.
Akhunov is co-author of one article. He says both genes described in the new articles come from wheat’s wild relatives.
New alarm system
“Our gene is some kind of surveillance molecule that will try to sense if [the] pathogen is invading or not,” Akhunov says.
He says wheat plants don’t sense that Ug99 is invading because the fungal proteins that used to set off alarms have mutated.
The newly described genes restore the wheat plant’s ability to recognize the invading fungus, says plant biologist Jan Dvorak at the University of Califoria at Davis, co-author of the other new article.
“The gene for resistance is a gene which gives the wheat plant a sensor again," says Dvorak. "It says, ‘Ah, we missed this guy.’ And the wheat plant suddenly is able to see again.”
Breeding better wheat
Eduard Akhunov says researchers could use genetic engineering to quickly put both genes into wheat plants at the same time. But he says now may not be the time because many people don’t trust gene-splicing technology.
“Maybe in the future," Akhunov says. "Because until the public is ready for that, I don’t think there is a way of using that approach.”
Others say genetic engineering may not save much time because of advances in conventional breeding. When conventional breeders mate two plants, they use genetic markers to find offspring with the genes they want.
“Now you have the perfect markers," says Jose Costa, head of grain crop research at the U.S. Department of Agriculture. "It makes things a lot easier and more targeted.”
Wheat varieties resistant to Ug99 have been released in several South Asian countries. More are on the way. But experts warn that diseases will continue to evolve, and fighting them is a never-ending battle.
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