09/05/08 – 10:24am (the great stem rust comeback)
The biblical story of Joseph heralded the onset of wheat plague: “Behold, seven heads of grain, thin and blasted with the east wind.” Millennia later, black stem rust fungus has emerged again in a virulent new form for which 90 percent of the world’s wheat varieties have no resistance.
|A new strain of wheat rust known as Ug99 is spreading from East Africa to the Middle East and could infect 90 percent of all wheat varieties. Breeders, led by Cornell, are working on developing new varieties that incorporate genetic traits like resistance to Ug99 and drought. The three heads of wheat shown here exhibit drought susceptibility.|
Spores of this new strain, known as Ug99, are now riding winds and blasting wheat fields from Uganda, where it was discovered in 1999 (hence Ug99), to Kenya, Ethiopia, Sudan and Yemen. This year, spores have crossed the Arabian Peninsula to Iran. The deadly fungus appears to be on a course to threaten the rest of Asia as well as North Africa.
The fungus, Puccinia graminis, creates brick-red pustules on wheat stems that produce 100 billion spores per hectare (2.5 acres). Researchers are worried that the prolific stem rust will gain a foothold in South Asia, which produces more than 15 percent of the world’s wheat and holds one-sixth of the world’s population. Globally, wheat accounts for an average of between one-third and one-half of each person’s daily calories.
To make matters worse, the world’s wheat stocks are at a 30-year low, driving prices up by almost six times their level five years ago. While high prices are a boon for U.S. farmers, many growers in the developing world — Afghanistan, India and Ethiopia — produce food only for their families, living largely outside the cash economy.
“I don’t hear anyone saying we are near a food shortage, but this is a fragile situation and if one of the major wheat producers has a substantial setback, we could have a food shortage,” said wheat breeder Richard Ward. He is the expert hired by Cornell to coordinate the international Durable Rust Resistance in Wheat project, funded by a $26.8 million grant from the Bill & Melinda Gates Foundation to protect the world’s poor farmers against Ug99 and wheat rust.
The world’s current wheat situation results in part from higher demand from the growing middle class in India and China. Affluence in China has created more meat-eaters, requiring that more acreage be devoted to feed grains. In India, urbanites are consuming more wheat. Also, U.S. farmers have increased corn (maize) production for ethanol in recent years, while droughts have withered crops in Australia.
But, Ward said, “even if all that has happened in the last years had not happened, Ug99 and its related strains of stem rust are a strategic threat to global food security. Period.”
In a genetic arms race, wheat and Puccinia graminis genes have co-evolved; plant proteins recognize pathogen proteins, and a genetic change as small as a single nucleotide (the smallest unit of genetic information) in either organism can make a plant susceptible or resistant. In the world of agriculture, it is the plant breeder’s job to develop new wheat varieties that are resistant to wheat rust.
“As plant breeders, we try to keep the plant ahead,” said Ronnie Coffman, a Cornell professor of plant breeding who is the international rust resistance wheat project’s director.
The last major outbreaks of stem rust occurred in North America between 1950 and 1954, when losses approached 40 percent of the spring wheat production in some years. Since then, with the exception of a few smaller outbreaks, “Wheat stem rust [has] dropped off the radar screen completely,” said Ward. “We have a whole generation of plant breeders who don’t even know what it looks like.”
But to the horror of breeders in a Ugandan nursery in 1999, Ug99 pustules were found covering wheat varieties carrying genes that stem rust had never defeated before. “We now know that Ug99 defeats more of the known stem rust resistance genes than [in] any other [previous] stem rust race,” said Ward.
In a fight against time, plant breeders are working to develop and test new wheat varieties at national research facilities in the Rift Valley in Kenya and in Ethiopia, the only places where field testing with Ug99 is safe. Using traditional plant breeding (as opposed to transgenic engineering), breeders are using the research facilities to accelerate the creation and distribution of resistant wheat varieties.
Poor farmers in Ug99’s path who cannot afford fungicides or crop losses are especially dependent on the fruits of wheat breeders’ labors. The solution, according to Ward, is no small task. “It sounds extraordinary to say, but what we need to do is replace much of the wheat in the world with wheat that is resistant to this race of stem rust,” he said.