Spread of wheat blast disease puts new urgency on researchers

K-State plant pathologist leads project working to locate resistance genes that will help wheat beat the deadly fungus.

Picture a wheat disease so virulent that it can wipe out 100% of yield on infected plants. Now, imagine that no known chemistry controls it when weather favors disease, and two decades of study of wheat germplasm has turned up only one gene that confers only partial resistance.

Its name is wheat blast, and it is alive and well in Brazil, where it was first discovered in 1985, as well as in Bolivia, Paraguay and northern Argentina. In 2016, it wiped out whole fields in Bangladesh, infecting almost 16% of the cultivated acreage of the country.

Nobody is sure how it got to Bangladesh, but it’s now poised to move into India and other parts of South Asia where more than 300 million people depend on wheat for a major portion of their diet, and scientists are scrambling for answers.

Barbara Valent, Kansas State University distinguished professor of plant pathology, is on the front line of defense, both in an effort to help South American and Asian farmers and to prepare U.S. farmers to fight should the deadly pathogen arrive in U.S. fields.

From a Biosecurity Level 3 laboratory inside the Biosecurity Research Institute, her team has been working for eight years to unlock the genetic secrets that will confer resistance to the fungus that causes wheat blast, Magnaporthe oryzae.

"So far, we are not finding resistance genes. We have located only one gene, and it only offers partial resistance. We know that fungicides are not nearly effective enough against it. We are truly frightened of this disease," Valent says.

“The fungus thrives in warm, wet environments, and when weather conditions are right, nothing seems to stop its destruction,” she says.

Researchers know that it is a cousin of the strains of Magnaporthe oryzae that cause rice blast and a close cousin of other strains that cause a turfgrass disease called gray leaf spot. Each strain is host-adapted. So far, only one instance has been documented on wheat in the U.S., and that was in Kentucky in 2011 when a single head was found.

"In that instance, we know it was not a South American strain that was in Kentucky, but one of the strains that cause the turfgrass disease. We learned that the turfgrass fungus already has some ability to infect wheat, but the climate in the U.S. hasn't been quite right during the wheat growing season," she says. "But with that single head, we know that U.S. farm fields are not safe from infection.”

So far, scientists know that the blast fungus can live in wheat residue, that it can move on the wind or that it can be transferred in seed, which makes it a threat to trade in countries where it has been found.

For eight years, using two competitive grants from the USDA National Institute of Food and Agriculture, Valent has labored to find the elusive wheat blast resistance genes. She leads a project that includes field and laboratory trials in four countries — the U.S., Brazil, Paraguay and Bolivia. More than a half-dozen researchers are working with Valent at K-State, along with scientists at six other universities, the USDA-ARS and agricultural agencies in South America. They have made progress, but not enough progress.

"We've taken a multiple-level approach," Valent says. "Rice has about 100 genes that provide resistance to blast, which leads us to believe that this is a very old disease in rice, maybe as much as 7,000 years old. So far, we have identified and cloned about 25 of the rice genes, and we are trying to see if that genetic material could be used to confer resistance in wheat."

Even if her team is able to do that, using it would involve genome editing or genetic modification, and that could be problematic in the marketplace, so they are also staying focused on finding genes in wild wheats and wheat parent lines.

"We know that this fungus can overcome a single gene quickly — it has already started to defeat the gene we found that confers partial resistance. What we need are a half-dozen genes that we can stack together and give the wheat plant more defenses," Valent says.

She adds she is somewhat concerned about the disease grabbing a foothold in the U.S. without being immediately identified because, at first glance, it resembles a much more common pathogen, fusarium head blight.

"If you look closely, you can tell the difference because fusarium has kind of salmon-orange tinge and blast is gray," she says. "But we need to get people educated on what to look for. If it gets here and we don't catch it fast, we'll find ourselves in the same predicament as Brazil, Bolivia and Bangladesh."

Until Valent's research team can come up with a genetic answer, farmers in stricken regions cope by strictly controlling planting date in an effort to get the wheat headed out before the rainy season.

"You can't treat it, so you manage around it," she says. "This is one scary disease."

What Valent and her colleagues need now is a source of funding to continue the work that has already been done. The $5.5 million USDA competitive grant that has funded the last five years of research will run out at the end of 2017.

In early March, Valent joined others in the Supporters of the Ag Research Foundation in Washington, D.C., to lobby for the funds to continue her research, as well as other critical ag projects around the country.

"The danger of losing funding is that much of the progress made in years of work just disappears. The published papers are still there, but the teams and the infrastructure for field testing all need funding, and without it they go away and progress is lost.

"I'm very concerned about the future of ag research," she says. "So many researchers can't get funding for projects that are really important science. The struggle hurts the next generation, too, because so many of our graduates or younger students decide they don't want to struggle in ag, and they go elsewhere."

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