Alien Pathogens Research Articles

FIRST REPORT AND MOLECULAR IDENTIFICATION OF CHILLI VEINAL MOTTLE VIRUS IN ITALY

Chilli veinal mottle virus (ChiVMV), a member of the genus Potyvirus, family Potyviridae, has recently being reported as a prevailing virus of chilli pepper in eastern Asia causing severe losses. The virus is easily transmitted by several aphid species in a nonpersistent manner. In Italy, an increasing interest in this crop has led to an intensified germplasm introduction and exchange of seeds, cultivars and plantlets from all over the world, often overlapping human migration flows, and de facto without any phytosanitary control. A two-year survey, aimed at investigating about viral diseases spreading in chilli pepper, allowed to identify for the first time in Italy two alien viruses, first pepper vein yellows virus (PeVYV - Polerovirus) then ChiVMV, that, on the basis of their epidemiological behaviours, represent an hypothetical risk for cultivations of chilli pepper and other solanaceous plants. In the present work, an Italian ChiVMV isolate has been identified by sequencing the gene coding for the coat protein. Evolutionary and phylogenetic inference revealed that the Italian isolate clustered close to isolates from continental China, showing a lower environmental pressure. Despite this first outbreak was in a singular spot in a metropolitan area, the risk that viruliferous aphids could rapidly spread the stylet-borne ChiVMV to neighboring no-commercial gardening and farming is high. This communication also aims to highlight that phytosanitary measures are difficult to be applied to prevent the introduction of alien pathogens by vegetable material of minor crops either by trade or amateurs exchanges as well as by people communities.

Effects of Host Variability on the Spread of Invasive Forest Diseases

Biological invasions, resulting from deliberate and unintentional species transfers of insects, fungal and oomycete organisms, are a major consequence of globalization and pose a significant threat to biodiversity. Limiting damage by non-indigenous forest pathogens requires an understanding of their current and potential distributions, factors affecting disease spread, and development of appropriate management measures. In this review, we synthesize innate characteristics of invading organisms (notably mating system, reproduction type, and dispersal mechanisms) and key factors of the host population (namely host diversity, host connectivity, and host susceptibility) that govern spread and impact of invasive forest pathogens at various scales post-introduction and establishment. We examine spread dynamics for well-known invasive forest pathogens, Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, Hosoya, comb. nov., causing ash dieback in Europe, and Cryphonectria parasitica, (Murr.) Barr, causing chestnut blight in both North America and Europe, illustrating the importance of host variability (diversity, connectivity, susceptibility) in their invasion success. While alien pathogen entry has proven difficult to control, and new biological introductions are indeed inevitable, elucidating the key processes underlying host variability is crucial for scientists and managers aimed at developing effective strategies to prevent future movement of organisms and preserve intact ecosystems.

THE ROLE OF RESEARCH AND INNOVATION IN CROP PROTECTION: THE CONTRIBUTION OF ISAGRO

Research of agrochemical industry is driven mainly by the complexity of the regulatory requirements and by the growing sensibility for the safety of environment and users; factors leading to a significant increase of resources needed for developing and registering a new agrochemical. Furthermore, globalization is increasing the risk of introduction of alien pests or pathogens. The Research Center of Isagro, placed in Novara, combining high level of competencies in Biol- ogy, Chemistry and Formulation Technology, is operating to provide farmers with innovative solutions in line with new requirements. The research of chemicals, still the base of a rational crop protection program, is looking for molecules more targeted, effective and sustainable and featured by new mode of actions to counteract possible risk of resistance. New typologies of formulations, or delivery systems , will help to rejuvenate existing active ingredients. Innovative formulations of copper products (i.e. Airone®) may overcome the strong restrictions of dosage rate proposed for EU. Antagonistic fungi and bacteria are efficiently used in integrated crop management program (i.e. Remedier®). Research is targeting purity of production processes, effective formulations and shelf-life at room temperature; many aspects of the mode of actions are still to be investigated. Concerning “Natural Products” (i.e. plant extracts, essential oils, etc.) there are lot of studies from Academics but still few practicable solutions for market. Efficient industrial scale-up, standard quality of active ingredient and fitness in crop programs are the main objectives for research. In Insect control, the use of biodegradable materials will be key in the pheromone dispenser systems. Also, more sus- tainable products are required to replace the old fumigants banned for their eco-toxicological issues.

Alien Pathogens on the Horizon: Opportunities for Predicting their Threat to Wildlife

AbstractAccording to the Convention on Biological Diversity, by 2020 invasive alien species (IAS) should be identified and their impacts assessed, so that species can be prioritized for implementation of appropriate control strategies and measures put in place to manage invasion pathways. For one quarter of the IAS listed as the “100 of the world's worst” environmental impacts are linked to diseases of wildlife (undomesticated plants and animals). Moreover, IAS are a significant source of “pathogen pollution” defined as the human‐mediated introduction of a pathogen to a new host or region. Despite this, little is known about the biology of alien pathogens and their biodiversity impacts after introduction into new regions. We argue that the threats posed by alien pathogens to endangered species, ecosystems, and ecosystem services should receive greater attention through legislation, policy, and management. We identify 10 key areas for research and action, including those relevant to the processes of introduction and establishment of an alien pathogen and to prediction of the spread and associated impact of an alien pathogen on native biota and ecosystems. The development of interdisciplinary capacity, expertise, and coordination to identify and manage threats was seen as critical to address knowledge gaps.

Taxonomic similarity, more than contact opportunity, explains novel plant–pathogen associations between native and alien taxa

Novel associations between plants and pathogens can have serious impacts on managed and natural ecosystems world-wide. The introduction of alien plants increases the potential for biogeographically novel plant-pathogen associations to arise when pathogens are transmitted from native to alien plant species and vice versa. We quantified biogeographically novel associations recorded in New Zealand over the last 150yr between plant pathogens (fungi, oomycetes and plasmodiophorids) and vascular plants. We examined the extent to which taxonomic similarity, pathogen traits, contact opportunity and sampling effort could explain the number of novel associates for host and pathogen species. Novel associations were common; approximately one-third of surveyed plants and pathogens were recorded with at least one biogeographically novel associate. Native plants had more alien pathogens than vice versa. Taxonomic similarity between the native and alien flora and the total number of recorded associations (a measure of sampling effort) best explained the number of novel associates among species. The frequency of novel associations and the importance of sampling effort as an explanatory variable emphasize the need for effective monitoring and risk assessment tools to mitigate the potential environmental and economic impact of novel pathogen associations.

The susceptibility of European tree species to invasive Asian pathogens: a literature based analysis

Alien invasive pathogens have caused numerous disastrous epidemics around the globe during the last two centuries. The frequency of these catastrophes has increased in parallel with the increase of international plant trade. Effective control of the risks requires understanding of factors governing vulnerability of indigenous plants. We tested whether the threat caused by alien pathogens of Asian origin is random among various tree species in Europe or whether it relates to their distribution range. A database including distribution ranges of 75 European tree species and literature-derived information on their susceptibility to invasive forest pathogens (IFPs) of Asian origin was compiled. Analysis on this database indicated that the susceptibility to Asian pathogens is significantly more common among tree species that occur only within Europe than among species with distributional ranges from Europe to Siberia (disease susceptibility percentage, DSP, 52 and 19 %, respectively). Notably, all severely attacked tree species are strictly European while tree species with distribution ranges extending from Europe to Siberia show at most only mild or moderate symptoms of Asian IFPs. Furthermore, the proportion of European broadleaf tree species susceptible to Asian IFPs is significantly higher than that of conifer species. Our results suggest that in Europe, Asian pathogens cause a higher risk to temperate and Mediterranean forests, largely composed of broadleaved species with distributional ranges restricted to Europe, than to boreal forests dominated by conifers distributed to Siberia.

New records from Lithuania of fungi alien to Europe

First records from Lithuania of the ascomycete Ophiostoma novo-ulmi and basidiomycetes Clathrus archeri, Leucocoprinus cepistipes, and Stropharia rugosoannulata are presented. All four species are alien to Europe and two, C. archeri and S. rugosoannulata, have never been recorded in the eastern part of the Baltic Sea region before. Also, a reassessment of the status in Lithuania of the alien pathogen Hymenoscyphus fraxineus and its close relative, the non-pathogenic H. albidus indigenous to Europe, indicates that only H. fraxineus occurs in Lithuania. Descriptions of the examined fungi are presented, and remarks on their habitats and distribution are provided.

Historical occurrence of alien arthropods and pathogens on trees in Canada

The Canadian Forest Invasive Alien Species (CanFIAS) database provides point records of alien arthropod (insects and mites) and pathogen (fungi) species found on trees in Canada extracted from more than 100 years of national surveys. Each record includes a species identification, location, year of observation, and host association and is linked electronically to its original source. More than 175 000 records of 329 alien arthropod species and 11 plant pathogens are available. Historical rates of detection, as indicated by first records, were greatest in the decades following the two world wars. The overall rate has been approximately three species per year since 1900. Richness of alien species is greatest in the Coastal and Great Lakes–St. Lawrence forest ecozones and lowest in the Subalpine and Tundra ecozones. The alien species most significant in terms of extent of invasion and damage to trees are tree-host specialists, feeding on or infecting mostly one or two genera in a single plant family. Important commercial trees including pine, spruce, poplar, and birch and amenity genera including willow, cherry, and maple host the greatest diversity of alien species. Sap-feeding insects are the most speciose feeding group, but foliage-feeding and wood-boring insects and plant pathogens cause the most damage.

Fraxinus sogdiana, a Central Asian ash species, is susceptible to Hymenoscyphus fraxineus

Susceptibility of new host trees is an essential prerequisite for the alien pathogens. Today, an acute problem in Europe is ash dieback, caused by Hymenoscyphus fraxineus. Among the possible invasion routes of this fungus to Europe from its natural range in easternmost Asia, an arrival alongside the unbroken, passing the whole Eurasia chain of ranges of ash species should not be ignored, at least not before the determination of the western extent of the natural range of the pathogen. We established that in Estonia the ash species Fraxinus sogdiana, growing naturally in the "bottleneck" of that belt, in Central Asia, is susceptible to H. fraxineus. It is the first record of H. fraxineus on a Central Asian ash species.

Colonization history, host distribution, anthropogenic influence and landscape features shape populations of white pine blister rust, an invasive alien tree pathogen.

White pine blister rust is caused by the fungal pathogen Cronartium ribicola J.C. Fisch (Basidiomycota, Pucciniales). This invasive alien pathogen was introduced into North America at the beginning of the 20th century on pine seedlings imported from Europe and has caused serious economic and ecological impacts. In this study, we applied a population and landscape genetics approach to understand the patterns of introduction and colonization as well as population structure and migration of C. ribicola. We characterized 1,292 samples of C. ribicola from 66 geographic locations in North America using single nucleotide polymorphisms (SNPs) and evaluated the effect of landscape features, host distribution, and colonization history on the structure of these pathogen populations. We identified eastern and western genetic populations in North America that are strongly differentiated. Genetic diversity is two to five times higher in eastern populations than in western ones, which can be explained by the repeated accidental introductions of the pathogen into northeastern North America compared with a single documented introduction into western North America. These distinct genetic populations are maintained by a barrier to gene flow that corresponds to a region where host connectivity is interrupted. Furthermore, additional cryptic spatial differentiation was identified in western populations. This differentiation corresponds to landscape features, such as mountain ranges, and also to host connectivity. We also detected genetic differentiation between the pathogen populations in natural stands and plantations, an indication that anthropogenic movement of this pathogen still takes place. These results highlight the importance of monitoring this invasive alien tree pathogen to prevent admixture of eastern and western populations where different pathogen races occur.

Evidence of threat to European economy and biodiversity following the introduction of an alien pathogen on the fungal–animal boundary

Recent years have seen a global and rapid resurgence of fungal diseases with direct impact on biodiversity and local extinctions of amphibian, coral, or bat populations. Despite similar evidence of population extinction in European fish populations and the associated risk of food aquaculture due to the emerging rosette agent Sphaerothecum destruens, an emerging infectious eukaryotic intracellular pathogen on the fungal–animal boundary, our understanding of current threats remained limited. Long-term monitoring of population decline for the 8-year post-introduction of the fungal pathogen was coupled with seasonal molecular analyses of the 18S rDNA and histological work of native fish species organs. A phylogenetic relationship between the existing EU and US strains using the ribosomal internal transcribed spacer sequences was also carried out. Here, we provide evidence that this emerging parasite has now been introduced via Pseudorasbora parva to sea bass farms, an industry that represents over 400 M annually in a Mediterranean region that is already economically vulnerable. We also provide for the first time evidence linking S. destruens to disease and severe declines in International Union for Conservation of Nature threatened European endemic freshwater fishes (i.e. 80% to 90 % mortalities). Our findings are thus of major economic and conservation importance.

Using avian surveillance in Ecuador to assess the imminence of West Nile virus incursion to Galápagos.

Infectious disease emergence represents a global threat to human, agricultural animal and wildlife health. West Nile virus (WNV) first emerged in the Americas in 1999 following its introduction to New York from the Old World. This flavivirus rapidly spread across much of North America, causing human, equine and avian mortalities and population declines of multiple wild bird species. It has now spread to Central and South America, and there is concern that the virus will reach the Galápagos Islands, a UNESCO World Heritage Site famous for its unique biodiversity, with potentially catastrophic results. Here, we use wild bird surveillance to examine the current WNV status in the Galapagos Islands and around the Ecuadorian city of Guayaquil (the main air and sea port servingGalápagos). We conducted serosurveys of wild birds on three Galápagos Islands (Baltra, San Cristobal and Santa Cruz) with direct transport links to the South American continent. In addition, dead birds killed by car collisions on Santa Cruz were tested for WNV infection. On mainland Ecuador, serosurveys of wild birds were conducted at three sites around Guayaquil. No evidence of WNV seropositivity or infection was detected. Although wider testing is recommended on the mainland, the study highlights a limit of WNV spread within South America. Our results indicate the continued absence of WNV on Galápagos and suggest the current likelihood of human-mediated transport of WNV to Galápagos to be low. The risk of emergence will almost certainly increase over time, however, and stringent biosecurity and surveillancemeasures should be put in place to minimise the risk of the introduction of WNV (and other alien pathogens) to Galápagos.

Incorporating climate change into pest risk models for forest pathogens: a role for cold stress in an era of global warming?

Climate change may alter the distribution and activity of native and alien pathogens that infect trees and, in severe cases, cause tree death. In this study, potential future changes in climate suitability are investigated for three forest pathogens that occur in western North America: the native Arceuthobium tsugense subsp tsugense, hemlock dwarf mistletoe, and two alien invasive species, Dothistroma septosporum, the cause of red band needle blight or Dothistroma needle blight, and Phytophthora ramorum, the cause of sudden oak death or ramorum blight. Specifically, the software CLIMEX is used to calculate Cold-Stress, Heat-Stress, and Dry-Stress indices for each pathogen in 98,224 grid cells in North America. Downscaled climate projections from the general circulation models CGCM1, CSIROMk2, and HadCM3 drive forecasts for 2020, 2050 and 2080. These climate projections are then analyzed to forecast shifts in the geographic extent of abiotic stresses that are severe enough to directly kill pathogen propagules and prevent year-round establishment of these pathogens. Cold stress currently has a major impact on climate suitability for all three pathogens; heat stress is likely to become more significant in the future. I forecast that the geographic extent of cold stress will decline from its current levels by a constant 5% (± 1%) of all grid cells in each 30-yr projection horizon for all three pathogens. Forecasts suggest the extent of heat stress will increase concurrently by 4% (± 1%) in each 30-yr projection horizon. Drought stress shows no consistent trend over time. No disproportionate effect of climate change on the two alien invasive pathogens over the native is forecasted. These results suggest that forecasts of future climate suitability for pathogens based on historical climate normals are accurate for less than 30 yrs. Adaptive management strategies in forestry will be needed to respond as these changes unfold.

Simple visualization of climate change for improving the public perception in forest pathology / Kliimamuutuste visualiseerimise lihtne viis seoste paremaks tajumiseks metsapatoloogias

Abstract In several national and international meetings of forest and general plant pathology, when discussing possible causes of current arrivals of new alien pathogens in Estonia, we demonstrated the climate characteristic “monthly mean temperatures” as coloured grid-boxes, colours of which indicate the statistical relation of the definite months’ characteristic to its’ long time mean value. It was met with approval and evaluated as suitable and pictorial way for the visualization of shorter (until some few decades) drastically differing periods in climate warming for more trustworthy connecting of these two scientifically-experimentally only heavily connectable natural processes - climate warming and epidemics of alien forest pathogens. During the winters of the 20th century, apparently not only freezing, but also warming periods had caused serious aftermaths in forest pathology

Climate change and forest diseases: using today’s knowledge to address future challenges

The health of the earth’s forests and urban green spaces is increasingly challenged by the outcomes of human activities, including global climate change. As climate changes, the role and impact of diseases on trees in both forest ecosystems and in urban settings will also change. Knowledge of relationships between climate variables and diseases affecting forest and urban trees is reviewed, with specific emphasis on those affecting foliage, shoots, and stems. Evidence that forest diseases are already responding to the earth’s changing climate is examined (e.g., Dothistroma needle blight in northern British Columbia) as are predicted scenarios for future changes in impact on forests by other tree diseases. Outbreaks of tree diseases caused by native and alien pathogens are predicted to become more frequent and intense – this and other general predictions about the effects of climate change on forest and tree diseases are discussed. Despite the uncertainty that accompanies such predictions it is imperative that researchers, forest and urban tree managers, and policy makers work together to develop and implement management strategies that enhance the resilience of the worlds’ forests and urbanized trees. Strategies discussed include monitoring, forecasting, planning, and mitigation.

The effectiveness of phytosanitary controls in preventing the entry of Colletotrichum acutatum in the UK strawberry sector

Phytosanitary legislation is widely thought to be the most effective means of limiting the entry of alien pathogens without hindering trade. However, there is increasing evidence of limitations and weaknesses in phytosanitary systems worldwide. One such case is the entry and establishment of Colletotrichum acutatum in the UK in the 1980s. To investigate this further, data sets of disease incidence gathered by the authorities responsible for plant health between 1984 and 2008 were analysed to determine how and why the pathogen entered the UK and became established on strawberries. Results suggest that the disease entered the UK in 1982 on plants originating from the USA, a year earlier than the first UK record of the disease was reported. At least 54 further cases of infested plant material breached phytosanitary procedures and entered the UK, 75% of which originated from EU countries. Moreover, internal trade transmission was found to be highly influential in the successful spread of the disease. The effectiveness of phytosanitary procedures is limited when the sector is importing large numbers of plants from nurseries that have a track record of selling infested plant material, even if they are accompanied by a plant passport. By taking greater responsibility in limiting the spread of quarantine diseases, nurseries throughout the EU have an important role to play in limiting the entry of alien pathogens.

Alien pathogens of forest trees in Austria

Based on information in the literature and unpublished records a brief synthesis on alien pathogens of forest trees in Austria is presented. A total of 29 pathogens were recorded, consisting of one bacterium, nine Phytophthora species, 14 ascomycetes, three anamorphic fungi and two basidiomycetes. The majority of alien pathogens (23 out of 29) occur on hardwood species. Six pathogens have had a high impact on their host trees and have considerably impaired their use in forestry and/or their role in ecosystems. Four of the six pathogens with high impact affect hardwood trees. Due to climate change the importance of some alien forest pathogens already present in Austria may increase in the future. Key words: Invasive forest pathogens, introduced pathogens, emerging forest diseases, biological invasion, forest pathology.

Assessing the Cost of an Invasive Forest Pathogen: A Case Study with Oak Wilt

Economic assessment of damage caused by invasive alien species provides useful information to consider when determining whether management programs should be established, modified, or discontinued. We estimate the baseline economic damage from an invasive alien pathogen, Ceratocystis fagacearum, a fungus that causes oak wilt, which is a significant disease of oaks (Quercus spp.) in the central United States. We focus on Anoka County, Minnesota, a 1,156 km(2) mostly urban county in the Minneapolis-Saint Paul metropolitan region. We develop a landscape-level model of oak wilt spread that accounts for underground and overland pathogen transmission. We predict the economic damage of tree mortality from oak wilt spread in the absence of management during the period 2007-2016. Our metric of economic damage is removal cost, which is one component of the total economic loss from tree mortality. We estimate that Anoka County has 5.92 million oak trees and 885 active oak wilt pockets covering 5.47 km(2) in 2007. The likelihood that landowners remove infected oaks varies by land use and ranges from 86% on developed land to 57% on forest land. Over the next decade, depending on the rates of oak wilt pocket establishment and expansion, 76-266 thousand trees will be infected with discounted removal cost of $18-60 million. Although our predictions of removal costs are substantial, they are lower bounds on the total economic loss from tree mortality because we do not estimate economic losses from reduced services and increased hazards. Our predictions suggest that there are significant economic benefits, in terms of damage reduction, from preventing new pocket establishment or slowing the radial growth of existing pockets.

ALIEN INVASIVE PATHOGENS: THE MAJOR THREAT TO OUR FOREST ECOSYSTEMS IN A TIME OF RAPID CLIMATE CHANGE

Forest ecosystems face unprecedented challenges from the rising rate of influx of alien invasive pests and pathogens resulting from increased global trade. Moreover, climate change predictions suggest that many additional alien pests and pathogens may become problems in forests as temperatures increase and rainfall patterns change. Recent indications of the potential for pathogens to transfer between hosts and the inter-specific hybridisation possible between related pathogens increase concerns over the possibility of escalations in damage in the future. Why are these organisms such a threat? Using examples drawn from wide-scale environmental damage caused to tree populations and forest ecosystems in Europe and elsewhere in the world, in this talk, we will illustrate the potential of alien pathogens to reduce biodiversity, alter ecosystems beyond recognition and impact on human requirements of forests. Classic examples of devastation by alien invasive pathogens affecting trees include Dutch elm disease, caused by Ophiostoma novo-ulmi, Jarrah dieback caused by Phytophthora cinnamomi, canker stain disease of Platanus caused by Ceratocystis platani, and white pine blister rust arising from accidental trans-Atlantic transfer of Cronartium ribicola. Many other examples exist in Europe and elsewhere in the world. Each of these pathogens still causes severe ecosystem damage in areas of introduction. Recent findings obtained from the application of state-of-the-art tools in molecular biology are reshaping our knowledge of alien invasive pathogens. The advent of these molecular biological techniques has greatly enhanced our ability to analyse aspects related to the biology, taxonomy, hidden biodiversity and temporal and spatial structuring of genetic diversity in organisms. Molecular diagnostic assays have resulted in improved detection methods for pests and pathogens based on molecular profiles, that are essential for accurate and rapid detection and enhanced understanding of the pathways of dispersal locally and internationally. This information greatly increases the reliability of pest risk assessment procedures and the development of phytosanitary measures aimed at eradicating, containing or managing these pests. The possibility of regulating the ‘plants for planting’ pathway, one of the major routes through which alien invasive problems are now entering and being dispersed in Europe, will be discussed.

Micro- and macrospatial scale analyses illustrates mixed mating strategies and extensive geneflow in populations of an invasive haploid pathogen

Sexual reproduction in fungi involves either a single individual (selfing) or two individuals (outcrossing). To investigate the roles that these two strategies play in the establishment of an invasive alien pathogen, the Eucalyptus leaf-infecting fungus, Teratosphaeria (Mycosphaerella) nubilosa was studied. Specifically, the genetic diversity of the pathogen was investigated at micro and macrospatial scales. Interestingly, while data obtained at microspatial scales show clearly that selfing is the main reproductive strategy, at macrospatial scales the population genetic structure was consistent with a genetically outcrossing organism. Additional analyses were performed to explore these apparently discordant results at different spatial scales and to quantify the contribution of selfing vs. outcrossing to the genotypic diversity. The results clearly show that the fungus has a mixed mating strategy. While selfing is the predominant form of mating, outcrosses must have occurred in the pathogen that increased the genotypic diversity of the fungus over time. This mating strategy, coupled with the high levels of geneflow between distant populations of the pathogen, has created an even distribution of maximum diversity from the smallest (leaf) to largest scales (>500 km), which will make breeding for resistance difficult. These data illustrate the evolutionary potential and danger of the introduction of multiple genotypes of a potentially outcrossing pathogen, especially when it has a high dispersal potential.