OREGON STATE UNIVERSITY

Gene to help U.S. hazelnut growers fight blight

07/02/1997

CORVALLIS - The blight threatening the North America hazelnut industry apparently is going to get its comeuppance.

Scientists at Oregon State University have identified the single, dominant gene that gives hazelnuts resistance to eastern filbert blight, a fungal disease. Their goal is to have a completely immune, good-yielding variety of hazelnuts, which most growers call filberts, by 2004.

For growers who can't wait that long, OSU plant breeder Shawn Mehlenbacher released one moderately resistant variety early this year and will soon have another that combines some blight resistance with good yields and excellent kernel quality.

Meanwhile, resourceful growers must use a combination of scouting, pruning and fungicides to keep good trees around as long as they can. That costs money, though, and many who have had the blight in their orchards more than 10 years could be forced out of the business unless they pay the cost of extensive replanting.

Working with Mehlenbacher is OSU plant pathologist Kenneth Johnson, who has learned how eastern filbert blight works and is helping growers manage orchards to keep trees growing well as long as they can.

Almost 98 percent of the hazelnuts produced in North America - $20 million worth - are grown on 30,000 acres in western Oregon from just north of Portland to just south of Eugene. Eastern filbert blight is spreading southward in the Willamette Valley and has reached the communities of Aurora and St. Paul.

"Blight-causing spores come out all winter," Johnson said, "but trees aren't susceptible until mid-March, especially after one of those 10- to 25-hour rainstorms western Oregon is famous for.

"By mid-April, the reservoir of spores is depleted," Johnson said. "So the best time to spray fungicides for effective control is between mid-March and mid-April."

Uncontrolled blight produces cankers that girdle branches and limbs, eventually killing the tree.

 

A recent OSU survey of 141 growers showed 98 percent of those with diseased orchards are employing one to several cultural control methods. These include pruning, replacing diseased pollinator trees, and removing volunteer seedlings. Eighty-eight percent of these growers are applying fungicides at least once per season.

All that effort has its costs. Many growers don't have the energy for all the work, nor the money because of low hazelnut prices. In the long-run, blight-resistant varieties - or better yet, blight-immune ones - would be the best bet.

On that score, Mehlenbacher has good news.

The gene that confers blight immunity has been found in the variety Gasaway. Unfortunately, this is a hazelnut variety known for poor yields, late maturity, long nut shape and poor kernel quality.

But Mehlenbacher has been crossing and backcrossing to get that gene where he wants it - in a good-yielding, good-quality hazelnut. His target for releasing a blight-immune, acceptable commercial variety is 2004.

In the meantime, his testing has revealed other promising resistant varieties.

"One, Tonda di Giffoni, is not immune when we inoculate it with blight in the greenhouse, but it will stay disease-free for many years in the orchard," Mehlenbacher said.

Another, Gem, is not quite as resistant, but almost. Gem is a grower selection from Oregon released in the 1940s. Its weakness is that it is susceptible to big bud mite and lacks winter hardiness.

Early this year Mehlenbacher and the OSU Agricultural Experiment Station released Lewis, a cross between experimental variety OSU 17-28 and the Willamette variety. Lewis ranks near Gem and Willamette in blight resistance. It is resistant to big bud mite, and it is winter hardy.

In a few months, Mehlenbacher expects to release Clark, a sister seedling of Lewis from the same cross.

"Clark is not quite as blight resistant as Lewis, but it has yielded well in preliminary trials and has excellent kernel quality. Growers should like it," Mehlenbacher said.