Tospovirus Jumps from Seed to Plant

July 23, 2016 02:59 AM

Learn what the first viral transmission means for soybeans

Viruses in soybean seeds are troublesome but viruses in plants can cost bushels. However, when a virus infects the seed and is passed to the plant it could challenge the health of the seed supply.

A member of the tospovirus group, called soybean vein necrosis virus (SVNV) has achieved just that—seed to plant virus transmission. SVNV threatens 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 it can show up in the leaves.”

They have detected SVNV in 6% of the seed they’ve tested, but suspect the number could be higher. In a field with 140,000 plants per acre that could mean 8,400 seeds could be infected and transfer the virus to the plant.

What does this mean for your potential 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, which seems to impact yield more.

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,” Smith says. “That might sound small but it turns out to make a big impact.”

If you’re growing high-oleic soybeans, pay special attention when scouting and check for this virus. In addition, if you grow seed beans consider testing plants with suspicious lesions to ensure they don’t pass the virus along to another generation.

Testing is simple: Send in tissue samples with lesions to your local testing lab, usually a university. You can send samples without symptoms, but diagnosis is much simpler with plants showing symptoms. In some cases you might need to tell lab technicians to test for SVNV specifically.

There’s not much you can do when 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.

You don’t need to lose sleep over this virus, Smith assures. “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 it is out there. We want to understand what the impact is so there’s value in reporting it [on your farm].” 

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