New genes resistant to phytophthora root rot (PRR) have been identified by Ohio researchers.

In the past, single-dominant resistance genes (Rps) have successfully managed the disease. But in Ohio, the soilborne, yield-robbing disease has been known to defeat Rps genes, says Anne Dorrance, an Ohio State University plant pathologist.

"We've actually received many calls over the years where soybean fields that have Rps-1k, the most recently utilized of all the Rps genes, have had a lot of phytophthora root rot damage," Dorrance says.

At least 10% of Ohio's soybean fields had to be replanted in 1997, a wet year, she adds, because the disease can defeat Rps genes. Single-dominant resistant genes only have a useful life of eight to 15 years. That's because the phytophthora organism can adapt and develop new ways to survive, Dorrance explains.

In the study, Dorrance and other researchers evaluated over 1,000 soybean plant introductions for phytophthora root rot resistance. Of those, 120 were resistant to Race 7, 17, 25, 31 and an undesignated race. Further screening is in progress with race 28 and 33 strains.

The earliest that growers might see varieties with the new phytophthora resistance will be six to eight years from now, Dorrance estimates.

(A.F. Schmitthenner, A.E. Dorrance, et al, Ohio State University)