Organic Broadcaster

Farmers, researchers team up to trial potato varieties for organic production

By Ruth Genger & Marie Flanagan

This cross between Huckleberry and Red Endeavor was one of the potatoes selected by farmers for the potato variety trials. Photo by Ruth Genger

When Maria Carter’s parents emigrated from the Netherlands to America in 1956, they brought with them knowledge about how to grow seed potatoes. As they put down roots in North Dakota, they put down tubers to start their new seed potato farm. They knew that healthy seed potatoes were a necessity for potato growers, and they knew how to produce them.

Potatoes are usually grown from the eyes of tubers rather than seeds; growers replant the whole potato or pieces of it. These tubers are referred to as “seed potatoes,” even though they are not true seeds.

While the Carters primarily produced conventional certified seed potatoes for more than 50 years, they had become interested in growing seed potatoes under certified organic conditions as well—sometimes referred to as “double-certified” seed potatoes. Only a handful of farms in the U.S. produce double-certified seed potatoes—both certified organic and certified free from yield-limiting diseases, an important factor since tubers can carry several potato diseases. In the Midwest, Vermont Valley Community Farm in Wisconsin has produced doubled-certified seed potatoes since 2003.

When the Carters first tried growing organic seed potatoes, they had little success. Then, at the 2017 MOSES Organic Farming Conference, Maria Carter met Ruth Genger, a researcher at the University of Wisconsin who organizes on-farm and research-station organic variety trials to select for potato varieties that excel under organic management. From their conversation, Carter and Genger saw a need and an opportunity to create a regional network of farmers to grow desired specialty varieties for organic seed potato production.

Since new potato breeding line evaluations rarely include organic production environments, Genger and Carter talked about using a regional network of farmers to evaluate and select outstanding lines from crosses between existing varieties. With support from a $199,106 NCR-SARE Research and Education grant, they went about turning this vision of participatory breeding and organic seed potato production into a reality.

In addition to Carter, 15 farmers across the region and on tribal lands teamed up with Genger between 2014 and 2018 to trial production of high-quality organic seed potatoes, and to learn about and engage in the on-farm selection of potato breeding lines from true potato seeds.

Trialing Minitubers
Their initial on-farm trials used “minitubers,” produced in greenhouses to avoid insect vectors of disease, as planting stock. The trials took place at five diversified organic vegetable farms. Field production from minitubers generally resulted in low yields, likely due to weed competition with the less vigorous plants that typically emerge from minitubers. An exception occurred at Paradox Farm in Minnesota, where use of the Ruth Stout method of heavy mulching resulted in good yields. Production from minitubers was also successful in hoophouse plots at Snug Haven Farm in Wisconsin, where the protected conditions allowed for earlier planting and harvest, and weed pressure was low.

Planting tubers that were set aside for the following year at Paradox Farm and at the White Earth Land Recovery Project, another participating farm, gave yields comparable to potato crops planted with purchased certified seed potatoes. Results from these trials suggest that more intensive management of potato crops grown from minitubers, including mulching and hand weeding, may be required to make this a viable method for seed potato production. Additionally, while conventional production uses minitubers of 0.5-1 inch diameter, larger minitubers produce more vigorous plants and may be more successful in organic production.

Foundation Seedlots
Foundation seed potatoes (seed potatoes tested to ensure that disease levels are below a strict threshold) were planted in trials at 16 farms in Wisconsin, Minnesota, and North Dakota across three years of trials. Farmers planted foundation seedlots alongside their production fields and provided samples of harvested tubers to Genger for disease testing.

Genger’s research team tested tubers for the most common disease that limits seed potato production in Wisconsin, Potato Virus Y (PVY), which is spread by aphids and infected tubers. PVY stunts plants and reduces yield, and some strains of the virus can discolor tuber flesh. Certified seed potatoes must have less than 5% incidence of PVY and other viruses.

Across the three years of trials, 74 seedlots out of 107 tested seedlots had low enough levels of PVY to achieve certification. Farms located in regions with large-scale potato production were more likely to have a high incidence of PVY in their seedlots. Participants growing smaller acreages of potatoes more isolated from large-scale potato production had lower or no incidence of PVY, potentially due to isolation from sources of viral inoculum.

Potato Breeding
To begin the breeding project, Genger crossed potato varieties that were good performers in previous organic variety trials, including several with resistance to potato viral diseases or late blight, and tolerance to potato pests such as Colorado potato beetle and potato leafhopper. Parents included popular yellow varieties Carola and Yukon Gold, red varieties Red Endeavor and Chieftain, specialty varieties Spartan Splash, Barbara and Picasso, and heirloom varieties from the Seed Savers Exchange collection such as Huckleberry and Aylesbury Gold.

Potato berries—small green fruits that resemble unripe tomatoes but are not edible—were collected, and the seed was extracted and distributed to participating growers. Since none of the participating growers had ever started potatoes from “true” potato seeds (TPS), Genger guided farmers through the process of preparing the seeds. Potato seeds, which are similar to but smaller than tomato seeds, germinate best in slightly warmer conditions of around 75 degrees Fahrenheit in the day and 60-70 degrees at night. Temperature spikes over 80 degrees can delay germination.

Seedling vigor can be quite variable in breeding populations, and the most robust seedlings can be selected and potted up to individual pots when the seedlings are 2-3 inches tall. Participating growers transplanted potato seedlings into field or garden plots when they were 30-40 days old, ideally before plants had begun to produce tubers. Since potatoes do not breed true, each TPS-derived plant produced a unique tuber type.

Growers observed plant characteristics such as vigor and pest tolerance and selected their favorite individuals at harvest based on tuber yield and appearance. Zachary Paige, with the White Earth Land Recovery Project, saved tubers from five populations to replant. Paige commented that eating quality from his selected lines was as good as the parent potatoes. He continued to save and replant his favorite line, a cross between Yukon Gold and Chieftain, for another two years.

Researchers at the West Madison Agricultural Research Station trial potato varieties for organic production. Photo by Ruth Genger

Four lines selected by two other participants (Paul Whitaker of Wausau, Wisconsin, and Pat Dunn of Middleton, Wisconsin) were included in Genger’s organic potato variety trials at West Madison Agricultural Research Station in 2019. Three of these lines, derived from crosses between the varieties Huckleberry, Picasso, and Red Endeavor, yielded well in comparison to standard varieties. The fourth, from a cross between Spartan Splash and Red Endeavor, gave lower yields of particularly attractive multicolor tubers and may be suited to garden production.

Participants in this research are working to prove that farmer-selected lines from potato breeding populations can equal or out-perform parental lines. Zachary Paige is working with TPS to select potato lines suited to his growing conditions. He is currently collaborating with the Organic Seed Alliance and five other growers in his region to evaluate the economic feasibility of certified seed potato production and other seed enterprises. This project is funded by an NCR-SARE Partnership grant. As part of the project, Paige is facilitating educational workshops on seed saving as well as selling seed for a range of vegetables.

Maria Carter was able to identify optimal varieties for her growing conditions in North Dakota, and now her farm is the second farm producing organic certified seed potatoes in the region.

“It has been a gift to do this project with Ruth,” Carter said. “We’d been trying to grow organic seed potatoes on and off for about 10 years. Of course, I had
a lot of potato knowledge and background, but we didn’t have enough information to do the organic potatoes. Ruth solidified some things for us with her knowledge and varieties. We’ve been selling our organic seed potatoes using the internet, and last year was a fantastic year for us; we’ve reached our goals and then some. I have a son attending North Dakota State University, and he is looking forward to coming back to be involved in our organic seed potato business line.”

Learn more about this potato project on the SARE project reporting website. Search by project number LNC14-358, or contact the NCR-SARE office for more information.

Read more about Genger’s potato breeding research in this article from a 2015 Organic Broadcaster.

Ruth Genger has been researching organic seed potato production and variety selection since 2007 at the University of Wisconsin-Madison. Marie Flanagan is the Communications Specialist for North Central Region SARE, one of four regional offices that manage a nationwide grants and education program to advance sustainable agriculture.

From the January | February 2020 Issue

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