Research Turns to Cloning in an Attempt to Save Ash Trees

May 30, 2018

It’s been about 20 years since the invasive emerald ash borer first showed up in the U.S. and started killing ash trees. It’s claimed millions of the trees and remains a big threat to Ohio forests. But there is new hope for an ash-tree comeback. One researcher thinks she’s making progress by breeding resistance to the pest.

Jennifer Koch is a research biologist with the U.S. Forest Service. We’re taking an off-road vehicle down a winding path at the Northern Research Station near Delaware State Park. It’s impossible to see from nearby U.S. Route 23, but a fenced-off plot hold hundreds of ash trees. They’re all related to Koch and her team’s study of what are known as lingering ash trees.

“So they were all selected because there were in areas where ash (borer) had already come through and killed probably over 99 percent of trees in that stand, but they remained alive and had healthy canopies.”

Koch says that’s because they appear to have some natural defense mechanisms against the ash borer. A big one is they don’t seem to attract adult beetles looking for food.

“So if a tree is not preferred for feeding by an Emerald Ash Borer or if it lacks the cues that draw an adult to feed on it, there’s a better chance it won’t have as many eggs layed on it,” she said.

Koch says lingering ash also seem to be an inhospitable home for freshly hatched larva. Those are what burrow under the bark, leaving those tell-tale squiggly lines and eventually killing the tree.

On lingering ash, more larva die, and ones that live are smaller, so trees are more likely to survive. That’s an extremely valuable characteristic for modern ash trees.

Koch says shoots sprouting from the trees are signs they are dying or struggling to survive.
Credit STEVE BROWN / WOSU

Literal cloning
So Koch is cloning them. Not genetic modification, but clonal duplicates of the lingering ash, literally cut from part of the parent tree. Koch points out a healthy tree that’s surrounded by others killed by the ash borer.

“And so we have grafted from this tree so we can keep it alive through its clonal replicates that are vegitatively propagated, and they continue to use it for breeding purposes.”

Maybe most importantly, Koch says the cloned trees appear to be even more resistant to the ash borer. They’re waiting on the next generation of seeds to see if they’re even more resistant. That, Koch hopes, could eventually bring restoration of the ash tree.

'The goal is for us to keep ash alive and on the landscape ... until we reach sort of a new equilibrium.'

Koch says she thinks the Delaware research station is the only place in the country using a traditional tree- breeding approach to fighting the ash borer. It could save the ash tree.

“That’s exactly our goal, is to save ash as a species and get it to a level that it’s a sustainable, healthy species that we can retain in our North American forests. It’s an important species," Koch said.

"The goal is for us to keep ash alive and on the landscape and allow it to continue to co-evolve with bio control, with emerald ash borer, until we reach sort of a new equilibrium and it becomes more like a native pest where you might see an outbreak here and there on a stressed tree, but not something that’s going to cause massive mortality rates.”