Spring 2021


Yi Wang, assistant professor of horticulture, and graduate students Guolong Liang (left) and Trevor Crosby (right) are shown here in a potato research plot at the Hancock Agricultural Research Station in July 2019. Photo by Michael P. King


It’s the number one vegetable crop in the United States. Wisconsin happens to be its third largest producer (after Idaho and Washington), with 3.1 billion pounds and 68,000 acres harvested in 2019. It comes in russet and red, yellow and purple, in fingerlings and petites. It can be frozen or fresh, dehydrated or refrigerated, roasted or grilled, scalloped or au gratin, mashed or smashed.

That’s right — it’s the nutritious and delicious, versatile and delectable, potato.

Despite its many virtues, this vegetable gets a bad rap as a junk food. That’s because one of the most common cooking methods — frying — depletes nutrients while upping the calories. There’s also the less-than-healthy fixings we often heap upon them. But on their own, prepared properly, potatoes boast high levels of fiber, antioxidants, and several vitamins. And they contain zero fat and cholesterol, little sodium, and less than 10% of the recommended daily intake for carbohydrates.

The potato is a near-complete source of nutrition, and many now tout it as a superfood, one that the developing world relies upon. Potatoes also have untapped potential for the U.S. and beyond. This is why CALS scientists are working hard to find better ways to grow and breed them. Here are two examples of horticulture experts breaking new ground on the sandy soils of potato research fields.

Hyperspectral Imaging Shines New Light on Crop Growth

This is a potato farming fact of life: During critical stretches of the growing season, nitrogen levels in potato plants need to be closely monitored. By keeping careful track of nitrogen status in their crop, farmers can make sure they apply fertilizer in the most efficient and sustainable way possible.

The most common monitoring approach involves collecting large numbers of petioles — the part of the plant that connects leaflets to stems. The samples are mailed to a lab for a quick nitrate analysis; within a few days, results tell growers whether they need more nitrogen fertilizer to get a proper yield. The system works, but it has its downsides, says Yi Wang, assistant professor in the Department of Horticulture.

An unmanned aerial vehicle carrying a hyperspectral camera collects data from potato fields at the Hancock Agricultural Research Station. The goal is to develop computer- assisted models that help farmers better manage fertilizer applications. Photo by Beckett Hills

“Collecting the petioles is time-consuming and labor-intensive,” she says. “And sometimes the results can be misleading because a lot of factors can affect petiole nitrate numbers, such as weather conditions or the time of day of sample collection. Plus, the results don’t catch spatial variation [of nitrogen needs] within the field.”

Wang, who focuses her research on sustainable vegetable production, is also an extension specialist, so she pays close attention to the needs of farmers. And she knows the status quo isn’t ideal for them. Insisting there must be an easier, faster, and more comprehensive way for potato growers to assess the true nitrogen needs of their crops, Wang and her team have set out to find one — and prove its effectiveness.

She’s leading a new project, funded by a $475,000 grant from the U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture, that involves collecting data with a hyperspectral camera mounted on a UAV (unmanned aerial vehicle) or low-flying airplane. The camera gathers images as the plane passes over research plots with potato plants grown at different nitrogen levels. Researchers then process and use the data to develop computer-assisted models that link the imagery with in-season plant nitrogen status and end-of-season yield, quality, and economic return.

“The ultimate goal of the project is to assist potato growers with their nitrogen management using a platform that blankets the entire field in a timely manner, unlike the traditional petiole nitrate testing,” Wang explains. “My collaborators and I hope to develop an online program that will translate the hyperspectral images into information about when to apply fertilizer, and how much to apply, so that maxi- mum profitability can be achieved for the growers with minimum environmental impacts.”

Hyperspectral cameras are powerful pieces of equipment, able to capture images that detect hundreds or thousands of spectral bands of sunlight reflected from the crop canopy, explains Trevor Crosby, a graduate student in Wang’s laboratory.

“Factors that cause variation in canopy health — such as nutrient status, water status, or disease pressures — are all related to the spectral reflectance, so they can be visualized in the hyperspectral images,” he says. “We use image processing to extract the most useful information for our research project.”

And there’s certainly a sizeable pile of data to process. One flight over a 70-by-150-meter research field can collect dozens of images, each with hundreds of spectral bands. It takes long hours to crunch the numbers, so the research team is looking to expedite the image processing.

The challenges of this complex project led Wang to bring in two key collaborators. Phil Townsend, professor in the Department of Forest and Wildlife Ecology, is a national leader in utilizing remote sensing technologies (see “Drones, Joysticks, and Data-Driven Farming” in the summer 2018 issue of Grow). And Paul Mitchell, professor and extension specialist in the Department of Agricultural and Applied Economics, is helping with the economic analysis that informs the computer model’s nitrogen application recommendations.

These processed aerial images of potato research plots show the reflectance of certain spectral bands, which indicate the nitrogen sufficiency ordeficiency of different varieties. Image by Beckett Hills

Crosby is taking the lead on collecting ground measurements for the project, gathering a wide array of data from the field research plots at different potato growth stages over the course of several growing seasons. He’s looking at leaf area index, leaf and vine total nitrogen content, and environmental factors, such as soil moisture and temperature, solar radiation, and wind speed. At harvest, he measures total tuber yield and size profile. Using the measurements, Crosby will develop advanced models to link the hyperspectral imagery with the ground measurements.

Finding optimal fertilization levels through these models could lead to positive outcomes in the real world, and not just in terms of farm profitability. Excess fertilizer often finds its way into groundwater, leading to nitrate contamination. High nitrate levels are linked with numerous health problems in people and aquatic plant overgrowth that can cause ecological damage.

“With all the issues in the state around nitrates in groundwater, we need to find ways to make better use of our fertility inputs, and we are hopeful that Yi’s new project can help direct those efforts,” says Andy Diercks BS’93, a fourth-generation potato grower at Coloma Farms, LLC. “The potential is significant. Yi’s new project represents an opportunity to really leap forward [in nitrogen management].”

This is just one of Wang’s ongoing efforts to support potato and vegetable growers in Wisconsin. Her portfolio of research focuses on cutting-edge technologies that can improve irrigation, nitrogen, and storage management for common vegetables in the state. This includes potatoes, of course, but also green beans, dry beans, and sweet corn. She shares her findings with farmers through the UW Vegetable Crop Update e-newsletter, grower meetings, farm visits, field days, and her Proud to be a spudbadger! YouTube channel.

For the hyperspectral imaging project, Wang’s team plans to provide results online through a publicly available spreadsheet, at least in the near term. But with additional funding, they hope to develop a free app that growers can use on smart phones and tablets. Many, including Diercks, eagerly await these next steps.

“Hyperspectral imaging has the potential to show the plant’s response to deficiencies in inputs before the human eye can see that response,” says Diercks. “If we can gain a few days in responding to nutrient stress, the impact to the health of the plants would be quite significant, not to mention the possibility of using less inputs to remedy the situation — which would be a serious win-win.”

‘Potato 2.0’ Will Speed Up Breeding and Yield Better Varieties

Although potatoes may be a superfood to some, they’re far from perfect. For one, they present a big challenge for plant breeders who are trying to develop more savory, sustainable, storable, and growable varieties.

“Potato may be the world’s leading vegetable crop, but it hasn’t realized the genetic gains needed to keep pace with industry and consumer demands,” says Jeff Endelman, associate professor in the Department of Horticulture and leader of the university’s potato breeding program.

Jeffrey Endelman, associate professor in the Department of Horticulture, stands in front of the Walnut Street Greenhouse, where he conducts potato research on the UW campus.

One of the main hurdles when breeding potatoes is its tetraploid genome. Tetraploids inherit two sets of chromosomes from each parent, instead of just one set like humans and most animals. “Tetraploidy is common enough among flowering plants that scientists believe it has advantages on evolutionary time scales,” says Endelman. “But for plant breeders, it makes it difficult to understand the genetics of traits and get rid of unfavorable genes through selection.”

To circumvent the challenges of tetraploidy, potato breeders around the world — in an effort informally known as Potato 2.0 — are working to reinvent cultivated potato as a diploid crop.

“One reason to do this is the simplicity,” says Shelley Jansky MS’84, PhD’86, a USDA Agricultural Research Service scientist and professor emeritus of horticulture who has spent her career working with wild potatoes to identify genes for traits that potato breeders deem important. “Another reason is that most wild potatoes are diploid, so it’s just easier to make the crosses on the same level.”

Potato 2.0 builds on groundbreaking breeding work Jansky and others started at the Hancock Agricultural Research Station around eight years ago. Although all major potato varieties worldwide are tetraploid, the Jansky team created a diploid potato variety by crossing a cultivated potato with a wild one and discovered that it displayed desirable characteristics.

“At harvest, the potatoes looked just like what you’d see in a regular breeding program,” says Jansky. “They were the same size, had the same yield. So that really made me think, boy, why are we working so hard to go up to the tetraploid level when maybe we can just do this at the diploid level and still get the same quality?”

From left, Lin Song, a Ph.D. student with the Endelman lab, and, from Rhinelander Agricultural Research Station, research gardener Jaden Olski and superintendent Becky Eddy, prepare slices of diploid potatoes for frying in the kitchen at Hancock Agricultural Research Station as part of an assessment of different varieties. Photo by Michael P. King

Given this prior work, it’s no surprise that UW–Madison is now serving as the lead institution for Potato 2.0, which is funded through a $3 million award from the USDA Specialty Crop Research Initiative and $3 million in matching funds from PepsiCo (the parent company of potato chip and snack food producer Frito-Lay) and eight collaborating universities and research institutions.

The first step of the project is to produce diploid potatoes that still have the optimal genetics of their tetraploid relatives. This is done by pollinating tetraploid potato with existing special diploids that can act as “haploid inducers.” Haploid induction is a technique used in many crop species to reduce chromosome numbers. It results in an embryo without the chromosomes of the pollen donor.

“Our goal is to create and sequence the genomes of 100 diploid potatoes, representing the russet, chip, and red market types that make up most of U.S. potato production,” explains Endelman.

The next step is to create lines that can be maintained as “true seed,” which is potato jargon for what everyone else simply calls seed. The “seeds” currently used in potato production are whole or pieces of tuber with at least one “eye,” from which sprouts develop to generate the next crop. But seed tubers are bulky and expensive to transport.

“It takes about 2,000 pounds of seed tubers to plant one acre, but the amount of true seed needed would fit in the palm of your hand,” says Endelman.

Seed tubers also act as vectors for diseases, such as Verticillium wilt, soft rot, silver scurf, common scab, and Potato Virus Y. It’s another problem the use of true seeds could address.

The color of crushed diploid potato chips is analyzed by a spectrometer. Photo by Michael P. King

“Nearly every major disease the potato gets is carried in seed tubers,” Jansky says. “None of them are in true seeds.”

Another major focus of the project is to produce inbred, or self-pollinated, lines. Although it may sound trivial, this is actually a big challenge in diploid potatoes, which typically lack the ability self-pollinate. But self-pollination is key to creating hybrid lines with big boosts in yield. That crossbreeding process took decades in the early 20th century for corn breeders, but Endelman hopes to do it more quickly in potato now that researchers have the genomic tools needed.

Endelman is excited to see the future impacts of the project across the potato industry, in Wisconsin and beyond. “This project marks a turning point for Potato 2.0 in the U.S., and everyone is enthusiastic about the potential to more efficiently deliver genetic improvements for disease resistance, climate resilience, nutritional value, and more.”

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