Bringing back the ashes – applying metabolomic approaches to save UK ash trees

Ash dieback (ADB), caused by the invasive fungus Hymenoscyphus fraxineus (Hf), has been a destructive disease of European ash (Fraxinus excelsior). First discovered in Poland in 1992 it arrived in the UK in 2012. This epidemic has serious implications for the UK landscape and society as a whole. More than 100 million UK ash trees are threatened by this devastating fungal pathogen that has already killed millions of trees across Europe and DEFRA estimate the cost of ADB to exceed £15 billion.

There is extensive genetic heterogeneity between European ash, and there is to date no evidence for classical plant gene-for-gene resistance. As infective pathogen spores exist for months we hypothesised that ash trees had pre-formed, rather than inducible, chemical defences to ADB.

We recently published our initial untargeted metabolite profiling of resistant and susceptible Danish ash trees (because the disease had been there longer, and hence they had identified resistant trees) and identified a number of metabolites that discriminated between the two classes. Among those discriminant metabolites, we found a class of secondary metabolites which were more abundant in ADB susceptible trees, than resistant trees (see Sollars et al. 2017, Nature; Sambles et al. Scientific Data 2017) known as iridoid glycosides.

This has potential major repercussions; Iridoid glycosides are insect feeding deterrents and in the USA an insect called the Emerald Ash Borer (EAB) is killing 10’s of millions of ash trees. So, if we breed ADB resistant ash (which will take decades!), will they all succumb to EAB (it is already in Russia) when it eventually arrives in the UK)?

This project will, (i) characterise the diversity of iridiods in UK and European ash trees, (ii) contrast to those in ash species which are unaffected by either EAB and ADB and (iii) develop both targeted and untargeted pipelines for looking at identifying further potential ash metabolites that as associated with resistance to ADB.
Techniques that will be undertaken during the project:
- Untargeted metabolomics – data acquisition, processing and interpretation.
- Computer pipeline development for untargeted methods.
- Identification of discriminate features and developing targeted profiling assays for resistant ash trees.
- Analytical chemistry and NMR techniques.
- Microbiology – culturing of fungi