A synoptic review of plant disease epidemics and outbreaks published in 2022.

This scientometric study reviews the scientific literature and CABI distribution records published in 2022 to find evidence of major disease outbreaks and first reports of pathogens in new locations or on new hosts. This is the second time we have done this, and this study builds on our work documenting and analysing reports from 2021. Pathogens with three or more articles identified in 2022 literature were: Xylella fastidiosa, Bursaphelenchus xylophilus, Meloidogyne species complexes, Candidatus Liberibacter asiaticus, Raffaelea lauricola, Fusarium oxysporum formae specialis and Puccinia graminis f. sp. tritici. Our review of CABI distribution records found 29 pathogens with confirmed first reports in 2022. Pathogens with four or more first reports were: Meloidogyne species complexes, Pantoea ananatis, grapevine red globe virus and Thekopsora minima. Analysis of the proportion of new distribution records from 2022 indicated that grapevine red globe virus, sweet potato chlorotic stunt virus and Ca. Phytoplasma vitis may have been actively spreading. As we saw last year, there was little overlap between the pathogens identified by reviewing scientific literature versus distribution records. Strikingly, too, there was also no overlap between species assessed to be actively spreading in this year's study and those identified last year. In general, introduction of new pathogens and outbreaks of extant pathogens threaten food security and ecosystem services. Continued monitoring of these threats is essential to support phytosanitary measures intended to prevent pathogen introductions and management of threats within a country.

Epidemiology and Management of Plant Viruses Under a Changing Climate.

Plant viruses are an ever-present threat to agricultural production and provide a wide array of symptoms resulting in economic losses throughout the world. Diseases can be transmitted by insect vectors, as well as through pollen, seed, and other means. With the increased globalization of agriculture, the introduction of new viruses from exotic locations and their establishment in new production regions and even new crops is a growing concern. Advancing knowledge of the epidemiology of plant viruses including development of new diagnostic methods, virus surveillance, and modeling, virus ecology and evolution, virus interactions with insect vectors, and other factors are important toward reducing the spread of plant viruses and managing virus diseases.

What Can Be Learned by a Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2021?

A synoptic review of plant disease epidemics and outbreaks was made using two complementary approaches. The first approach involved reviewing scientific literature published in 2021, in which quantitative data related to new plant disease epidemics or outbreaks were obtained via surveys or similar methodologies. The second approach involved retrieving new records added in 2021 to the CABI Distribution Database, which contains over a million global geographic records of organisms from over 50,000 species. The literature review retrieved 186 articles, describing studies in 62 categories (pathogen species/species complexes) across more than 40 host species on six continents. Pathogen species with more than five articles were Bursaphelenchus xylophilus, 'Candidatus Liberibacter asiaticus', cassava mosaic viruses, citrus tristeza virus, Erwinia amylovora, Fusarium spp. complexes, F. oxysporum f. sp. cubense, Magnaporthe oryzae, maize lethal necrosis co-infecting viruses, Meloidogyne spp. complexes, Pseudomonas syringae pvs., Puccinia striiformis f. sp. tritici, Xylella fastidiosa, and Zymoseptoria tritici. Automated searches of the CABI Distribution Database identified 617 distribution records new in 2021 of 283 plant pathogens. A further manual review of these records confirmed 15 pathogens reported in new locations: apple hammerhead viroid, apple rubbery wood viruses, Aphelenchoides besseyi, Biscogniauxia mediterranea, 'Ca. Liberibacter asiaticus', citrus tristeza virus, Colletotrichum siamense, cucurbit chlorotic yellows virus, Erwinia rhapontici, Erysiphe corylacearum, F. oxysporum f. sp. cubense Tropical race 4, Globodera rostochiensis, Nothophoma quercina, potato spindle tuber viroid, and tomato brown rugose fruit virus. Of these, four pathogens had at least 25% of all records reported in 2021. We assessed two of these pathogens-tomato brown rugose fruit virus and cucurbit chlorotic yellows virus-to be actively emerging in/spreading to new locations. Although three important pathogens-'Ca. Liberibacter asiaticus', citrus tristeza virus, and F. oxysporum f. sp. cubense-were represented in the results of both our literature review and our interrogation of the CABI Distribution Database, in general, our dual approaches revealed distinct sets of plant disease outbreaks and new records, with little overlap. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Proposal of a ranking methodology for plant threats in the EU.

Following a request of the European Commission, EFSA and ANSES, beneficiary of the EFSA tasking grant on horizon scanning for plant pests (GP/EFSA/ALPHA/2017/02), developed a methodology to order by risk non-regulated pests recently identified through the monitoring of media and scientific literature. The ranking methodology proposed at the end of the pilot phase was based on the scoring of pests under evaluation following 16 criteria related to the steps of the pest risk assessment scheme. The multicriteria matrix of scores obtained was then submitted to the multicriteria analysis method PROMETHEE. The pilot methodology was tested on a limited number of pests (14 pests identified during the monitoring activity, and 4 'control' pests whose well-known risk should be reflected either in a positive or negative score), then applied on all non-regulated pests identified through the media and scientific literature monitoring in the first 2 years of the project. After having collected feedback from the targeted final users (EU risk managers), the methodology underwent a few refinements: (i) implementation of the methodology to a set of already assessed reference pests from EFSA opinions, (ii) exclusions of three criteria from the scoring phase, (iii) identification of pests proposed for further action ('positive' pests), using a threshold defined after scoring the reference pests.

Epidemiological and ecological consequences of virus manipulation of host and vector in plant virus transmission.

Many plant viruses are transmitted by insect vectors. Transmission can be described as persistent or non-persistent depending on rates of acquisition, retention, and inoculation of virus. Much experimental evidence has accumulated indicating vectors can prefer to settle and/or feed on infected versus noninfected host plants. For persistent transmission, vector preference can also be conditional, depending on the vector's own infection status. Since viruses can alter host plant quality as a resource for feeding, infection potentially also affects vector population dynamics. Here we use mathematical modelling to develop a theoretical framework addressing the effects of vector preferences for landing, settling and feeding-as well as potential effects of infection on vector population density-on plant virus epidemics. We explore the consequences of preferences that depend on the host (infected or healthy) and vector (viruliferous or nonviruliferous) phenotypes, and how this is affected by the form of transmission, persistent or non-persistent. We show how different components of vector preference have characteristic effects on both the basic reproduction number and the final incidence of disease. We also show how vector preference can induce bistability, in which the virus is able to persist even when it cannot invade from very low densities. Feedbacks between plant infection status, vector population dynamics and virus transmission potentially lead to very complex dynamics, including sustained oscillations. Our work is supported by an interactive interface https://plantdiseasevectorpreference.herokuapp.com/. Our model reiterates the importance of coupling virus infection to vector behaviour, life history and population dynamics to fully understand plant virus epidemics.

The Epidemiology of Plant Virus Disease: Towards a New Synthesis.

Epidemiology is the science of how disease develops in populations, with applications in human, animal and plant diseases. For plant diseases, epidemiology has developed as a quantitative science with the aims of describing, understanding and predicting epidemics, and intervening to mitigate their consequences in plant populations. Although the central focus of epidemiology is at the population level, it is often necessary to recognise the system hierarchies present by scaling down to the individual plant/cellular level and scaling up to the community/landscape level. This is particularly important for diseases caused by plant viruses, which in most cases are transmitted by arthropod vectors. This leads to range of virus-plant, virus-vector and vector-plant interactions giving a distinctive character to plant virus epidemiology (whilst recognising that some fungal, oomycete and bacterial pathogens are also vector-borne). These interactions have epidemiological, ecological and evolutionary consequences with implications for agronomic practices, pest and disease management, host resistance deployment, and the health of wild plant communities. Over the last two decades, there have been attempts to bring together these differing standpoints into a new synthesis, although this is more apparent for evolutionary and ecological approaches, perhaps reflecting the greater emphasis on shorter often annual time scales in epidemiological studies. It is argued here that incorporating an epidemiological perspective, specifically quantitative, into this developing synthesis will lead to new directions in plant virus research and disease management. This synthesis can serve to further consolidate and transform epidemiology as a key element in plant virus research.

Coinfections by noninteracting pathogens are not independent and require new tests of interaction.

If pathogen species, strains, or clones do not interact, intuition suggests the proportion of coinfected hosts should be the product of the individual prevalences. Independence consequently underpins the wide range of methods for detecting pathogen interactions from cross-sectional survey data. However, the very simplest of epidemiological models challenge the underlying assumption of statistical independence. Even if pathogens do not interact, death of coinfected hosts causes net prevalences of individual pathogens to decrease simultaneously. The induced positive correlation between prevalences means the proportion of coinfected hosts is expected to be higher than multiplication would suggest. By modelling the dynamics of multiple noninteracting pathogens causing chronic infections, we develop a pair of novel tests of interaction that properly account for nonindependence between pathogens causing lifelong infection. Our tests allow us to reinterpret data from previous studies including pathogens of humans, plants, and animals. Our work demonstrates how methods to identify interactions between pathogens can be updated using simple epidemic models.

Modelling Vector Transmission and Epidemiology of Co-Infecting Plant Viruses.

Co-infection of plant hosts by two or more viruses is common in agricultural crops and natural plant communities. A variety of models have been used to investigate the dynamics of co-infection which track only the disease status of infected and co-infected plants, and which do not explicitly track the density of inoculative vectors. Much less attention has been paid to the role of vector transmission in co-infection, that is, acquisition and inoculation and their synergistic and antagonistic interactions. In this investigation, a general epidemiological model is formulated for one vector species and one plant species with potential co-infection in the host plant by two viruses. The basic reproduction number provides conditions for successful invasion of a single virus. We derive a new invasion threshold which provides conditions for successful invasion of a second virus. These two thresholds highlight some key epidemiological parameters important in vector transmission. To illustrate the flexibility of our model, we examine numerically two special cases of viral invasion. In the first case, one virus species depends on an autonomous virus for its successful transmission and in the second case, both viruses are unable to invade alone but can co-infect the host plant when prevalence is high.

Pest categorisation of Phymatotrichopsis omnivora.

The Panel on Plant Health performed a pest categorisation of Phymatotrichopsis omnivora, the causal agent of Phymatotrichum root rot of more than 2,000 dicotyledonous plant species, for the EU. The pest is listed as Trechispora brinkmannii in Annex IAI of Directive 2000/29/EC. P. omnivora is a well-defined fungal species and reliable methods exist for its detection and identification. It is present in south-western USA, northern Mexico, Libya and Venezuela. The pest is not known to occur in the EU. P. omnivora has an extremely wide host range; quantitative impacts have been documented for Gossypium spp. (cotton), Medicago sativa (alfalfa), Malus domestica (apple), Prunus persica (peach) and Vitis vinifera (grapevine) as the major cultivated hosts. All major hosts and pathways of entry of the pest into the EU are currently regulated, except for soil and growing media attached or associated with plants originating in Libya. Host availability and climate and edaphic matching suggest that P. omnivora could establish in parts of the EU and further spread mainly by human-assisted means. The pest infects the roots causing wilting and death of its host plants. The introduction of the pest in the EU territory would potentially cause direct and indirect impacts at least to cotton, alfalfa, apple, peach and grapevine production. The main uncertainties concern the host range, the extrapolation to the EU of the climatic and edaphic conditions favouring the disease in some of the infested areas, the role of conidia in the epidemiology of the disease and the magnitude of potential impacts to the EU. P. omnivora meets all the criteria assessed by EFSA for consideration as potential Union quarantine pest. The criteria for considering P. omnivora as a potential Union regulated non-quarantine pest are not met, since the pest is not known to occur in the EU.

Guidance on commodity risk assessment for the evaluation of high risk plants dossiers.

Article 42 of the European Regulation (EU) 2016/2031, on the protective measures against pests of plants, introduces the concept of 'high risk plants, plant products and other objects' that are identified on the basis of a preliminary assessment to be followed by a commodity risk assessment. Following a request of the European Commission, this Guidance was developed to establish the methodology to be followed when performing a commodity risk assessment for high risk commodities (high risk plants, plant products and other objects). The commodity risk assessment performed by EFSA will be based on the information provided by the National Plant Protection Organisations of non-EU countries requesting a lifting of import prohibition of a high risk commodity. Following international standards on pest risk analysis, this Guidance describes a two-step approach for the assessment of pest risk associated with a specified commodity. In the first step, pests, associated with the commodity, that require risk mitigation measures are identified. In the second step, the overall efficacy of proposed risk reduction options for each pest is evaluated. A conclusion on the pest-freedom status of the commodity is achieved. The method requires key uncertainties to be identified.

The Epidemiology of Xylella fastidiosa; A Perspective on Current Knowledge and Framework to Investigate Plant Host-Vector-Pathogen Interactions.

Insect-transmitted plant diseases caused by viruses, phytoplasmas, and bacteria share many features in common regardless of the causal agent. This perspective aims to show how a model framework, developed originally for plant virus diseases, can be modified for the case of diseases incited by Xylella fastidiosa. In particular, the model framework enables the specification of a simple but quite general invasion criterion defined in terms of key plant, pathogen, and vector parameters and, importantly, their interactions, which determine whether or not an incursion or isolated outbreak of a pathogen will lead to establishment, persistence, and subsequent epidemic development. Hence, this approach is applicable to the wide range of X. fastidiosa-incited diseases that have recently emerged in southern Europe, each with differing host plant, pathogen subspecies, and vector identities. Of particular importance are parameters relating to vector abundance and activity, transmission characteristics, and behavior in relation to preferences for host infection status. Some gaps in knowledge with regard to the developing situation in Europe are noted.

Pest categorisation of Listronotus bonariensis.

The Panel on Plant Health performed a pest categorisation of Listronotus bonariensis (Coleoptera: Curculionidae), the Argentine stem weevil, for the EU. L. bonariensis is a well-defined species, recognised as a serious pest of pasture grasses, especially Lolium spp. and Poa annua, in New Zealand, and a rare pest of cereals in Argentina, Brazil and New Zealand. Larvae feed within the tillers and stems of grasses; adults can cut emerging cotyledons although they usually graze on leaves. Larval damage is most serious. Larval feeding causes a reduction in pasture quality that impacts on the production of grazing animals. L. bonariensis is not known to occur in the EU and is listed in Annex IIAI of Council Directive 2000/29/EC. L. bonariensis established in New Zealand via imported grass seeds and has been intercepted on grass seeds entering the EU. Considering the climatic similarities of the regions where the pest occurs and the very great extent to which hosts are grown across the EU, L. bonariensis has the potential to establish within the EU with two or three generations possible per year. Impacts could occur in grassland pastures and perhaps occasionally in cereals. In New Zealand, endophytic fungi occurring on potential hosts deter L. bonariensis from ovipositing on leaves and are toxic to larvae. Whether endophytic fungi on grasses in Europe could provide some resistance to L. bonariensis is uncertain. Phytosanitary measures are available to reduce the likelihood of introduction of this weevil. L. bonariensis fits all of the criteria assessed by EFSA to satisfy the definition of a Union quarantine pest. L. bonariensis does not meet the criterion of occurring in the EU territory for it to be regarded as a Union regulated non-quarantine pest.

Pest categorisation of Tecia solanivora.

The Panel on Plant Health performed a pest categorisation of Tecia solanivora (Lepidoptera: Gelechiidae) the Guatemalan potato tuber moth, for the EU. T. solanivora is a well-defined species which feeds exclusively on Solanum tuberosum. It was first described from Costa Rica in 1973 and has spread through Central America and into northern South America via trade of seed potatoes. It has also spread to Mexico and the Canary Islands and most recently to mainland Spain where it is under official control in Galicia and Asturias. Potatoes in the field and storage can be attacked. Some authors regard T. solanivora as the most important insect pest of potatoes globally. T. solanivora is currently regulated by Council Directive 2000/29/EC, listed in Annex II/AI as Scrobipalpopsis solanivora. Larvae feed and develop within potato tubers; infested tubers therefore provide a pathway for pest introduction and spread, as does the soil accompanying potato tubers if it is infested with eggs or pupae. As evidenced by the ongoing outbreaks in Spain, the EU has suitable conditions for the development and potential establishment of T. solanivora. The pest could spread within the EU via movement of infested tubers; adults can fly and disperse locally. Larval feeding destroys tubers in the field and in storage. In the warmer southern EU, where the development would be fastest, yield losses would be expected in potatoes. Measures are available to inhibit entry via traded commodities (e.g. prohibition on the introduction of S. tuberosum). T. solanivora satisfies all of the criteria assessed by EFSA to satisfy the definition of a Union quarantine pest. It does not satisfy EU regulated non-quarantine pest (RNQP) status because it is under official control. There are uncertainties over the effectiveness of preventing illegal imports via passenger baggage and the magnitude of potential impacts in the cool EU climate.

Pest categorisation of Toxoptera citricida.

The European Commission requested EFSA to conduct a pest categorisation of Toxoptera citricida (Hemiptera: Aphididae), an oligophagous aphid developing and reproducing parthenogenetically on tender leaf and flower flush of citrus (Rutaceae). T. citricida is a taxonomic entity with reliable methods available for detection and identification. It is regulated in the EU by Council Directive 2000/29/EC where it is listed in Annex IIAI as a harmful organism whose introduction and spread into the EU shall be banned. T. citricida is native to tropical regions of Southeast Asia and has spread to most citrus-growing areas worldwide, except California and the Mediterranean basin, causing significant damage to citrus as it is the most efficient vector of the Citrus tristeza virus (CTV). T. citricida occurs in Madeira and, with a restricted distribution, in the north-west of the Iberian Peninsula, mostly on backyard citrus trees. This may have hindered the effectiveness of the official control measures in these areas. There are further phytosanitary measures in place in the EU in order to limit entry via traded commodities. Citrus plants for planting are regulated and are a closed pathway. However, there is uncertainty regarding host status of some non-rutaceous plants on which this aphid has been recorded and so other plant genera may provide additional pathways. The EFSA Plant Health Panel concludes that the establishment of T. citricida in the main EU citrus growing areas around the Mediterranean would have significant impacts because of its ability to vector CTV. Considering the criteria within the remit of EFSA to assess the status as a potential Union quarantine pest (QP), as a potential protected zone quarantine pest (PZQP) or as a potential regulated non-quarantine pest (RNQP), T. citricida meets with no uncertainties the criteria assessed by EFSA for consideration as a potential Union QP.

Pest categorisation of the Gonipterus scutellatus species complex.

The Panel on Plant health performed a pest categorisation of the Australian Eucalyptus snout-beetle Gonipterus scutellatus (Coleoptera: Curculionidae), for the EU. G. scutellatus should be referred as the G. scutellatus species complex because it includes several cryptic species. A complete nomenclature of the species present in the EU is still pending. It is a quarantine pest listed in Annex IIB of Council Directive 2000/29/EC. Protected zones are in place in Greece and Portugal (Azores). In the EU, it has been found in Italy, France, Spain and Portugal. It only consumes Eucalyptus species leaves. The main pathways of spread are the trade of Eucalyptus timber, hitchhiking in various commodities, trade of apple fruit as well as of plants for planting or plant parts. Spread by flight is also possible. The climate of the EU protected zones is similar to that of the Member States (MS) where the G. scutellatus complex is established, and the pest's main host plants are present. The damaged trees suffer die-back and the development of epicormics shoots. Severe attacks may provoke massive amounts of tree death. Biological control by using the egg parasitoid wasp Anaphes nitens is the most effective control measure. Some species within the G. scutellatus complex are not yet present in the EU (including G. scutellatus sensu stricto) and might therefore be considered as potential union quarantine pests for the EU territory. At least two species within the G. scutellatus complex (most likely G. platensis and Gonipterus species no. 2) meet the criteria assessed by EFSA for consideration as potential protected zone quarantine pests for the territory of the protected zones: Greece and Portugal (Azores). The criteria for considering the G. scutellatus complex as a potential regulated non-quarantine pest for the EU are not met since plants for planting are not the main pathway.

Pest categorisation of Xanthomonas oryzae pathovars oryzae and oryzicola.

The EFSA Panel on Plant Health performed a pest categorisation for Xanthomonas oryzae pathovars oryzae (Xoo) and oryzicola (Xoc), the causal agents of the bacterial blight and the bacterial leaf streak of rice, respectively. These pathovars are widely distributed in Asia, Africa and Australia. Xoo is also reported in some states of the USA and in some other countries of America. The identity of both pathovars is well established and efficient identification methods are available. The major host is cultivated rice (Oryza sativa), but different Oryza spp. as well as Poaceae weeds are reported as alternative hosts, with some uncertainty concerning the actual host range. Both pathovars are seed associated, despite the fact that seed transmission is still controversial for Xoo. Both pathovars are already regulated in Directives 2000/29/EC, on harmful organisms for plants, and 66/402/EEC, on the marketing of cereal seeds. The main pathway for entry is seed. Should these pathovars enter into EU, they may establish and spread, and they may have an impact on the rice crops, with uncertainties. The knowledge gaps identified are (1) the quantity of EU importation of rice seeds, (2) the risk of introduction through unprocessed rice for consumption, (3) the suitability of the EU growing climate conditions for the bacteria to establish and spread, (4) role of seed transmission (Xoo), (5) the role of weeds in the epidemiology and especially in seed transmission and dispersal, (6) host range of weeds. As none of the pathovars is known to occur in the EU, they do not meet one of the criteria for being considered as Union regulated non-quarantine pests. Nevertheless, both pathovars meet the criteria assessed by EFSA for consideration as Union quarantine pest.

Evaluation of a paper by Guarnaccia et al. (2017) on the first report of Phyllosticta citricarpa in Europe.

The Plant Health Panel reviewed the paper by Guarnaccia et al. (2017) and compared their findings with previous predictions on the establishment of Phyllosticta citricarpa. Four species of Phyllosticta were found by Guarnaccia et al. (2017) in Europe. P. citricarpa and P. capitalensis are well-defined species, with P. citricarpa recorded for the first time in Europe, confirming predictions by Magarey et al. (2015) and EFSA (2008, 2014, 2016) that P. citricarpa can establish in some European citrus-growing regions. Two new species P. paracitricarpa and P. paracapitalensis were also described, with P. paracitricarpa (found only in Greece) shown to be pathogenic on sweet orange fruits. Genotyping of the P. citricarpa isolates suggests at least two independent introductions, with the population in Portugal being different from that present in Malta and Italy. P. citricarpa and P. paracitricarpa were isolated only from leaf litter in backyards. However, since P. citricarpa does not infect or colonise dead leaves, the pathogen must have infected the above living leaves in citrus trees nearby. Guarnaccia et al. (2017) considered introduction to be a consequence of P. citricarpa having long been present or of illegal movement of planting material. In the Panel's view, the fruit pathway would be an equally or more likely origin. The authors did not report how surveys for citrus black spot (CBS) disease were carried out, therefore their claim that there was no CBS disease even where the pathogen was present is not supported by the results presented. From previous simulations, the locations where Guarnaccia et al. (2017) found P. citricarpa or P. paracitricarpa were conducive for P. citricarpa establishment, with number of simulated infection events by pycnidiospores comparable to sites of CBS occurrence outside Europe. Preliminary surveys by National Plant Protection Organisations (NPPOs) have not confirmed so far the findings by Guarnaccia et al. (2017) but monitoring is still ongoing.

The principles and methods behind EFSA's Guidance on Uncertainty Analysis in Scientific Assessment.

To meet the general requirement for transparency in EFSA's work, all its scientific assessments must consider uncertainty. Assessments must say clearly and unambiguously what sources of uncertainty have been identified and what is their impact on the assessment conclusion. This applies to all EFSA's areas, all types of scientific assessment and all types of uncertainty affecting assessment. This current Opinion describes the principles and methods supporting a concise Guidance Document on Uncertainty in EFSA's Scientific Assessment, published separately. These documents do not prescribe specific methods for uncertainty analysis but rather provide a flexible framework within which different methods may be selected, according to the needs of each assessment. Assessors should systematically identify sources of uncertainty, checking each part of their assessment to minimise the risk of overlooking important uncertainties. Uncertainty may be expressed qualitatively or quantitatively. It is neither necessary nor possible to quantify separately every source of uncertainty affecting an assessment. However, assessors should express in quantitative terms the combined effect of as many as possible of identified sources of uncertainty. The guidance describes practical approaches. Uncertainty analysis should be conducted in a flexible, iterative manner, starting at a level appropriate to the assessment and refining the analysis as far as is needed or possible within the time available. The methods and results of the uncertainty analysis should be reported fully and transparently. Every EFSA Panel and Unit applied the draft Guidance to at least one assessment in their work area during a trial period of one year. Experience gained in this period resulted in improved guidance. The Scientific Committee considers that uncertainty analysis will be unconditional for EFSA Panels and staff and must be embedded into scientific assessment in all areas of EFSA's work.

Guidance on Uncertainty Analysis in Scientific Assessments.

Uncertainty analysis is the process of identifying limitations in scientific knowledge and evaluating their implications for scientific conclusions. It is therefore relevant in all EFSA's scientific assessments and also necessary, to ensure that the assessment conclusions provide reliable information for decision-making. The form and extent of uncertainty analysis, and how the conclusions should be reported, vary widely depending on the nature and context of each assessment and the degree of uncertainty that is present. This document provides concise guidance on how to identify which options for uncertainty analysis are appropriate in each assessment, and how to apply them. It is accompanied by a separate, supporting opinion that explains the key concepts and principles behind this Guidance, and describes the methods in more detail.

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.