By Kym Pokorny
In the fall of 1986, plant breeder Shawn Mehlenbacher arrived at Oregon State University. One month later came the first report of eastern filbert blight from a Willamette Valley hazelnut orchard. The two events seemed fated.
EFB, a fungal disease that can wipe out an orchard, had been devasting trees on the East Coast for almost a century. Oregon could easily follow suit.
Many people thought the fungus would never jump the Columbia River from southwest Washington, where the first infected trees on the West Coast were found in an orchard in 1968. But it did, and in the mid-1970s the disease took hold of the moderately susceptible Barcelona variety of trees in an orchard near Damascus at the northern end of the Willamette Valley. It quickly spread.
When Mehlenbacher reached Oregon, farmers were desperate for help, as they watched the disease’s bullet hole-shaped cankers pockmark their way through groves. He collaborated with his predecessor, Maxine Thompson, walking through orchards, going tree to tree to tree as he sponged up the knowledge she’d built over 17 years as the hazelnut breeder at OSU. Mehlenbacher began keeping his own meticulous records in an 8-by-14-inch green ledger. He still does. It’s easier, he says, than using a computer.
Thompson focused on breeding trees with improved traits — better nuts, earlier harvest, vigor, thickness and size of shell, — but switched her attention to eastern filbert blight when she found an unaffected tree surrounded by ranks of disease-ridden trees in southwest Washington. That discovery was named “Gasaway” and provided the resistant gene for many of Mehlenbacher’s disease-resistant releases.
Top U.S. Producer
Hazelnuts (Corylus avellana) — or filberts as they’re often called — thrive in the mild Mediterranean climate of the Willamette Valley. The nuts grow so well, Oregon rates No. 1 in production for the country. Having 99% of the crop, it is ranked third in the world behind Turkey and Italy in tonnage produced.
“The world market for hazelnuts is huge,” Mehlenbacher says. “If we double production, we will have no trouble selling it at a premium price. We do a better job than our competitors.”
Undermining that success is eastern filbert blight (Anisogramma anomala), which could destroy an industry worth $202 million to Oregon.
The blight takes its time killing a tree. It takes seven to 10 discouraging years for the cankers to spread and the leaves to start turning brown, a sure sign of infection. Through management practices like pruning and appropriate spraying, growers can mitigate the disease but not stop it.
The eastern filbert blight fungus releases a sticky, white ooze during wet weather. As wind spreads the spores, they settle on young shoots and penetrate cells where infection occurs. Eventually,
cankers — or stroma — appear and start to girdle branches, which die back as the scourge expands.
Mehlenbacher, who was raised on a farm in western New York, came to Oregon from Rutgers University, where he worked with peaches, apples and apricots. He quickly got on board with hazelnuts, a passion that’s persisted for 33 years. No, he says, he’s not bored with hazelnuts.
“It’s not so much the hazelnuts but the genetic diversity in plants that fascinates me,” he says. “I’m lucky to have a job I love that doesn’t feel like a job. I get to work in the field, in the lab, in the greenhouse; I get to teach and review manuscripts. There’s always something new. It’s exciting. Besides they’re healthy and make everything taste better.”
That may be, but plant breeders, especially tree breeders, must be patient. It takes 17 years from the time two parents are crossed, to the release of the best seedling as a new variety. Every year, Mehlenbacher, his research assistants and graduate students plant about 5,000 seedlings. Almost all will fall to the chainsaw because of disease.
Generating Crop Load
At harvest time, in September and October, Mehlenbacher grabs his ledger and heads to the OSU research farm in Corvallis. Often, he can be found sitting on a stool with 60 acres of hazelnut trees spread out behind. Wearing his usual knit cap and plaid shirt, he scoops up nuts and separates each one from its husk. For days he’ll walk row by row, tree by tree taking notes on crop load, nut shape and size, and how easily nuts release from the husk. Then they’re transported to the Nut House, an affectionally named field lab where the nuts are dried, counted, cracked by hand and evaluated again – 7.2 million in Mehlenbacher’s three-decade career. If the trees don’t come up to snuff, they’re out, he says.
“They get a ‘D’ for discard,” adds Mehlenbacher with a smile. “If they’re good, we’ll keep the tree. We don’t keep many, though.”
One of the first to show promise was Jefferson, an offspring of Gasaway. Mehlenbacher and his group collected pollen, crossed strains by hand and came up with 144 promising seedlings. They released only one.
That was 2009. Since then it’s become the standard for the in-shell market that demands big, easy-to-crack nuts. Growers took to it immediately and began replacing “Barcelona” orchards with the EFB-resistant variety.
A Hopeful Turnaround
In 1987, a year after Mehlenbacher joined the breeding program at OSU’s College of Agricultural Sciences, Rich Birkemeier discovered eastern filbert blight in his orchard near Canby. He had just planted 130 acres of “Ennis,” an excellent variety for market, but highly susceptible to EFB. It shook him out of denial.
“By 1994, it blew up; we had blight on every tree on the farm,” he recalls. “We pruned out diseased wood as best we could and sprayed with fungicide. I thought we were doing OK.”
That year, Birkemeier invited a group of hazelnut growers to his farm. He shared a dour story of his war against eastern filbert blight.
“At the end of the tour, they drove off, and I was standing there exhausted and discouraged,” he says. “Then Shawn walked up to me. He handed me his card with the name of three experimental varieties. He had a tear in his eye. ‘Here Rich, you may want to try these. They’re not immune, but they’re much better than what you’ve got.’”
Mehlenbacher’s generosity led Birkemeier to graft enough trees for 200 acres. He found one variety that did remarkably well. It was named “Lewis,” and he says it kept him in business. But by 2000, he started noticing blight in young trees. With a program of careful pruning and spraying fungicides tested by Jay Pscheidt, professor and plant pathologist with OSU’s College of Agricultural Sciences, he’s been able to manage it as much as it can be managed. In the meantime, he’s replacing some Lewis trees with newer disease-resistant varieties, but it takes four years for them to bear nuts.
“Remember we’re dealing with a fungus that reproduces with an infinite number of spores spread by rain in winter,” Birkemeier says. “When you have 5% of an infinite number, it’s still an infinite number, and that’s what we’re dealing with.”
Resistance in the Genes
Mehlenbacher and his crew fight to stay ahead of these destructive fungi by keeping new trees in the breeding stream. Advances in genetics sped up the process by allowing him to determine in the lab whether a new seedling has immune genes. Instead of moving trees into the field where it takes years to determine resistance, they use a lab process to identify highly resistant seedlings based on the presence of DNA markers. The ability to score them for eastern filbert blight resistance at that early stage saves hundreds of hours, time that could be invested in preparing fields and transplanting trees.
“We only had markers for the Gasaway gene, the first variety found to be resistant to eastern filbert blight; now we have 100 sources of genetic resistance to EFB,” explains Mehlenbacher, who has traveled to more than 20 countries collecting seeds and plant cuttings. “We have imported seeds and cultivars from all over the world. As we study them, we find which ones transmit resistance to their offspring. Sometimes none; sometimes 50%.”
While the lab process speeds identification of resistant trees, they still need to be evaluated in the field. EFB resistance is not necessarily a sign that the variety will succeed. The crosses start a course of evaluation that includes monitoring for best characteristics including nut size and color, how easily they let go of the husk, yield, vigor, growth habit and ease of cracking.
Traditionally, Oregon focused on the in-shell nut, or what’s called the “holiday nut bowl” version. But the market has shifted. Demand now calls for smaller nuts or kernels that are used in candy, cookies and other processed foods. One of the biggest markets is Ferrero SpA, makers of Nutella and the world’s largest buyer of hazelnuts. OSU and the company have been in talks in the past about Ferrero supporting research in exchange for breeding information. Although the negotiations fell though, Mehlenbacher says the door remains open.
“We ended up with zero from Ferrero,” he says, “but we showed we’re the ones to come to about hazelnuts. Everyone does. We’re the largest breeding program in the world, bigger than all the rest put together. We’re 5% of the world crop doing 95% of the breeding.”
New Varieties Under Development
Eventually, the disease will defeat the resistance bred into trees like Jefferson. On the East Coast, where the disease is native and has been devastating hazelnut orchards for more than 100 years, new forms of eastern filbert blight have already appeared.
“It’s an ongoing battle,” says Mehlenbacher. “We’re OK for a while, but the fungus will eventually change and be able to overcome resistance. Two years ago, it was found that Gasaway is no longer resistant back east.”
With more varieties in the pipeline, Mehelenbacher is confident that whoever takes over his work will continue to produce EFB-resistant trees and keep ahead of the insidious disease. That day is not too far off. In four-and-a-half years, Mehelenbacher plans to hang up his cracking hammer and retire.
“It wouldn’t have been the same if Shawn had not been here,” says Wayne Chambers, a grower since 1964. “It wouldn’t be much of an industry without him. It’d be pistachios, I guess. Hopefully, we can continue to utilize his services on a different level, as a consultant maybe. Will he stay in the game? He’d better.”
Mehlenbacher smiles as he stands in his field lab cracking nuts one by one. His life’s work has changed the face of the Oregon hazelnut industry. He’s pleased when he thinks about the future. He’ll leave a legacy. And he doesn’t intend to stop. Even in retirement, he plans to breed the tree that’s been his life’s work.