Abstract
Phytophthora ramorum and Phytophthora kernoviae are exotic plant pathogens that have only recently been described in the last decade. P. ramorum was first confirmed in Great Britain in 2002, whilst P. kernoviae was first discovered here in 2003. Both species represent a threat to ornamental and wild shrubs and trees. Ornamental plants in heritage gardens can be seriously affected, as can susceptible trees in woodlands where leaf hosts (principally Rhododendron ponticum) occur and drive epidemics; heathland species, especially Vaccinium species are also considered at high risk. P. ramorum is present in various parts of Europe and is also reported as an introduced exotic plant pathogen in the USA; it is currently subject to EC emergency phytosanitary measures, which are under review. Following an EU-wide Pest Risk Analysis (PRA) the EC Standing Committee for Plant Health (SCPH) have provisionally agreed that P. ramorum should become listed as a harmful organism within the EC Plant Health Directive (2000/29/EC) with phytosanitary measures yet to be defined and agreed. P. kernoviae is recorded in Great Britain and in Eire, as well as in New Zealand. A UK PRA for P. kernoviae was also reviewed by the EC SCPH and there has been provisional agreement that P. kernoviae should be subject to emergency EU phytosanitary measures, again yet to be defined and agreed. In April 2009, Defra launched a five-year campaign to manage the risks and diseases caused by these quarantine pathogens in woodlands, gardens, heathland and in the hardy ornamental plant trade in England and Wales. Part of this campaign is to conduct a programme of research to support the overall disease management activities which aim to reduce pathogen inoculum to epidemiologically insignificant levels. A number of projects have been funded by Defra which have investigated the epidemiology of outbreaks caused by P. ramorum and P. kernoviae in England (PHO194, PHO195, PHO414, PHO308). These projects have established methodologies for the investigation of key aspects of the epidemiology and developed new quantitative diagnostic approaches for investigating persistence and dispersal. Studies to date have provided valuable epidemiological data, which have contributed to the development of pest risk analyses and pest eradication and containment strategies. However, there are still key gaps in our knowledge, particularly as there is relatively limited information available about the epidemiology of P. kernoviae compared to P. ramorum. The objective of this project is to study key aspects of the epidemiology of P. ramorum and P. kernoviae in order to evaluate current and potential future risk, thereby informing disease management actions and future policy for these two regulated pathogens. The research proposed here will support the key policy objective within the Research Workstream (as detailed in the ROAME A) to ensure that by the end of Year 3 (April 2012) the factors driving pathogen spread and disease development are better understood. The project will include a detailed comparative laboratory study to examine the effects of temperature, humidity (including leaf wetness) on sporulation, germination, infection and survival of P. kernoviae and P. ramorum and define the minimum, maximum and optimal conditions for growth of the pathogens. Experimental work at outbreaks sites will examine the potential for aerial dispersal by the two pathogens and investigate the influence of host species and environment on infection and dispersal. The results generated will be used to examine whether epidemiological data can be used to identify risk periods for dispersal and infection. Because the pathogens can infect and spread through a wide range of hosts, risk assessment demands good knowledge of host pattern and density. Part of the work will therefore investigate how these data can be obtained cost effectively. The epidemiology and host data collected will also be supplied to the Cambridge University/Rothamsted Research/Fera modelling teams to examine the relative risks posed by epidemics in rhododendron, heathland species and larch and for estimation of the potential impact of control strategies on further spread in support of strategy development within the Phytophthora Disease Management Programme. This monitoring work will link in with complementary research being carried out under funding from the Scottish Government into the risks posed by P. ramorum and P. kernoviae to similar ecosystems in Scotland. The results generated will be used by both research projects to further inform risk analyses for P. kernoviae and P. ramorum in Scotland and England & Wales. Project outputs will be relevant to independent stakeholders, landowners and garden end-users, facilitating disease management. Core outputs from the work will be regularly disseminated to policy makers, stakeholders in the most appropriate formats, including contributions to recommendations and practical guides for disease management and eradication action at outbreak sites of P. ramorum and P. kernoviae in the natural and semi-natural environment. Additional research specifically relating to P. ramorum on larch has been added into the project (from Autumn 2010 to March 2013).
United Kingdom