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Potato industry keys in on mop-top

By John O’Connell

Capital Press

The potato industry is increasing its focus on potato mop-top virus and has proposed to include research on the tuber disease in a five-year, multi-state grant.

A team of 29 potato scientists from 11 institutions in nine states has applied to add potato mop-top virus — a crop disease that’s widespread in U.S. fields but has mostly flown under the industry’s radar — to a five-year grant to research tuber-necrotic viruses.

The current grant, which emphasizes necrotic potato virus Y strains, expires this month. Stewart Gray, a plant pathologist with USDA’s Agricultural Research Service and Cornell University, is lead on the grant, seeking $8.5 million in federal dollars, plus some matching industry funds.

He expects an announcement in September on the application — which also covers PVY and tobacco rattle virus, a disease often mistaken for mop-top.

Mop-top is vectored by the protozoa-like powdery scab organism, which can survive in soil for several years and can’t be controlled with chemicals. The disease can cause rotting arcs in tubers and reduce yields but is usually latent and goes unnoticed.

“We’re trying to be proactive and understand what the potential problems are (with mop-top) and come up with better solutions than just abandoning the land for potatoes,” Gray said.

About five years ago, Oregon State University plant pathologist Phil Hamm collected soil samples from potato fields in several states, testing for both scab and mop-top. He found positive samples in a half dozen states in which the disease hadn’t previously been confirmed.

“We found mop-top in every state where we had substantial soil, including all of the major potato producing states,” Hamm said.

Hamm said the grant will investigate how differences in mop-top isolates may contribute to symptom expression. He anticipates a new test his lab has developed to simultaneously screen for six tuber-necrotic viruses, including mop-top, should also aid in grant research.

Hamm speculates susceptible varieties, such as Yukon gold and red-skinned potatoes, and cool and moist conditions may also contribute to symptom flare-ups. The grant proposes the first broad study of North American potato varieties for mop-top resistance.

Mop-top has been flagged as an “emergence disease of importance” by the Pacific Northwest Research Consortium, which allocates $1.5 million annually toward cooperative research by the Washington, Idaho and Oregon potato commissions, according to Raina Spence, director of industry outreach for the Washington State Potato Commission. She said the disease will also be a priority once USDA-ARS fills its Washington potato virologist position.

Lynn Wilcox, an Idaho Potato Commissioner who has dealt with mop-top in his fields in the Rexburg area, said trade challenges presented by the disease can be as significant as impacts on yield, quality and storability. He’s had loads rejected by Mexico based on positive mop-top tests in latent spuds. He believes mop-top has become increasingly troublesome in pockets of Eastern Idaho during the past four years, though he’s uncertain how prevalent it will be this season.

“There are some areas of Idaho that are affected pretty severely by mop-top,” Wilcox said, adding he believes the disease warrants more extensive research.

University of Idaho Extension potato pathologist Phil Nolte doubts mop-top is becoming more widespread. He simply believes the industry is looking for it now and better able to test it against other diseases with similar symptoms.



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