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Frost derails disease test

Smith: 'There's 195 different varieties and some of them are in different stages'


Capital Press

POCATELLO, Idaho -- Officials say test plots planted in Brawley, Calif., to confirm the absence of disease in Idaho seed potatoes have been damaged by frost.

Gary Smith, area manager with Idaho Crop Improvement Program, remains hopeful that the plants will rebound from the damage so more leaf samples can be taken to test growers' seed for potato virus Y and potato virus A.

Smith said his program planted nearly 900 seed lots, including a few from Nevada, from late October to early November. The plants sustained frost damage on Jan. 4, when temperatures in Brawley dipped to 31 degrees for several hours.

At the time, Smith said most of the plants were less than 7 inches tall. Despite the frost damage, Smith said the leaves were still useful for testing when he arrived in California on Jan. 7. He had time to take leaf samples from roughly half of the lots.

However, a second frost further damaged plants on Jan. 17. Smith said the grower overseeing the seed lots advised him to wait and give the plants yet to be sampled time to recover.

Since 2007, Idaho Crop Improvement Program has relied on enzyme-linked immunosorbent assay testing, which utilizes color changes caused by the presence of antibodies to confirm the presence of disease.

"To totally shut down our project, it has to freeze (plants) clear down to the ground," Smith said.

The good news, Smith said, is that the extended forecast in the Brawley area calls for much warmer weather.

"There's 195 different varieties and some of them are in different stages," Smith said. "Somewhere in that line we're going to save some of them. As long as there's green tissue there, we're all right."

Smith said he's checked tubers in the lots, and they appear to be sprouting. If necessary, he said tubers could be used in lieu of leaves for testing, but that process would be far more labor intensive and could delay grow-out results.

Smith said visual testing of plants in the winter grow-out plots are used to detect certain diseases, such as potato leafroll virus and bacterial ring rot. Fortunately, he noted those diseases are relatively uncommon. If foliage is sufficiently recovered within a few weeks of completing leaf sampling, he hopes to visually check a couple of lots that growers fear sustained chemical damage.

University of Idaho Extension seed potato specialist Phil Nolte said if all goes well, results of the winter grow-out should be available within three weeks.

"We're always concerned when we have a frost, but we think we're going to get what we need from the winter test," Nolte said.

Alex Karasev, a potato virus Y researcher with UI, said virus rates have declined in Idaho seed since 2007, when the state began using ELISA testing of winter grow-out samples for seed recertification.

"The number of seed lost rejected for recertification has declined over the years, starting in 2007 when this rule change occurred," Karasev said. "That means the rule was actually beneficial for the industry, and it's important that it continues to be the same way, the laboratory testing and using the tests to make management decisions."


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