Race to Resistance
Oregon State University wheat researchers address threat to world food security
By Nick Houtman
Video by Justin Smith
For 10,000 years, wheat production has been a battle against rust. It's not the kind that eats holes in the fenders of old cars. This rust is a fungus that can damage or even kill wheat plants, causing up to 100 percent loss in grain production. Its spores can travel by wind, on bird wing or on tourists' clothing. On a leaf or stem, it erupts into yellow, orange or brown blisters and diverts the plant's energy from making grain to the care and feeding of more fungus.
Rust diseases evolve rapidly to overcome resistance from wheat. In fact, says Jim Peterson, head of OSU's wheat breeding program, "wheat varieties are regularly lost from production, often within a few years of release, due to appearance of new, deadly strains of the fungus. In the Northwest, stripe rust has been our most critical threat. Epidemics were common and widespread prior to 1970, as rust routinely overcame resistance in new varieties."
A notable exception is the variety Stephens developed by OSU wheat breeder Warren Kronstad and released in 1977. A leading variety in production for over 30 years, Stephens has provided exceptionally durable resistance to the stripe rust fungus. Resistance to this disease remains a critical requirement in OSU's efforts to develop new varieties.
Rust disease can infect many types of plants, but each fungal strain is picky. It targets one type of plant or even specific plant parts. As the name implies, stem rust invades wheat stems, choking off the plant's vascular lifeline. Leaf rust steals nutrients from leaves as it grows. Stripe rust, a type common in the Pacific Northwest, also attacks leaves but appears as bright yellow stripes.
Out of Africa
Today, another type of rust, far from the golden wheat belt of Oregon and Washington, concerns Peterson. Known as Ug99 (it was discovered in Uganda in 1999), this virulent race of stem rust has spread throughout the highlands of East Africa, across the Red Sea to Yemen and, in 2008, into Iran. The breadbaskets of Pakistan and India, which account for nearly 20 percent of the world's wheat, could be next. Russia, China and even the United States are well within reach, as wind-blown spores can travel thousands of miles.
"Ug99 has defeated nearly all major resistance genes deployed around the world, leaving huge production areas at great risk of catastrophic yield losses," Peterson wrote in a recent report for the National Wheat Improvement Committee, which he chairs.
As if that weren't alarming enough, OSU plant pathologist Chris Mundt raised the stakes in a 2009 report published in The American Naturalist. He and colleagues demonstrated that disease epidemics often do not travel at a constant velocity, as has been predicted in standard approaches to biological invasions. Instead, they move in "accelerating waves." Their analysis held as true for wheat stem and stripe rusts as it did for West Nile Virus, potato late blight and avian influenza.
No wonder, then, that Peterson called Ug99 a "time bomb" in a Los Angeles Times story last summer. "It moves in the air, it can move in clothing on an airplane. We know it's going to be here (the United States). It's a matter of how long it's going to take," he said.
Peterson is mindful of what's at stake. Wheat is the world's third most abundantly grown grain after corn and rice. As much as 80 percent of world wheat is currently being produced from varieties that are now highly-susceptible to Ug99. In developing countries, where farmers don't have access or money to purchase emergency fungicides, Peterson emphasizes that the threat of local food shortages or even widespread famine is very real.
Mr. Peterson Goes to Washington
While cool springs protect the Pacific Northwest from Ug99, other regions of the United States wheat belt are highly vulnerable. In his role as chair of the National Wheat Improvement Committee, Peterson has led a $5 million initiative to fund rust research and develop Ug99-resistant varieties. With support from the National Association of Wheat Growers, the milling and baking industry, and allied barley and oat groups, he has promoted a coordinated strategy of gene discovery, deployment and accelerated breeding. In Washington D.C., he and his allies raised awareness on Capitol Hill, meeting with staffs of up to 55 congressional representatives and senators each year, as well as with the Undersecretary of Agriculture and other USDA administrators.
"It hasn't been easy to capture new federal funding," says Peterson, who holds the Warren Kronstad Wheat Research Chair at OSU. "Additional funding for rust research was proposed by both Senate and House in FY07 and FY08 only to be lost in the final appropriations bills." This past year, he and his colleagues succeeded with a new $1.5 million appropriation for rust research through the USDA Agricultural Research Service. An additional $1.0 million has been appropriated to USDA-ARS for rust research in FY10.
Oregon State University has long played a central role in international germplasm exchange, which, with the appearance of these new virulent rusts, is more important than ever. In the search for new resistance genes and resistant varieties, Peterson and his colleagues import hundreds of seed stocks each year from the International Winter Wheat Program based in Turkey, which is a collaboration among the International Center for Maize and Wheat Improvement (CIMMYT), the International Center for Agricultural Research in the Dry Areas (ICARDA) and the Turkish national program. Based in Mexico, CIMMYT was responsible for much of the Green Revolution under the leadership of famed agronomist Norman Borlaug. Syria-based ICARDA conducts dryland research on wheat and barley.
"We grow these materials under quarantine," says Peterson, "and then distribute the resulting seed stocks as parent material to over 35 wheat breeding programs throughout the U.S. and South America. We have the only permit granted by the USDA-APHIS (Animal and Plant Health Inspection Service) for field growing seed stocks from Turkey. This year, the international nurseries include valuable new sources of resistance to Ug99."
Trouble is, it can take ten or more years to develop a new variety. In order to speed up that process, OSU plant geneticist Oscar Riera-Lizarazu leads efforts to identify and track valuable genes that can provide disease resistance, stress tolerance and improved milling and baking quality. He and graduate students Dolores Vazquez of Mexico and Martin Quincke of Uruguay have already succeeded in identifying new genes and associated molecular markers for resistance to stripe rust and important soil-borne diseases. With molecular markers in hand, genes can be more efficiently tracked and recombined into varieties that provide superior levels of disease resistance in a shorter amount of time.
As Mundt has shown, time may be running out with Ug99. Scientists have seen first-hand how quickly disease-resistant wheat can succumb to rapidly evolving pathogens. In 1998, OSU released Foote (named for former OSU wheat breeder Wilson Foote), a new variety with resistance to Septoria leaf blotch, an important disease that had hampered production of Stephens and other varieties in the Willamette Valley. Foote was quickly adopted and valley farmers increased their wheat plantings to about 14,000 acres. In 2003, a new stripe rust race appeared that overcame Foote's defenses. "Growers had to spray fungicide up to three times and quickly abandoned the variety," says Peterson.
The replacement for Foote came in 2007 with the new OSU variety Goetze. Named for the former OSU Extension Cereals Specialist Norm Goetze, the variety has improved resistance to stripe rust, as confirmed by molecular markers, combined with an outstanding yield record in OSU trials. Peterson expects to see more than 250,000 acres planted to wheat in the Willamette Valley in 2010, mostly with Goetze.
Wheat is one of the Northwest's most important exports. Portland and Vancouver, Washington, constitute the largest wheat export harbor in the country, shipping an estimated 10.4 million metric tons, more than 28,000 tons per day, in 2008. Grain stocks come both by barge down the Columbia and by train from the Midwest.
Since 2002, OSU has released nine new high-yielding wheat varieties that currently account for more than 60 percent of winter wheat grown in Oregon and approximately 30 percent of that grown in Washington. Peterson has calculated that, based on a conservative estimate of five additional bushels per acre, OSU varieties earned growers an additional $12 million in Oregon and $21.5 million in Washington in 2009 alone. In addition, sales of OSU's herbicide tolerant Clearfield varieties have returned $2.4 million in royalties to OSU since 2003.
The search for new genes and breeding of varieties with resistance to Ug99 is a top priority for Peterson, American wheat breeders and geneticists and the world wheat research community. For their role in developing the national strategy to combat Ug99, he and his USDA colleagues received the Secretary of Agriculture's Group Honor Award of Excellence in 2008. Peterson was the only non-USDA scientist to be recognized.
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