Research HighlightsBreeding Targets Target Spot and Other Disease Resistance
By Laura Temple
The foliar disease target spot causes irregular lesions on soybean leaves that often have concentric zones of color around the center, inspiring its name. Target spot has been found in hot, humid conditions throughout the Southeast, where it can noticeably reduce yield, but it has also been identified in Iowa and other soybean-growing regions.
“Some soybeans have resistance to target spot, but it has not been well-documented,” says Dr. Jenny Koebernick, soybean and cotton breeder and assistant professor for Auburn University. “While target spot hasn’t yet caused huge soybean yield losses in Alabama, it is a problem in other states.”
Koebernick is leading a soybean breeding project to understand the mechanism of resistance to this disease. The project, funded by a checkoff investment from Alabama Soybean Producers, leverages genetic work done on other types of disease resistance to better layer protection from multiple disease into new varieties.
“Information gathered in the 1980s and ’90s calls some soybeans resistant to target spot, but it doesn’t document the level of resistance or how it works,” she says. “We are using current technology to properly understand why resistance differs amongst those lines claiming to be resistant. In addition, hundreds of lines have never been exposed to the disease. Breeders call the process of exposing lines to the disease and documenting how the plant reacts ‘screening.’”
To screen for resistance, Koebernick’s team conducted greenhouse trials, inoculating soybeans from many different lines with target spot. They then examined the genetics of surviving plants to identify common genes likely to be responsible for providing resistance.
“We are trying to understand the genetic mechanism for resistance,” she explains. “Once we identify how it works and the level of resistance conferred, we will be able to develop markers that will screen large populations of soybeans without the need to inoculate with the disease itself.”
Her work on target spot also builds on previous work on Cercospora leaf blight resistance in soybeans, funded by the national soy checkoff. That research helped identify lines to investigate for target spot resistance. She says the current work is focusing on soybeans showing resistance to both diseases.
Linking Resistance with Iron Chlorosis Tolerance
The alkaline soils of the Alabama Black Belt, a major soybean-production region in the state, adds unique challenges for soybean breeders. Soybeans grown in these soil types need tolerance to iron chlorosis, which turns the plants yellow and inhibits their ability to photosynthesize.
“Our research is bridging iron chlorosis tolerance and disease resistance,” Koebernick explains. “We’ve reviewed research that links iron chlorosis tolerance with phenylpropronid production. Separate research linked phenylpropornids with cultivars resistant to target spot. As we infect soybeans with tolerance to iron chlorosis and monitor the response, we hope to verify and connect this information.”
As a breeder, she believes this long-term genetic work will add value to soybeans for farmers in Alabama and beyond. She is also gaining insight to apply to future breeding challenges.
“As we suggest and confirm underlying resistance mechanisms, we can explore similar principles for other diseases and crops,” Koebernick says. “For example, target spot is also an issue in cotton. As we understand resistance in soybeans, we may get direction to help address genetic resistance in cotton.”
This project was funded by the soybean checkoff. To find research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.