Invasion potential of Agrilus planipennis and other Agrilus beetles in Europe: import pathways of deciduous wood chips and MaxEnt analyses of potential distribution areas

Bark‐ and wood‐boring beetles in the genus Agrilus (Coleoptera: Buprestidae) can survive wood‐chipping, and Agrilus planipennis has established in North America and European Russia with devastating impacts on forest ecosystems. The work presented in this paper combined import statistics of deciduous wood chips, Maximum entropy modelling (MaxEnt) of climatic similarities, and the distribution of potential tree hosts to predict the likelihood of four selected North American Agrilus species to become introduced and established in Europe. In agreement with the EU's energy‐policy target of increased use of wood chips, there was a linear or exponential increase in European imports of deciduous wood chips during the past 10 years from countries harbouring potentially harmful Agrilus species. MaxEnt showed high environmental suitability in Europe for the four selected Agrilus species, particularly in Eastern Europe and European Russia for A. anxius, A. bilineatus and A. planipennis and in southern Europe for A. politus. Documented susceptible host trees are widely distributed in the predicted areas of Agrilus distribution in Europe, and these areas receive large quantities of deciduous wood chips from countries where these and other Agrilus species are present. Thus, it was concluded that the fundamental conditions for introduction and establishment of Agrilus species in Europe are in place.     

Multiplex real-time PCR assays for the detection and identification of Heterobasidion species attacking conifers in Europe

Four species of the destructive forest pathogen Heterobasidion annosum sensu lato (s.l.) are present in Europe: H. annosum sensu stricto (s.s.), H. abietinum and H. parviporum are native species, while H. irregulare is a non-native invasive species currently reported only in Italy, yet recommended for regulation throughout Europe. In this study, real-time PCR detection tests were developed for each of the four species, which can be used simultaneously or individually thanks to probes labelled with species-specific fluorescent dyes. The different performance criteria of each assay were evaluated, and it was determined that they were theoretically capable of detecting amounts of DNA corresponding to 311, 29 and 29 cell nuclei in H. annosum s.s., H. irregulare and H. parviporum, respectively. The specificity of each assay was assessed with a wide set of strains. Real-time PCR tests successfully detected Heterobasidion species from 36 fruiting bodies taken from the forest, as well as from artificially inoculated or naturally infected wood samples. The multiplex real-time PCR assays developed in this study could have practical applications both in forest management and in phytosanitary monitoring.     

Ranking of invasive woody plant species for management on Réunion Island

The native flora of Réunion Island in the Indian Ocean is threatened by invasive woody plants introduced for agriculture, forestry or as ornamentals. We reviewed archives to identify woody plants introduced since colonisation and ranked the biological impact of the main non‐indigenous species on native vegetation. The relationship between cumulative number of non‐indigenous plants and population follows an s‐shaped curve, but the rate of introduction was mainly determined by historical periods with five main introduction phases identified. A total of 318 introduced woody species were recorded with 132 identified as naturalized in natural ecosystems. Of these, 26 of the more serious invasive species (i.e. having a large biological impact on the new environment) were selected and ranked by biological impact to native ecosystems. Hiptage benghalensis, Ligustrum robustum var. walkeri, Acacia mearnsii, Ulex europaeus and Psidium cattleianum were identified as having the highest invasiveness capacity and the greatest impacts on succession and utilization of resources in natural areas. A strategy is required to manage high‐priority invasive species and reduce the rate of non‐indigenous plant introductions to the island.     

From horticulture and biofuel to invasion: the spread of Miscanthus taxa in the USA and Europe

Species of the genus Miscanthus (Poaceae) have recently become widely planted for ornamental and industrial uses. Yet these large perennial grasses have several traits that suggest a high invasion potential. To inform the debate on the benefits and risks of introducing these new biofuel crops, this publication summarises the invasion of Miscanthus species in Europe and the USA. Databases from North America were interrogated, and occurrence data from a variety of European sources were examined. In both continents, M. sinensis and M. sacchariflorus have recently spread rapidly, although invasion started earlier in the USA and both species are more widespread there. Both species mostly colonise grasslands and ruderal habitats. In addition, some escapes of the hybrid M. × giganteus, which has a particularly strong invasion potential because of its vigorous growth and greater capacity to establish in cool climates, have already been recorded. We conclude that the invasion potential of Miscanthus species needs to be thoroughly tested, the incipient invasions in Europe and the USA monitored and, if required, planting restrictions should be adopted.     

Population structure and genetic diversity suggest recent introductions of Dothistroma pini in Slovakia

Dothistroma pini is one of two pathogens causing Dothistroma needle blight (DNB), a foliar disease of pines. The species was redefined in 2004 and subsequently recorded in several European countries. In Slovakia, the first report of the pathogen was in 2013. In this study, the population structure, genetic diversity, and reproductive mode of 105 isolates collected from 10 localities and seven hosts were determined in Slovakia. Species-specific mating type markers, ITS haplotype determination, and 16 microsatellite markers were used to characterize and genotype the isolates. Overall, 15 unique multilocus haplotypes (MLHs) based on microsatellite markers and three ITS haplotypes were identified. Three independent methods (DAPC, STRUCTURE, EDENetwork) separated the isolates into two distinct population clusters corresponding with ITS haplotypes. A high level of clonality was recorded suggesting that conidia are the primary source of pathogen dispersal. The low genetic diversity, predominantly asexual reproductive mode of the pathogen, and the fact that most isolates were collected from introduced tree species and native species in artificially planted urban greenery, supports the hypothesis that D. pini has been recently introduced into Slovakia.     

Feeding and oviposition of <Emphasis Type="Italic">Anoplophora chinensis</Emphasis> on ornamental and forest trees

Studies were conducted on maturation feeding and oviposition of Anoplophora chinensis (Forster) (Coleoptera: Cerambycidae), a recently introduced quarantine pest in Europe on different plant species of great importance for urban and forest environments in Italy. The tested plant species were Aesculus hippocastanum, Acer negundo, A. campestris, Castanea sativa, Corylus avellana, Platanus x acerifolia, Quercus petrea, Q. pubescens, Q. rubra, Tilia platyphyllos, Ulmus minor and U. pumila. Tested adults of A. chinensis originated from a population of a recently infested site in Italy (Rome) and all experiments were conducted in a walk-in insect cage under quarantine conditions. Adults of A. chinensis showed a maturation feeding preference for twigs of Acer species (A. negundo and A. campestris) and for C. avellana. In the oviposition experiments conducted on bolts of tested plant species, A. chinensis females did not show clear preferences and some data did not reflect the preferences shown during the feeding experiments. Nevertheless, A. negundo and A. campestris were well accepted plant species for oviposition besides A. hippocastanum and T. platyphyllos.     

Impacts of exotic forest pathogens on Mediterranean ecosystems: four case studies

Mediterranean ecosystems are hotspots of biodiversity. Because of a coincidence of high species richness and human presence, Mediterranean biodiversity is particularly threatened by processes such as habitat degradation, fragmentation and loss, pollution, climate change and introduction of invasive species. Invasive tree pathogens are among the problematic exotic species of California, Chile, the Mediterranean, South Africa and Australia. In this review, we provide an update on a selection of non-native tree pathogens currently posing a threat in Mediterranean ecosystems. The impact of exotic forest pathogens range from large-scale tree and shrub mortality in native ecosystems (Phytophthora ramorum on the West Coast of the USA) to disruption of plantations of exotic (e.g., Seiridium cardinale on planted Monterey cypress in California, Fusarium circinatum on Monterey pine worldwide) and native trees (introduction of the North American Heterobasidion irregulare in stone pine woodland in Italy). Genetic analyses are instrumental in improving our understanding and management of these outbreaks. There is a need for more empirical data on how novel pathosystems are likely to develop under novel climates, as well as interdisciplinary collaborations among forest pathologists, theoretical modellers and climatologists. The magnitude of the observed effects of some exotic tree diseases makes it important to try and minimize the risk of the inadvertent movement of plant pathogens when planning assisted migration activities to enable plant species to cope with rapid climate change.     

Phytophthora diversity and the population structure of Phytophthora ramorum in Swiss ornamental nurseries

Invasive oomycete pathogens have been causing significant damage to native ecosystems worldwide for over a century. A recent well‐known example is Phytophthora ramorum, the causal agent of sudden oak death, which emerged in the 1990s in Europe and North America. In Europe, this pathogen is mainly restricted to woody ornamentals in nurseries and public greens, while severe outbreaks in the wild have only been reported in the UK. This study presents the results of the P. ramorum survey conducted in Swiss nurseries between 2003 and 2011. In all 120 nurseries subjected to the plant passport system, the main P. ramorum hosts were visually checked for above ground infections. Phytophthora species were isolated from tissue showing symptoms and identified on the basis of the morphological features of the cultures and sequencing of the ribosomal ITS region. Phytophthora was detected on 125 plants (66 Viburnum, 58 Rhododendron and one Pieris). Phytophthora ramorum was the most frequent species (59·2% of the plants), followed by P. plurivora, P. cactorum, P. citrophthora, P. cinnamomi, P. cactorum/P. hedraiandra, P. multivora and P. taxon PgChlamydo. The highest incidence of P. ramorum was observed on Viburnum × bodnantense. Microsatellite genotyping showed that the Swiss P. ramorum population is highly clonal and consists of seven genotypes (five previously reported in Europe, two new), all belonging to the European EU1 clonal lineage. It can therefore be assumed that P. ramorum entered Switzerland through nursery trade. Despite sanitation measures, repeated P. ramorum infections have been recorded in seven nurseries, suggesting either reintroduction or unsuccessful eradication efforts.     

Fungi as potential factors limiting natural regeneration of pedunculate oak (Quercus robur) in mixed-species forest stands in Poland

Dieback of young Quercus robur seedlings can limit natural regeneration in mixed-species forest stands in Poland. The aim of this study was to examine the role of fungi in the dieback of oak seedlings in central Europe. Fungi were isolated from the stems and roots of Q. robur, from both healthy seedlings and seedlings with symptoms, that were sampled from four stands in Poland. In total, 111 distinct taxa were identified. Ascomycota was dominant, representing 95.6% of the isolates. Among the taxa identified, Alternaria alternata, Colletotrichum fioriniae, Colletotrichum godetiae, Coniella quercicola, Diaporthe eres, Gnomoniopsis paraclavulata, Ilyonectria rufa, Mucor genevensis, Penicillium glandicola, Tubakia dryina, and Umbelopsis changbaiensis were most frequently isolated, and were consistently found in stems and roots of both healthy and diseased plants. The community compositions of fungi in healthy and diseased stems were similar, although Fusarium species, especially Fusarium sp. 1 (FTSC 5) and F. sporotrichioides, were found mainly in seedlings with symptoms. The pathogenicity of the most consistently isolated species from stems and roots of diseased seedlings was tested on Q. robur seedlings. F. sporotrichioides caused the largest lesions on inoculated seedlings. Six weeks after inoculation, D. eres, C. fioriniae, G. paraclavulata, T. dryina, and F. sporotrichioides killed 0%–18.8% of seedlings, while I. rufa and Ilyonectria pseudodestructans did not cause any lesions or other symptoms. This study is the first comprehensive report suggesting that massive fungal attack can lead to oak seedling dieback in mixed-species forest stands in central Europe.     

Occurrence and pathogenicity of Armillaria tabescens on almond in Greece 1

Armillaria tabescens was detected in almond orchards in three different localities of central Greece (Fthiotis county). Mycelial fans of the fungus were observed in the roots and the base of the trunk of dead or dying trees. Symptoms of gummosis were also evident on the bark of infected trees. One of the orchards had been established on land cleared of a Quercus coccifera forest. A. tabescens was identified from basidiocarps developed in vitro, as well as in haploid–haploid mating tests with testers from France. This is the first report of A. tabescens on almond in Europe. Although the fungus has been characterized as a weak parasite or even non-pathogenic to other hosts, it caused considerable damage in almond orchards. In inoculation trials, it was shown that one-year-old almond trees were susceptible to three Armillaria species tested: A. mellea, A. gallica and A. tabescens. The most virulent species in these tests was A. mellea while the least virulent was A. tabescens. The pathogenicity tests verified the ability of A. tabescens to be pathogenic to almond.     

Phytophthora agathidicida: research progress,cultural perspectives and knowledge gaps in the control and management of kauri dieback in New Zealand

Kauri (Agathis australis), which is one of the world's largest and longest-living conifer species, is under threat from a root and collar dieback disease caused by the oomycete pathogen Phytophthora agathidicida. The noted incidence of kauri dieback has increased in the past decade, and even trees >1000 years old are not immune. This disease has profound effects on both forest ecosystems and human society, particularly indigenous Māori, for whom kauri is a taonga or treasure of immense significance. This review brings together existing scientific knowledge about the pathogen and the devastating disease it causes, as well as highlighting important knowledge gaps and potential approaches for disease management. The life cycle of P. agathidicida is similar to those of other soilborne Phytophthora pathogens, with roles for vegetative hyphae, zoospores and oospores in the disease. However, there is comparatively little known about many aspects of the biology of P. agathidicida, such as its host range and disease latency, or about the impact on the disease of abiotic and biotic factors such as soil health and co-occurring Phytophthora species. This review discusses current and emerging tools and strategies for surveillance, diagnostics and management, including a consideration of genomic resources, and the role these play in understanding the pathogen and how it causes this deadly disease. Key aspects of indigenous Māori knowledge, which include rich ecological and historical knowledge of kauri forests and a holistic approach to forest health, are highlighted.     

Occurrence of soilborne Phytophthora species in declining broadleaf forests in Hungary

Invasive Phytophthora species are responsible for severe tree diseases in many forest ecosystems in Europe. In Hungary, the symptoms were first noted when P. alni infection led to a serious decline and mortality of alder stands in the late 1990s. Between 2001 and 2009, over 300 soilborne Phytophthora isolates were collected from declining broadleaf forests in Hungary, and 10 Phytophthora species identified based on morphological traits and the molecular characteristics of the internally transcribed spacer (ITS) regions of the nuclear ribosomal DNA. The most diverse species spectrum, found in diseased alder stands, included P. gonapodyides, P. gregata, P. inundata, P. lacustris, P. megasperma, P. plurivora, one informally designated taxon: P. taxon hungarica, and one unnamed species P. sp.1. P. cactorum and P. plurivora isolates were prevalent in the soil of a declining eastern black walnut forest, and three species, P. gonapodyides, P. multivora and P. plurivora were recovered from a declining oak stand. More than one ITS-based genotype was identified for four species, including six genotypes for P. gonapodyides, and two each for P. cactorum, P. plurivora and P. inundata. The high genetic diversity of the P. gonapodyides isolates may indicate that the species is indigenous to the region. In contrast, the frequently recovered, widely distributed P. lacustris with a single ITS genotype may represent a recent colonizer. The P. multivora isolates are, to date, the first reported from a European native forest.     

Species spectra,distribution and host range of cucurbit powdery mildews in the Czech Republic,and in some other European and Middle Eastern countries

The occurrence and geographic distribution of powdery mildew on cucurbits was studied in the Czech Republic, Austria, France, Germany, Great Britain, Italy, Slovakia, Slovenia, Spain, Switzerland, the Netherlands, as well as in Turkey and Israel, during the period 1995–2000. In total, 599 leaf samples with powdery mildew symptoms were collected from cucurbits from 166 locations within the Czech Republic; an additional 69 samples were collected from 42 locations elsewhere. Two powdery mildews (Golovinomyces cichoracearum and Podosphaera xanthii) were identified. The host range included the cultivated cucurbits (Cucumis melo, C. sativus, Cucurbita pepo, C. maxima, and Citrullus lanatus) and several other species. P. xanthii was the only powdery mildew pathogen found in Spain, Israel, and Turkey. P. xanthii and G. cichoracearum were detected in the other surveyed countries, occurring in both mixed infections and separately. In the more northerly latitudes and higher elevations, G. cichoracearum is more often the single species. G. cichoracearum was the dominant powdery mildew species in the Czech Republic (detected in 98.8% of the locations there); P. xanthii was found as the lone species in 1.2% of locations. At 28.4% of locations, G. cichoracearum was found with P. xanthii as mixed infections. The hyperparasitic fungus Ampelomyces quisqualis was found in 30% of the samples from the Czech Republic and was also recorded in Austria, Italy, Slovenia, Switzerland, and Great Britain.     

Diversity of Phytophthora species in natural ecosystems of Taiwan and association with disease symptoms

In 2013 a survey of Phytophthora diversity was performed in 25 natural and seminatural forest stands and 25 rivers in temperate montane and subtropical lowland regions of Taiwan. Using baiting assays, 10 described species and 17 previously unknown taxa of Phytophthora were isolated from 71.5% of the 144 rhizosphere soil samples from 33 of 40 tree species sampled in 24 forest stands, and from 19 rivers: P. capensis, P. citrophthora, P. plurivora, P. tropicalis, P. citricola VII, P. sp. × botryosa‐like, P. sp. × meadii‐like and P. sp. occultans‐like from Clade 2; P. palmivora from Clade 4; P. castaneae and P. heveae from Clade 5; P. chlamydospora and P. sp. forestsoil‐like from Clade 6; P. cinnamomi (Pc), P. parvispora, P. attenuata nom. prov., P. flexuosa nom. prov., P. formosa nom. prov., P. intricata nom. prov., P. × incrassata nom. prov. and P. × heterohybrida nom. prov. from Clade 7; P. sp. palustris and five new hybrid species from Clade 9. The A1 mating type of Pc was widespread in both montane and lowland forests and rarely associated with disease, whereas the A2 mating type was limited to lowland forests and in some cases causing severe dieback. Most other Phytophthora species were not associated with obvious disease symptoms. It is concluded that (i) Taiwan is within the centre of origin of most Phytophthora taxa found, (ii) Pc A2 is an introduced invasive pathogen, and (iii) interspecific hybridizations play a major role in speciation and species radiations in diverse natural ecosystems.     

Eradication and control of invasive alien plants in the Mediterranean Basin: towards better coordination to enhance existing initiatives

The European and Mediterranean Plant Protection Organization (EPPO), in the framework of its activities in the Mediterranean Basin, launched a questionnaire to gather information on eradication actions and control actions for invasive alien plants. Thirty‐four (34) eradication actions were reported, 16 occurring in Spain, 7 in Italy, 7 in France, 1 in Portugal, 1 in Malta, and 2 on the southern rim of the Mediterranean, with 1 in Israel and 1 in Tunisia. Twenty‐two (22) species were targeted, and the habitats where such actions were undertaken most frequently were coastal dunes, sandy shores and aquatic ecosystems. Most of the species that have been the object of an eradication action were known invasive species recorded in the EPPO lists, such as Ailanthus altissima, Buddleia davidii, Carpobrotus spp., Eichhornia crassipes, Ludwigia peploides, Pennisetum setaceum, Pistia stratiotes, Solanum elaeagnifolium and Sicyos angulatus. Other eradicated species have a limited distribution in the EPPO region and may represent emerging invasive plants, such as Ambrosia confertifolia, Cylindropuntia rosea, Leersia oryzoides, Leptochloa fusca subsp. uninervia and Marsilea drummondii. Control actions concerning 90 species were also reported. A large number of eradication actions, as well as management actions, are therefore happening in Mediterranean countries. At present countries appear to operate with complete autonomy, without consulting neighbouring countries or other stakeholders within the country. There is therefore a need for coordination of new eradication actions.     

Phytophthora acerina sp. nov., a new species causing bleeding cankers and dieback of Acer pseudoplatanus trees in planted forests in northern Italy

A severe dieback of Acer pseudoplatanus trees was noticed in planted forest stands in northern Italy in 2010. Affected trees showed collar rot and aerial bleeding cankers along the stems, leading to crown dieback and eventually death. An unknown Phytophthora species was consistently isolated from necrotic bark and xylem tissue and from rhizosphere soil. Based on its unique combination of morphological and physiological characters and phylogenetic analysis, this new taxon is here described as Phytophthora acerina sp. nov. Phylogenetic analysis of ITS, cox1 and β‐tubulin gene regions demonstrated that P. acerina is unique and forms a separate cluster within the ‘P. citricola complex’, closely related to P. plurivora. Phytophthora acerina is homothallic with smooth‐walled oogonia, thick‐walled, mostly aplerotic oospores with a high abortion rate, paragynous antheridia, and persistent, morphologically variable semipapillate sporangia. Four to 5‐week‐old cultures produced globose to subglobose, appressoria‐like and coralloid hyphal swellings and characteristic stromata‐like hyphal aggregations. Optimum and maximum temperatures for growth are 25°C and 32°C, respectively. Genetic uniformity of all 15 studied isolates and the apparent absence of this species in the extensive surveys of nurseries, forests and seminatural ecosystems conducted in the previous two decades across Europe indicate a recent clonal introduction to northern Italy. Under‐bark inoculation tests demonstrated high aggressiveness of P. acerina to A. pseudoplatanus indicating that this pathogen might be a serious risk to maple plantations and forests in Europe.     

Spread of Impatiens glandulifera from riparian habitats to forests and its associated impacts: insights from a new invasion

Impatiens glandulifera is a globally successful invader that primarily spreads along riparian habitats; however, during the last ~20 years, it has started to colonise forests, but little has been published on impacts of this recent spread. Several factors may have contributed to this phenomenon: (i) high propagule pressure from large and widespread riparian populations, (ii) extensive anthropogenic and natural disturbances in the forest ecosystems, (iii) increased use of forest machinery efficiently spreading the seeds together with (iv) a wide environmental tolerance of the species. The impacts of I. glandulifera on native communities in forests are manifold. Contrasting effects are reported on native plant species diversity, richness and growth of saplings of co-occurring species, as well as negative effects on soil mycorrhizal fungi. We suggest that the eradication of I. glandulifera populations in forests is more feasible than along watercourses because the recolonisation in forests is limited and, in some cases, populations are outcompeted by woody species during succession.     

Bark beetle outbreak on weakened ash trees and applied control measures1

Ash dieback symptoms were noticed for the first time in 2004 in Slovakia. Information suggests that symptoms occurred before this, but not on such a large scale. The pathogen was isolated from necrotic wounds in 2007 and tests confirmed the pathogenicity of the isolate. From February 2009, a forest enterprise from Eastern Slovakia applied control measures in the field against a secondary pest, the bark beetle Hylesinus fraxini Panzer. A total of 527 trap trees were prepared on a site of approximately 200 ha. Trap trees were densely infested, and the authors judged the method as very effective against H. fraxini.     

Native and exotic coniferous species in Europe – possible host plants for the potentially invasive Siberian moth,Dendrolimus sibiricus1 Tschtv. (Lepidoptera,Lasiocampidae)

The performance of young larvae of the potentially invasive Siberian moth Dendrolimus sibiricus Tschtv. has been studied for the first time on the native and exotic coniferous species which are widely distributed and of considerable commercial value in Europe. Picea, Abies, the introduced Pinus species (five‐needle pine only), and species from the exotic genera Pseudotsuga and Cedrus (all Pinaceae) are found to be suitable hosts for pest development. Two‐needle pines and species from non‐native Tsuga (also Pinaceae) are poor hosts in terms of larval performance though they may support growth of neonates (most sensitive to food quality). Coniferous species from other families: Taxaceae and Cupressaceae are inedible for the pest. The fact that the Siberian moth is able to survive and develop on all the tested genera of Pinaceae and that some of them constitute two thirds of the European forests underline how harmful this defoliator could be in the case of its introduction into European countries.