An international team of scientists have identified candidate resistance genes that could protect ash trees from the Emerald Ash Borer (EAB), a deadly pest that is expected to kill billions of trees worldwide.
In the new study, published in Nature Ecology & Evolution, researchers from Queen Mary University of London and the Royal Botanic Gardens, Kew, sequenced the genomes of 22 species of ash tree (Fraxinus) from around the world and used this information to analyze how the different species are related to each other.
Meanwhile, collaborators from the United States Department of Agriculture Forest Service in Ohio tested resistance of more than 20 ash tree species to EAB by hatching eggs attached to the bark of trees, and following the fate of the beetle larvae. Resistant ash trees generally killed the larvae when the insects burrowed into their stems, but susceptible ones did not.
The research team observed that several of the resistant species were more closely related to susceptible species than to other resistant species. This meant the UK-based genome scientists were able to find resistance genes, by looking for places within the DNA where the resistant species were similar, but showed differences from their susceptible relatives.
Using this novel approach, the scientists revealed 53 candidate resistance genes, several of which are involved in making chemicals that are likely to be harmful to insects.
The findings suggest that breeding or gene editing could be used to place these resistance genes into ash species currently affected by EAB.
EAB has killed hundreds of millions of ash trees in North America over the last 10 years, including in Ontario farm woodlots. While individual ash trees can be protected by using insecticides, the only long-term solution for saving American ash populations is to breed trees with resistance to EAB.
In the study, the U.S. researchers found that European ash was more resistant to EAB than the North American species. However, European ash trees are already affected by an epidemic of the fungal disease, ash dieback, and experts have yet to understand how the two threats might interact.
The study also involved colleagues from the United States Department of Agriculture’s Agricultural Research Service and the Teagasc Forestry Development Department, Dublin, Republic of Ireland.
Dr. Laura Kelly, an academic visitor at Queen Mary, Research Leader in Plant Health at the Royal Botanic Gardens, Kew and first author of the study, said: “Ash trees are key components of temperate forest ecosystems and the damage caused by EAB also puts at risk the many benefits that these forests provide.
“Our findings suggest that it may be possible to increase resistance in susceptible species of ash via hybrid breeding with their resistant relatives or through gene editing. Knowledge of genes involved in resistance will also help efforts to identify trees that are able to survive the ongoing threat from EAB, and in turn, could facilitate restoration of ash woodlands in areas which have already been invaded.”