Potato Seed Research

A University of Idaho graduate student aims to shed light on U.S. potato farmers’ tolerance levels of certain economically impactful diseases affecting potato seed and whether their preferences align with seed certification program standards.

Pragati Dahal, from Nepal, will study the issue for her master’s thesis in applied economics, working under advisor Chris McIntosh, head of the Department of Agricultural Economics and Rural Sociology (AERS). Professor Jason Winfree and Associate Professor Alexander Maas, who are also in AERS, are assisting in the research.

For her work, Dahal has been awarded the Joe and Terri Guenthner Graduate Scholarship, honoring the career of Joe Guenthner who conducted research on behalf of the potato industry for more than 33 years as a professor of agricultural economics at U of I. The $1,779 scholarship is awarded annually to a full-time graduate student enrolled in the College of Agricultural and Life Sciences who wishes to pursue a career in the potato industry.

Dahal believes her project could help reduce wasted potato seed while providing more options for potato farmers during seed shortages.

“The tolerance levels for potato certification have been assigned, but we are not sure whether the commercial growers would use the potato tubers with disease percentage higher than the assigned tolerance levels” Dahal said. “If we better understood farmers’ preferences for seed potato quality, we would have a much clearer understanding of the seed potato market.”

The U of I research team will develop a survey to distribute at events attracting large numbers of potato growers, such as Potato Expo 2025, scheduled for next January in Orlando, Florida, and the 57th Annual Idaho Potato Conference, scheduled for next January in Pocatello. They also aim to recruit growers to participate via potato industry trade magazines. The survey will key in on major diseases affecting potato seed growers across the country, including potato virus Y (PVY).

In Idaho, any potato seed sold must meet the standards of the Idaho Crop Improvement Association (ICIA), which is the agent designated by the Regents of the University of Idaho as the state’s seed certifying agency. Commercial growers who meet certain guidelines may also opt to replant their own seed. On average, 1.05% of seed acres entered for ICIA certification were rejected during field inspection from 2008 through 2023.

When PVY exceeds 1%, ICIA prohibits seed growers from recertifying seed – which entails replanting it to produce additional seed and exponentially increases any disease in the lot. Idaho has no restrictions on the percentage of PVY that commercial potato growers may plant, though some states, such as Wisconsin and Michigan, restrict commercial growers from planting seed with more than 5% PVY.

“Everyone assumes that commercial growers don’t care up to about 10% PVY, but nobody has actually measured that,” McIntosh said. “We can inform these certification systems.”

Dahal was previously involved in a project modeling potential economic losses based on the percentage of PVY in a seed lot compared with clean seed. Her team concluded that a low percentage of PVY had very low effect on revenue, though potato variety also played an important role.

American Falls potato farmer Klaren Koompin, who raised both commercial and seed potatoes, agrees that variety is an extremely important consideration when assessing an acceptable level of PVY in seed, as well as the specific strain of PVY. For example, Koompin has planted Umatilla Russet seed with upwards of 15% of the N-Wilga PVY strain and sustained virtually no losses in his commercial crop. He’s also sustained major losses from far less PVY with combinations of other strains and varieties. Koompin advises farmers who have a seed lot that tests high for PVY to take it to ICIA to test the strain.

“I’d like to see more research done on what varieties are subject to what strains,” Koompin said.

Alan Westra, ICIA’s area manager, has found supply and demand also shape growers’ perceptions regarding acceptable disease thresholds in potato seed.

“Two springs ago when seed was short, there wasn’t enough to go around, and there wasn’t much discussion about virus,” Westra said. “This year there’s too much seed, and commercial growers are asking about disease ratings because they can pick and choose.”

Published in Catching Up with CALS