Ash trees at research station

More than 20 species of ash trees are tested for their resistance to emerald ash borer at the U.S. Department of Agriculture's Forest Service research station in Delaware, Ohio.

An international team of researchers has identified resistance genes that could protect ash trees from the emerald ash borer. Scientists from Queen Mary University of London and the Royal Botanic Gardens, Kew, have sequenced the genomes of 22 species of ash tree from around the world. They're using the information to analyze how the different species are related to each other.

Meanwhile collaborators from the U.S. Department of Agriculture Forest Service research station in Delaware, Ohio, tested resistance of more than 20 ash tree species to emerald ash borer by hatching eggs attached to the bark of trees. The researchers then followed the fate of beetle larvae. When larvae burrowed into stems of resistant trees they died.

Several of the resistant species studied were more closely related to susceptible species than to other resistant species. The United Kingdom-based scientists were able to find resistance genes by looking for places within the deoxyribonucleic acid – DNA – where the resistant species were similar but showed differences from their susceptible relatives. Using that approach the scientists revealed 53 candidate resistance genes, several of which are involved in producing chemicals that are likely to be harmful to insects. The findings suggest that breeding or gene editing could be used to place resistance genes into ash species.

“Ash trees are key components of temperate-forest ecosystems and the damage caused by emerald ash borer puts at risk the many benefits that forests provide,” said Laura Kelly, research leader in plant health at the Royal Botanic Gardens and first author of the study. “Our findings suggest it may be possible to increase resistance in susceptible species via hybrid breeding with their resistant relatives or through gene editing. Knowledge of genes involved in resistance also will help efforts to identify trees that are able to survive the ongoing threat from emerald ash borer. That could facilitate restoration of ash woodlands in areas that have already been invaded.”

The American researchers found that European ash was more resistant to the borer than the North American species. But European ash trees are already affected by an epidemic of ash dieback, a fungal disease. Further research is needed to understand how the two threats might interact. The study recently was published in “Nature Ecology & Evolution.” Visit nature.com and search for “Convergent molecular evolution among ash species” for more information.