COULD WHEAT RUST AWAY?
In February, 1999, scientists noticed brown bumps, looking like fuzz-covered scales, on stems of wheat at a nursery at the Kalengyere Research Station in southwestern Uganda. This wheat rust became known as Ug99, named for the year and the country. This wheat in Uganda, however, was not supposed to get stem rust at all, because the plants included Sr31, a gene that protected wheat from previously known forms of stem rust.
Ug99 could have been just another rust that attacks wheat, joining the others: brown, black, and yellow. But Ug99 looks worse. In fact, it has the attention of agricultural officials around the world, and with good reason. "Worst case scenario for this disease under ideal conditions of susceptible wheat varieties, sufficient and available pathogen inoculum, and the right climatic conditions," says Colin Wellings of the University of Sydney in Australia, "is complete crop failure." Other experts agree that Ug99 could be devastating. "Ug99 threatens world-wide wheat production," says Kay Simmons, national program leader of plant genetics and grain crops at the US Department of Agriculture. "It has the potential to destroy many commercially grown wheat varieties in Africa, Asia, and could threaten most wheat-growing countries of the world."
This would not be the first wheat disaster. In 1950, a stem rust took out about 70% of North America's wheat crop. In 1970, Victoria, Australia, lost about 25% of its wheat to stem rust, as well. Nonetheless, some features of Ug99 look even more dangerous.
For one thing, Ug99 is on the move. It's already impacted crops in Ethiopia, Kenya, and Uganda. At a symposium on wheat rust held in Sydney early in 2007, Rick Ward, coordinator of the Global Rust Initiative, said that Ug99 will probably head toward Syria and Iraq.
Beyond spreading, Ug99 could also be changing. In 2005, tests showed that 17 of Australia's 75 wheat cultivars could be attacked by Ug99. Some of the resistant cultivars depended on Sr24, another rust-resistance gene. However, Robert Park, chair of cereal rust research at the Grains Research Development Corporation in Australia, says, "There are some pathotypes of this organism that can overcome Sr24." Those pathotypes would make 29 of Australia's cultivars susceptible to Ug99.
In any case, scientists need some way to take on Ug99. Fungicides offer one approach. Wellings, however, calls that approach "relatively expensive and difficult to apply in a timely manner on large-scale, extensive cropping systems." Alternatively, scientists could breed wheat to resist Ug99. Wellings says that is "effective, cheap, but can take a relatively long time to develop resistant varieties with the right combination of adaptation, yield, and product quality." Still, possibilities for breeding a Ug99-resistant wheat already exist. Simmons says, "There are good sources of genetic resistance in some wheat varieties and wild relatives of wheat that can be used."
The keys to fighting Ug99 will probably be teamwork and money. Wellings says that stopping Ug99 will take "a coordinated, international approach combining research and development of resistant wheats, and the willingness to have these extended to farming communities." He adds, "This will require, among other things, serious funding."
