COVER STORY: The race against Ug99

FARGO, N.D. -- Wheat breeders in the United States and around the world are anxiously waiting to begin crossing a newly developed resistant wheat hybrid with their commercial varieties in hopes of stopping the destructive black stem rust known as...

FARGO, N.D. -- Wheat breeders in the United States and around the world are anxiously waiting to begin crossing a newly developed resistant wheat hybrid with their commercial varieties in hopes of stopping the destructive black stem rust known as Ug99.

The Ug99 fungus first was discovered in Ugandan wheat fields in 1999 (hence the name) and since has spread on the wind to several other African countries. In 2007, Ug99 jumped the Red Sea, the Persian Gulf and Saudi Arabia to land 700 miles away in western Iran. Everywhere it goes, it damages up to 70 percent of the wheat crop and, according to the Food and Agriculture Organization of the United Nations, has become more virulent since it started to spread.

Thus, as its range increased unchecked, U.S. agriculture began to take notice.

"Ug99 is really tough because so much of the world's wheat, including ours domestically, is susceptible to this, and it is dangerous," says Dr. Michael Edwards, research leader at the U.S. Department of Agriculture's Cereal Crops Research Unit in Fargo, N.D.

The last outbreak of stem rust in North America occurred in the 1950s, destroying 42 percent of the North Dakota crop as well as lesser, though still ruinous, portions of the rest of the U.S. crop.


The concerns

The immediate concerns are for the impoverished countries that have suffered multiple years of failed wheat crops and that five of the countries now in Ug99's path produce about 160 million acres of wheat annually, or about 25 percent of the world wheat crop. About 80 percent of the varieties available there are based on the SR24 gene, which confers resistance to the past strains of stem rust. According to a United Nations report, the fungus "recently invaded Iran faster than predicted and could cause mass starvation if it hits India before new resistant strains are ready."

In response, 17 international research organizations, including USDA's Agricultural Research Service, have joined forces to find an answer for Ug99. Working together under an umbrella of funding and coordination, the Durable Rust Resistance in Wheat project was initiated.

The coordination efforts are being managed by Cornell University's College of Agriculture and Life Sciences. They are ensuring that research work is not being duplicated and that multiple approaches to the problem are being investigated.

Its primary goal is to "mitigate that threat through coordinated activities that will replace susceptible varieties with durably resistant varieties, created by accelerated multilateral plant breeding," a release says.

The news for the U.S. seems to be better for the time being, given the distance from these Ug99 outbreaks. However, if the disease did find its way to the Northern Plains through some means other than the wind, it would find very fertile fields for its purposes because every one of the wheat varieties raised in North Dakota, South Dakota and Minnesota are based on that same SR24 gene that Ug99 is defeating halfway around the world.

Fortunately, multiyear fungicide trials are uncovering effective controls against Ug99. Among them are Folicur and Stratego.

The catch


Research geneticist Dr. Steven Xu works with Edwards in Fargo, combating leaf spot, scab and the Hessian fly, a threat to wheat in Kansas and Oklahoma.

"In 2007, we got a call to work on the international effort to combat this disease," he says.

Xu and his team at ARS have been tasked with developing a resistant wheat that can be bred with advanced commercial lines to produce a viable hybrid that is resistant to Ug99.

There is a catch, though. Because genetically engineered wheat, as a food crop, has not yet been accepted by most countries, Xu and everyone else involved in the research efforts have to create a Ug99-resistant breed without the benefits of much of modern genetic engineering.

"This not gene-splicing," Xu says. "It's not Roundup Ready, so to speak."

The good news is that he is one of just a few active research geneticists who are experienced in the older science of chromosome engineering. In the 1980s, almost all of the wheat genetic labs were using chromosome engineering, then the leading edge of genetics technology, he says.

However, it is a very labor-intensive discipline because identifying successful hybrids had to be done without being able to verify the presence of actual genes. Back then, all they could do was test the plant's behavior. If they were trying to introduce a gene that caused a wheat stalk to be stronger, then they would have to raise it to maturity before they knew anything. It was an even longer process to verify whether the plant had picked up any of the hundreds or thousands of undesirable genetic instructions from the donor plant. Therefore, with the advent of the quicker, computer-based molecular biology, which both manipulated and identified genes, most research facilities dropped chromosome engineering in favor of the quicker, cheaper discipline.

"Very few people are still working on the traditional cytogenetic work, or chromosome engineering," Xu says.


The Fargo laboratory and one in Kansas are the only ARS facilities left that work in chromosome engineering. Therefore, the project leaders at Cornell divided up the search for resistant wheat through chromosome engineering between the two facilities.

Goat grass

There are nine known rust-resistant genes that are effective against Ug99, Xu says. His team will work with four of the resistant wild grass genes and the Kansas team with the other five.

Xu now is working on SR39, the most promising of the four genes assigned him. His goal is to insert SR39 into wheat through traditional crossing.

"Unfortunately, all of the genes effective against Ug99 are not from wheat," he says. "These are from wheat grasses."

The wheat grasses he refers to are wild grasses of various heights, sometimes referred to as "goat grass." Being a grass, it is related to wheat, though only as a very distant relative.

He and his team have to identify, isolate and cross one of these Ug99-resistant wild grass genes into some kind of wheat without the wheat becoming more of a wild grass than a food crop.

"Basically, what we need to do is introduce this gene to the cultivars of wheat and try to only incorporate the gene itself and eliminate the garbage, the genetic junk," he says.


That "genetic junk" would impose other wild grass characteristics on the wheat, not just the ability to fend off Ug99.

Another part of his challenge comes with where SR39 is found.

Traffic cops and

primitive wheat

But to do this, they have to get by the cops.

"These grasses are sufficiently distant, as relatives from wheat, that this is not an easy thing to do," Edwards says.

If they were to try to cross their wild grass with just any wheat, there would be a problem. Nature has endowed all wheat with what is called a "Ph gene." Edwards calls it the traffic cop for wheat genes.

"These are naturally occurring regulatory genes in the wheat plant to help protect the integrity of the plant's genes," he says. "They prevent nonviable combinations."


These cops normally would prevent successful crosses between wild grass and wheat.

But there is a primitive Chinese spring wheat in Xu's genetic arsenal that has a "dysfunctional" traffic cop, Edwards says.

Xu can slip genetic material, the chromosomes that resist Ug99, past these traffic cops and safely into the genetic makeup of the primitive wheat. The Chinese spring wheat then can be successfully crossed with modern commercial breeds.

"In a sense, the Chinese spring is a bridge between the wild relative and the commercial wheat," Edwards says.

Process of elimination

After he's got that bridge working, Xu and his team still need to get rid of the genetic junk that resides in the goat grass with the Ug99-fighting material. Doing this requires a long, painstaking process of elimination.

He'd started by crossing wild grass plants with 1,100 primitive wheat plants. Of those crosses, 588 had at least some of the Ug99-resistant gene in their own genetic makeup.

Xu's team then had to find which of those had only the tiny portion that resists Ug99. They use a fluorescent scanning technique, which requires microscopic inspection of each plant at the chromosome level. This also is slow, time-consuming work.


But they just recently have finished the screening of all 588 plants and found 175 that carry the resistance, but without all the genetic junk.

"These 175 plants are now close to maturity in the greenhouse," Xu says.

The new hybrid

In theory, the new genetics of the 175 hybrids will not affect yield, maturity cycles or any of the other characteristics important to modern commercial wheat.

"But we still need to test it," he says. "In the last phase of the project, we introduce it to the commercial cultivars and then do the testing for yield and quality."

"This germ plasm has to be crossed with a commercial variety, an advanced line that one of the breeders would have in their program, and pick up the higher quality of their line," Edwards says. "Then you can have a hybrid of this germ plasm and the variety and have the best of both worlds."

Xu expects the new SR39 hybrids to be ready for commercial breeders by the end of the year, after which ARS immediately will release the germ plasm to the public.

"Being the ARS, we are open to anybody by policy," Edwards says.

They already have a long list of breeders and researchers waiting to test the new wheat.

"People are waiting for this worldwide," Xu says.

They will start by shipping 50 seeds to the Nation Seed Storage Laboratory in Fort Collins, Colo., for safe keeping. After that, the breeders will get 5,000 seeds and, with a little luck and a few years, be able to release new varieties of wheat that can stand up to Ug99 to growers all over the world.

After that, Edwards hopes he will be able to say that no news is good news.

"It's sort of ironic that, if they are successful, no one will know what the big deal was because it won't become an epidemic," Edwards says.

But research will at least have been reminded of the value of combining new and old technologies and of traffic cops and primitive wheat.

Rust fighters

Fungicides being used successfully against Ug99 in Africa and the Middle East:

Alto Super












Cotaf 5C
























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