Zebra chip discovery in Pacific Northwest spuds raises questions

11/18/2011 05:58:00 PM
Vicky Boyd

Zebra chip has been found in scattered potato fields in parts of the Columbia Basin and in Idaho, marking the first time the disease has been confirmed in the Pacific Northwest.

Although the discovery is surprising, Phil Hamm, a plant pathology professor and superintendent of Oregon State University’s Hermiston Agricultural Research & Extension, says growers shouldn’t be alarmed by it.

“There are maybe only a dozen or so fields where you’d call it more than incidental,” he says of the Columbia Basin finds. “And there are maybe only five or six fields that I’m aware of that it’s an issue.”

Potato processing contracts allow for a small percentage of internal defects before a load is rejected. In all but a few of the fields where zebra chip was confirmed, the amount of internal discoloration was far below the contract limit, Hamm says.

In the Columbia Basin, the disease was first found in the production area south of the Tri- Cities—Kennewick, Pasco and Richland—of Washington and into Oregon.

Since then, additional infected fields have been found farther north, but again at very low levels, he says.

Hamm says growers brought in tuber samples that had the telltale zebra chip symptoms. Further testing confirmed the Candidatus Liberibacter bacteria-like organism.

“Basically, growers were doing their normal thing out digging, cutting a few potatoes and just looking around,” Hamm says of how infected potatoes were found.

The disease has been identified in several varieties, including Russet Ranger, Umatilla Russet, Pike, Alturas, Russet Norkotah and a red selection.

Low disease incidence in Idaho

The discovery of zebra chip in Idaho wasn’t totally unexpected, based on earlier reports in Oregon and Washington, says Nora Olsen, Extension potato specialist and storage researcher with the University of Idaho in Kimberly.

The disease was confirmed in Idaho after a state grade inspector stationed at a packinghouse sent a sample of an unknown internal defect into the University of Idaho, she says.

The sample was eventually traced back to a Jerome County field. Subsequent surveys found a very low incidence of zebra chip in the field, Olsen says.

She says researchers also surveyed plots at the university’s Kimberly Research and Extension Center and found zebra chip, again at very low levels.

“We didn’t see any symptoms in our plots, as we were walking those fields a lot,” she says. Since then, the university has received other samples that tested positive for zebra chip. The disease is at low enough levels that it’s not causing issues for growers, Olsen says.

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