JEROME, Idaho - University of Idaho researchers say the prevalence of a potato virus Y strain that causes necrosis in tubers dropped dramatically in testing of infected plant samples from Idaho's 2013 winter grow-out.
As part of potato seed recertification through Idaho Crop Improvement Association, the industry raises winter test plots in a warm climate to test for PVY and other diseases.
For the past four seasons, UI virologist Alexander Karasev and seed potato pathologist Phil Nolte have taken the PVY testing a step further, determining the specific strain responsible for roughly 1,000 symptomatic winter grow-out plant samples.
In the early 2000s, Karasev said the PVY profile began shifting away from the ordinary strain, called PVYO, toward PVYNTN, which includes genetic material from another parent virus. PVYO reduces yields but has visible signs and is relatively easy to manage, Karasev said. Plants with NTN, however, aren't always symptomatic, and the strain can also create rings in certain varieties, such as Yukon Gold.
"We don't quite know why it was happening. The composition was changing, and the PVYO strain was losing ground," Karasev said.
During the first three seasons that his lab tested for PVY strains, Karasev said NTN was responsible for roughly 20 percent of infections. According to data Karasev recently announced, NTN has dropped to 11 percent of Idaho infections, though it's maintained its foothold in other states.
Karasev said additional years of data will be needed to determine if the decline represents a trend or an anomaly, but he speculates his testing program may be responsible for the drop. While growers can re-certify seed potatoes from lots with less than 2 percent PVY infection, Nolte encourages them to remove seed with any trace of NTN from their systems.
"We would like to think this is the reason the NTN proportion is going down, because we keep pursuing this particular strain," Karasev said. "We would like to eliminate it completely. We don't know if that's possible."
Karasev said NTN infections haven't been confined to any specific seed production area of the state but tend to cluster among individual growers.
Early this spring, Idaho Crop Improvement released 2013 grow-out results confirming a general drop in PVY. In 2007, when the grow-out became a certification program requirement, 27 percent of seed lots had greater than 2 percent PVY and were ineligible for re-certification. Only 14 percent of lots were ineligible in the 2013 grow-out.
"The growers when we have the right information, we make the right decision and don't plant it back," said Ashton seed grower Clen Atchley.
Atchley predicts PVY will drop again in the 2014 grow-out because pressure from aphids, which spread PVY, was down this season.
The PVY strain typing project was supported by the Idaho State Department of Agriculture and a $54,000 grant from the Idaho Potato Commission.
"This is exactly the kind of project the IPC looks to fund - one that can have a fairly immediate impact in a positive way and with measurable results," said IPC President and CEO Frank Muir.