Clean Tubers, from Test Tube to Plate

Years before that french fry landed on your plate, the plant that would eventually give rise to the spud your fry was cut from was sealed away deep in a secureaccess building, growing slowly in a test tube inside a locked growth chamber.

At least, that’s the case if it was the product of the Wisconsin Seed Potato Certification Program (WSPCP), a 104-year-old CALS program dedicated to supplying Wisconsin seed potato farmers with quality, disease-free tubers.

All that security helps keep these important plants clean, and clean is a big deal for potatoes. Because they are grown from the eyes of tubers, or seed potatoes, rather than from true seeds, potatoes can easily carry bacterial and viral diseases in their starchy flesh from generation to generation. The solution is exacting cleanliness and rigorous testing at every stage of potato propagation.

WSPCP supplies 70 percent of the seed potatoes for Wisconsin’s 9,000 acres of farmland dedicated to propagating seed potatoes. The program certifies 200 million pounds of seed potatoes every year, enough to plant roughly 90,000 acres for commercial growing. Those spuds are then sold to commercial potato growers in Wisconsin, in other states, and around the world to be turned into farm-fresh potatoes, chips, and fries.

Each one of those potatoes’ progenitors once passed through the hands of two plant pathology researchers at UW–Madison, Andy Witherell and Brooke Babler BS’06 MS’10. In about three months, they can turn a handful of small potato plants growing in test tubes into hundreds. Multiply that by dozens of different varieties of potatoes — Caribou Russet, Magic Molly, German Butterball — and together Witherell and Babler produce tens of thousands of potato plantlets every year.

The two scientists work out of the Biotron, a facility on the UW–Madison campus designed to replicate any climate needed for research. The building’s secure access and clean protocols help them scrub the potato plants of any diseases and propagate them in sterile environments until they’re ready to plant in soil.

“This is a good place to grow plants because we’ve got a system that’s really clean,” Witherell says. “The Biotron air is filtered, and we have a clean room to work with.”

The researchers start by sterilizing an eye of a tuber and then inducing it to grow in a sterile container full of a jelly-like growth medium containing bacteria- and virus-inhibiting chemicals. As the spud sprouts into a small plant, they ramp up the heat to try to kill off any viruses. Then they clip off a portion of the shoot and replant it in a clean test tube of growth medium.

Brooke Babler and Andy Witherell check on micropropagated potato plants housed in test tubes at the Biotron Laboratory. (Photo by Bryce Richter)

Babler and Witherell can keep their plantlets in stasis in cold storage until the call comes in — 308 plantlets of Dark Red Norland are needed by July. Babler pulls out a box with several plantlets and takes them to the clean room, a space about the size of a parking space. On a sterile work surface, she takes out a scalpel and slices the plants into several pieces before replanting them in a new box. Just a small portion of one plant’s stem will grow an entirely new plant under the right conditions.

In this way, eight potato plants become 30. Four weeks later, those 30 become 80; then 80 become 310. They are all genetically identical clones of one another, and they are all still clean.

Thousands of plantlets of different varieties are shipped to the program’s farm in Rhinelander, Wisconsin, where they are grown hydroponically or in pots to begin producing tubers. Over several generations, one plant gives rise to many spuds, which in turn are replanted to make even more potatoes. In a few growing seasons, what once was handled by Witherell and Babler in the Biotron now weighs hundreds of millions of pounds and requires the work of two dozen independent, certified farms to manage.

Along their journey, the potatoes are screened for diseases that might have crept in. After Babler and Witherell leave the Biotron for the day (they only enter the facility once per day to better avoid bringing in pathogens from outside), they work in Russell Laboratories, where they help run diagnostic tests on potatoes to screen for viral and bacterial infections.

“Part of the certification process is to walk the fields and visually assess plants for the disease,” says Babler, a native of Viroqua, Wisconsin, who earned her UW–Madison degrees in both plant pathology and horticulture. “You can visually assess plants, but sometimes you can’t tell exactly what the disease is. So the inspectors ship the plants back to us, and we do diagnostics throughout the growing season.”

As part of her research, Babler is developing an improved test for a relatively new potato disease, Dickeya. The bacteria can spoil up to a quarter of a farmer’s yield under the right conditions and has recently taken hold in North America. Seed potato programs like the WSPCP are designed to detect and restrict the spread of new diseases like Dickeya, which spread primarily through infected seed potatoes.

Only those potatoes with a healthy pedigree get the WSPCP seal of approval. A portion of the sale of each bag of potatoes that commercial growers buy, certified to be as clean as possible, supports this years-long, labor-intensive process.

It’s a certification well worth the price — ensuring that Wisconsin potato growers continue to succeed, helping keep the state one of the top producers of potatoes in the country.

“Interwoven tapestry” of lakes and land: Iceland

Swarms of midges rise out of a lake in northern Iceland in such enormous numbers every spring and summer that they can impair breathing and darken the sky, giving the lake its name—Myvatn, or “midge lake.”

CALS entomology professor Claudio Gratton and other ecologists are trying to understand why the midge population can fluctuate by 100,000-fold across a decade, and what impact these massive swarms have on the surrounding landscape. It’s becoming clear that the billions of midges falling on land fertilize and alter the vegetation on the lakeside, but the causes behind such large fluctuations in the insects’ population remain a mystery.

Gratton’s research aims to better understand lake-dominated environments, including those of Wisconsin.

Lake Myvatn sits at the edge of the Arctic Circle, where the sun barely sets from May to August. The ecosystem is extreme yet simple; a relatively small number of species, like the midges, dominate. This bare-bones environment is perfect for exploring complex interactions within ecosystems.

In 2006, when Gratton first saw the huge numbers of midges rising out of the lake and dying on land, he thought of them as a living transfer of nutrients from water to shore. Gratton calculated that the midges were the nutritional equivalent of scattering a half-million Big Macs around the edge of the lake, which is about the size of Lake Mendota in Madison. He wondered how the lakeside responded to this nutritional glut.

To test how the midges alter the landscape, Gratton’s laboratory set up experimental plots in the vegetation around the lake. In some, they added dead midges; in others, they used netting to exclude them.

Over the years, Gratton’s team saw that where they added midges, grasses flourished. Normally starved of nutrients in the poor soil and outcompeted by heartier plants, the grasses took off in response to the influx of rotting- midge fertilizer. The research explained why grass grew in some areas and withered in others.

“Only by understanding the linkage between midges and grass can you explain this pattern in nature,” says Gratton. “The lake is causing that to happen.” Gratton was originally introduced to Lake Myvatn by colleague Tony Ives, a professor of zoology who has a lifelong connection to the island and researches fluctuations in the midge population.

Local shepherds have long called the grass in midge-infested areas “midge grass”—they
harvest the grass and feed it to their flocks. Gratton’s work suggests that the shepherds’
folklore contained a kernel of truth, and that midges might indirectly nourish the sheep by encouraging more grass growth.

Gratton and colleagues are extending these studies to the lake-filled Wisconsin landscape. Gratton and postdoctoral researcher Mireia Bartrons, now at the University of Vic in Spain, developed a model of how insect emergencies from Wisconsin lakes affect lakeside ecosystems. With more than 15,000 lakes and 34 percent of the state lying within 200 meters of a lake or stream, the scientists expect aquatic insects to affect a large share of the state.

Gratton sees ecosystems, whether in Iceland or the American Midwest, as an interwoven tapestry of interactions rather than isolated patches of land or water.

“The character of the land would change without these lakes,” says Gratton. “Our landscapes are completely interconnected.”