Viruses in your soybean seeds are bad. So are viruses in your soybean plants. Until now, they were two separate issues - but no longer. A member of the Tospovirus group, called Soybean vein necrosis virus (SVNV) has achieved just that—seed-to-plant virus transmission. SVNV could threaten to reduce seed quality, oil content and even yield in some areas.
“This is the first virus in this group to be proved to transfer from seed to plant,” says Damon Smith, University of Wisconsin assistant professor of field crops pathology. “In soybeans, it usually doesn’t cause major symptoms in seeds, but when transferred to seedlings can show up in the leaves.”
Researchers have detected the virus in 6% of the seed they’ve tested, but suspect that number could be higher. In a field with a population of 140,000 plants per acre, that could mean 8,400 seeds could be infected and transfer the virus onto the plants.
What are the potential implications for those 8,400 infected plants? First, look for visible symptoms.
Lesions appear along the veins, Smith says. They are yellow to dark brown and can appear on any trifoliate. Exact timing of when you see lesions depends on where you live. It appears the earliest in southern states right before flowering, researchers say seems to impact yield more.
Courtesy of Damon Smith, University of Wisconsin
Negative yield impacts are minimal, with the exception of southern states where SVNV affects the crop longer into the season. The more concerning impact is seed quality, Smith says.
“We’ve detected a 1% reduction in oil content,” he says. “That might sound small but it turns out to make a big impact.”
Farmers growing high-oleic soybeans might pay special attention when scouting and check for this virus. In addition, farmers who grow seed beans might consider testing plants with suspicious lesions to ensure they don’t pass the virus along to the next generation.
Farmers should send in these tissue samples with lesions to their local testing lab, usually a university. Diagnosis is much simpler with plants showing symptoms versus no symptoms. In some cases, it will hlep to tell lab technicians to test for SVNV specifically.
There’s not much farmers can do once a plant is infected. The virus can be carried by certain insects, but foliar insecticides have not proven effective and they do nothing to control seed-to-plant carryover.
“With virus diseases we usually rely on inherent genetic resistance to manage them,” Smith says.
But Smith's final piece of advice? Don’t need to lose sleep over this virus.
It’s the most widespread soybean virus, from the Gulf to Canada, but it’s not the type that will decimate a crop,” he says. “Our message is you need to be aware that it is out there. We want to understand what the impact is so there’s value in reporting it (on your farm).”