A new species of Pythium, a water mold that attacks soybeans and corn in saturated soils, has been identified in Ohio.

Anne Dorrance, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center, says Pythium delawarii was labeled as a new species when its characteristics didn't match any of the more than 200 described Pythium species. There are at least 24 species found in Ohio that impact corn and soybeans.

The research was published in the March/April issue of the journal Mycologia.

"To identify a new species is an interesting process because Pythium species have different shapes. Their mycelium takes on a different shape and their fruiting structures can be different from one species to another. This new species didn't fit any of the known Pythium descriptions," says Dorrance. "The final evidence was the DNA sequencing, which didn't match any of the described species. It was proof that we indeed did have something that wasn't in any of the data banks."

Pythium pathogens are water molds that attack soybean or corn seeds, as well as a number of other crops via the plant roots in saturated soil conditions. They are one of the major causes of crop replants, and are becoming more economically important because of the continued rise in seed costs.

"What used to not be as big of an issue far as crop management decisions is becoming a bigger issue. Seed is a huge input for producers and a huge input for companies to produce it. With seed costs continuing to increase, producers can't afford to be replanting their crop due to disease issues," says Dorrance. "We are seeing more instances of Pythium over the past five years and it's more important in Ohio because we are farming clay soils that just hold the water. Getting plants up and going in these heavy clay fields is really a challenge."

The new Pythium species was isolated from an Ohio field that experienced persistent stand establishment problems. So far the new species has been identified in a small number of locations across the state and doesn't appear to be very aggressive.

"This isn't a super aggressive species. The extent of its infection was forming lesions on the roots," says Dorrance. "But it is an unusual species in that it thrives in warmer temperatures later in the season on older plants. People tend to identify Pythium mostly as a disease that thrives in cold soils in the spring on younger plants. There is such a broad range of species out there that it's unwise to use one label for all species. Never make a rule because there will be something in biology that will break it."

The discovery would aid in future management of Pythium diseases and help in the breeding of new cultivars for resistance and new chemistries for seed treatment compounds.

"Right now we are looking at how fungicides affect it and studying the current germplasm for resistance," says Dorrance.