ISU researchers look for genetic solution to SDS in soybeans

Soybean sudden death syndrome (SDS), identified 45 years ago in Arkansas, has already claimed the No. 2 spot for soybean yield loss. Across much of the country, university researchers and private companies are trying

to find a solution for this devastating disease.

One of the biggest obstacles to getting a handle on SDS is that it's a tricky disease. It infects soybean roots when it's young, but symptoms show up in the leaves when the plant is at the early reproductive stage. Early diagnosis is very difficult,

and the disease can sometimes be confused for other diseases or deficiencies.

Research at Iowa State University (ISU) might be an important contributor to beating the disease. Using genome-wide association and epistatic study, a mapping analysis aiming to find single gene and gene-gene interaction that associated with disease resistance, Jiaoping Zhang, post-doctoral research associate in the department of agronomy, and Asheesh Singh, ISU agronomy assistant professor and soybean breeder, have identified promising gene candidates they believe are responsible for genetic resistance to SDS.

"High-density markers and diverse population used in our study result in high mapping resolution and allow us to narrow down the distance between the markers and the resistant genes" Zhang says. "This can increase the efficiency of marker-assisted breeding."

Better breeding efficiency means new cultivars that could potentially help farmers get here faster. Currently the group isn't quite ready to release cultivars, but has identified parent sources for potential new cultivars. "Some germplasm lines are more resistant than others—that's what we use for parent lines," Zhang says.

Resistance to SDS is quantitative. Instead of relying on one exceptionally effective resistant gene, researchers are looking for a group of genes that contain resistant qualities, because

the more genes, the better.

"There might not be a way to make soybeans completely resistant (with genetics alone)," Singh says. "But we could enhance the expression of resistance."

Genetic resistance could help fight the disease with no additional cost to the farmer since protection is covered by the seed bill. Zhang appreciates that benefit.

"Some seed treatments may help control the disease, but breeders are always trying to find genetic resistance resources," he says.

He and Singh do, however, recommend a systems approach.

"When no completely resistant soybean cultivar is available, there is a need to incorporate both genetics and chemical type controls to increase profitability," Singh says.