Our Organisation Search
Quick Links
Toggle: Topics

ExAl Project

Phytophthora alni causes a serious dieback disease of Common Alder (Alnus glutinosa) and threatens its survival in Irish landscapes.
Beneficial microbiota can promote plant health directly as bio-stimulants and/or indirectly as biocontrol agents against pests and pathogens.


Common alder is a traditional Irish tree species that has a prodigious ecological importance, particularly within wetlands as they tend to promote diversity due to their soil nutrient enrichment and colonisation abilities. Alder tends to be frequently found alongside rivers providing stability to the banks, preventing soil erosion, as well as providing a valuable habitat and food sources to a diverse wildlife.

Over the last two decades, alder has become threatened by the pathogen Phytophthora alni, which tends to infect alder through its roots. This pathogen has been identified throughout Europe and has recently been detected in Northern Ireland, indicating that this disease has infiltrated Ireland and has potentially spread throughout Ireland, infecting many more alder populations. Many symptoms of this disease have been sighted within Ireland including crown thinning, bleeding trunk cankers, and/or death of alder trees.

Since alder is such an important resource, the decline of this species can potentially result in substantial economic and ecological loss. Microbial communities associated with trees are relatively diverse and can influence the growth and tolerance of trees to abiotic factors. In addition, the microbial communities present can be influenced by the type of tree host and the environmental conditions therein. Previous studies have shown that the presence of certain microbes have the ability to provide a beneficial role by positively contributing to the overall growth and development of trees.

Aim of the project

The primary aim of this project is to explore the microbiome of alder trees and its associated rhizosphere to identify potential bio-agents and improve disease tolerance against the root rot pathogen Phytophthora alni. This is a collaborative project with Dr Kieran Germaine, SETU Carlow and Dr Dheeraj Rathore, Teagasc.

The main objectives include:

  1. Identify beneficial microbes
  2. Culture the cultivable beneficial microbes
  3. Perform antagonistic studies of these cultivable microbes against the pathogen

Firstly, initial analysis of the alder microbiome will involve the identification and categorisation of susceptible and tolerant genotypes. Samples will be collected from the Teagasc alder gene bank in Oak Park which contains a collection of alder genotypes.

Analysis will include a leaf extraction assay technique to identify the degree of tolerance between each genotype tested, followed by using molecular techniques to identify several beneficial microbes with bio-agent potential. Once identified, a literature review will be completed to determine potential benefits and bio-agent characteristics through research studies that have been conducted worldwide.

An element of this objective is to study the core microbiome of alder trees throughout Ireland, which will include analysing several compartments of alder (leaf, bark, root, and rhizosphere) at one particular point of the year to determine if microbial communities differ at various sections of the tree. By focusing on the core and stable microbiome, the likelihood of identifying stable and potential bio-agents that can be sustained by the tree over extended timeframes will increase.

Secondly, the next objective is to try and isolate and culture these beneficial microbes identified in objective 1. Less than 1% of forestry microbes are cultivable in a laboratory so not all previously identified microbes can be cultured. Any successfully cultured microbes will be tested and verified using molecular techniques. In addition, by researching these cultured microbes through published literature, their growth-promoting / beneficial role and pathogenic inhibition capabilities can be discovered.

For the final objective, any identified and cultured beneficial microbes from the second objective will be used for antagonistic studies against the disease using a series of in vitro and in planta methods. This will allow a rapid selection of microbes with potential bio-agent / bio-stimulant traits which can potentially improve and enhance tolerance of susceptible alder against this pathogen.

Pot plant trials may also be established to define the role of the individual microbes and microbial assemblages, which will allow the identification of protective / tree health-promoting microbiomes followed by experimental infection of alder trees with Phytophthora alni. The best performing microbes / microbial assemblages can be selected for future field trials and long-term future assessments.

Expected outcome

The goal of this research is to provide comprehensive microbiome analysis of tolerant and susceptible alder trees to identify cultivable beneficial microbes that can be used as potential bio-agents / bio-stimulants to increase species tolerance against the pathogen Phytophthora alni. The ExAl Project will strengthen ongoing breeding efforts to develop improved, disease-tolerant alder genotypes.

Further information


The ExAl Project is funded by the Irish Research Council (IRC) Government of Ireland Scholarship Programme.