Northern Research Station News Releases

Scientists identify genes tied to ash trees' resistance to emerald ash borer

Discovery holds promise for the future of ash trees

Fraxinus mandshurica, one of the highly resistant ash species, dissected 8 weeks after egg placement. The small, early instar larva has not developed as fully as would be expected in a highly susceptible species and is also a darker color, appearing unhealthy. In addition, the tissue surrounding the larva is browning indicating a defense response is being mounted by the host tree. USDA Forest Service photo by Dave Carey. Delaware, OH, May 26, 2020 - May 26, 2020 - Over the two decades since an invasive insect called the emerald ash borer (EAB) arrived in the United States, scientists have searched for ways to stop the bright green pests that have killed billions of the Nation’s ash trees and continue to gnaw through many more. An international team of scientists working together over several years has studied EAB resistance of ash species and has identified the types and locations of genes involved in that resistance. The findings, published yesterday in the journal Nature Ecology and Evolution and available at suggest that breeding could be used to increase resistance in ash species currently susceptible to EAB. 

In the United States, USDA Forest Service researchers evaluated EAB-resistance of 26 ash species in greenhouse experiments by placing EAB eggs onto the trees, then tracking the fate of the larvae. Resistant trees generally killed most of the larvae, while the majority of larvae survived in susceptible trees. The most highly resistant species were all native to Asia, where EAB originated. Variation in the level of susceptibility was observed in the remaining species. The five species of North American ash that are considered endangered, were confirmed to be highly susceptible using this bioassay while other North American and European ash species had relatively less susceptibility.

While susceptibility of the different ash species was being assessed by scientists in Ohio, the genomes of 22 of them were sequenced by researchers at Queen Mary University of London and the Royal Botanic Gardens, Kew. Scientists compared the sequences of over 1,400 genes across species looking for evolutionary patterns of variation that co-occur in species with resistance. Using this novel approach, 53 candidate genes were identified, many of which were known to be involved in insect resistance in other plants.

“Our findings suggest that it may be possible to increase resistance in susceptible species of ash via breeding with their resistant relatives or through gene editing,“ said Laura Kelly, an academic visitor at Queen Mary, Research Leader in Plant Health at the Royal Botanic Gardens, Kew and the study’s lead author. 

“These candidate resistance genes, once validated, have the potential to greatly expedite the breeding process and the production of improved planting stock for restoration of EAB-decimated forests,” said Jennifer Koch, a research biologist with the USDA Forest Service’s Northern Research Station in Delaware, Ohio, and a co-author of the study.

In addition to Kelley and Koch, co-authors include Forest Service lab technician Dave Carey; Forest Service researcher Mary Mason; Alan T. Whittemore of the USDA Agricultural Research Service; and Queen Mary University researchers William J. Plumb, Endymion D. Cooper, William Crowther, Stephen J. Rossiter, and Richard J. A. Buggs.


The mission of the Northern Research Station is to improve people's lives and help sustain the natural resources in the Northeast and Midwest through leading-edge science and effective information delivery.


The mission of the U.S. Forest Service, an agency of the U.S. Department of Agriculture, is to sustain the health, diversity and productivity of the nation's forests and grasslands to meet the needs of present and future generations. The agency manages 193 million acres of public land, provides assistance to state and private landowners, and maintains world-renowned forestry research and wildland fire management organizations. National forests and grasslands contribute more than $30 billion to the American economy annually and support nearly 360,000 jobs. These lands also provide 30 percent of the nation's surface drinking water to cities and rural communities; approximately 60 million Americans rely on drinking water that originated from the National Forest System.


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Last modified: May 26, 2020