Research HighlightsScreening Builds Knowledge for Soybean Cyst Nematode Management
By Laura Temple
Soybean cyst nematodes, or SCN, come in multiple types, depending on their ability to overcome and reproduce on SCN-resistant soybeans. Researchers use the HG type test to determine what types of SCN live in tested soils. The test takes its name from the abbreviation of Heterodera glycines, the scientific name for SCN.
Soybeans come in countless varieties, bred for yield and an array of offensive and defensive characteristics. University agronomists commonly screen regional varieties to provide farmers with third-party data about those characteristics.
“As SCN appears to become more virulent, or able to overcome and reproduce on sources of SCN resistance for soybeans, farmers need specific data to select the best varieties to manage SCN in different fields,” says Horacio Lopez-Nicora, assistant professor of soybean pathology and nematology at Ohio State University. “We are screening both SCN populations and soybean varieties to provide Ohio farmers that information.”
The Ohio Soybean Council invests checkoff dollars in this screening. The information from this research classifies commercial soybean cultivars based on their level of resistance to specific SCN types. Knowing the level of SCN resistance in soybean varieties will enable farmers to make more informed decisions when selecting varieties to plant.
Typing Nematodes
As Ohio farmers submit soil samples for SCN counts, Lopez-Nicora takes nematodes from samples with high pressure, with counts above 500 eggs per 100 cubic centimeters of soil. He then multiplies those SCN populations in the greenhouse for HG typing.
HG types carry the numbers 0 through 7. The number comes from the population’s ability to reproduce on specific sources of SCN resistance. That information can indicate the potential virulence of a field’s SCN population for different soybeans.
For example, an SCN population with an HG type designation that includes the number 2 means that it can reproduce on PI 88788, which is indicator line 2 in the HG type system. PI 88788 is the most commonly available source of resistance in Midwestern soybean varieties. However, the most prevalent SCN populations in the Midwest can effectively reproduce on PI 88788-derived resistant soybean cultivars.
“I want farmers to know more than just their SCN count,” he explains. “I think they need to know their SCN type, because experience shows us not all SCN and SCN resistance genetics are the same.”
Screening Varieties
Details on SCN resistance genetics and the level of resistance can be difficult to find for commercial soybean varieties. To provide more accurate information, Lopez-Nicora partners with Laura Lindsey, professor of soybeans and small grains for Ohio State University, who supplies more than 100 soybean varieties from her annual performance trials.
In the greenhouse, Lopez-Nicora tests those varieties in soils containing different SCN HG types. Then he monitors the reproduction rate of each type of SCN on those varieties relative to an SCN-susceptible soybean. With that data, he calculates a female index, or FI. Based on FI, soybean cultivars are further classified as highly resistant, resistant, moderately resistant, low resistance and no resistance.
“For each SCN type, we will share the female index for the varieties we test,” he explains. “Farmers will be able to see that one variety might be very effective for one type of SCN, with a reproduction rate of just 12%, while the same variety might have a reproduction rate of 80% for another SCN type, like type 2. Then, if farmers know their SCN type and the response of soybean cultivars to that specific nematode, they can choose a soybean variety that will manage their SCN population well.”
He notes that a reproduction rate above 60% on a soybean variety containing PI 88788 means that variety is allowing SCN populations to increase over time. Lopez-Nicora adds that the next step for this research will be to do in-field trials with known SCN types to screen soybean varieties for resistance.
“Similar research has been done in Iowa, but farmers in this region plant different soybean varieties,” he says. “This work will fill an information gap for the eastern side of the Midwest.”
Published: Jan 8, 2024
