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Idaho crop association offers advanced spud ring rot testing


Capital Press

IDAHO FALLS, Idaho -- Idaho Crop Improvement Association has updated its technology and begun offering the potato industry the most advanced test available for detecting bacterial ring rot.

Following a ring rot flare-up last season, the association invested about $30,000 in a polymerase chain reaction machine and began accepting seed growers' samples at the beginning of April.

University of Idaho Extension seed pathologist Phil Nolte said businesses within the Idaho potato industry have agreed to cover the new machine's cost.

"Anybody who thinks they need a test performed, this is the place and the method to use," Nolte said.

Idaho seed certification uses a visual ring rot test, which can miss latent symptoms, but customers may request additional laboratory testing. Idaho growers wanting the most assurance had been sending samples to North Dakota and Indiana for PCR testing, accustomed to high shipping costs and backlogs.

The seed industry has zero tolerance for ring rot, rejecting any lots with traces of the disease. Lamb Weston has also advised its commercial growers that spuds with more than half a percent of ring rot will be rejected next season.

Ring rot, easily spread on poorly sanitized equipment by a vascular pathogen that causes tuber necrosis, tends to resurface every decade. Regarding last season's ring rot losses, Nolte said, "I've heard the word millions thrown around."

PCR heats DNA in samples to separate strands, making them receptive to fusing with probes bearing DNA segments that match the bacteria. The process replicates bacterial DNA so it's detectable by the machine.

Nolte said PCR is far more sensitive than the lab's long-standing enzyme-linked immuno sorbent assay test, which will remain available for growers.

Sherry Laug, manager of the association's Idaho Falls lab, said growers requesting a PCR test should send samples from the stolon scars of individual spuds. The lab agitates water-filled cups containing up to 200 samples to release bacteria. The water is then poured into wells of trays to analyze in the machine.

Laug said a standard PCR test involving 1,200 tuber samples costs $300 per seed lot. ELISA generally tests 400 tubers for roughly $180 per seed lot.

Neil Gudmestad, a North Dakota State University plant pathologist and a leading ring rot expert, aided Idaho with PCR training. He's found PCR detects about 13 of 20 infected tubers, compared with one in 20 under ELISA tests.

"There just isn't enough infrastructure in the U.S. for ring rot testing," Gudmestad said. "I would expect the largest potato state and the largest seed certification group in the country would have the ability to do that."

Gudmestad, Nolte and USDA research plant pathologist Jonathan Whitworth have made a collaborative grant request to research how to bring PCR testing to individual fields.

Gudmestad is now working with Washington State University to add PCR ring rot testing.

"If it doesn't take a lot of time and a lot of transportation costs, the costs of actual testing are nominal enough that we can get this ring rot testing off the ground and solve our ring rot problem," Gudmestad said.


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