Future world wheat crops threatened by Ug99 stem rust

NASHVILLE, Tenn. - A virulent strain of wheat stem rust, Ug99, that sprung up in Africa in 1999 has now spread into Iran and threatens to spread into other wheat producing regions of Asia and eventually the entire world.

That was the warning Dr. Jim Peterson, wheat breeder at Oregon State University and chair of the National Wheat Improvement Committee (NWIC), re-ported to the NAWG Research and Tech-nology Committee during the Commodity Classic in Nashville.

Ug99 is a race of stem rust that blocks the vascular tissues in cereal grains including wheat, oats and barley. Unlike leaf or stripe rusts that may reduce crop yields, Ug99-infected plants may suffer up to 100 percent loss.

The significance of Ug99 being in Iran is the fact that it is now at the front door of major wheat production areas in Asia, namely Pakistan and India, which ac-counts for 20 percent of the annual world wheat production. Peterson noted there is a possibility that large movements could take place almost overnight if certain wind conditions prevail at the right time.

There was a recent three-day wind event recorded by CIMMYT (Spanish acronym for International Maize and Wheat Improvement Center) that had strong wind currents moving from Yemen, where Ug99 is present, across Pakistan and India and going all the way to China.

“Luckily there weren't any rust spores in Yemen at that time - it was off cycle,” Peterson said. “But this raises concern that if things happen in the right sequence, widespread of this disease could happen quickly. And CIMMYT estimates that from two-thirds to three-quarters of the wheat now planted in India and Pakistan are highly susceptible to this new strain of stem rust. We have a billion people who live in this region and they are highly dependent on wheat for their food supply.”

Another challenge that Ug99 rust presents is its ability to change. In 2006 a change was noted that now makes many of our Great Plains winter wheat varieties susceptible to the new strain. And this year, another variant has been noted that will make the winter wheats grown in the eastern areas of the U.S. vulnerable, according to Peterson.

At the present time, he noted, about one-half of the winter wheat and 75 to 80 percent of the spring wheat acreage in the U.S. is planted in varieties that are susceptible to Ug99, putting about 1.4 billion bushels of annual wheat production at risk. “Now, my concern as a plant breeder is there isn't much to work with right now if you look at the wheat variety candidates and the germplasm behind those varieties - and we are looking about three-quarters of that material being susceptible to Ug99,” he said.

“In addition, 75 to 80 percent of our breeding material is also susceptible to this disease. We are running out of resistant genes to deploy in the face of this highly virulent disease.”

In response to this growing threat, Dr. Norman Borlaug has issued a call to action to find a way to reduce the impact of Ug99. Borlaug, according to Peterson, is concerned that all of the advancement made in the past few decades during his “Green Revolution,” may be eliminated by an outbreak of Ug99. One of the cornerstones of the Green Revolution was the development of rust resistant wheat varieties, but this disease threatens to eliminate the majority of those developed varieties.

A Global Rust Initiative was put together in 2006 to help raise people's awareness and develop strategies on how to respond to this disease, with the goal to develop some varieties with resistance against Ug99.

Peterson noted there are some things that can be done in the short term, but he cautioned these are only short term fixes.

“In the U.S. we only have two sources of resistance, near term, that we could release if Ug99 was staring us in the face,” Peterson said, “and both of those sources have other problems that don't make them ideal varieties.”

This resistant material is being distributed world wide in an effort stay ahead of Ug99, but Peterson pointed out this might not be possible, owing to the rapid way Ug99 can change.

And even if a new resistant variety was ready to be released today it would take two or three years' seed increase in order to have just enough wheat seed for 20 percent of the acres planted to wheat in the world.

Marker gene technology is also ongoing, which is another short term measure that will allow plant breeders to identify the specific gene site that is attacked by Ug99 rust. During this time when additional funding is needed for research work on Ug99, U.S. funding for such international centers such as the International Agricul-tural Research Center and CIMMYT, is on the budget chopping block because funding earmarks by Congress is placing those monies elsewhere.

“We are looking at the most critical time we have seen in years, and our commitment to these international centers is not only being reduced, but may actually go to zero in a very short period of time,” Peterson said.

“These funding cuts are going to impact our food security,” he added. “I hope someone in (Washington) D.C. will wake up and recognize that long-term commitment to the international centers has to be continued and has to be there for our own food security as well.”

Work is also being done by the USDA's Agricultural Research Service (ARS) on this matter. Much of the research is being done by Dr. Yue Jin at the ARS Cereal Grains Disease Lab at the University of Minnesota in St. Paul. He has made several trips to Kenya in an effort to develop resistant wheat varieties.

In the search for resistant varieties, over 1000 wheat lines have been grown in Kenya, which has been a large accomplishment, since winter wheat does not naturally grow in Kenya, and needs to be started in a growth chamber and then transplanting those plants by hand out in the field.

Another breakthrough occurred last year when scientists were able to complete sequencing the Ug99 organism, which gives scientists the ability to understand how the organism operates. That may help them in developing wheat lines that are resistant. But this isn't going to happen overnight, especially since genetically modified wheat is not permitted at this time.

“We need to turn over all of our wheat varieties in the United States in the next four or five years if we are going to stay ahead of this thing,” Peterson noted. “That's not an insignificant task. It's going to take a commitment and additional resources to make it work. And it has to be done without jeopardizing the quality of the wheats we are used to using.”

The National Association of Wheat Growers (NAWG) and the National Wheat Improvement Committee (NWIC) have been working for a number of years to secure funding from Congress to research resistance to Ug99 and will be seeking additional funding for both USDA's Agricultural Research Service and the U.S. wheat research community to address the ongoing threat.