Scientific Opinion on the Pest Risk Analysis onPhytophthora ramorumprepared by the FP6 project RAPRA

Pest categorisation of Guignardia laricina

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Guignardia laricina, a well‐defined and distinguishable fungal species of the family Phyllostictaceae. The pathogen is regulated in Council Directive 2000/29/EC (Annex IAI) as a harmful organism whose introduction into the EU is banned. G. laricina is native to East Asia and causes a shoot blight disease of Larix spp. Major hosts of G. laricina are European larch (Larix decidua) and two North American larch species (Larix laricina (tamarack) and Larix occidentalis (Western larch)). Larix kaempferi (Japanese larch) is reported as susceptible. The only other host in nature is Douglas fir (Pseudotsuga menziesii), which is reported as an incidental host, but various other conifers have been reported as susceptible following artificial inoculation, including Picea abies. The fungus is not known to occur in the EU but could enter via plants for planting (including artificially dwarfed plants) and cut branches of Larix spp. It could establish in the EU, as hosts are present and climatic conditions are favourable. The pathogen would be able to spread following establishment by natural dissemination of ascospores and pycnospores and by human movement of infected plants for planting. Should the pathogen be introduced in the EU, impacts can be expected in larch forests, plantations and nurseries, leading to reduced tree growth and ecosystem service provision. The key uncertainties concern the current distribution and level of impacts in the native range of the pathogen. The criteria assessed by the Panel for consideration as a potential quarantine pest are met. As the pest is not present in the EU, not all criteria for consideration as a regulated non‐quarantine pest are met.

Pest categorisation of Mycodiella laricis-leptolepidis

Following a request from the European Commission, the EFSA Panel on Plant Health (PLH) performed a pest categorisation of Mycodiella laricis‐leptolepidis, a well‐defined and distinguishable fungal species of the family Mycosphaerellaceae. The former species name Mycosphaerella laricis‐leptolepis is used in the Council Directive 2000/29/EC. The pathogen is regulated in Annex IAI as a harmful organism whose introduction into the EU is banned. M. laricis‐leptolepidis is native to East Asia and causes a disease known as needle cast of Japanese larch (Larix kaempferi = Larix leptolepis) and Kurile larch (Larix gmelinii). European larch (Larix decidua) was found to be susceptible to the disease as introduced tree in Japan. The fungus could enter the EU via plants for planting and cut branches of Larix spp. It could establish in the EU, as hosts are present and climatic conditions are favourable. The pathogen would be able to spread following establishment by human movement of infected plants for planting and by dissemination of ascospores. Should the pathogen be introduced in the EU, impacts can be expected due to needle loss in larch forests and plantations, thus leading to reduced tree growth and ecosystem service provision. The use of resistant/tolerant varieties can reduce the impacts. The key uncertainties are the knowledge gaps concerning (i) the potential range of spread through ascospores and (ii) the level of impacts in the native range of the pathogen. The criteria assessed by the Panel for consideration as a potential quarantine pest are met. For regulated non‐quarantine pests, the criterion on the pest presence in the EU is not met.

Sudden oak death: interactions of the exotic oomycete Phytophthora ramorum with naïve North American hosts

Ten years after a threatening and previously unknown disease of oaks and tanoaks appeared in coastal California, a significant amount of progress has been made toward the understanding of its causal agent Phytophthora ramorum and of the novel pathosystems associated with this exotic organism. However, a complete understanding of the ecology and epidemiology of this species still eludes us. In part, our inability to fully understand this organism is due to its phylogenetic, phylogeographic, phenotypic, and epidemiological complexities, all reviewed in this paper. Most lines of evidence suggest that the high degree of disease severity reported in California is not simply due to a generalized lack of resistance or tolerance in naïve hosts but also to an innate ability of the pathogen to survive in unfavorable climatic conditions and to reproduce rapidly when conditions become once again favorable.