July 20, 2004

SIUC Country Column: Some commercial soybean varieties lack disease resistance

by K.C. Jaehnig

Some commercial soybean varieties billed as resistant to soybean cyst nematode, or SCN, quite simply ... aren't.

"We found a fair number -- as high as 20 percent, depending on year -- that actually don't contain the level of resistance farmers need," said Jason P. Bond, a Southern Illinois University Carbondale plant pathologist.

"The most economical way to manage SCN is by using resistant varieties, so this is important information for farmers to have."

Bond is part of a joint effort by SIUC scientists and researchers at the University of Illinois aimed at learning more about the nematodes, helping farmers manage them and developing new resistant varieties. The Illinois Soybean Program Operating Board is funding the project, which got off the ground in 2001.

Last year, scientists at both universities screened more than 400 of the 500+ resistant soybean varieties now on the market against four different nematode populations. Details appeared in this year's VIPS -- Varietal Information Program for Soybeans -- an information source funded by the Soybean check-off that allows farmers to compare, among other features, resistance of varieties at different locations. Visit its Web site at www.VIPSoybeans.org. Screening of more than 630 lines will take place again this season.

Research teams from both universities also collected soil samples from counties in the southern part of the state last year and the year before in order to see how well the nematodes they found could reproduce on resistant soybean varieties.

While analysis is continuing, early results at UI show that nematodes in five of the six fields sampled could reproduce on resistant varieties currently being sold to farmers. SIUC researchers have found nematode reproduction on resistant varieties in seven of 15 fields.

"While this is preliminary data, it is surprising that such a high percentage can reproduce on the predominant resistance source," Bond said.

Research teams will continue to collect samples from southern counties this season and will expand their focus to include central counties as well. In addition, UI researchers are working on a molecular-level test that could assess, through tests on a single young nematode, how virulent -- in terms of its ability to reproduce on resistant varieties -- a particular population actually is.

"This would make it easier for us to test an individual farmer's sample," Bond said. "We can't do that now because of the amount of time and labor involved."

At SIUC, Bond and breeder Michael E. Schmidt are working with resistant germplasm as yet untapped by commercial breeders.

"We're looking for lines with broad resistance that would probably do well in a number of fields," Bond said.

"In fact, Mike's program has been able to identify several lines that have this broad resistance."