Drought Could Harm Future Varieties

Some disease-resistant soybeans won’t be properly tested this summer

The summer’s drought could affect future soybean varieties’ resistance to wet-weather diseases, such as Phytophthora. Anne Dorrance, researcher at The Ohio State University, talks with Beyond the Bean about the Phytophthora pathogen and how this dry growing season could wreak havoc on future Phytophthora-resistant soybeans.

Q: Why does Phytophthora matter in dry years like this one?

A: This year, with the drought, it’s a real challenge for breeding companies. They aren’t going to get any information on Phytophthora since the pathogen thrives in wet conditions. But they’re going to end up moving germplasm forward that hasn’t been screened in the field against this pathogen. That’s a challenge, but if we can get the markers tied to the genes, it’s not going to make any difference what the growing environment is. So that’s the long-term goal of this project.

Q: How serious can losses from Phytophthora be?

A: We’ve had some growers recently who had varieties with only a single gene that had no partial resistance behind it, and they had a 50 percent yield loss.

It just wipes the field out. The first stage — you just have a reduction in stand. You have to go back in and replant, so there’s an added input cost — and actually a very expensive one. The soybean plant is susceptible to Phytophthora all of its life, but we see a lot more damage when stem rot occurs at this time through flowering stage, until those pods are filled out.

Phytophthora is a killer; it doesn’t just rob yield. It will just take the plant out totally when the plant is susceptible.

Q: What conditions lead to Phytophthora?

A: This problem hits most often on the old lake-bed soils in northeast Indiana, northeast Illinois and northwest Ohio; around areas that flood; predominately around rivers; on soils that are at least 20 percent clay. There are many regions that farm these heavy clays. So regionally, the only place that’s had a tough time identifying it is Kansas. For the rest of the Midwest, anywhere around rivers or where old lakebeds used to be, Phytophthora is present.

Phytophthora does like it to be a bit warmer. The soil temperatures have to be above 60-65 degrees Fahrenheit, so it’s a little bit later-season in Ohio. Southern Illinois sees it a little bit earlier. But it’s really those saturated soil conditions. Across the Midwest you have these rain events where you’ll get two inches at once. It’s those types of rain events that help to promote conditions for Phytophthora.