Invasive Phytophthora pathogens are causing significant economic damage to agricultural, horticultural and forestry crops worldwide, as well as ecological damage to native plant species in wider environments. Traded plants are a well-documented pathway for Phytophthora pathogens, facilitating their spread both nationally and internationally. The goal of the ID-PHYT project was to develop a co-ordinated strategy for the early detection of Phytophthora pathogens in plant nurseries and traded plants for planting across EU and third countries to inform best practice.

Protocols for nursery sampling and detection of Phytophthora using an eDNA metabarcoding method plus a traditional baiting method were successfully shared and validated across project teams in six partner countries (FR, GB, GR, IE, IT, USA) with RU conducting baiting analyses only. All nine partner countries (including AT and NZ), contributed to the development of a stakeholder map and a subsequent online stakeholder survey, translated from English into eight different languages, which sought to gain insight into sector perceptions on biosecurity and best practice.

The final nursery sampling dataset consisted of 1011 pooled samples collected from thirteen plant nurseries across six countries. This included 647 root samples and 364 water samples with 627 samples analysed by baiting and 384 samples analysed by metabarcoding. Sample metadata and a set of key nursery management data were also collected for downstream analyses conducted using hierarchical Bayesian mixed models. A high diversity of Phytophthora (65 known Phytophthora species including quarantine-regulated species and some first country records) was detected across the 13 sampled nurseries. Phytophthora was found in the irrigation water at several of the nurseries highlighting water management as a key priority area for improvement. High risk hosts with consistent Phytophthora associations included Fagus, Ligustrum, Thuja, Lavandula, Quercus and Choisya spp. Other nursery risk factors which increased the likelihood of Phytophthora-positive samples included reliance on greater than 50% imported plant stock and growing a high diversity of plant genera. Analyses were also able to identify Phytophthora species’ sensitivities to substrate (water versus root), nursery latitude and detection method (baiting versus metabarcoding) which assists understanding of their lifestyle and habit and sensitivity to detection method, facilitating further prediction of risk.

The stakeholder survey elicited 97 responses from individuals in a range of roles associated with the plant trade across eight countries. Respondents listed over 100 different pests and pathogens of concern, with Phytophthora species and Xylella fastidiosa most frequently cited. Boot washing, quarantining plants and training staff in plant health were seen as important biosecurity management. Communicating how biosecurity practices can and do reduce the risk and impact of plant pests and pathogens increased uptake of important phytosanitary measures by the sector. For example, one of the UK nurseries, upon realising that their open irrigation reservoir held eight different Phytophthora species, subsequently invested in sinking a borehole to access clean groundwater for irrigation.

One major outcome of the project was the co-design of a concise, best-practice guidance document based on scientific evidence translated from English into partner country languages and disseminated through each country’s trade association channels. The best practice guidance highlights the key plant biosecurity considerations for growers and focuses on the need to understand high risk hosts and pathways, improved water management and plant growing conditions, awareness of symptoms and the importance of having staff trained in plant health knowledge.