PHYTO-THREATS: addressing threats to uk forests and woodlands from phytophthora; identifying risks of spread in trade and methods for mitigation

Sarah Green*, David E. L. Cooke, Mike Dunn, Louise Barwell, Bethan Purse, Daniel S. Chapman, Gregory Valatin, Alexandra Schlenzig, Jane Barbrook, Tim Pettitt, Colin Price, Ana Pérez-Sierra, Debra Frederickson-Matika, Leighton Pritchard, Peter Thorpe, Peter J. A. Cock, Eva Randall, Beatrix Keillor, Mariella Marzano

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

16 Citations (Scopus)


The multidisciplinary ‘Phyto-threats’ project was initiated in 2016 to address the increasing risks to UK forest and woodland ecosystems from trade-disseminated Phytophthora. A major component of this project was to examine the risk of Phytophthora spread through nursery and trade practices. Close to 4000 water and root samples were collected from plant nurseries located across the UK over a three-year period. Approximately half of the samples tested positive for Phytophthora DNA using a metabarcoding approach with 63 Phytophthora species identified across nurseries, including quarantine-regulated pathogens and species not previously reported in the UK. Phytophthora diversity within nurseries was linked to high-risk management practices such as use of open rather than closed water sources. Analyses of global Phytophthora risks identified biological traits and trade pathways that explained global spread and host range, and which may be of value for horizon-scanning. Phytophthoras having a higher oospore wall index and faster growth rates had wider host ranges, whereas cold-tolerant species had broader geographic and latitudinal ranges. Annual workshops revealed how stakeholder and sector ‘appetite’ for nursery accreditation increased over three years, although an exploratory cost-benefit analysis indicated that the predicted benefits of introducing best practice expected by nurseries outweigh their costs only when a wider range of pests and diseases (for example, Xylella) is considered. However, scenario analyses demonstrated the significant potential carbon costs to society from the introduction and spread of a new tree-infecting Phytophthora. Thus, the overall net benefit to society from nurseries adopting best practice could be substantial.
Original languageEnglish
Article numbere1617
Number of pages22
Issue number12
Publication statusPublished - 23 Nov 2021


  • Phytophthora
  • Plant nursery
  • Risk models
  • Trait analyses
  • Stakeholder perspectives
  • Accreditation
  • Cost--benefit
  • Carbon costs


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