Genetic fingerprinting has determined the new strain of Eastern Filbert Blight attacking Oregon hazelnut orchards is a homegrown mutant rather than an invader from another region.

The finding by Oregon State University scientists indicates the fungal pathogen has evolved locally, thwarting disease resistance from the Gasaway cultivar that’s been bred into newer hazelnut tree varieties.

A single mutation

“It just takes a single mutation in one of these spores to overcome or not recognize the Gasaway resistance. That’s what we think happened,” said Ken Johnson, the OSU plant pathologist who conducted the genetic analysis.

Hazelnut varieties released by OSU have so far relied on a single gene that allows the trees to withstand the blight, apparently causing the fungus to adapt to that defense, Johnson said.

Single-gene resistance often depends on the plant’s ability to discern the pathogen’s molecular signature, but organisms can change to avoid detection, he said.

“If the fungus gives up the molecule that’s being recognized, then it’s off to the races,” Johnson said. “It’s happened many times before in agriculture.”

Last year, OSU confirmed a new variant is responsible for an outbreak of Eastern Filbert Blight on trees that normally withstand the disease in the northern Willamette Valley.

Further DNA testing has now revealed the new strain’s genetic markers don’t match an East Coast version of the pathogen that can also overcome Gasaway resistance, Johnson said.

Meanwhile, the new variant has the same genetic markers as the older type of Eastern Filbert Blight that infects susceptible hazelnut orchards, demonstrating it wasn’t imported from outside the region, he said.

Fingerprints match

“The fingerprints between those two orchards are absolutely identical,” Johnson said. “That’s our evidence it’s homegrown, based on molecular technology.”

The context for the new strain’s outbreak also suggests it was caused by a local mutant, as the “hot spot” was discovered in the middle of an orchard near Woodburn, Ore., rather than appearing at its edge, he said.

Farmers have been planting EFB-resistant hazelnut varieties in recent years, but the Willamette Valley still has plenty of old orchards that aren’t being treated and offer the fungus opportunities to evolve, Johnson said.

“We’re producing a lot of spores on susceptible trees,” he said.

While it’s unfortunate the Gasaway resistance hasn’t proved to be as durable as hoped, the upside is that a local variation of the disease will probably be more predictable than an invader, Johnson said.

“If it was born here, then we know what we have,” he said.

‘A bitter pill to swallow’

The evolution of a new variant is a numbers game, with a particular mutation occurring on one spore out of millions, which then infects a hazelnut tree that wasn’t sprayed with fungicides, said Nik Wiman, an OSU orchard specialist who works with hazelnut growers.

“It’s a bitter pill for the industry to swallow,” he said.

Eastern Filbert Blight has a “large genome” that’s “capable of producing a lot of variations,” Wiman said. “There’s a cascade of events that can lead to new variants.”

Roughly 25,000 acres of the Oregon hazelnut industry’s nearly 100,000 acres are planted to older, susceptible trees, some of which aren’t well managed or even abandoned, Wiman said.

“It does provide a refuge for the disease,” he said.

More research needed

Given the new strain’s origin as a homegrown mutant, more research is needed on how quickly the fungus is capable of evolving, Wiman said.

“I don’t know we have a good grasp on that at all,” he said.

The same management techniques will apply to a homegrown mutant as to an outside invader, and the blight’s unlikely to be any more virulent or destructive than the original strain, Wiman said.

However, its appearance could discourage some farmers from planting until OSU releases hazelnut trees stacked with two or more genes that confer resistance, he said.

“It affects the decision-making process going forward,” Wiman said.

The hazelnut industry is better prepared for the new variant than it was roughly 40 years ago, when the disease initially showed up in Oregon orchards, said Bruce Chapin, a farmer near Salem, Ore.

Not only have decades of research better equipped growers to control the disease, but OSU is already working on new hazelnut cultivars with more than one source of resistance, he said.

“It’s in the pipeline, coming this way,” Chapin said.

Though the new variant may sway some planting decisions, farmers are unlikely to totally forgo expanding if hazelnut prices continue improving, he said.

“It may flatline it for a while,” Chapin said. “It won’t stop people from planting. It may slow it down for a while.”

The mutant strain’s impact on acreage will probably become clearer after this spring, once farmers understand how well the new form of disease responds to treatments, said Larry George, a hazelnut grower and president of the George Packing Co.

If the new strain does impede planting, that would contribute to the industry’s unexpected growth slowdown in recent years, which is likely to leave Oregon with excessive processing capacity, he said.

“You have multimillions of dollars of capital that have been spent,” but that processing equipment may never be fully used, George said.

The danger of Oregon’s acreage stalling is it may hinder demand for the state’s hazelnut crop among food manufacturers, he said. “The industry could stagnate, which is bad because there’s no way to scale the market development.”

On the bright side, the new strain may compel farmers to abide by a stricter treatment regimen to prevent the blight’s spread and further adaptation, he said.

“It’s a big motivator to do the correct agronomy,” George said. “If everyone’s treating aggressively, we’re going to see a lower likelihood of a future mutation that’s more dangerous.”