Soybean varieties resistant to phytophthora root rot have started to lose the battle against their fungal enemy. The result is yield losses from 3 to 30 bu/acre, according to Ohio State University (OSU) plant pathologists.

But a new soybean gene just discovered at OSU may make resistance a reality again. It's the first time in nearly two decades that a gene showing resistance to the disease has been discovered.

“Preliminary research results indicate that the new gene is effective against Phytophthora isolates collected from 50 locations in Ohio. It's a major find,” says Anne Dorrance, OSU plant pathologist. “Only one isolate per field was tested, so there is still much work that needs to be done to see if the gene is effective against the majority of pathogen populations in the field.”

Named Rps8, the new gene also has excited scientists because it was found on a new area of the soybean genome. The new position makes it easier for researchers to breed this new trait into new and existing cultivars.

The good thing about the new gene is that it probably hasn't been seen in U.S. germplasm lines before because of its new location, says Dorrance. “So there is a high probability that it will be effective.”

The next step for researchers is to evaluate the gene's effectiveness in the field and incorporate it into cultivars adapted to Ohio's soil conditions and field characteristics.

Similar evaluations are planned in Illinois. “With help from seed company representatives and regional extension educators, we've collected and tested more than 200 soil samples from soybean fields with a history of phytophthora root rot or similar seedling health problems,” says Dean Malvick, plant pathologist with the University of Illinois.

Malvick and his research team obtained phytophthora isolates from many of the soil samples and tested them against soybean varieties with the three major phytophthora resistance genes available in Illinois.

“As expected, we found that many of the isolates from Illinois can defeat the first of the resistance genes and that a smaller number can defeat the second type,” he says. “Unfortunately, we have found in our preliminary work that a few aggressive isolates can defeat all three of the resistance genes commonly found in commercial soybean varieties sold in the state,” he says.

Malvick plans to test the aggressive isolates from Illinois against the new gene from OSU.

OSU's Dorrance hopes they have the answer to the pest that drops soybean yields across the Midwest. “If this new gene proves to be effective against a broad population, it could last anywhere from 8 to 20 years,” she says. “We're hoping to boost the effectiveness to last 25-30 years by combining this gene with Rps genes that have been used in the past, plus partial resistance.”