Retaining the Ashes: The potential for ash populations to be restored following the dieback epidemic

Lead Research Organisation: National Institute of Agricultural Botany
Department Name: Centre for Research

Abstract

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Technical Summary

Ash dieback, caused by the invasive fungus Hymenoscyphus fraxineus (Hf), has been a destructive disease of European ash (Fraxinus excelsior) since 1992 and was first seen in the UK in 2012. While most trees are very susceptible to this alien pathogen, a small minority are less diseased. As ash in Europe was not previously exposed to Hf, this project aims to understand the evolutionary origin of this polymorphism in terms of the forces of natural selection which act on dieback-susceptibility.

We have assembled 328 diverse ash lines from the UK, including many which have low dieback-susceptibility even at heavily affected sites. In Objective 1, we will estimate the contributions of resistance and disease escape to low susceptibility in this collection in replicated field trials exposed to natural infection. We will use controlled inoculation in lab and greenhouse experiments to investigate components of resistance and assess the divergence of resistance in the UK from that in continental Europe.

In a limited sample of trees from Denmark, dieback-susceptibility was correlated with levels of iridoid glycosides in uninfected leaves. In Objective 2, we will combine untargeted metabolite analysis by LC-QToF-MS with transcriptome analysis to survey a very wide range of secondary metabolites (SM), both constitutive and induced on infection, and identify SM and biosynthetic pathways that discriminate responses of resistant and susceptible ash to Hf. We will then test the association between SM and responses to Hf across our panel of ash lines.

Diverse SM, including iridoid glycosides, reduce attack by invertebrate herbivores by acting as repellants, anti-feedants or toxins. In Objective 3, we will test the hypothesis that certain SM mediate a trade-off between responses of ash to dieback and to certain insects, by testing if dieback-resistance and levels of key SM in ash clones are correlated, positively or negatively, with insect feeding, growth and reproduction.

Planned Impact

Ash dieback has caused severe damage to European ash (Fraxinus excelsior) since it was first observed in north-eastern Europe in 1992. It was first seen in the UK in 2012 but may have been present here since c.2000. Although the fungus kills juvenile shoots quickly, disease progress in mature trees is slow but relentless, causing death in 5-10 years. In the most severely affected counties of the UK, almost all trees are infected and some ash woods have been devastated. It is striking, however, that a minority of ash trees are much less diseased than others of the same size and age nearby.

Ash is a keystone species in the natural environment which supports diverse wildlife, a source of high-quality timber for furniture, tools and sporting goods and an important tree for landscaping and shade in urban and rural settings including residential areas, car parks and industrial estates. Perhaps the most significant benefit of ash is for ecosystem services, including such as flood prevention by preventing run-off of rainwater from fields, soil erosion and collapse of river and canal banks.

We have assembled a panel of 328 ash genotypes, known as JENNIFER, for use in this project and as a resource for future research. An important impact of this project is that JENNIFER contains a substantial number of lines with strong partial resistance to dieback. Seed from trees such as these has the potential to re-establish ash for all the purposes mentioned above, although further selection will be needed to identify plants with good form for timber production. A previous project discovered genetic markers for resistance among trees from Denmark but they have limited power to predict resistance in ash from the UK. Moreover, reliance on a few markers should be avoided in plant breeding, to minimise the risk of pleiotropy or linkage drag with undesirable traits. Further understanding of the pathology, diversity and ecology of ash dieback in the UK is therefore required.

In a small sample of the Danish study population, certain secondary metabolites (SM), assigned as iridoid glycosides (IG), were associated with susceptibility to dieback. IG are well-known as compounds which deter insect herbivory in diverse plants but it is not yet known why low IG levels are associated with resistance to dieback. It is thus possible that if selection for dieback-resistance were to reduce levels of IG, susceptibility to herbivores such as insects could be enhanced, so replacing one destructive agent by another and thwarting attempts to restore ash populations. An insect of special concern is another invasive alien species, the emerald ash borer, which has been extremely destructive in the USA, Canada and Russia. Fraxinus species contain many diverse SM, however, so it may be possible to select for (or against) different metabolites which confer resistance (or susceptibility) to dieback and to herbivores, or even for metabolites which have positive effects on both types of bio-antagonist. Exciting advances in technology for identifying low levels of metabolites mean it will soon be possible to select F.excelsior breeding stock with a high probability of good resistance to dieback and to herbivores, based on sensing of multiple odours.

The project will also contribute essential information for informed selection and replanting of ash with lower susceptibility to dieback, for the benefit of public bodies, charities and forestry companies concerned with tree-planting. It will reveal the diversity of dieback-resistance in ash from the UK and indicate the risk of trade-offs between dieback-resistance and deterrence of herbivores mediated by secondary metabolites. In particular, it will help greatly to predict the likely damage by emerald ash borer, should that highly destructive beetle ever become established in the UK. It will also identify traits which can be selected in order to promote disease escape.

Publications

10 25 50
 
Description We developed a high throughput method for producing and inoculating ascospores of the ash dieback pathogen (H. fraxineus) for testing leaf susceptibility.
Results so far suggest that although most of the ash accessions seem to be very susceptible, there are several accessions from across UK with moderate to high resistance.
Exploitation Route The technique will speed up future testing.
Identification of accessions with hist resistance or susceptibility to the ash dieback pathogen will enable us to focus our metabolomics work on these accessions.
Sectors Agriculture, Food and Drink,Environment

 
Description 'Tree Cutting Ps and Qs: propagation quality and production quantity
Amount £495,000 (GBP)
Organisation Department For Environment, Food And Rural Affairs (DEFRA) 
Sector Public
Country United Kingdom
Start 07/2022 
End 03/2025
 
Description Two undergraduate projects on Ash dieback pathogen biology 
Organisation University of Kent
Department School of Biosciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Dr Mat Papp-Ruppar provided overall supervision to the two undergraduates working at NIAB EMR.
Collaborator Contribution Dr. Ian Brown of the University of Kent provided his expert input on microscopic techniques.
Impact (1) Georgina Hurle investigated the spread of ash dieback in the ash leaves of susceptible and resistant UK ash accession with quantitative PCR. (2) Oliver dean investigated the spread of ash dieback in the ash leaves of susceptible and resistant UK ash accession with fluorescent microscopy. Both projects were very successful and have shed new light into disease progression. The data generated contribute to evidence for a new proposal.
Start Year 2018
 
Description Discussion with Government (Defra) representative about the project and its impact 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact We have organised several project consortium online meetings and invited DEFRA representative to join the meeting to disseminate the project outputs, get their view on the project progress and potential outcomes that could influence either legislation or future research on ash dieback
Year(s) Of Engagement Activity 2020
 
Description Oral presnetation on trade offs between herbivory and ADB resistance at a Defra-organised workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact We presented the results on the trade offs between herbivory and ADB resistance have been presented in a talk on Defra Resilient Ash Research Workshop 6th Sept 2022.
Year(s) Of Engagement Activity 2022
 
Description Participated BBC South East Programme 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact NIAB EMR's work on Ash Die-back was featured on BBC 1's South East Today programme last night (01/10/2019).
Year(s) Of Engagement Activity 2019
 
Description Participated a BBC Kent programme on ash dieback 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Dr. Mat Papp-Rupar joined in with a feature on Ash Die-back on BBC Radio Kent last Friday 29th of Nov.

Kent County Council is expecting to be spending millions of pounds on clearing infected Ash trees in public access woodlands and along highways/footpaths.
Year(s) Of Engagement Activity 2019
 
Description Poster and 5 min video at the Treescapes 2021 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Presented a poster as well as 5 min video describign hte project research outcomes .
Year(s) Of Engagement Activity 2021
URL https://rfs.org.uk/events/treescapes-2021/