Source: AgAnswers, an Ohio State Extension and Purdue Extension Partnership

A wheat disease that's bitten farmers across the nation's midsection could soon be defanged, thanks to Purdue University research.

Fusarium head blight, commonly called head scab, destroyed billions of dollars worth of wheat crops in the 1990s and is eating away at yields this year. A Purdue breeding project has produced a wheat variety with strong resistance to head scab.

While the variety isn't 100 percent resistant to Fusarium, it is not far off, said Herb Ohm, professor of agronomy and wheat breeder. The resistant variety should be available to growers in time for fall 2005 winter wheat planting, he said.

"This new wheat line represents a high degree of resistance," Ohm said. "With this line and others that will be released in the next several years, a farmer might lose 2 percent of a crop to head scab, compared to susceptible varieties where they might lose 20 percent.

"While it's not complete resistance, it's pretty close. Looking ahead, I think head scab is going to be manageable and a lot less severe than it has been in the last 10 years."

Head scab is a fungal disease that attacks the wheat head where ears of grain — or spikes — develop. The disease can interrupt a wheat plant's grain-making ability, resulting in low yield. The Fusarium graminearum fungus also produces deoxynivalenol (DON), a compound extremely toxic to humans and livestock. Wheat grain with even trace amounts of DON is difficult to market.

Fusarium thrives in warm, wet conditions like those that settled over Indiana in May and June. Because head scab appears after wheat is well established and around mid-grain fill, there is little a farmer can do to stop the infection.

Cornstalks serve as a Fusarium host. The fungus can move from corn into wheat when wheat is sown into disked cornstalks. Reduced tillage has increased the frequency and severity of head scab infection. The Fusarium fungus also causes ear and stalk rot in corn. In corn the fungus is known as Gibberella zeae.

Fusarium outbreaks cost wheat growers in Indiana, Ohio, Illinois and Michigan more than $300 million in 1995 and 1996. Farmers in the Dakotas and Minnesota lost about $1 billion in 1993 alone to the disease.

Head scab is showing up this year as wheat harvest progresses. Ohm estimated Fusarium-related crop losses as high as 20 percent in some areas.

Indiana farmers are expected to harvest 440,000 acres of winter wheat in 2004, the Purdue-based Indiana Agricultural Statistics Service (IASS) reported Wednesday (June 30). On May 20 the IASS estimated average yield at 63 bushels per acre.

Wheat breeders have been working on head scab resistance for years, Ohm said. Ohm and other Purdue researchers began their search for Fusarium resistance 13 years ago.

"There are two main types of resistance that we have been working with," Ohm said. "One is the mechanical exclusion of Fusarium fungal spores from getting into the plant during flowering."

In "closed flowering" resistance, the wheat plant grows without exposing its flowers to fungal invaders. Minus a front door through which to enter, Fusarium spores cannot attach themselves to wheat heads.

"The other type of resistance that we've been working with is Type II, where the host resistance inhibits the spread of the fungus after infection," Ohm said. "We've found that compared to other varieties, about one-fourth of the spikes in our new variety become infected. For example, while a susceptible, or open-flowered, variety may have 40 percent of its spikes infected in a particular field, this new line would probably have 10 percent of its spikes infected."

Ohm added the Purdue line also contains resistance characteristics that quarantine head scab in two or three spikelets — grain rows — thus limiting the disease's spread.

Locating resistant genes and crossbreeding them with wheat varieties adapted to the United States has been a long, arduous process, Ohm said.

"The difficult thing with developing good levels of resistance to this fungus is that no one gene that we have discovered in wheat provides enough protection by itself," he said. "We've had to combine two or more genes for resistance in the same variety to give adequate protection. That's not easy, because these resistance genes come from donor varieties — or genotypes — from other parts of the world.

"We've identified a number of Chinese lines that have very good resistance. There are a couple of European and South American lines that have proven resistance. The trouble is, none of these varieties are adapted to the United States. In fact, some of them are spring wheats rather than winter wheats."

The resistance genes Ohm identified are effective across all soft and hard wheat varieties.

Purdue will license its head scab-resistant wheat line, Ohm said. Varieties with the gene package should be available through Agricultural Alumni Seed Improvement Association of Romney, Ind., among others, he said.