PHYTO-THREATS: Addressing Threats to UK Forests and Woodlands from Phytophthora; Identifying Risks of Spread in Trade and Methods for Mitigation

Abstract

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.

Perceptions of Biosecurity-Based Accreditation in the Plant Trade: A UK Example

“…In the UK, relatively recent examples include ash dieback caused by the fungal pathogen Hymenoscyphus fraxineus and Phytophthora ramorum, with the spread of Phytophthora pathogens in traded plants and accumulating in plant nurseries a particular problem due to their extensive host ranges and ability to persist in soil and water [5][6][7]. Indeed, a recent study investigating Phytophthora diversity in UK plant nurseries found 63 different Phytophthora species including quarantine regulated pathogens and species not previously recorded in the UK, highlighting the need for improved biosecurity across the plant trade [8]. Early detection of pests and diseases is notoriously difficult [9] and relies on extensive surveillance and monitoring systems, often resourced by government inspection and related research.…”

An open-access T-BAS phylogeny for emerging Phytophthora species

“…Additionally, Phytophthora species have been clustered into two invasiveness groups based on host range as either generalists or specialists [ 8 ]. The categorization of each taxon into broad or specific host range could provide useful information to determine the potential invasiveness of a given species and be of use to regulatory agencies attempting to conduct risk analysis [ 8 , 10 ].…”

“…ramorum , responsible for the disease known as sudden oak death and P . cinnamomi , a generalist species with a wide host range [ 7 – 10 ]. In western Africa, P .…”

THAPBI PICT - a fast, cautious, and accurate metabarcoding analysis pipeline

“…This method is revolutionising areas of research including wildlife conservation, ecological processes and microbiology, by highly-sensitive detection of biodiversity across many taxa simultaneously (Arulandhu et al, 2017). Metabarcoding enables early detection of invasive threats to plant and human health in support of biosecurity (Batovska et al, 2021;Green et al, 2021), and is applicable to many complex and intractable systems, such as soil (Ahmed et al, 2019), in which standard methods of microbial isolation and characterisation are impractical or costly.…”

“…We describe THAPBI PICT v0.14.1 (intended to be increased to v1.0.0 for publication of this article), a metabarcoding tool developed as part of the UKRI-funded Tree Health and Plant Biosecurity Initiative (THAPBI) Phyto-Threats project, which focused on identifying Phytophthora species in commercial forestry and horticultural plant nurseries (Green et al, 2021). Phytophthora (from Greek meaning plant-destroyer) is an economically important genus of oomycete plant pathogens that causes severe losses and damage to plants in agricultural, forest and natural ecosystems.…”