244 results found
Jeger MJ, 2021, The impact of climate change on disease in wild plant populations and communities, Plant Pathology, 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.
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
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
Benford D, Halldorsson T, Jeger MJ, et al., 2018, Guidance on Uncertainty Analysis in Scientific Assessments, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
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, The principles and methods behind EFSA's Guidance on Uncertainty Analysis in Scientific Assessment, EFSA JOURNAL, Vol: 16, ISSN: 1831-4732
Jeger MJ, Madden LV, van den Bosch F, 2017, 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.
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.
Jeger MJ, 2017, Editorial, EUROPEAN JOURNAL OF PLANT PATHOLOGY, Vol: 149, Pages: 243-243, ISSN: 0929-1873
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.
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.
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
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.
Hamelin FM, Allen LJS, Prendeville HR, et al., 2016, The evolution of plant virus transmission pathways, Journal of Theoretical Biology, Vol: 396, Pages: 75-89, ISSN: 1095-8541
The evolution of plant virus transmission pathways is studied through transmission via seed, pollen, or a vector. We address the questions: under what circumstances does vector transmission make pollen transmission redundant? Can evolution lead to the coexistence of multiple virus transmission pathways? We restrict the analysis to an annual plant population in which reproduction through seed is obligatory. A semi-discrete model with pollen, seed, and vector transmission is formulated to investigate these questions. We assume vector and pollen transmission rates are frequency-dependent and density-dependent, respectively. An ecological stability analysis is performed for the semi-discrete model and used to inform an evolutionary study of trade-offs between pollen and seed versus vector transmission. Evolutionary dynamics critically depend on the shape of the trade-off functions. Assuming a trade-off between pollen and vector transmission, evolution either leads to an evolutionarily stable mix of pollen and vector transmission (concave trade-off) or there is evolutionary bi-stability (convex trade-off); the presence of pollen transmission may prevent evolution of vector transmission. Considering a trade-off between seed and vector transmission, evolutionary branching and the subsequent coexistence of pollen-borne and vector-borne strains is possible. This study contributes to the theory behind the diversity of plant–virus transmission patterns observed in nature.
Pautasso M, Jeger MJ, 2016, How long does it take to deliver a peer review report? A decade of data from the European Journal of Plant Pathology, EUROPEAN JOURNAL OF PLANT PATHOLOGY, Vol: 144, Pages: 231-233, ISSN: 0929-1873
Kiss L, Holb IJ, Rossi V, et al., 2015, Foreword: Special issue on fungal grapevine diseases, European Journal of Plant Pathology, Vol: 144, Pages: 693-694, ISSN: 1573-8469
Brown N, Jeger M, Kirk S, et al., 2015, Spatial and temporal patterns in symptom expression within eight woodlands affected by Acute Oak Decline, Forest Ecology and Management, Vol: 360, Pages: 97-109, ISSN: 0378-1127
Acute Oak Decline (AOD) is a newly defined condition in the UK that forms a distinct component within the wider oak decline complex. It can be identified by distinctive stem symptoms, dark liquid seeping out between the bark plates from areas of necrosis in the cambial tissue, which are found in conjunction with signs of the two spotted oak buprestid Agrilus biguttatus. Novel bacterial species have been isolated from the inner bark necrosis, but little is known regarding the spatial and temporal patterns of AOD symptoms expression. This study presents the results from eight plots across southern and central England monitored for three to four years between 2009 and 2012. These data give a first description of the epidemiology of AOD. Findings suggest affected trees occur in localised clusters rather than at random through the plots, pointing to biotic rather than wider scale environmental effects such as drought. In addition, contagion (spread of symptoms between neighbouring trees) was demonstrated. Previously, mortality was described as occurring soon after infection; current data suggests this is longer than two years. 23.5% of oak with both stem bleeds and exit holes in 2009 died during the monitoring period. Exit holes were observed on hosts for the first time in the final years before death linking them to the later stages of decline. Finally, a large proportion of lightly infected individuals have been shown to form callus over the previous year’s stem symptoms and enter remission. This finding suggests host resistance may provide some scope for management of AOD.
Jeger MJ, Xu X-M, 2015, Modelling the dynamics of a plant pathogen and a biological control agent in relation to flowering pattern and populations present on leaves, Ecological Modelling, Vol: 313, Pages: 13-28, ISSN: 0304-3800
A flexible model for biological control of a plant pathogen affecting host flowers is developed which takes into account the transfer of both the plant pathogen and the biological control agent (BCA) from the leaves to flowers. Because flowers, other than in ornamental plants, are largely ephemeral, the emphasis in analysis is on the rates of transfer and establishment on flowers. The form of the model analysed depends upon: the pattern of flowering for a particular host plant, a single instantaneous flush or continuous seasonal production; the effect of flowering phenology and morphology on transfer of both the pathogen and BCA; and the transient dynamics of such transfer. In the case of a single instantaneous flush, the relative importance of mycoparasitism and competition in protecting flowers during their short period of blooming is assessed. Where flowering is continuous but transfer lags behind because of floral phenology or morphology, a comparison is made between the initial levels of the pathogen and the BCA as they transfer to the flowers, depending again on the relative contribution of mycoparasitism and competition over the extended period of blooming. Differential rates of transfer of the pathogen and the BCA, depending on their time-dependent population densities on leaves, have a major impact on eventual biocontrol outcomes. The model results are used to analyse biocontrol strategies for contrasting host-pathogen systems which show different flowering patterns and biological control mechanisms. For Erwinia amylovora causing fireblight in pome fruit trees, an inundative biocontrol strategy targeting flowers is supported. In Botrytis cinerea, there is considerable potential for a strategy based on the establishment of BCAs on leaves for some of the plant hosts affected.
Baker R, Bragard C, Caffier D, et al., 2015, Risk to plant health in the EU territory of the intentional release of the bud- galling wasp Trichilogaster acaciaelongifoliae for the control of the invasive alien plant Acacia longifolia, EFSA JOURNAL, Vol: 13
Jeger MJ, van den Bosch F, McRoberts N, 2015, Modelling transmission characteristics and epidemic development of the tospovirus-thrip interaction, ARTHROPOD-PLANT INTERACTIONS, Vol: 9, Pages: 107-120, ISSN: 1872-8855
Brown N, Inward DJG, Jeger M, et al., 2014, A review of Agrilus biguttatus in UK forests and its relationship with acute oak decline, Forestry, Vol: 88, Pages: 53-63, ISSN: 0015-752X
Agrilus biguttatus Fab. (Coleoptera: Buprestidae) is a European bark-boring beetle whose larvae feed in the vascular tissue of oak trees. Until recently, it was considered rare in Britain, but sightings have become more frequent and it is often found on weakened trees suffering from Acute Oak Decline (AOD). This rapidly acting syndrome is characterized by patches of dark sticky fluid exuding from cracks on the trunk, with areas of necrotic tissue beneath, probably caused by a pathogenic bacterial component. However, the frequent association of AOD with the larval galleries and distinctive adult exit holes of A. biguttatus has raised concerns that the beetle may be contributing to the AOD syndrome or hastening the mortality of affected trees. This review evaluates the potential role of A. biguttatus in the AOD complex. Information on the beetle's life cycle and ecology is assessed along with the apparent increase in its abundance and distribution in the UK, and likely mechanisms of host selection. Oak tree defences against the beetle are discussed, as well as risk factors influencing susceptibility. Research on related Agrilus species is reviewed so that insights into the relationship between the beetle, the bacteria and the host tree can be made through comparisons with more extensively studied species. Possible management options in an AOD context are considered, and priority areas for future research are identified.
Denman S, Brown N, Kirk S, et al., 2014, A description of the symptoms of Acute Oak Decline in Britain and a comparative review on causes of similar disorders on oak in Europe, FORESTRY, Vol: 87, Pages: 535-551, ISSN: 0015-752X
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