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New potato virus strain has industry attention
Yukon Gem, on display during the University of Idaho Extension Potato Conference, is one of several varieties considered highly susceptible to new strains of Potato Virus Y and could be lost to commercial production in the U.S. (CINDYSNYDER/For the Times-News)

POCATELLO — A potato virus, around for years, is mutating.

That’s got both researchers and industry leaders worried.

Growers have grown used to seeing some signs of Potato Virus Y, better known as simply PVY, in fields. The disease causes foliar damage and infected plants must be taken out of certified seed fields, but otherwise the virus hasn’t really been a threat.

That could be changing. Researchers are finding new strains of the virus damaging tubers with little apparent injury to an infected plant’s leaves. When potato specialists in the U.S. surveyed PVY strains between 2004 and 2006, they found 70 percent of the identified strains were the ordinary PVY that causes leaf damage but not tuber damage.

By 2010, surveys showed tuber necrotic strains are increasing in both incidence and distribution, said Stewart Gray, a plant pathologist with the Agricultural Research Service in New York. Tuber necrotic strains accounted for 18 percent, up from 6 percent previously, and ordinary strains had fallen to 53 percent.

“This is no longer just a seed certification problem,” Gray told potato growers during the University of Idaho Extension Potato Conference last week. “The problem now affects all aspects of potato production.”

The primary concern is that PVY will become a major quality disease for the entire U.S. potato industry as it did in Europe in the 1980s. Potato varieties that European producers have reliably grown can no longer be planted there because of PVY. Here in the U.S., researchers are concerned that highly susceptible varieties such as Yukon Gold, Yukon Gem and Highland could be lost here. Ranger Russet and Alturas are considered moderately susceptible.

As long as commercial growers could get seed and PVY didn’t affect yield much, growers could handle some virus, said Jonathan Whitworth, a research plant pathologist with the ARS in Aberdeen, Idaho. But as the strains change to more of the necrotic type, even commercial growers will have to pay more attention to PVY.

One reason that necrotic strains may be slower to take hold in the U.S. is that PVY doesn’t like the cold. Gray and Whitworth expect to see more tuber necrosis when they survey potato producing regions in Texas and South Carolina.

“If we start to see loads of potatoes rejected because of PVY at processing plants and shipping points in the South, that will eventually come back to Idaho seed growers,”

Whitworth said. “We’re at a tipping point. We don’t see a lot of necrotic strains when we do our surveys but they are there. If we do nothing, we will end up in the same situation as Europe.”

Phil Nolte, UI extension see potato specialist at Idaho Falls, said about 10 loads of potatoes in the Pacific Northwest have already been rejected because of PVY quality problems.

Another emerging issue is that infected plants that do not show much foliar or tuber damage, can still be affected by PVY. Researchers at the University of Wisconsin, are studying the impacts of when infection occurs and how well tubers store. Susceptible varieties have shown a two-fold increase in weight loss or shrink and also reduce specific gravity, which affects processing quality.

Because PVY cannot be cured, prevention is paramount. Gray recommends planting only certified seed to avoid problems but the shift in PVY strains is creating challenges for certified growers as well.

“A good looking crop in the field does not translate into disease-free tubers,” Gray said. “Post harvest data is more important than summer inspections.”

While aphids can spread the disease, Gray doesn’t suggest a large scale aphid control program. Rather he emphasizes removing infected plants and planting healthy tubers.

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