British ash trees are evolving resistant traits to combat ash dieback, evident from DNA sequences found in numerous specimens.

This discovery is promising, according to Richard Buggs at the Royal Botanic Gardens in Kew, England, although complete resistance in ash trees is not anticipated soon. “A breeding program may be necessary to assist nature in this process,” he states.

Ash dieback, caused by the fungus Hymenoscyphus fraxineus, progressively impairs the tree’s capacity to transport water. It began its spread across Europe in the 1990s and made its way to the UK in 2012.

The demise of ash trees leads to increased carbon dioxide release and threatens various species that depend on these trees for their ecosystem. Additionally, fallen trees pose risks to people and property. “There are numerous ash trees close to footpaths and roads, creating significant hazards,” Buggs notes.

Buggs’ team compared genomes of 128 adult European ash trees. Since fungi take considerably longer to kill mature trees than younger ones (Fraxinus excelsior), this also included 458 seedlings at a location called Marden Park in Surrey. They discovered thousands of variations previously linked to resistance were more prevalent in younger trees, likely because those without such variations perished.

This study provides the most comprehensive genetic insight into evolutionary responses observed in nature. “The significance of this research is its ability to characterize the genetic foundation and demonstrate the changes occurring within a single generation,” Buggs explains.

However, each gene variant offers only a marginal effect, failing to provide complete resistance. As the older ash trees diminish and fungal spores decrease, the rate of evolutionary change may also slow in the future. This indicates that younger ash trees might have better survival prospects, Buggs suggests.

“It poses a major challenge, but these trees won’t vanish entirely,” he remarks. “Our findings inspire hope that some of these younger ash trees may mature and undergo natural selection for subsequent generations, if feasible.”

Ash dieback has yet to invade North America; however, the emerald ash borer (Agrilus planipennis) has been introduced, actively decimating ash tree populations there. The outcome of both ash dieback and the emerald ash borer coexisting in the same region remains uncertain but might exacerbate the issue.

“Globalization is mixing insects and pathogens across the globe, leading to increasing challenges for these trees, and it is becoming increasingly difficult for them to adapt,” Buggs states. “Trees now face threats they have never experienced before, and at unprecedented speeds.”

He believes interventions are essential to help trees withstand these pressures, such as creating resistant hybrids between resilient species and native trees.

“One potential solution is to enhance the genetic diversity of trees globally, keeping pace with the array of pests and pathogens we are spreading,” he concludes.