A new soybean gene, showing resistance to Phytophthora root rot, has been identified – the first time in nearly 20 years a gene exhibiting effectiveness against the disease has been discovered.

Ohio State University plant pathologists and soybean breeders, who made the discovery, have named the new gene Rps8. The germplasm containing the gene will be licensed for breeding purposes.

Anne Dorrance, an Ohio State plant pathologist with the Ohio Agricultural Research and Development Center, says the discovery is a "major find" in the war against Phytophthora root rot. She emphasizes, however, that at least another year of work needs to be completed before it can be determined just how effective the new gene is in protecting cultivars in the field.

"This is a big discovery over a just seven-year span of research," says Dorrance. Ohio State researchers have been screening soybean germplasm lines searching for that "diamond in the rough" since the mid-90s.

"Preliminary research results indicate that the new gene is effective against Phytophthora isolates collected from 50 locations in Ohio," says Dorrance. "Only one isolate per field was tested, so there is still much more work that needs to be done to see if the gene is effective against the majority of pathogen populations in the field, of which there could be thousands."

Despite the work cut out for them, researchers are excited about the preliminary test results. Effectiveness against multiple isolates could breathe new life into the struggle to control Phytophthora that growers are slowly losing.

Previous Ohio State research has shown that Phytophthora populations in Ohio soybean fields are adapting to plants carrying root rot resistant genes, specifically Rps1a, Rps1b, Rps1c, Rps1k, Rps3a and Rps6. These single genes are available in commercial cultivars.

Researchers found in Phytophthora isolates collected from soybean production fields in Ohio, that 95% of the fields sampled killed plants containing Rps1a gene; 65% containing Rps1b; 73% containing Rps1c; 78% containing Rps1k; 51% containing Rps3a; and 52% containing Rps6.

"Phytophthora root rot is the single biggest threat to soybean production. Reduction in yield from the disease can range anywhere from five to 30 bu/acre, depending on the resistance package in the variety. If a million acres of soybeans were infected by this pathogen, that could mean a loss of $120 million for the farmer," says Dorrance. "If this new gene proves to be effective against a broad population, it could last anywhere from eight to 20 years. We are 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."