Offseason strawberries are not known for such great flavor — they come from too far away and are bred for sturdiness — but she's betting her career that locally grown fall and winter fruit will one day rival the most sumptuous June berries.
Arriving shortly after dawn on a nippy November morning, this U.S. Department of Agriculture plant breeder at the Beltsville Agricultural Research Center is about to demonstrate how close — or far — her dream is to coming true. At first, there's no sign of any plants. They are hidden under clear plastic tarps pulled tight over thigh-high, yard-wide hoops. Lewers slams her gloved fist against the top of one of these tunnels, sending ice flying. Collaborators John Enns and Phil Edmonds knock ice off another row with sticks.
Acting like mini-greenhouses in the cold, the tunnels are sprayed with warm water to take the chill off when the temperature drops below freezing. As a result, ice builds up. Nonetheless, the tunnels have put year-round strawberries in reach of the Mid-Atlantic and other eastern states. The researchers roll up the plastic sides of one row, revealing the bushy growth of dark green crowns adorned with red, pink, light green and yellow fruit in various stages of ripeness. Enns and Edmonds pick the ripest, and Lewers inspects each one, rating its appearance on a scale of 1 (barely recognizable as a berry) to 9 (a fruit lover's dream come true).
There's a long, somewhat checkered history of breeders trying to convert strawberries from once-a-year bloomers to plants that flower over and over again. Success in the 1980s revolutionized the industry in California, whose climate is mild enough to encourage year-round fruit. On the East Coast, though, much more work was required to successfully grow these "ever- bearing" or "day neutral" varieties: Plant breeders had to come up with ways to make their berries follow the postman's creed, such that neither rain nor snow nor heat (gloom of night doesn't matter) would stop this crop.
That so many of the berries Lewers is inspecting today earn a top score signals long-sought success. "Just smell them," she says, offering them to her visitors. "Just in time for Thanksgiving."
Modern strawberries date to the 1700s, when a French spy brought a Chilean coastal strawberry plant back to Europe, and it was crossed with a North American woodland strawberry. These "June berries" became the iconic fruit of early summer. Spring's relatively short days prompt flowering, which ceases as the days get longer, limiting fruit production to a short, month-long season. Given consumer demand and high prices, growers for more than a century have sought out plants that kept flowering no matter how long the day. In a 1917 USDA Farmers' Bulletin, George Darrow — who started the pick-your-own industry with a farm in Greenbelt, Md. — touted the benefits of several of these very "hardy" plants that under favorable conditions produced berries until hard frosts occurred. "But they were pretty much a novelty and were never grown to any great extent," says James Hancock, an emeritus strawberry breeder at Michigan State University in East Lansing.
Royce Bringhurst changed that, especially for California. He was called "Mr. Strawberry" on the University of California at Davis campus, and in the 1950s, he crossed cultivated California strawberries with wild relatives that he collected from the Wasatch Mountains in his home state, Utah. Since then, the Davis program has released more than 20 such "day neutral" varieties, helping to make California the nation's top strawberry producer, with harvests from March through November. In 2015, 91 percent of U.S. strawberries came from that state.
Bringhurst sent some of those wild relatives to Beltsville. The USDA released two local ever-bearing varieties in 1981, but "they never took off in a large way," because summers on the East Coast were too hot for fruit to develop, says Hancock. When Lewers started her Beltsville job in 2001, she decided to devote her career to the challenge. Back then, the local produce movement had barely begun, yet Lewers had an uncanny sense of the future, says Julia Harshman, a UC Davis plant breeder.
Recently, strawberries have edged in as one of the top five fruits eaten in the United States, with annual consumption averaging about 8 pounds per person. "There are a lot of people who want to be able to go to the market every day of the year and get them," says Glenn Cole, a UC Davis plant breeder. Most come from California, where breeders have emphasized bigger and firmer fruit for more efficient harvesting and shipping. "Most people agree that East Coast strawberries taste better," says Harshman. So local strawberries could have an edge.
Ever-bearers can benefit growers as well. According to 2015 figures from the USDA, strawberries bring in about $38,000 per acre early in the season (compared with less than $4,000 per acre for sweet corn later in the year), making them a key cash crop for many small farmers. Yet with the June berries, one severe rain at the wrong time can ruin an entire year's crop. "If [ever-bearers] get damaged, it's not so bad because they keep blooming," says Enns.
Fifteen years ago, Lewers had her work cut out for her. "It's an intense crop with lots of moving parts." says Harshman, but Lewers was up for the challenge. "Most plant breeders are passionate about what they do, but Kim is exceptionally passionate about her work."
First, Lewers had to solve the summer slump in production. Eventually, she and David Fleisher, an agricultural engineer with the USDA Agricultural Research Service, figured out that fruiting shuts down when the soil — not the air or the plant itself — gets too warm. That insight led to the adoption of white plastic instead of black plastic, which is tightly tucked over raised beds to reduce weeds, and other steps. Still, summer rains in this region tended to ruin the fruit anyway. So the researchers tried chest-high tunnels, which were too unwieldy, fragile and labor-intensive.
On a visit to Brazil in 2006, she noticed that farmers there used low tunnels. By 2013, she was convinced they were the best way to grow ever-bearing strawberries anywhere in the eastern half of the United States. In tunnels, she gets 1 ½ pounds of strawberries per plant, double the production in the open air, and three times the marketable yield.
Lewers says growers testing tunnels across the country are impressed; in New Hampshire and New York, for example, the tunnels protect the berries from damaging rains and extend the growing season. "It just makes a momma proud," says Lewers.
Deciding on the best-tasting ones is most challenging. Whereas a single compound defines a raspberry's flavor; strawberries pack more than 20, combinations of which affect each person's taste buds differently. "There's lots of opinions on flavors and berries," says Cole.
So Enns and Lewers tussle over the flavor. Sometimes, they detect grape, coconut, pineapple, peach or burnt sugar flavors. But what Enns relishes as a pleasant musk, Lewers perceives as moldy. What she recognizes as a rosy tang, Enns spits out because the fruit is soapy to him. Another flavor that she likes, "he says, 'tastes like garbage,' " says Lewers, a sensitivity that 1-in-3 people have. If a flavor passes muster, they put a dozen healthy berries from that cross into a clear egg carton, refrigerate them, and check how rotten each has become after a week and two weeks. Plants with the longest-lasting berries are used in the next year's crosses.
It's a balancing act. Improvements in one trait can cause a setback in another. As a result, "I don't have everything in one package," Lewers says. For now, they must use California varieties. "In the fall, they sweeten up really nice," says Enns. So even locally grown California strawberries are a big hit.
I visited Lewers two days before Thanksgiving. With glee, I showed up at Thanksgiving dinner with a bowlful. Not quite ruby red, and even with white tops, the fruit didn't look quite ripe. But biting into it brought a pleasant surprise. "Wow! That's really sweet," said my sister-in-law, Ginger Butcher. Her food scientist daughter, Alex Mlynarski, fantasized about serving them on a tart with whipped cream. "You wouldn't have to alter them in any way," she said. But she was adamant they could not be local. "There's no way you're still growing strawberries here."
Oh, yes, there is. It's true this crop had a close call this past spring, when a cold snap brought 11-degree temperatures. Lewers was out all night to keep ice from building up too much as she ran the sprinklers nonstop. That may seem extreme, but if a farmer is on a financial edge, "he can just get out there and do it," she says. She picked one more round of berries after Thanksgiving and "the fruit were larger and sweeter," she reports. She could have continued harvesting but stopped because she has been sick, and her doctor ordered her to stay out of the dry air for the time being.
But she's already looking ahead. "I look forward to trying to keep the tunnels going all through the winter, possibly next winter," she says. "So call me in May of 2019 to see how it went."
Pennisi is a senior correspondent for Science magazine.
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