Carolyn Riddell

Projects

Project Lead: Carolyn Riddell
The oomycete Phytophthora ramorum has caused substantial losses of Scottish forests in recent years due to widespread mortality of European larch trees (Larix decidua). Since 2009, legislation and policies have been implemented to control P. ramorum outbreaks on larch including the use of a 250 m larch ‘fire-break’, although it is unclear whether this distance is optimal for disease control. A project funded by Scottish Forestry is using a P. ramorum-specific qPCR assay to compare several spore trapping techniques for quantifying wind- and rain-borne inoculum and to better estimate inoculum dispersal distance. This project adds value to that of the Scottish Forestry-commissioned work, through evaluation of metabarcoding as an alternative method to both monitor P. ramorum inoculum dispersal and detect a broader range of aerially dispersed Phytophthora species. A second objective is to determine the lineage composition of P. ramorum inoculum throughout the observed peak sporulation period.

Impact: Timely management and prioritisation of policy to manage P. ramorum and facilitate early forecasting of other Phytophthora outbreaks.
Project Lead: April Armstrong
The oomycete Phytophthora ramorum has caused substantial losses of Scottish forests in recent years due to widespread mortality of European larch trees (Larix decidua). Infected trees are subject to statutory felling notices in an effort to reduce sporulation potential. Nevertheless, there are concerns about the multiple pathways by which spores might be transferred to new sites. There have been assessments of soil moved by mountain biking and walking/running resulting in evidence to support the Forestry Commission’s Keep-it-Clean campaign. This study will assess soil/plant material collected from commercial harvesting equipment (tyres, treads, mud guards etc.). PHC support will enable a wider range of diagnostic tests to be carried out, testing the robustness of the methods and examining the potential for multiple Phytophthora species to be transferred.

Impact: Add to the evidence base underpinning public and sector-facing biosecurity campaigns and improve disease management and restrict spread of the disease.

Publications

Forestry, Environment | Final Report and Policy Document

Assessing spread of Phytophthoras in Scottish forests by recreational and harvesting activities using comparative qPCR and metabarcoding techniques

February 2024

Pathogens from the genus Phytophthora pose some of the greatest threats to tree health and are likely to become increasingly prevalent in the UK as the climate becomes warmer and wetter. This project added new data based on a DNA metabarcoding approach to determine the Phytophthora species diversity in soil samples and sampled material from timber harvesting operations alongside those of recreational activities.

Forestry, Horticulture, Environment | Final Report and Policy Document

Metabarcoding analysis of Phytophthora diversity in spore traps and implications for disease forecasting in the P. ramorum management zone

May 2021

Surveillance and monitoring of airborne pathogens is a key tool in the management of healthy forests and controlling disease outbreaks. A Scottish Forestry-funded project was carried out in autumn 2019 to validate different spore-trapping techniques for monitoring airborne P. ramorum inoculum using a species-specific qPCR assay. This project aimed to add further value to the Scottish Forestry project by investigating the suitability of DNA metabarcoding for screening spore trap samples for P. ramorum and other Phytophthora species, seeking early data for aerially dispersed Phytophthora species that may become problematic in UK forests. The study highlighted the value of both monitoring P. ramorum dispersal and detecting other Phytophthora species, to predict and understand changes in disease severity in UK tree host species. Recommendations included that the use of both rain and wind-borne inoculum capture methods might be advantageous due to the variety of weather conditions under which inoculum can disperse.  Lineage testing in Southwest Scotland should be carried out to look at the prevalence of lineage EU1 in the EU2 area and to monitor for presence of North American lineages. Development of a new DNA barcode more specific to Phytophthora would be beneficial.