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February 21, 2024

A recent University of Idaho study concluded that for most, but not all, potato cultivars, the length and width of the finished tubers is influenced by growing conditions.

The study findings support the possibility of using potato variety trial data to create a predictive model for selecting cultivars capable of growing to optimal dimensions when raised anywhere in the Pacific Northwest. Length-to-width accounts for 13% of the overall potato postharvest score in variety trials done by Washington State University (WSU), and processors value elongated tubers as they can be cut into fries with minimal waste.

Rhett Spear, an assistant professor of plant sciences who conducts potato variety evaluations at the U of I Aberdeen Research and Extension Center, spearheaded the project, reviewing 15 years of trial data from Aberdeen; Othello, Washington; and Hermiston, Oregon.

While some cultivars evaluated were extremely sensitive to their environment, a handful, such as Palisade Russet, produced tubers of a consistent size and shape regardless of growing location and variability in conditions. The length and width of most cultivars was moderately sensitive to growing conditions.

“Collectively, our results suggest an opportunity for genetic selection of elongated potato phenotypes that are stable across locations with minimum variation in length and width,” Spear said.

Spear’s research team also included Julia Piaskowski, director of statistical programs with U of I’s College of Agricultural and Life Sciences; Jacob Blauer, an assistant professor of potato physiology with WSU; Mark Pavek, a professor specializing in potatoes with WSU; and Richard Knowles, a professor emeritus with WSU.

Among the many variables evaluated, the study shows that prolonged exposure to higher heat can lead to shorter and rounder potatoes. Other variables that may impact tuber shape include day length, with longer periods of dark during the growing season contributing to an increase in tuber length.

Though no two growing seasons are exactly alike, Washington potato farmers typically have a 15- to 20-day longer growing season with warmer weather than farmers in eastern Idaho. Eastern Idaho farmers have about 25 minutes more darkness and temperatures that average 5 to 7 degrees cooler during the crucial bulking period of potatoes.

“It may not be 100% perfect but based on the statistics here and the information we’ve gathered, if we have a certain length to width here in Aberdeen, we could predict with a certain amount of accuracy what that length to width would be in Washington, for example,” Spear said. “This seems to have been anecdotal for years but it’s good to put some numbers to it and show there really is a difference.”

Published in Catching Up with CALS

Rhett Spear, an assistant professor of plant sciences who conducts potato variety evaluations at the U of I Aberdeen Research and Extension Center, spearheaded the project, reviewing 15 years of trial data.

About the University of Idaho

The University of Idaho, home of the Vandals, is Idaho’s land-grant, national research university. From its residential campus in Moscow, U of I serves the state of Idaho through educational centers in Boise, Coeur d’Alene and Idaho Falls, nine research and Extension centers, plus Extension offices in 42 counties. Home to nearly 11,000 students statewide, U of I is a leader in student-centered learning and excels at interdisciplinary research, service to businesses and communities, and in advancing diversity, citizenship and global outreach. U of I competes in the Big Sky and Western Athletic conferences. Learn more at


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