Scab outbreak has silver lining

MU wheat geneticist Anne McKendry examines an experimental soft red winter wheat variety in her research plots at the Bradford Research and Extension Center east of Columbia. Since 1997, McKendry has collaborated on a national initiative to develop wheat varieties with functional resistance to Fusarium head blight, or scab. MU photo by Jason Jenkins [Click to enlarge]

Although a widespread outbreak of wheat scab across Missouri this year has dashed some producers' hopes of repeating the record-breaking soft red winter wheat harvest of 2003, there is a silver lining to such outbreaks, a University of Missouri wheat geneticist said.

"Between severe weather and a complex of diseases, especially scab, it's been a below-average year for many wheat farmers," said Anne McKendry, MU associate professor of agronomy. "But the high levels of natural scab infection actually allow us to make greater progress toward identifying new scab-resistant lines in our breeding program, and that will benefit producers in the long-run."

Scab, or Fusarium head blight, is a fungal disease that infects wheat seed heads as grain begins to form. Prolonged moisture and warm temperatures at heading increase the potential for yield loss, causing blank and shriveled kernels on all or part of the head. In the worst cases, a toxin is produced that makes the wheat unmarketable.

Since 1997, McKendry and scientists at 16 other land-grant universities have collaborated on the U.S. Wheat and Barley Scab Initiative, a project to develop wheat varieties with scab resistance.

McKendry is evaluating 25,000 head rows, each a unique genetic line with the potential to become a new soft red winter wheat variety, at various sites across Missouri this year.

"Of the 25,000, we'll save about 10 percent, or 2,500 lines, to add to our yield trials," she said. "Having scab expressed naturally on a line makes our selection more efficient. We can eliminate lines that are totally and moderate susceptible right away, saving two to three years of subsequent testing and speeding the next scab-resistant winter wheat to the marketplace."

The first soft red winter wheat variety to result from the initiative was Truman, named for Missouri farmer and 33rd U.S. President Harry S. Truman, which was released to certified seed growers in 2003 and will be available to producers this fall.

"Truman is now our standard for scab resistance, which is around 90 percent," McKendry said. "As we evaluate the 3,000 to 4,000 lines in various stages of yield trials each year, they have to equal or surpass Truman, not only in scab resistance, but in about 30 other traits such as yield, maturity date, grain milling qualities and resistance to other diseases."

She added that "even resistance to scab is more complicated than a simple 'yes' or 'no.' There are five categories of scab resistance we evaluate, five qualities the plant has to possess to be considered resistant."

The categories include resistance to initial infection, or how many florets on the head become infected when exposed to scab spores, and resistance to scab spread, or how far the disease travels up or down the seed head once a floret is infected.

McKendry's program is considered to have some of the most resistant "as yet unreleased" material of any wheat breeding program in the United States.

"We have two scab-resistant lines under evaluation for release to certified seed growers this year, both of which are siblings to Truman," she said. "One is well-suited for double-cropping and exhibits higher yield potential; the other has the best scab resistance of any line we've produced."

McKendry said the decision on whether to release the new lines will be made later this summer.

"This year has been a litmus test for Truman," McKendry said. "The heading window was narrower this year, leaving more of the crop susceptible to scab. While I hate to see an outbreak like this, I'm anxious to see how Truman performed."