Summary
Phytophthora species, most notably P. ramorum and P. austrocedri, are posing serious threats to forest and woodland ecosystems in Britain. Since 2021, cryptic outbreaks of an apparently newly invasive pathogen, P. pluvialis, have also been increasingly detected on western hemlock and Douglas fir in commercial forestry plantations. This project uses Illumina eDNA metabarcode sequencing to examine the diversity of Phytophthoras in soil and water at a range of forest, woodland and public garden sites across Britain to facilitate early pathogen detection and to better predict risk.
Research Objectives
The objectives of this research project are to:
- examine Phytophthora diversity in soil, stream water and rainwater at forest, woodland and public garden sites in Scotland.
- assess the feasibility of using Illumina eDNA metabarcoding for longer-term monitoring of Phytophthora pathogens in the wider environment.
- provide evidence to inform biosecurity and remediation policy aimed at limiting the introduction, spread and impact of Phytophthora diseases.
Latest Update
From 2014-2019, Illumina sequencing was used to analyse Phytophthora species diversity in soil samples collected from fourteen public garden/amenity woodland sites in Scotland. Sites chosen either had previous Phytophthora outbreaks or were regarded as high risk due to importation of large quantities of plants/soil in recent years.
A high diversity of Phytophthoras was detected at all sites, corresponding overall to 23 Phytophthora species as well as twelve as-yet undescribed oomycete sequences. Phytophthora pseudosyringae and P. austrocedri, both of which cause serious damage to trees, were the two most abundant Phytophthora species detected and were present at nearly all of the sites.
In a second wide-ranging project, metabarcoding and baiting methodologies aimed at detecting Phytophthora were applied to soil, stream water, and rainwater samples collected over a full calendar year (2022-2023) from seventeen forest sites across Britain, many of which were P. pluvialis outbreak sites. Thirty-five Phytophthora species were detected across all sites, substrates, and detection methods, with most detections occurring in stream water by metabarcoding. The three most frequently detected species (in order of abundance) were P. pluvialis, P. gonapodyides and P. ramorum. The regulated pathogens P. austrocedri, P. kernoviae and P. lateralis were also detected. A new species record for the UK, P. ornamentata, was detected in soil and stream water at two sites, one in Scotland and one in Wales.
Phytophthora pluvialis was most frequently detected in March, with rainfall trap metabarcoding data suggesting peak aerial dissemination in late winter/early spring. The pathogen was also detected consistently in soil by metabarcoding, indicating high potential for vectoring by humans and animals.
