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Corn+Soybean Digest

Cease and resist: Soybean lines appear to slow rust

More than 500 soybean lines planted in nearly 4,000 plots will be evaluated in Ohio this season for potential resistance to soybean rust.

Ohio State University's Soybean Breeding Program has joined a nationwide effort to identify resistance to the disease, which growers, plant pathologists, agronomists, specialists and industry representatives have been preparing for all season. So far, rust's bark has been worse than its bite, with reported sightings in only two states.

"Our fungicide program is only going to be a short-term solution to manage soybean rust," says Anne Dorrance, an Ohio State plant pathologist with the Ohio Agricultural Research and Development Center (OARDC). "If we are looking at managing the disease on this many soybean acres, then we are going to need host resistance."

Ohio State, partnering with the Ohio Soybean Council, is following on the heels of the USDA, which evaluated commercial soybean varieties from an Illinois performance test and found that a small proportion of plant lines appeared to carry slow-rusting resistance.

"We put everything in the ground, including the kitchen sink," says Steve St. Martin, an OARDC soybean breeder. "If there is indication that some commercial varieties are showing some difference, then there is a chance that perhaps the varieties we are testing will show some resistance as well."

Slow-rust resistance refers to a process of slowing down the development and spread of the disease, so that fewer spores develop per leaf and extending the period between infections. Slow-rust resistance could mean fewer fungicide applications for growers, or no applications at all.

Soybean rust has more life cycles per season than Phytophthora and, therefore, has a higher mutation rate. So we want a slow-rusting partial resistance so it just slows the whole thing down. The rust will penetrate the plant and begin to grow, but it just doesn't seem to take a foothold."

The soybean varieties chosen for the evaluation are being planted later in the plots, beginning this month, to take advantage of soybean rust arriving late in fields, if it shows up in Ohio at all.

"We want to make sure that we have plant material to work with come September," Dorrance says. "If soybean rust hits Ohio, and hits the OARDC Western and Northwestern research branches where the varieties are being tested, we'll have results this year."

The project is a one-time study, part of a series of experiments funded through a $100,000 grant from soybean check-off dollars.

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