Wheat killer

by Arvin Donley
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With global wheat stocks projected to fall to the lowest level in 30 years in 2007-08, any event causing an unexpected drop in production could send shockwaves through the world’s wheat markets.

While drought, such as the one that has devastated the last two wheat crops in Australia, is the most common threat to production, scientists say a potentially more serious problem is developing in East Africa and the Arabian Peninsula, where a new and virulent wheat fungus is plaguing the region and has the potential to spread to other parts of the world.

The new form of wheat stem rust, called Ug99 because it first emerged in Uganda in 1999, is capable of attacking a wide range of wheat varieties and can destroy entire wheat fields, said Dr. Rick Ward of the International Maize and Wheat Improvement Center (CIMMYT) in El Batan, Mexico.

Fearing that this new strain of stem rust could adversely impact the world’s food supply if it is not contained, the Rome, Italy-based Food and Agriculture Organization (FAO) recently joined the Global Rust Initiative (GRI), an international consortium whose mission is to fight plant fungus diseases around the world. CIMMYT and the Syrian-based International Center for Agricultural Research in the Dry Areas (ICARDA) are also part of the consortium.

Stem rust spores are mostly carried by wind over long distances and across continents. FAO Director-General Dr. Jacques Diouf said last April that global wheat yields could be at risk if the stem rust spreads to major wheat producing countries. The disease has spread from Uganda to Kenya, Ethiopia and Sudan, and was discovered last April in Yemen. Scientists said the Ug99 found in Yemen has mutated into a more virulent strain than the one that originated in East Africa.

Ward, who also serves as coordinator of GRI, told World Grain that Ug99 has actually mutated twice since being identified in Yemen. He said there are about 50 genes in a given wheat variety that can stop stem rust but nearly as many corresponding genes in the fungus that can defeat those genes in the wheat plant.

"It’s very alarming because we are talking about fewer than 10 functional genes out of the 50 to begin with that can stop stem rust, and we’ve lost two of them," Ward said. "When you lose a gene that can stop stem rust it’s like losing an antibiotic (for human diseases)."

Ward estimates that up to 90% of all wheat varieties planted around the globe are susceptible to the new strain.

"The fungus can spread rapidly and has the potential to cause global crop epidemics and wheat harvest losses of several billion dollars," Diouf said. "This could lead to increased wheat prices and local or regional food shortages. Developing countries that are relying on wheat and do not have access to resistant varieties will be particularly hard hit."

Ward said the Ug99 stem rust spores will most likely travel from Yemen northward along the Red Sea to Egypt or through the Saudi Arabian Peninsula through the Middle East. Ward said the stem rust could easily spread to major wheat-producing countries such as Turkey, India and China. Countries in the predicted, immediate pathway grow more than 65 million hectares of wheat, accounting for 25% of the global wheat harvest, according to the FAO.

"If we don’t control this stem rust threat, it will have a major impact on food security, especially since global wheat stocks are at a historic low," said M.E. Tusneem, chairman of Pakistan’s Agriculture Research Council.

In the late 1980s, a virulent strain of yellow rust, a wheat disease similar to stem rust, took an almost identical path as Ug99, emerging in East Africa and crossing the Red Sea into Yemen. It then moved into the Middle East and Central Asia, eventually reaching the wheat fields of South Asia within four years. Major yellow rust epidemics were recorded in Egypt, Syria, Turkey, Iraq, Iran, Afghanistan and Pakistan, with wheat losses totaling more than $1 billion.

One concern that Ward and other scientists have is that Ug99 will spread into countries that have large populations of barberry plants, which often serve as an alternate host for stem rust spores and are notorious for spawning new races of stem rust.

"That really scares the heck out of me," Ward said. "Turkey and countries to the north and east of Turkey have a lot of barberry."

Wind currents can carry stem rust spores remarkable distances. In the 1950s epidemic in the United States, where more than 40% of the nation’s spring wheat crop was destroyed, scientists found that spores had been carried more than 600 miles from the Central Plains, where winter wheat is harvested, to states in the Northern Plains such as Minnesota and North Dakota, where most of the spring wheat is grown.

Ward said many scientists believe a stem rust outbreak in Australia many years ago was due to spores traveling in the jet stream from Angola, nearly 7,000 miles away. That’s why Ward believes it is "very likely" that major wheat producing nations like Australia, the United States and Canada eventually will have to deal with the Ug99 strain, even though the disease is currently concentrated in countries halfway around the world.

The stem rust crisis in the 1950s led to a new form of worldwide cooperation among wheat scientists, spearheaded by Nobel laureate wheat scientist Norman Borlaug, who was a key figure in the "Green Revolution" in the late 1960s and early 1970s. This international alliance of scientists led to the development of wheat varieties that, for the most part, resisted the onslaught of stem rust until 1999, when the Ug99 strain was discovered.

As of now, there is no mechanism for reporting sightings of stem rust and for following up on those reports, said Ward. But an effort has begun to improve surveillance and reporting procedures for Ug99.

In mid-March, a meeting was held at ICARDA headquarters in Aleppo, Syria to launch a cereal rust monitoring system. The meeting included representatives from more than 10 "at-risk" nations as well as officials from the FAO, the University of Sydney in Australia, the University of the Orange Free State in South Africa, the U.S. Department of Agriculture’s Cereal Disease Laboratory, and Agriculture and Agri-Food Canada. As part of the effort to imple

ment a monitoring system, ICARDA will expand its capacity to manage information on the distribution and nature of stem rust, Ward said.

"We plan to get more boots on the ground and eyes on the crops, and to teach protocols for taking samples," Ward said. "What we’re trying to do is get a baseline on the current crop."

In Egypt, a country that Ward believes will be dealing with Ug99 in the very near future, a meeting was recently held in which a large number of extension agents were told how to identify stem rust and whom to contact should they see it.

Ward said a number of fungicides have proven to be effective in killing stem rust, but many farmers in developing countries cannot afford them.

He said the ultimate weapon against Ug99 will be the development of new wheat varieties with improved genetic defenses. GRI scientists have already identified promising experimental wheat materials with resistance to Ug99. But from the first breeding trials to growing new, rust-resistant varieties in farmers’ fields on millions of hectares takes a lot of time and effort.

Borlaug, who won the Nobel Peace prize in 1970 for his development of high-yield cereals that increased agricultural production in developing countries, said he is optimistic that answers can be found to keep Ug99 from spreading across the globe.

"We know what to do and how to do it," Borlaug said last year in a CIMMYT press release. "All we need are the financial resources, scientific cooperation and political will to contain this threat to world food security."