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College of Food, Agricultural, and Environmental Sciences


New Soybean Varieties Show Resistance to Root Rot

July 11, 2001

WOOSTER, Ohio - Ohio State University researchers have identified new soybean varieties that exhibit both partial and complete resistance to Phytophthora sojae, a pathogen responsible for severe production losses.

But farmers may have to wait several years for a commercial product if a resistant gene is found that could be introduced into Ohio varieties, said Anne Dorrance, a plant pathologist at the university's Ohio Agricultural Research and Development Center.

"If we do find a novel resistant gene, we're going to be breaking open the champagne," she said. "This would be a major find."

Dorrance and OSU plant pathologist Fritz Schmitthenner evaluated 1,015 soybean plant introductions (varieties found in other countries) and found that 32 of them exhibited complete resistance to Phytophthora and 130 exhibited high levels of partial resistance. All of the varieties originated from South Korea and were obtained from the U.S. Department of Agriculture Soybean Germplasm Collection in Urbana, Ill.

Phytophthora sojae causes soybean root rot and is a major problem in Midwest states that have heavy clay soils, such as Ohio. Heavy rains saturate the soil producing areas with standing water, which provides an outlet for the pathogen to infect plant roots. The fungus grows in the roots and into the plant stem, eventually killing the plant. Dorrance said last year 20-40 percent of Ohio's soybean crop was lost to plant diseases, mainly caused by Phytophthora. The outlook on this year's crop is poor. Early heavy rains aided in root rot development and a recent lack of rain may put additional stresses on the soybean plants because of underdeveloped root systems.

"The timing right now is perfect to find a new gene and get it out in the market," said Dorrance, adding that Phytophthora is slowly adapting to current soybean resistant genes. "We are continuously putting pressure on those resistant genes. Eventually they will no longer hold up to the pathogen."
Dorrance said the next step in research is to identify the gene in the South Korean soybean varieties that are showing resistance to Phytophthora and introduce it into current commercial varieties in the hopes those varieties will carry the resistant gene. "If we do find the gene, it may be five or six years before we can get out a completely resistant variety, and four or five years before we could release a partial-resistant variety," she said. OSU horticulturists Steve St. Martin and Ron Fioritto are conducting the genetic work.

Though a completely resistant variety is ideal, Dorrance said varieties that show partial resistance are also exciting. "Partial resistance basically means that the pathogen has little effect on the plant once it has grown up and out of the ground," she said. "Partial resistance varieties can be very effective, sometimes having a 30-percent difference in yields compared to soybean plants that have no resistance to Phytophthora at all, depending on the disease pressure."

The genetic studies on the new soybean varieties are scheduled to be completed by this fall and next spring. Funding for the project is supported by the Ohio Soybean Council. Some of the results from the research conducted by Dorrance and Schmitthenner are available online at The report is also discussed in OARDC research bulletin 1193 available at the OARDC Department of Plant Pathology, 1680 Madison Ave., Wooster, OH 44691.

Candace Pollock
Anne Dorrance