Publications
271 results found
Jeger MJ, 2023, Tolerance of plant virus disease: Its genetic, physiological, and epidemiological significance, Food and Energy Security, Vol: 12, Pages: 1-27, ISSN: 2048-3694
The development and use of tolerance have been proposed as an alternative or complementary method to host resistance in the management of plant diseases, including those caused by viruses. There has been much ambiguity among plant pathologists, plant breeders, and agronomists in the meaning of tolerance and how it can be operationally defined, but a modern consensus seems to have emerged. Tolerance is a relative term that means a limited reduction in host plant fitness (reproduction or survival) in relation to pathogen load throughout or during a defined period of plant development and growth such as the reproductive stage. This emphasizes the need to study reproductive stage disease tolerance. Despite this apparent consensus, there remain questions over the use of model plant systems, the genetic background of tolerance, its physiological expression, and epidemiological consequences of its deployment in crops, in comparison with host resistance. Most examples of tolerance reviewed here are for plant virus systems, although other pathogen taxa are referred to, as is tolerance as a natural phenomenon in wild plants including crop relatives. An argument is made for studying commonalities and interactions in host responses to biotic and abiotic stressors; in particular, whether virus infection can mitigate the impact of heat, cold, drought and salinity stress in plants. Finally, we review the use of mathematical models as a means of evaluating the strategy of using tolerance in disease and crop management.
Jeger MJ, Fereres A, Malmstrom CE, et al., 2023, Epidemiology and Management of Plant Viruses Under a Changing Climate., Phytopathology, Vol: 113, Pages: 1620-1621, ISSN: 0031-949X
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.
Jeger M, Hamelin F, Cunniffe N, 2023, Emerging Themes and Approaches in Plant Virus Epidemiology., Phytopathology, Vol: 113, Pages: 1630-1646, ISSN: 0031-949X
Plant diseases caused by viruses share many common features with those caused by other pathogen taxa in terms of the host-pathogen interaction, but there are also distinctive features in epidemiology, most apparent where transmission is by vectors. Consequently, the host-virus-vector-environment interaction presents a continuing challenge in attempts to understand and predict the course of plant virus epidemics. Theoretical concepts, based on the underlying biology, can be expressed in mathematical models and tested through quantitative assessments of epidemics in the field; this remains a goal in understanding why plant virus epidemics occur and how they can be controlled. To this end, this review identifies recent emerging themes and approaches to fill in knowledge gaps in plant virus epidemiology. We review quantitative work on the impact of climatic fluctuations and change on plants, viruses, and vectors under different scenarios where impacts on the individual components of the plant-virus-vector interaction may vary disproportionately; there is a continuing, sometimes discordant, debate on host resistance and tolerance as plant defense mechanisms, including aspects of farmer behavior and attitudes toward disease management that may affect deployment in crops; disentangling host-virus-vector-environment interactions, as these contribute to temporal and spatial disease progress in field populations; computational techniques for estimating epidemiological parameters from field observations; and the use of optimal control analysis to assess disease control options. We end by proposing new challenges and questions in plant virus epidemiology.
Jeger MJ, Fielder H, Beale T, et al., 2023, What Can Be Learned by a Synoptic Review of Plant Disease Epidemics and Outbreaks Published in 2021?, Phytopathology, Vol: 113, Pages: 1141-1158, ISSN: 0031-949X
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
Jeger MJ, 2022, The impact of climate change on disease in wild plant populations and communities, Plant Pathology, Vol: 71, Pages: 111-130, ISSN: 0032-0862
Disease in wild plant populations has received less attention from plant pathologists than diseases of managed plants in agriculture, horticulture, and plantation forestry. Plant ecologists, however, have contributed much to an understanding of how pathogens, other plant–microbe interactions, and arthropods affect population structure and community assemblages of wild plants. Consequentially, this lack of attention has meant that the potential impacts of climate change on disease in wild plant populations are less appreciated than on major food crops, where modelling of such impacts is now well established. However, plant ecologists and soil microbiologists have long studied long-term climatic effects through a combination of observational studies and manipulative field experiments. Here, strategies are discussed to bring together these different perspectives into an integrated approach to address the future impacts of climate change on plant, environmental, and ecosystem health. The approach taken will be first to note the temporal and spatial scales that can be considered, ranging from microhabitats to whole biomes, review what is known about climate change impacts on natural vegetation, referring briefly to climate change impacts on crop diseases, and then what is known about impacts in wild populations at both the individual species and also the ecosystem level. The more general area of plant–soil–microbe–pathogen interactions is covered as one of the more important areas where climate change may have much impact on plant health through indirect rather than direct effects. The special cases of introduced invasive plants and the connectedness of agricultural systems with the wider landscape are discussed.
Tayeh C, Mannino MR, Mosbach-Schulz O, et al., 2022, Proposal of a ranking methodology for plant threats in the EU, EFSA JOURNAL, Vol: 20
Cunniffe NJ, Taylor NP, Hamelin FM, et al., 2021, Epidemiological and ecological consequences of virus manipulation of host and vector in plant virus transmission., PLoS Computational Biology, Vol: 17, Pages: 1-41, ISSN: 1553-734X
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.
Jeger M, Beresford R, Bock C, et al., 2021, Global challenges facing plant pathology: multidisciplinary approaches to meet the food security and environmental challenges in the mid-twenty-first century, CABI Agriculture and Bioscience, Vol: 2, Pages: 1-18, ISSN: 2662-4044
The discipline of plant pathology has an expanding remit requiring a multi-faceted, interdisciplinary approach to capture the complexity of interactions for any given disease, disease complex or syndrome. This review discussed recent developments in plant pathology research and identifies some key issues that, we anticipate, must be faced to meet the food security and environmental challenges that will arise over coming decades. In meeting these issues, the challenge in turn is for the plant pathology community to respond by contributing to a wider forum for multidisciplinary research, recognising that impact will depend not just on advances in the plant pathology discipline alone, but on interactions more broadly with other agricultural and ecological sciences, and with the needs of national and global policies and regulation. A challenge more readily met once plant pathologists again gather physically at international meetings and return to the professional and social encounters that are fertile grounds for developing new ideas and forging collaborative approaches both within plant pathology and with other disciplines. In this review we emphasise, in particular: the multidisciplinary links between plant pathology and other disciplines; disease management, including precision agriculture, plant growth and development, and decision analysis and disease risk; the development and use of new and novel plant protection chemicals; new ways of exploiting host genetic diversity including host resistance deployment; a new perspective on biological control and microbial interactions; advances in surveillance and detection technologies; invasion of exotic and re-emerging plant pathogens; and the consequences of climate change affecting all aspects of agriculture, the environment, and their interactions. We draw conclusions in each of these areas, but in reaching forward over the next few decades, these inevitably lead to further research questions rather than solutions to the
Jeger MJ, 2020, The epidemiology of plant virus disease: towards a new synthesis, Plants, Vol: 9, ISSN: 2223-7747
Epidemiology is the science of how disease develops in populations, with applications inhuman, animal and plant diseases. For plant diseases, epidemiology has developed as a quantitativescience with the aims of describing, understanding and predicting epidemics, and intervening tomitigate their consequences in plant populations. Although the central focus of epidemiology isat the population level, it is often necessary to recognise the system hierarchies present by scalingdown to the individual plant/cellular level and scaling up to the community/landscape level. This isparticularly important for diseases caused by plant viruses, which in most cases are transmittedby arthropod vectors. This leads to range of virus-plant, virus-vector and vector-plant interactionsgiving 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 diseasemanagement, host resistance deployment, and the health of wild plant communities. Over the last twodecades, 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 thegreater emphasis on shorter often annual time scales in epidemiological studies. It is argued here thatincorporating an epidemiological perspective, specifically quantitative, into this developing synthesiswill lead to new directions in plant virus research and disease management. This synthesis can serveto further consolidate and transform epidemiology as a key element in plant virus research.
Jeger M, Fereres A, Mauck K, et al., 2020, Reducing the spread of plant viruses through communication and global cooperation, VIRUS RESEARCH, Vol: 288, ISSN: 0168-1702
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Quinlan MM, Leach A, Jeger M, et al., 2020, Pest risk management in trade: The opportunity from using integrated combined measures in a systems approach (ispm 14), Outlooks on Pest Management, Vol: 31, Pages: 106-112, ISSN: 1743-1026
During the International Year of Plant Health, the role of pest risk management in trade is reemphasised. Systems Approach uses a combination of measures to reduce pest risk, making it more robust against failure than a single pre-export phytosanitary measure. The original context for formalising Systems Approach in an International Standard for Phytosanitary Measures (ISPM 14) is considered next to today’s global situation. A summary of advantages and challenges for implementation concludes with recommendations. The use of decision support tools is highlighted as one way to increase confidence in the efficacy of a system that may include very different types of measures with varying kinds of supportive evidence. Ultimately trust and confidence between trade partners is key to finding pest risk management that allows safe trade. At a time of global economic stress, this article encourages those involved in trade to embrace Systems Approach as an effective approach to preventing the spread of plant pests, as coordinated by the International Plant Protection Convention and its over 180 member countries.
Allen LJS, Bokil VA, Cunniffe NJ, et al., 2019, Modelling vector transmission and epidemiology of co-infecting plant viruses, Viruses, Vol: 11, ISSN: 1999-4915
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.
Hamelin FM, Allen LJS, Bokil VA, et al., 2019, Coinfections by noninteracting pathogens are not independent and require new tests of interaction, PLoS Biology, Vol: 17, ISSN: 1544-9173
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.
Bokil VA, Allen LJS, Jeger MJ, et al., 2019, Optimal control of a vectored plant disease model for a crop with continuous replanting, Journal of Biological Dynamics, Vol: 13, Pages: 325-353, ISSN: 1751-3758
Vector-transmitted diseases of plants have had devastating effects on agricultural production worldwide, resulting in drastic reductions in yield for crops such as cotton, soybean, tomato, and cassava. Plant-vector-virus models with continuous replanting are investigated in terms of the effects of selection of cuttings, roguing, and insecticide use on disease prevalence in plants. Previous models are extended to include two replanting strategies: frequencyreplanting and abundance-replanting. In frequency-replanting, replanting of infected cuttings depends on the selection frequency parameter ε, whereas in abundance-replanting, replanting depends on plant abundance via a selection rate parameter also denoted as ε. The two models are analysed and new thresholds for disease elimination are defined for each model. Parameter values for cassava, whiteflies, and African cassava mosaic virus serve as a case study. A numerical sensitivity analysis illustrates how the equilibrium densities of healthy and infected plants vary with parameter values. Optimal control theory is used to investigate the effects of roguing and insecticide use with a goal of maximizing the healthy plants that are harvested. Differences in the control strategies in the two models are seen for large values of ε. Also, the combined strategy of roguing and insecticide use performs better than a single control.
Baker E, Jeger MJ, Mumford JD, et al., 2019, Enhancing plant biosecurity with citizen science monitoring: comparing methodologies using reports of acute oak decline, Journal of Geographical Systems, Vol: 21, Pages: 111-131, ISSN: 1435-5930
Monitoring of forest pests and diseases is resource-intensive, requiring individual woodlands and trees to be visited and assessed for symptoms. Climate change and increased global connectivity are amplifying the scale of the monitoring challenge, with the number of new plant biosecurity threats increasing each year. Citizen science can increase the scale of pest and disease surveys. However, it is argued that citizen science data can be biased and inaccurate. This study examines potential biases in citizen science data by focusing on the case study of acute oak decline (AOD), a disease syndrome impacting native oaks within the UK associated with the beetle Agrilus biguttatus. Analysis was performed using two contrasting citizen science data set sources: the National Biodiversity Network (NBN) Atlas, which is a repository for citizen science data sets, and Tree Alert, a targeted citizen science project that encouraged landowners and the public to report the occurrence of AOD. For both data sets, detection was more likely in locations with higher Coleoptera reports, suggesting that there are hubs of recorder activity. For the NBN data set, A. biguttatus was more likely to be found in areas where historic parks and gardens were present. For the Tree Alert data set, A. biguttatus was less likely to be found on open access land, indicating that the programme was successful in engaging private landowners. These results indicate that understanding sources of bias within reporting schemes is an important step in data analysis and that the inclusion of structured survey designs would enable the extent of biases to be documented.
Jeger M, Bragard C, 2019, The epidemiology of xylella fastidiosa; a perspective on current knowledge and framework to investigate plant host-vector-pathogen interactions, Phytopathology: International Journal of the American Phytopathological Society, Vol: 109, Pages: 200-209, ISSN: 0031-949X
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.
Jeger MJ, 2018, Consequences of plant disease introductions: From crop loss mitigation to environmental impact, International Congress of Plant Pathology (ICPP), Publisher: AMER PHYTOPATHOLOGICAL SOC, ISSN: 0031-949X
Jeger M, Bragard C, Caffier D, et al., 2018, Guidance on quantitative pest risk assessment, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
Jeger MJ, Madden LV, van den Bosch F, 2018, Plant virus epidemiology: applications and prospects for mathematical modelling and analysis to improve understanding and disease control, Plant Disease, ISSN: 0191-2917
In recent years mathematical modelling has increasingly been used to complement experimental and observational studies of biological phenomena across different levels of organization (Chew et al. 2014). In this article we consider the contribution of mathematical models developed using a wide range of techniques and uses to the study of plant virus disease epidemics. Our emphasis is on the extent to which models have contributed to answering biological questions and indeed raised questions related to the epidemiology and ecology of plant viruses and the diseases caused. In some cases, models have led to direct applications in disease control, but arguably their impact is better judged through their influence in guiding research direction and improving understanding across the characteristic spatiotemporal scales of plant virus epidemics. We restrict this article to plant virus diseases for reasons of length and to maintain focus even though we recognize that modelling has played a major and perhaps greater part in the epidemiology of other plant pathogen taxa, including vector-borne bacteria and phytoplasmas.
Jeger M, Bragard C, Caffier D, et al., 2018, Evaluation of a paper by Guarnaccia etal. (2017) on the first report of Phyllosticta citricarpa in Europe, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
Benford D, Halldorsson T, Jeger MJ, et al., 2018, Guidance on Uncertainty Analysis in Scientific Assessments, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
Benford D, Halldorsson T, Jeger MJ, et al., 2018, The principles and methods behind EFSA's Guidance on Uncertainty Analysis in Scientific Assessment, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
Jeger MJ, 2017, Editorial, EUROPEAN JOURNAL OF PLANT PATHOLOGY, Vol: 149, Pages: 243-243, ISSN: 0929-1873
Thomas-Sharma S, Andrade-Piedra J, Carvajal Yepes M, et al., 2017, A Risk Assessment Framework for Seed Degeneration: Informing an Integrated Seed Health Strategy for Vegetatively Propagated Crops, Phytopathology, Vol: 107, Pages: 1123-1135, ISSN: 0031-949X
Pathogen buildup in vegetative planting material, termed seeddegeneration, is a major problem in many low-income countries. Whensmallholder farmers use seed produced on-farm or acquired outsidecertified programs, it is often infected. We introduce a risk assessmentframework for seed degeneration, evaluating the relative performance ofindividual and combined components of an integrated seed health strategy.The frequency distribution of management performance outcomes wasevaluated for models incorporating biological and environmental heterogeneity,with the following results. (1) On-farm seed selection can performas well as certified seed, if the rate of success in selecting healthy plantsfor seed production is high; (2) when choosing among within-seasonmanagement strategies, external inoculum can determine the relativeusefulness of ‘incidence-altering management’ (affecting the proportionof diseased plants/seeds) and ‘rate-altering management’ (affectingthe rate of disease transmission in the field); (3) under severe diseasescenarios, where it is difficult to implement management componentsat high levels of effectiveness, combining management componentscan be synergistic and keep seed degeneration below a threshold;(4) combining management components can also close the yield gapbetween average and worst-case scenarios. We also illustrate thepotential for expert elicitation to provide parameter estimates whenempirical data are unavailable.
Hilker FM, Allen LJS, Bokil VA, et al., 2017, Modeling Virus Coinfection to Inform Management of Maize Lethal Necrosis in Kenya, Phytopathology, Vol: 107, Pages: 1095-1108, ISSN: 0031-949X
Maize lethal necrosis (MLN) has emerged as a serious threat to foodsecurity in sub-Saharan Africa. MLN is caused by coinfection with twoviruses, Maize chlorotic mottle virus and a potyvirus, often Sugarcanemosaic virus. To better understand the dynamics of MLN and to provideinsight into disease management, we modeled the spread of the virusescausing MLN within and between growing seasons. The model allows fortransmission via vectors, soil, and seed, as well as exogenous sources ofinfection. Following model parameterization, we predict how managementaffects disease prevalence and crop performance over multipleseasons. Resource-rich farmers with large holdings can achieve goodcontrol by combining clean seed and insect control. However, croprotation is often required to effect full control. Resource-poor farmerswith smaller holdings must rely on rotation and roguing, and achievemore limited control. For both types of farmer, unless management issynchronized over large areas, exogenous sources of infection can thwartcontrol. As well as providing practical guidance, our modeling frameworkis potentially informative for other cropping systems in which coinfectionhas devastating effects. Our work also emphasizes how mathematicalmodeling can inform management of an emerging disease even whenepidemiological information remains scanty.
Jeger M, Bosque-Perez NA, Fereres A, et al., 2017, Building bridges between disciplines for sustainable management of plant virus diseases, VIRUS RESEARCH, Vol: 241, Pages: 1-2, ISSN: 0168-1702
Van den Bosch F, Jeger MJ, 2017, The basic reproduction number of vector-borne plant virus epidemics, Virus Research, Vol: 241, Pages: 196-202, ISSN: 0168-1702
The basic reproduction number R0 is a key parameter in plant disease epidemiology, which largely determines whether or not an epidemic will occur in a plant population. The next generation matrix approach to deriving and calculating the basic reproduction number of a plant virus epidemic is described. The approach is illustrated through a series of examples of increasing complexity, ranging from the simplest case of one vector transmitting one virus to a single host, to the case of multiple vectors, to combined horizontal (vector) and vertical (seed) transmission, and where vector control using insecticides is practised. The importance of parameters representing host and vector population dynamics and their interaction in the absence of disease is stressed, and the constraints these place on the calculation of the basic reproduction number. Finally, mention is made of further elaborations to the approach that could prove useful in plant virus epidemiology.
Hamelin FM, Hilker FM, Sun TA, et al., 2017, The evolution of parasitic and mutualistic plant-virus symbioses through transmission-virulence trade-offs., Virus Research, Vol: 241, Pages: 77-87, ISSN: 0168-1702
Virus-plant interactions range from parasitism to mutualism. Viruses have been shown to increase fecundity of infected plants in comparison with uninfected plants under certain environmental conditions. Increased fecundity of infected plants may benefit both the plant and the virus as seed transmission is one of the main virus transmission pathways, in addition to vector transmission. Trade-offs between vertical (seed) and horizontal (vector) transmission pathways may involve virulence, defined here as decreased fecundity in infected plants. To better understand plant-virus symbiosis evolution, we explore the ecological and evolutionary interplay of virus transmission modes when infection can lead to an increase in plant fecundity. We consider two possible trade-offs: vertical seed transmission vs infected plant fecundity, and horizontal vector transmission vs infected plant fecundity (virulence). Through mathematical models and numerical simulations, we show (1) that a trade-off between virulence and vertical transmission can lead to virus extinction during the course of evolution, (2) that evolutionary branching can occur with subsequent coexistence of mutualistic and parasitic virus strains, and (3) that mutualism can out-compete parasitism in the long-run. In passing, we show that ecological bi-stability is possible in a very simple discrete-time epidemic model. Possible extensions of this study include the evolution of conditional (environment-dependent) mutualism in plant viruses.
Brown N, Jeger M, Kirk S, et al., 2017, Acute Oak Decline and Agrilus biguttatus: The Co-Occurrence of Stem Bleeding and D-Shaped Emergence Holes in Great Britain, Forests, Vol: 8, ISSN: 1999-4907
Acute Oak Decline (AOD) is a new condition affecting both species of native oak,Quercus robur and Quercus petraea, in Great Britain. The decline is characterised by a distinctiveset of externally visible stem symptoms; bark cracks that “weep” dark exudate are found abovenecrotic lesions in the inner bark. Emergence holes of the buprestid beetle, Agrilus biguttatus areoften also seen on the stems of oak within affected woodlands. This investigation assesses the extentto which the external symptoms of these two agents co-occur and reveals the spatial and temporalpatterns present in affected woodland. Annual monitoring in eight affected woodlands showed thatstem bleeding and emergence holes frequently occur on the same trees, with new emergence holessignificantly more likely to occur when trees already have stem bleeds. Trials with coloured prismtraps confirm A. biguttatus was present at all experimental sites. Beetle emergence is linked primarilyto a few heavily declining trees, indicating that susceptibility may vary between hosts and that thosewith reduced health may be predisposed to AOD. Stem bleeds occur on trees in close proximity tothe locations of trees with exit holes.
Jeger MJ, Pautasso M, Stancanelli G, et al., 2016, The EFSA assessment of Trichilogaster acaciaelongifoliae as biocontrol agent of the invasive alien plant Acacia longifolia: a new area of activity for the EFSA Plant Health Panel?, EPPO Bulletin, Vol: 46, Pages: 270-274, ISSN: 0250-8052
This paper summarizes the first assessment by the European Food Safety Authority (EFSA) Plant Health (PLH) Panel of a biological control agent (BCA) of an invasive plant. This followed a request by the European Union (EU) Commission to assess the risk to plant health in the EU of an intentional release of the bud-galling wasp Trichilogaster acaciaelongifoliae for the control of Acacia longifolia. The EFSA PLH Panel also published a statement on the process of assessing the risk of the intentional releases of BCAs of invasive alien plants. Trichilogaster acaciaelongifoliae feeds on A. longifolia and Acacia floribunda. Acacia longifolia is an invasive alien plant species that has a negative effect on biodiversity and ecosystems in Portugal, whereas A. floribunda is not invasive in the EU. Both species are cultivated as ornamental plants in some EU countries. Climatic conditions in the EU are suitable for establishment of T. acaciaelongifoliae where host species are present. This BCA is moderately likely to spread in the EU by natural means, but could be intentionally moved to control A. longifolia in other locations. Its potential effects on invasive A. longifolia and on the cultivated ornamentals were assessed. The EFSA PLH Panel has shown with this work how such advice could be provided in the European Union.
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