Wych elm vs. Dutch elm disease: Giants, genomes and true grit in the Scottish Borders

We assign human qualities to animals without a second thought. The wise owl and the cunning fox will produce a smile, even though we know this is just a way of making meaning and building emotional connections. But do the same thing with plants and you will raise a few eyebrows.

Nevertheless, I find myself projecting the qualities of true grit onto an old wych elm growing beside Jedburgh Abbey. This roughly 200-year-old tree, with an impressive girth of 4.3 metres, has stood the test of time through decades of Dutch elm disease.

Before the fungus, Ophiostoma novo-ulmi, arrived in the Scottish Borders in the 1980s, there would have been wych elms in abundance in the valley of the Jed Water – the river that flows past the town. Today almost all the big elms are gone, killed by a fungal disease accidentally introduced to Britain on infected timber in the late 1960s and spread by an otherwise harmless bark beetle.

Now an innovative and surprisingly simple community initiative is joining forces with cutting-edge science to shed new light on one of our most notorious plant pathogens. As part of this, a Darwin Tree of Life team led by the Royal Botanic Garden Edinburgh (RBGE) will be taking tissue samples from the specimen at Jedburgh, from which we will sequence the entire genome of the wych elm (Ulmus glabra) in the hope of unlocking its genetic secrets.

The tree, which I call the Jedburgh Giant, stands beside the bandstand opposite the abbey, and from the right angle frames a picture postcard view of the 12th century building that is normally the focus of people’s interest.

But the Jedburgh Giant deserves our attention too. It, and other survivors, could hold the key to the recovery of the native elm in the Scottish Borders. We are all too familiar with pandemics now, but Dutch elm disease was a disaster for the elms of Europe. In Britain tens of millions of elms died and the disease continues to reach untouched elm populations in northern and western Scotland, possibly assisted by climate warming that enables elm bark beetles to colonise regions that might have been too cold in the past.

What is giving us hope for the future is that survivors, like the Jedburgh tree, do exist. They are thin on the ground and will take some finding, but they are majestic reminders of a lost landscape. The survivors may fight off infection or they may not attract the beetle in the first place. Either way, they are steadfastly surviving, unharmed by a disease that is all around them.

RBGE, working with the Borders Forest Trust, is asking the public to report old wych elms in the Scottish Borders. This pilot study will help us get a handle on what sort of number of survivors there actually are. Trees that exceed 2 metres  in girth — or put more simply, where an average person cannot link their hands when wrapped around the elm in a hug — would have been large enough to have been infected when the main wave of infection occurred in the 1980s. Elms below 20 years old are generally ignored by the beetles.

Sometimes elms survive by sheer remoteness from other trees as the beetles can only travel so far under normal circumstances. This means that the trees of greatest interest are both big and in areas where there is plenty of evidence of past disease.

Standing dead elms can persist for years, but another good sign of past disease is lots of young elms. These youngsters have often grown from the seeds of long dead elms and typically get knocked back by cycles of infection as they become big enough to attract the attention of the disease-harbouring beetles. The valley where the Jedburgh Giant grows is full of young elms, indicating that the old tree is a true survivor.

In the future it may be possible to bring together collections of surviving elms that have been grown from cuttings to preserve their unique genetic qualities. Such collections, if they contain sufficient genetic variation, could represent viable populations for future recolonization of suitable habitat. This is a long-term vision for the recovery of wych elm based on working with the natural resilience that appears to exist, albeit very rarely.

A major milestone on the way to understanding why so few elms survive will be pinpointing genetic variants that are linked to resilience. That is where the Darwin Tree of Life project comes in. By aiming to generate the first chromosomal-level, long-read full genome sequence for wych elm, the project marks a new chapter in understanding the genetic basis of disease resilience.

My colleague Dr Aline Finger, a conservation geneticist at RBGE, explains how critical these scientific advances could prove: “This is an exciting period for the application of genetic methods in plant science. Advances in recent years have started to transform our understanding of our flora and are opening-up new potential for the understanding of our environment and its resilience to disease.

“This seemingly small project in the Scottish Borders could one day be seen as playing a crucial role in providing answers to deep-rooted questions. At a time when 40% of all known plants are endangered in their natural habitats, advancements in knowledge cannot come quickly enough.”

If you would like to get involved in the Wych Elm Hunt in the Scottish Borders, visit  the Borders Forest Trust website for more information.

A conference on the plight of the elm and efforts to save it will also be taking place at Royal Botanic Gardens Kew on June 28th. See here for more details.

This article was adapted from the original, first published on the Botanics Stories section of the Royal Botanic Garden Edinburgh website.