P. Skelsey

Future environmental and geographic risks of Fusarium head blight of wheat in Scotland

Methods used to assess climate change risk for crop diseases often assume that both host and pathogen are present. Consequently, model output may misrepresent future growing seasons, due to a failure to reflect likely change at the landscape- and farm-scale and its impact on disease risk. In this study, data defining the spatial coverage of crops in Scotland were combined with spatially coherent, probabilistic climate change data to project the future risk of Fusarium head blight (FHB) in wheat. Primary inoculum was initially treated as non-limiting, and a widely accepted crop-disease-climate model for FHB risk assessment was used to project the risk of disease occurrence in over 50,000 crop locations. Primary inoculum was then treated as limiting, and an atmospheric dispersion model was used to modify projections according to the risk of inoculum dispersal from overwintering refugia to crop locations. In both cases it was predicted that FHB hazard will decrease in Scotland over time. Consequences for the species composition of the FHB complex and therefore the associated mycotoxin hazard were considered. To guide adaptation strategies, we also considered agronomic scenarios regarding potential climate-change-driven shifts in agricultural practices and planting patterns, and their effects on disease risk. We found that opportunities exist for increased cultivation of crops that are potent sources of Fusarium or Gibberella inoculum, and for movement of crops away from coastal areas vulnerable to sea-level rise, with little additional risk of FHB. These projections, made by considering the temporal and spatial coincidence of host and pathogen species under various climate change scenarios, suggest that improved control of FHB might not be a high priority for future food security in Scotland.

Pest and disease management: why we shouldn’t go against the grain

Given the wide range of scales and mechanisms by which pest or disease agents disperse, it is unclear whether there might exist a general relationship between scale of host heterogeneity and spatial spread that could be exploited by available management options. In this model-based study, we investigate the interaction between host distributions and the spread of pests and diseases using an array of models that encompass the dispersal and spread of a diverse range of economically important species: a major insect pest of coniferous forests in western North America, the mountain pine beetle (Dendroctonus ponderosae); the bacterium Pseudomonas syringae, one of the most-widespread and best-studied bacterial plant pathogens; the mosquito Culex erraticus, an important vector for many human and animal pathogens, including West Nile Virus; and the oomycete Phytophthora infestans, the causal agent of potato late blight. Our model results reveal an interesting general phenomenon: a unimodal (‘humpbacked’) relationship in the magnitude of infestation (an index of dispersal or population spread) with increasing grain size (i.e., the finest scale of patchiness) in the host distribution. Pest and disease management strategies targeting different aspects of host pattern (e.g., abundance, aggregation, isolation, quality) modified the shape of this relationship, but not the general unimodal form. This is a previously unreported effect that provides insight into the spatial scale at which management interventions are most likely to be successful, which, notably, do not always match the scale corresponding to maximum infestation. Our findings could provide a new basis for explaining historical outbreak events, and have implications for biosecurity and public health preparedness.

Crop connectivity under climate change: future environmental and geographic risks of potato late blight in Scotland

The impact of climate change on dispersal processes is largely ignored in risk assessments for crop diseases, as inoculum is generally assumed to be ubiquitous and nonlimiting. We suggest that consideration of the impact of climate change on the connectivity of crops for inoculum transmission may provide additional explanatory and predictive power in disease risk assessments, leading to improved recommendations for agricultural adaptation to climate change. In this study, a crop-growth model was combined with aerobiological models and a newly developed infection risk model to provide a framework for quantifying the impact of future climates on the risk of disease occurrence and spread. The integrated model uses standard meteorological variables and can be easily adapted to various crop pathosystems characterized by airborne inoculum. In a case study, the framework was used with data defining the spatial distribution of potato crops in Scotland and spatially coherent, probabilistic climate change data to project the future connectivity of crop distributions for Phytophthora infestans (causal agent of potato late blight) inoculum and the subsequent risk of infection. Projections and control recommendations are provided for multiple combinations of potato cultivar and CO2 emissions scenario, and temporal and spatial averaging schemes. Overall, we found that relative to current climatic conditions, the risk of late blight will increase in Scotland during the first half of the potato growing season and decrease during the second half. To guide adaptation strategies, we also investigated the potential impact of climate change-driven shifts in the cropping season. Advancing the start of the potato growing season by 1xa0month proved to be an effective strategy from both an agronomic and late blight management perspective.

Forecasting the spread of aerially transmitted crop diseases with a binary classifier for inoculum survival

The risk of between-field spread of disease is typically omitted from crop disease warning systems, as it is difficult to know the number and location of inoculum sources and thus predict the abundance of inoculum arriving at healthy crops. In this study we explored the utility of a simple approach to predicting risk of between-field spread, based on the estimated probability that inoculum will survive the transportation process. Using potato late blight as a case study, the effects of solar radiation on the viability of detached Phytophthora infestans sporangia were assessed. A model to estimate the probability of spore survival was derived using a binomial Generalized Linear Mixed Model (GLMM), and receiver operating characteristic curve (ROC) analysis and cross-validation were used to evaluate the global performance of the model as a binary classifier for discriminating between viable and non-viable sporangia. The model yielded an area under the ROC curve of 0.92 (95% CI = 0.90-0.93), signifying an excellent classification algorithm. Inspection of the curve provided a number of suitable decision threshold (or cut-off) probabilities for discriminating between viable and non-viable sporangia. The classifier was tested as a forecasting system for potato late blight outbreaks using 10 years of outbreak data from across Great Britain. There was a marked differentiation among the cut-offs, but the best prediction outcome was an accuracy of 89% with an alert frequency of 1 in 7 days. Our model can be easily modified or our methodology replicated for other pathosystems characterised by airborne inoculum. n nThis article is protected by copyright. All rights reserved.

Potential impacts of climate change on the threat of potato cyst nematode species in Great Britain

Potato cyst nematode (PCN) species have different temperature optima for various life cycle stages, therefore a risk assessment of the threat of PCN species under future climates is essential to guide adaptation strategies. Data defining the spatial coverage of potato crops in Great Britain were combined with probabilistic climate change data and a newly developed PCN life cycle model to project the future risk to potato crops from PCN. The model was based on the results of controlled environment experiments to investigate the effect of temperature on survival to female maturity using three PCN populations: Globoderaxa0pallida (Lindley) and G.xa0rostochiensis from the James Hutton Institute PCN collection, and a field population of G.xa0pallida (S-Fife). We found that projected increases in soil temperature could result in increased survival to female maturity for all three PCN populations, with greater increases expected for Scotland, followed by Wales then England. The largest projected increases in Scotland were for G.xa0pallida, whereas G.xa0rostochiensis showed the largest increases in Wales and England. We also investigated the potential impact of several agronomic adaptation strategies on projected PCN risk. The results from the model suggested that soil infestation levels would have to be reduced by up to 40% in order to negate projected increases in PCN risk, and that advancing the start date of the growing season or modifying planting patterns could be successful strategies to reduce future PCN risk. n nThis article is protected by copyright. All rights reserved.

Threat of establishment of non-indigenous potato blackleg and tuber soft rot pathogens in Great Britain under climate change

Potato blackleg and soft rot caused by Pectobacterium and Dickeya species are among the most significant bacterial diseases affecting potato production globally. In this study we estimate the impact of future temperatures on establishment of non-indigenous but confirmed Pectobacterium and Dickeya species in Great Britain (GB). The calculations are based on probabilistic climate change data and a model fitted to disease severity data from a controlled environment tuber assay with the dominant potato blackleg and soft rot-causing species in GB (P. atrosepticum), and three of the main causative agents in Europe (P. carotovorum subsp. brasiliense, P. parmentieri, Dickeya solani). Our aim was to investigate if the European strains could become stronger competitors in the GB potato ecosystem as the climate warms, on the basis of their aggressiveness in tubers at different temperatures. Principally, we found that the tissue macerating capacity of all four pathogens will increase in GB under all emissions scenarios. The predominant Pectobacterium and Dickeya species in Europe are able to cause disease in tubers under field conditions currently seen in GB but are not expected to become widely established in the future, at least on the basis of their aggressiveness in tubers relative to P. atrosepticum under GB conditions. Our key take-home messages are that the GB potato industry is well positioned to continue to thrive via current best management practices and continued reinforcement of existing legislation.