Iowa State University (ISU) researchers have discovered the mechanism that gives soybean cyst nematode (SCN) power over plants. This discovery doesn’t mean the pest is beaten just yet, but instead puts scientists in a better position to find long-term control methods.
For background: SCN is a sedentary parasite—it doesn’t move throughout a plant. Instead, it stays put and attacks the plant by feeding off the the cells that surround it for the lifespan of the nematode and the plant. To do this, the nematode reprograms infected cells into a feeding structure that provides them with nourishment while still keeping the plant alive. If the plant dies, so do the nematodes, so this reprograming is essential for their survival.
“Our key finding is a mechanistic understanding of one way the nematode alters the activity of plant genes. This is required to direct development of the feeding site within the plant root,” said Thomas Baum, ISU distinguished professor and plant pathology department chair, in a recent news release. “The nematode injects a mixture of proteins into plant cells. We discovered that one of these nematode proteins alters the conformation of the host plant’s genetic material, redirecting the plant’s gene expression machinery to enable parasitism.”
This new understanding is another piece to a complex puzzle, he added. With this information on hand, researchers will be able to piece together a larger and more clear understanding of this pest that costs farmers $1 billion annually.
The researchers surmise SCN likely uses more than this single protein to redirect plant cells into their optimal feeding structure. More discoveries like this could help scientists engineer new resistant crops.
With rising resistance, discoveries like this are critical. According to ISU, the number of soybean varieties with SCN resistance is down this year to 820, compared to more than 1,000 in 2017. In addition, fewer companies are selling resistant varieties.
Since 2006, about 97% of all soybeans with SCN resistance used the PI 88788 mechanism—and it’s starting to fail. Illinois, Iowa, Minnesota, Missouri and Ohio need to be especially mindful of resistance as SCN has been a long-standing pest in those states.
“You can have up to 30% yield loss in absence of symptoms,” says Kaitlyn Bissonnette, assistant Extension professor at the University of Missouri.
Knowing where SCN thrives is key to control—and why it’s critical to pull soil samples by management zone. Top of the list are sandy soils, high pH fields and low spots. SCN and sudden death syndrome (SDS) often go hand-in-hand. SCN injures the plant early, which can leave it more susceptible for the Fusarium pathogen in SDS.
The potential for yield loss is highest on fields that haven’t been previously hit by SCN because there are no natural enemies, says Greg Tylka, nematologist at Iowa State University.
The SCN Coalition and experts recommend the following best management practices for all fields:
- Use genetics with resistance, including PI 88788, which has resistance in some states, or Peking.
- “Seed treatments add some control, but many don’t last the whole season,” says Sam Markell, North Dakota State University Extension plant pathologist and professor.
- Crop rotation is important. Corn and wheat are non-host crops and can help decrease populations. It’s still necessary to test fields after corn and before soybeans to verify SCN levels.
SCN tests cost $1 to $2 per acre, but some state soybean checkoff programs offer cost assistance.