The researcher leading the work to revive Ireland’s ash population

The researcher leading the efforts to secure the future of ash trees in Ireland says he’s optimistic for the success of the project.

The work in breeding for tolerance to dieback disease in Ireland began in 2015, and Dr Dheeraj Rathore took up the challenge with Teagasc in 2021. Now he is heading up the new four year ‘Ash For Future’ project funded by the island’s two Departments of Agriculture. The project aims to select, propagate, and breed disease-tolerant ash genotypes to mitigate the damage caused by the invasive pathogen Hymenoscyphus fraxineus, which has been responsible for widespread ash dieback across Ireland.

“We are looking for Irish genotypes which have survived the dieback disease for the past 12 years,” Dr Rathore tells The Anglo-Celt, referring to the first notification of dieback in 2012 in Ireland.

“We also have two gene banks of European genetic material which have been collected from 15 different European countries and have been planted in two gene banks in Ireland, and we continuously assess them for any dieback signs - this also includes some of the Irish genotypes.”

Irish researchers and their European counterparts have come to the same grim conclusion: “There is no 100% resistance.”

Dr Rathore explains: “Resistance means you do not see any physical damage on the tree and tolerance means you do see some physical damage, but the tree can have varying levels of disease tolerance.

“This means a tree can be very susceptible and it will succumb to the disease. But a tree can be highly tolerant and it will show some sign of disease, but it will not die and it will continue to produce good quality timber, because the disease can be seen only on some twigs and branches, but not on the main trunk or cause economic loss. These are the trees we are focusing our work on at the moment.”

The Celt has heard it said a number of times in casual conversations that older ash trees are less susceptible to dieback.

“The research doesn’t show any relationship between the age of the tree and resistance or tolerance,” counters Dr Rathore. “What I can say is that the older trees will show mortality at a slower rate compared to young trees. It’s the nature of the disease.”

A tree’s ability to endure comes down to its genes.

“If the tree is susceptible genetically, which means it has a less number of genes which are involved in disease tolerance, they will die sooner than the trees which have higher level of tolerance, which means a higher number of genes - and will not die because of the disease. Those are the trees that will continue to survive along with the disease.”

Readers of a certain age will know ash isn’t the only tree to be devastated by disease in Ireland; our native wych elm was ravaged by Dutch Elm Disease in the last century.

Dr Rathore says that there was a blanket decision that wych elms posed a “health and safety risk” with the result “we lost a lot of trees”.

“I’m not saying that those would have definitely been tolerant, but there could have been a chance, and that’s what we see with the existing trees that are left in Cork and Louth and several other places that I have visited, that the trees have some sort of physiological barriers to the beetle and they have been surviving for these years.”

As such that is informing the decision to advise landowners who have a tree showing signs of good health and that does not pose a risk to leave standing.

He says “the main learning” from the work to bring back the elm was the impact of hybridisation.

“That is a scientific learning for us - that we can cross breed our European ash with Asiatic ash which is not susceptible to dieback and we can breed that way.”

Dr Rathore stresses that farmers and members of the public can play a “vital role” in supporting their work on conserving for ash. If you are aware of an ash tree with a healthy appearance, you can inform the researchers by reporting it. Simply search ‘Report a healthy ash tree Teagasc’ online and you will be brought to guidance on assessing the health of a tree and the correct point of contact. Likewise there is a similar system for reporting a healthy elm.

The ‘Ash For Future’ has a number of different components, including silviculture.

“Within the silviculture aspect, they are exploring the potential of multi-species trials, planting ash with other species. This approach might lead to the establishment of resilient multi-species forest systems instead of traditional monocultures. However, it is too early to draw definitive conclusions, as tree breeding is a long term process that requires extensive evaluations of the results to get robust conclusions.”

“I’m quite optimistic,” Dr Rathore said of the prospects for the Future of Ash.

“I drive around the country and I know that large numbers of trees are succumbing to the disease, and that is how it is going to be - that is how it is in the countries like Lithuania and other European countries where the disease came 12 to 15 years before coming to Ireland.

“But then up to five per cent of trees are showing higher level of tolerance and this is the population that is going to make up a stock of trees that we hope will be genetically diverse and that they will produce the next progeny so that they can be planted out to forests in the future.”

Dr Rathore says “preliminary results from ongoing research are quite positive” and he is hopeful the public will play their part.

“We clearly have varying level of disease tolerance, and we do have a number of trees in our collection, which is small in size, but highly tolerant trees, and that is why we are requesting the general public to report more Irish trees which are showing higher level of tolerance so we can expand this population size.”