Host genotype interacts with aerial spore communities and influences the needle mycobiome of Norway spruce.

The factors shaping the composition of the tree mycobiome are still under investigation. We tested the effects of host genotype, site, host phenotypic traits, and air fungal spore communities on the assembly of the fungi inhabiting Norway spruce needles. We used Norway spruce clones and spore traps within the collection sites and characterized both needle and air mycobiome communities by high-throughput sequencing of the ITS2 region. The composition of the needle mycobiome differed between Norway spruce clones, and clones with high genetic similarity had a more similar mycobiome. The needle mycobiome also varied across sites and was associated with the composition of the local air mycobiome and climate. Phenotypic traits such as diameter at breast height or crown health influenced the needle mycobiome to a lesser extent than host genotype and air mycobiome. Altogether, our results suggest that the needle mycobiome is mainly driven by the host genotype in combination with the composition of the local air spore communities. Our work highlights the role of host intraspecific variation in shaping the mycobiome of trees and provides new insights on the ecological processes structuring fungal communities inhabiting woody plants.

Vegetation type determines spore deposition within a forest-agricultural mosaic landscape.

Predicting fungal community assembly is partly limited by our understanding of the factors driving the composition of deposited spores. We studied the relative contribution of vegetation, geographical distance, seasonality and weather to fungal spore deposition across three vegetation types. Active and passive spore traps were established in agricultural fields, deciduous forests and coniferous forests across a geographic gradient of ∼600 km. Active traps captured the spore community suspended in air, reflecting the potential deposition, whereas passive traps reflected realized deposition. Fungal species were identified by metabarcoding of the ITS2 region. The composition of spore communities captured by passive traps differed more between vegetation types than across regions separated by >100 km, indicating that vegetation type was the strongest driver of composition of deposited spores. By contrast, vegetation contributed less to potential deposition, which followed a seasonal pattern. Within the same site, the spore communities captured by active traps differed from those captured by passive traps. Realized deposition tended to be dominated by spores of species related to vegetation. Temperature was negatively correlated with the fungal species richness of both potential and realized deposition. Our results indicate that vegetation may be able to maintain similar fungal communities across distances, and likely be the driving factor of fungal spore deposition at landscape level.

Invasive forest pathogens in Europe: Cross-country variation in public awareness but consistency in policy acceptability.

Political action can reduce introductions of diseases caused by invasive forest pathogens (IPs) and public support is important for effective prevention. The public's awareness of IP problems and the acceptability of policies aiming to combat these pathogens were surveyed in nine European countries (N = 3469). Although awareness of specific diseases (e.g., ash dieback) varied, problem awareness and policy acceptability were similar across countries. The public was positive towards policies for informational measures and stricter standards for plant production, but less positive towards restricting public access to protected areas. Multilevel models, including individual and country level variables, revealed that media exposure was positively associated with awareness of IP problems, and strengthened the link between problem awareness and policy acceptability. Results suggest that learning about IPs through the media and recognizing the associated problems increase policy acceptability. Overall, the study elaborates on the anthropogenic dimension of diseases caused by IPs.

Contrasting distribution patterns between aquatic and terrestrial Phytophthora species along a climatic gradient are linked to functional traits.

Diversity of microbial organisms is linked to global climatic gradients. The genus Phytophthora includes both aquatic and terrestrial plant pathogenic species that display a large variation of functional traits. The extent to which the physical environment (water or soil) modulates the interaction of microorganisms with climate is unknown. Here, we explored the main environmental drivers of diversity and functional trait composition of Phytophthora communities. Communities were obtained by a novel metabarcoding setup based on PacBio sequencing of river filtrates in 96 river sites along a geographical gradient. Species were classified as terrestrial or aquatic based on their phylogenetic clade. Overall, terrestrial and aquatic species showed contrasting patterns of diversity. For terrestrial species, precipitation was a stronger driver than temperature, and diversity and functional diversity decreased with decreasing temperature and precipitation. In cold and dry areas, the dominant species formed resistant structures and had a low optimum temperature. By contrast, for aquatic species, temperature and water chemistry were the strongest drivers, and diversity increased with decreasing temperature and precipitation. Within the same area, environmental filtering affected terrestrial species more strongly than aquatic species (20% versus 3% of the studied communities, respectively). Our results highlight the importance of functional traits and the physical environment in which microorganisms develop their life cycle when predicting their distribution under changing climatic conditions. Temperature and rainfall may be buffered differently by water and soil, and thus pose contrasting constrains to microbial assemblies.

Pest categorisation of Melampsora farlowii.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Melampsora farlowii, a well-defined and distinguishable fungus of the family Melampsoraceae. M. farlowii is the causal agent of a leaf and twig rust of hemlocks (Tsuga spp.) in eastern North America. The pathogen is regulated in Council Directive 2000/29/EC (Annex IAI) as a harmful organism whose introduction into the EU is banned. M. farlowii is not reported to be present in Europe and could enter the EU via host plants for planting and cut branches. Cones and fruits are listed as plant parts that can carry the pest in trade and transport, but are not regulated. The pathogen could establish in the EU, as climatic conditions are favourable and Tsuga spp. have been planted as ornamentals and in plantations in several EU countries. M. farlowii would be able to spread following establishment by human movement of host plants for planting and cut branches, as well as natural spread. Should the pathogen be introduced in the EU, impacts can be expected on Tsuga spp. plantations, ornamental trees and especially nurseries. Hemlock rust is considered a destructive rust attacking Tsuga spp., particularly Tsuga canadensis in nurseries. The main uncertainties concern whether the impact of the pathogen in plantations under European conditions could be different than observed in eastern North America, whether fruit/cones of Tsuga can be a pathway of entry, and the dissemination potential of the pathogen under European conditions. However, M. farlowii is found in North America in most of the natural distribution range of T. canadensis, suggesting little dispersal limitation of the pathogen. The criteria assessed by the Panel for consideration as a potential quarantine pest are met, whilst, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Cronartium harknessii, Cronartium kurilense and Cronartium sahoanum.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Cronartium harknessii, Cronartium kurilense and Cronartium sahoanum, which are well-defined and distinguishable tree fungal pathogens of the family Cronartiaceae. In 2018, these species were moved from the genus Endocronartium to the genus Cronartium. These pathogens are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) (as non-European Endocronartium spp.) as harmful organisms whose introduction into the EU is banned. These three fungi are autoecious rusts completing their life cycle on Pinus spp. C. harknessii is known as the western gall rust or pine-pine gall rust in North America (Canada, the USA and Mexico). C. kurilense and C. sahoanum are reported from Russia (North Kuril Islands) and Japan. The pathogens could enter the EU via host plants for planting and cut branches. The pathogens could establish in the EU, as climatic conditions are favourable and Pinus spp. are common. The pathogens would be able to spread following establishment by movement of host plants for planting and cut branches, as well as natural spread. Should these pathogens be introduced in the EU, impacts can be expected on pine forests, plantations, ornamental trees and nurseries. The pathogens cause formation of stem galls, which kill young trees and result in stem defect in older trees. The main knowledge gap concerns the limited available information on C. kurilense and C. sahoanum compared to C. harknessii. The criteria assessed by the Panel for consideration of C. harknessii, C. kurilense and C. sahoanum as potential quarantine pests are met, whilst, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Cronartium spp. (non-EU).

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Cronartium spp. (non-EU), a well-defined and distinguishable group of fungal pathogens of the family Cronartiaceae. There are at least 40 species described within the Cronartium genus, of which two are considered native to the EU (C. gentianeum and C. pini) and one has been introduced in the 19th century (C. ribicola) and is now widespread in the EU - these three species are thus not part of this pest categorisation. In addition, the non-EU C. harknessii, C. kurilense and C. sahoanum were already dealt with in a previous pest categorisation. All the non-EU Cronartium species are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) as harmful organisms whose introduction into the EU is banned. Cronartium spp. are biotrophic obligate plant pathogens. Many of the North American Cronartium species alternate between the aecial host Pinus spp. and telial hosts of various dicotyledonous plants. C. conigenum, C. orientale, C. quercuum and C. strobilinum have different Quercus spp. as their telial hosts. C. orientale and C. quercuum also infect Castanea spp. and Castanopsis spp. The pathogens could enter the EU via host plants for planting and cut flowers and branches. Non-EU Cronartium spp. could establish in the EU, as climatic conditions are favourable to many of them and Pinus and Quercus spp. are common. The pathogens would be able to spread following establishment by movement of host plants, as well as natural spread. Should non-EU Cronartium spp. be introduced in the EU, impacts can be expected on pine, oak and chestnut woodlands, plantations, ornamental trees and nurseries. The Cronartium species present in North America cause important tree diseases. Symptoms on Pinus spp. differ between Cronartium spp., but include galls, cankers, dieback of branches and stems, deformity, tree and cone death. The main knowledge gap concerns the limited available information on (sub)tropical Cronartium spp. The criteria assessed by the Panel for consideration of Cronartium spp. (non-EU) as potential quarantine pests are met, while, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Gymnosporangium spp. (non-EU).

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Gymnosporangium spp. (non-EU), a well-defined and distinguishable group of fungal plant pathogens of the family Pucciniaceae affecting woody species. Many different Gymnosporangium species are recognised, of which at least 14 species are considered not to be native in the European Union. All the non-EU Gymnosporangium species are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) as harmful organisms whose introduction into the EU is banned. Gymnosporangium spp. are biotrophic obligate plant pathogens. These rust fungi are heteroecious as they require Juniperus, Libocedrus, Callitropsis, Chamaecyparis or Cupressus (telial hosts) and rosaceous plants of subfamily Pomoideae (aecial hosts) to complete their life cycle. The pathogens could enter the EU via host plants for planting (including artificially dwarfed woody plants) and cut branches. They could establish in the EU, as climatic conditions are favourable and hosts are common. They would be able to spread following establishment by movement of host plants for planting and cut branches, as well as by natural dispersal. Should Gymnosporangium spp. (non-EU) be introduced in the EU, impacts can be expected in orchards, ornamental trees and nurseries. On telial hosts, these pathogens cause galls on stems, twigs and branches, and fusiform swellings on stems. Foliar infections on aecial hosts may lead to severe defoliations. The main knowledge gap concerns the limited available information on the biology, distribution range and impact of several non-EU Gymnosporangium spp. The criteria assessed by the Panel for consideration of Gymnosporangium spp. (non-EU) as potential quarantine pests are met, while, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Anisogramma anomala.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Anisogramma anomala, a well-defined and distinguishable fungal species of the family Valsaceae. The pathogen is regulated in Annex IIAI of Council Directive 2000/29/EC as a harmful organism whose introduction into the EU is banned on plants of Corylus L., intended for planting, other than seeds, originating in Canada and the USA. The fungus is native to eastern North America and causes eastern filbert blight on cultivated hazel, Corylus avellana, as well as on wild hazel (Corylus spp.). In the 1960s, the disease spread on infected plant material to Oregon, where it then threatened US hazelnut production in the Willamette Valley. The pest could enter the EU via plants for planting. Hosts and favourable climatic conditions are common in the EU, thus facilitating establishment. The pest would be able to spread following establishment through infected plants for planting and ascospore dispersal. A. anomala leads to canopy and yield loss and can cause death of Corylus trees. Should the pathogen be introduced into the EU, impacts can be expected not just on hazel as a crop and as an ornamental but also in coppices and woodlands, where Corylus species provide an important habitat. In Oregon, scouting for cankers, therapeutic pruning and copious fungicide applications are reported to be necessary (but costly measures) to continue hazelnut production in the presence of the disease. Breeding for resistance led to the selection of resistant cultivars. The main knowledge gaps concern (i) the role of deadwood and cut branches as potential entry pathways and means of spread and (ii) the susceptibility of C. avellana cultivars and of Corylus spp. in the wild in the EU. 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.

Pest categorisation of Bretziella fagacearum.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Bretziella fagacearum, a well-defined and distinguishable fungal species of the family Ceratocystidaceae. The species was moved from the genus Ceratocystis to a new genus Bretziella following phylogenetic analysis of the species and its close relatives. The former species name Ceratocystis fagacearum 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. B. fagacearum is only reported from the USA, where it causes a wilt disease on Quercus spp. Other hosts are reported based on inoculation trials, although Chinese chestnut (Castanea mollissima) is reported to be naturally infected. No North American oak species has been found to be immune to the disease. The European oak species Quercus robur, Quercus petraea and Quercus pubescens were found to be susceptible in inoculation experiments. The pest could enter the EU via wood (with and without bark, including wood packaging material), plants for planting and cut branches. Hosts and favourable climatic conditions are common in the EU, thus facilitating establishment. The pest would be able to spread following establishment by means of root grafts, insect vectors and movement of wood, plants for planting and other means. The pest introduction would have impacts in woodland and plantations, as oak wilt disease is often lethal in a short period of time. Wood treatment (debarking, kiln drying, fumigation), prompt removal of affected trees and creating root-free zones between affected and healthy stands are available control measures. The main knowledge gaps concern (i) the survival of the fungus in wood during transport and the association with propagation material, (ii) the presence of suitable vectors in Europe and (iii) the relative susceptibility of the oak species native to Europe under natural conditions. 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.

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.

Pest categorisation of Sphaerulina musiva.

Following a request from the European Commission, the EFSA Plant Health Panel performed a pest categorisation of Sphaerulina musiva, a well-defined and distinguishable fungal species of the family Mycosphaerellaceae. Following a recent phylogenetic analysis of the genus Septoria and other closely related genera, a new name (S. musiva) was introduced for the species. The former species name Mycosphaerella populorum 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. S. musiva is reported from North and South America and not known to occur in the EU. S. musiva causes Septoria leaf spots and cankers of poplar (Populus spp.). Of the poplars native to Europe, Populus nigra is reported as susceptible and Populus tremula as susceptible when planted in North America. The hybrid Populus x canadensis (arising from a cross of P. nigra and the North American Populus deltoides), widely grown in the EU, is also susceptible. The pest could enter the EU on plants for planting, cut branches, isolated bark and wood with and without bark. S. musiva could establish in the EU, as hosts are common and favourable climatic conditions are widespread, and could spread following establishment by natural dispersal and movement of infected plants for planting, cut branches, isolated bark and wood with or without bark. The pest introduction would have impacts in woodlands, plantations and nurseries. The pathogen is considered the most serious disease affecting hybrid poplar production in North America. Selection, breeding and planting of resistant species and clones are the main methods used to control the damage caused by the pathogen. There is some uncertainty on the geographical distribution of the pest in the Caucasus, the Crimean Peninsula and South America and on the level of susceptibility among Populus species native to Europe as well as Salix spp. 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.

Pest categorisation of Coniferiporia sulphurascens and Coniferiporia weirii.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Coniferiporia sulphurascens and Coniferiporia weirii, two well-defined and distinguishable fungal species of the family Hymenochaetaceae. The pathogens are regulated in Council Directive 2000/29/EC (Annex IAI, under the previous name Inonotus weirii for both species) as a harmful organism whose introduction into the EU is banned. The two pathogens are native to North America, where C. sulphurascens causes laminated root rot primarily in Douglas fir (Pseudotsuga menziesii) and grand fir (Abies grandis), while C. weirii causes cedar laminated root and butt rot mainly in cedars (Thuja plicata and Cupressus nootkatensis). C. weirii has been reported from Japan and China, and C. sulphurascens from China, Russia and Turkey. Neither species has been reported from the EU. C. sulphurascens may infect all conifers, while C. weirii is reported to mainly cause disease in tree species of Thuja spp. and Cupressus spp. The two pathogens could enter the EU mainly via wood with bark, isolated bark and plants for planting (including artificially dwarfed plants) of Pinaceae and Cupressaceae. Both fungi could establish in the EU, as hosts are present and climatic conditions are favourable. The two pathogens would be able to spread following establishment by the pathways mentioned for entry and also by dissemination of basidiospores and root contact with infected root/wood. Should the pathogen be introduced in the EU, impacts can be expected on coniferous woodlands, plantations and ornamental trees, thus leading to reduced tree growth and ecosystem service provision. The key uncertainties concern (i) the distribution of the two pathogens in Asia, (ii) the level of susceptibility of conifers native to Europe and (iii) the role of plants for planting as a pathway of entry and spread. For both pathogens, the criteria assessed by the Panel for consideration as a potential quarantine pest are met. As the two pests are not present in the EU, not all the criteria for consideration as regulated non-quarantine pests are met.

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 Melampsora medusae.

Following a request from the European Commission, the EFSA Plant Health Panel performed a pest categorisation of Melampsora medusae, a well-defined and distinguishable fungal species of the family Melampsoraceae. The pathogen is regulated in Annex IAI of Council Directive 2000/29/EC as a harmful organism whose introduction into the EU is banned. M. medusae is a heteroecious rust fungus with Populus spp. as primary telial hosts and various conifers (Larix, Pinus, Pseudotsuga, Abies, Picea and Tsuga spp.) as secondary aecial hosts. M. medusae is native to North America and has spread to South America, Africa, Asia, Oceania, as well as the EU, where M. medusae f. sp. deltoidae has been reported with a restricted distribution and low impacts from Belgium, south-west France and southern Portugal. The pest could spread to other EU countries, via dissemination of spores, movement of host plants for planting and cut branches. Climate is assumed not to be a limiting factor for the establishment of the pathogen in the EU. M. medusae is the most widespread and important Melampsora rust in North America. In western Canada, extensive damage has been reported to conifers and Populus spp. in nurseries and plantations as well as in woodlands. M. medusae is damaging in both Australia and New Zealand. The pest could have economic and environmental impacts in the EU if aggressive isolates of M. medusae were introduced into the EU. Import prohibition of host plants for planting is an available measure to reduce the risk of further introductions. Some resistant Populus cultivars are available. Moreover, increasing the genetic diversity of poplar plantations can prevent disease impacts. The main uncertainty concerns the factors explaining the low pathogenicity of the populations of M. medusae present in the EU. The criteria assessed by the Panel for consideration as a potential quarantine pest are met (the pest is present, but with a restricted distribution, and is officially under control). Given that plants for planting are not the main pathway of spread, not all criteria for consideration as a regulated non-quarantine pest are met.

Pest categorisation of Chrysomyxa arctostaphyli.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Chrysomyxa arctostaphyli, a well-defined and distinguishable fungal species of the family Coleosporiaceae. The pathogen is regulated in Council Directive 2000/29/EC (Annex IAI) as a harmful organism whose introduction into the EU is banned. C. arctostaphyli is native to North America and is the causal agent of spruce broom rust. C. arctostaphyli is a heteroecious rust with a 2-year life cycle alternating between the aecial host Picea spp. and the telial host Arctostaphylos spp. The main reported aecial host is P. engelmannii, but also P. abies, P. pungens, P. sitchensis, P. glauca, P. mariana and P. rubens (as well as Picea as a genus) are reported as hosts. The fungus is not known to occur in the EU but could enter via host plants for planting and cut branches. It could establish in the EU, as hosts are present and climatic conditions are favourable. The extent of overlap between the ranges of the telial and aecial hosts is greater in the EU than in North America. The pathogen would be able to spread following establishment by dissemination of spores and human movement of infected host plants. Should the pathogen be introduced in the EU, impacts can be expected in spruce woodland, plantations and on ornamental spruce trees, leading to reduced tree growth and associated ecosystem service provision. The main uncertainty concerns the level of susceptibility of P. abies and P. sitchensis under European conditions. 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 Arceuthobium spp. (non-EU).

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Arceuthobium spp. (non-EU), a well-defined and distinguishable group of parasitic plant species of the family Viscaceae, also known as dwarf mistletoes. These are flowering plants parasitising a wide range of conifers of the families Pinaceae and Cupressaceae. Arceuthobium species (non-EU) are regulated in Council Directive 2000/29/EC (Annex IAI) as harmful organisms whose introduction into the EU is banned. Many Arceuthobium species are recognised, with most dwarf mistletoes native in the New World, and north-western Mexico and the western USA as the centre of diversity for the genus. Only two Arceuthobium species are native (and reported to be present) in the EU (Arceuthobium azoricum and Arceuthobium oxycedrum), which are thus not part of this pest categorisation. Hosts of non-EU dwarf mistletoes include species of the genera Abies, Cupressus, Juniperus, Larix, Picea, Pinus, Pseudotsuga and Tsuga. Most Arceuthobium spp. can parasitise more than one species of conifer host. Dwarf mistletoes could enter the EU via host plants for planting and cut branches, but these pathways are closed. They could establish in the EU, as hosts are widespread and climatic conditions are favourable. They would be able to spread following establishment by human movement of host plants for planting and cut branches, as well as natural spread. Should non-EU dwarf mistletoes be introduced in the EU, impacts can be expected on coniferous woodlands, plantations, ornamental trees and nurseries. The main uncertainties concern (i) the precise distribution and host range of the individual Arceuthobium spp. and (ii) the level of susceptibility of conifers native to Europe. For Arceuthobium spp. (non-EU) as a group of organisms, the criteria assessed by the Panel for consideration as a potential quarantine pest are met, while, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Foliar fungi of Betula pendula: impact of tree species mixtures and assessment methods.

Foliar fungi of silver birch (Betula pendula) in an experimental Finnish forest were investigated across a gradient of tree species richness using molecular high-throughput sequencing and visual macroscopic assessment. We hypothesized that the molecular approach detects more fungal taxa than visual assessment, and that there is a relationship among the most common fungal taxa detected by both techniques. Furthermore, we hypothesized that the fungal community composition, diversity, and distribution patterns are affected by changes in tree diversity. Sequencing revealed greater diversity of fungi on birch leaves than the visual assessment method. One species showed a linear relationship between the methods. Species-specific variation in fungal community composition could be partially explained by tree diversity, though overall fungal diversity was not affected by tree diversity. Analysis of specific fungal taxa indicated tree diversity effects at the local neighbourhood scale, where the proportion of birch among neighbouring trees varied, but not at the plot scale. In conclusion, both methods may be used to determine tree diversity effects on the foliar fungal community. However, high-throughput sequencing provided higher resolution of the fungal community, while the visual macroscopic assessment detected functionally active fungal species.

Pest categorisation of Pseudocercospora pini-densiflorae.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Pseudocercospora pini-densiflorae, a well-defined and distinguishable fungal species of the family Mycosphaerellaceae. The regulated harmful organism is the anamorph Cercoseptoria pini-densiflorae (synonym Cercospora pini-densiflorae) with the corresponding teleomorph Mycosphaerella gibsonii. P. pini-densiflorae causes a needle blight of Pinus spp. also known as Cercospora blight of pines or Cercospora needle blight. P. pini-densiflorae is reported from sub-Saharan Africa, Central and South America, Asia and Oceania, but not from the EU. The pathogen is regulated in Council Directive 2000/29/EC (Annex IIAI) as a quarantine organism whose introduction into the EU is banned on plants (other than fruit and seeds) and wood of Pinus. The pest could enter the EU via plants for planting and other means (uncleaned seed, cut branches of pine trees, isolated bark, growing media accompanying plants, and mycorrhizal soil inocula). Hosts are widespread in the EU and favourable climatic conditions are present in Mediterranean countries. Pinus halepensis, Pinus nigra, Pinus pinea, Pinus pinaster and Pinus sylvestris are reported to be highly susceptible to the pathogen. The pest would be able to spread following establishment after introduction in the EU mainly on infected plants for planting. The pest introduction could have impacts in nurseries and young plantations. Cleaning seeds from needles and removing infected seedlings and pine litter from affected nurseries can reduce the risk of establishment in nurseries and of spread from nurseries to forests, especially given the limited scale of splash dispersal. The main knowledge gaps concern (i) the role of means of entry/spread other than plants for planting and (ii) the potential consequences in mature tree plantations and forests. The criteria assessed by the Panel for consideration as potential quarantine pest are met. For regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Pest categorisation of Gremmeniella abietina.

Following a request from the European Commission, the EFSA Plant Health (PLH) Panel performed a pest categorisation of Gremmeniella abietina, a well-defined species and distinguishable fungus of the family Godroniaceae. The species G. abietina includes several varieties, races and biotypes that are found in different geographical locations, on different hosts and that vary in aggressiveness. The pathogen causes diseases on Pinus species and other conifers such as Abies spp., Picea spp., Larix spp. and Pseudotsuga spp. known as Scleroderris canker in North America and Brunchorstia dieback in Europe. G. abietina has been reported from 19 EU Member States, without apparent ecoclimatic factors limiting establishment. The pathogen is a protected zone (PZ) quarantine pest (Annex IIB) for Ireland and the UK (Northern Ireland). The main European hosts are widespread throughout most of the EU and have been frequently planted in the PZ. The main means of spread are wind-blown ascospores, rain-splashed conidia, plants for planting and traded Christmas trees. Given that G. abietina is most damaging to species that are grown towards the limit of their range, impacts can be expected in the PZ, should the pathogen be introduced there. Risk reduction options include selection of disease-free planting material, nursery inspections, selection of planting sites at some distance from infested plantations, appropriate spacing between plants and thinning. The main uncertainties concern the indeterminate endophytic stage of the fungus, the pathogen distribution and the future taxonomic status of G. abietina, given its intraspecific diversity. All the criteria assessed by the Panel for consideration as potential PZ quarantine pest are met. The criterion of plants for planting being the main pathway for spread for regulated non-quarantine pests is not met: plants for planting are only one of the means of spread of the pathogen.