Crop architecture and crop tolerance to fungal diseases and insect herbivory. Mechanisms to limit crop losses

Plant tolerance to biotic stresses (mostly limited here to fungal pathogens and insects) is the ability of a plant to maintain performance in the presence of expressed disease or insect herbivory. It differs from resistance (the capacity to eliminate or limit pests and pathogens by genetic and molecular mechanisms) and avoidance (the ability to escape infection by epidemics). The ways to tolerance of pests and diseases are multiple and expressed at different scales. The contribution of organs to the capture and use of resources depends on canopy and root architecture, so the respective locations of disease and plant organs will have a strong effect on the crop’s response. Similarly, tolerance is increased when the period of crop sensitivity lies outside the period within which the pest or pathogen is present. The ability of the plant to compensate for the reduced acquisition of resources by the production of new organs or by remobilization of reserves may also mitigate biotic stress effects. Numerous examples exist in the literature and are described in this article. Quantification of tolerance remains difficult because of: (i) the large number of potential mechanisms involved; (ii) different rates of development of plants, pests and pathogens; and (iii) various compensatory mechanisms. Modelling is, therefore, a valuable tool to quantify losses, but also to prioritize the processes involved.     

The impact of global warming on plant diseases and insect vectors in Sweden

Cold winters and geographic isolation have hitherto protected the Nordic countries from many plant pathogens and insect pests, leading to a comparatively low input of pesticides. The changing climate is projected to lead to a greater rise in temperature in this region, compared to the global mean. In Scandinavia, a milder and more humid climate implies extended growing seasons and possibilities to introduce new crops, but also opportunities for crop pests and pathogens to thrive in the absence of long cold periods. Increased temperatures, changed precipitation patterns and new cultivation practices may lead to a dramatic change in crop health. Examples of diseases and insect pest problems predicted to increase in incidence and severity due to global warming are discussed.     

Klimawandel als neue Herausforderung für die Modellierung von Pflanzen und Schaderregern – eine kritische Betrachtung

Pests (weeds, insect pests and plant pathogens) represent a major constraint to crop yield even under current climate conditions. How is climate change going to influence pests and damage caused by them? Unfortunately, it is impossible to conduct holistic and multiple experiments which cover all possible combinations of soil, climate, plants, pests and all interactions among these components. Thus models have to be used to simulate the impacts of climate change to increase scientific understanding. This literature survey summarizes knowledge about known pest and crop models concerning the different approaches for modelling, the spatial and temporal scales of models, uncertainties resulting from work with chaotic systems and the quality of data used in models, discussing 13 critical points, which are describing problems, which have to be resolved, but give also some hints for developing new strategies for modelling and for improving models that are currently used. The problems most difficult to resolve are the impossibility to predict changes of pests themselves, the insufficient representation of the complexities of the relations in the system “climate-plant-pest-soil-socio-economic implications”, still too large uncertainties of climate and crop models, still too large spatial and temporal scales of used climate models and missing important physiological processes, like compensation and stimulation responses in crop models. These processes are the causes for changes in function norms and norms of responses to the environment of the new system “diseased plant”.     

Control of crop diseases through Integrated Crop Management to deliver climate-smart farming systems for low- and high-input crop production

Crop diseases affect crop yield and quality and cause significant losses of total food production worldwide. With the ever-increasing world population and decreasing land and water resources, there is a need not only to produce more food but also to reduce agricultural greenhouse gas (GHG) emissions to mitigate climate change and avoid land use change and biodiversity loss. Thus, alternative climate-smart farming systems need to adapt to produce more food per hectare in a more sustainable way than conventional high-input farming systems. In addition to breeding new high-yielding cultivars adapted to future climates, there is a need to deploy Integrated Crop Management (ICM) strategies, relying less on synthetic inputs for fertilization and crop protection and less on fossil fuel-powered machinery to decrease yield losses due to pest and pathogens and guarantee food security. In this review, we compare some low-input farming systems to conventional agricultural systems with a focus on ICM solutions being developed to reduce synthetic inputs; these include crop genetic resistance to pathogens, intercropping, canopy architecture manipulation, and crop rotation. These techniques have potential to decrease crop disease frequency and severity by decreasing amounts and dispersal of pathogen inoculum and by producing microclimates that are less favourable for pathogen development, while decreasing GHG emissions and improving environmental sustainability. More research is needed to determine the best deployment of these ICM strategies in various cropping systems to maximize yield, crop protection, and other ecosystem services to address trade-offs between climate change and food security.     

Why are plant pathogens under-represented in eco-climatic niche modelling?

Abstract

Eco-climatic niche models are powerful tools for assessing the potential range of plant pests and pathogens, widely applied in comprehensive pest risk assessments globally. We conducted a bibliometric analysis comparing the number of CLIMEX models developed for plant pathogens and plant arthropod pests. We found that plant pathogens were statistically significantly under-represented, with fungal plant pathogens less than half as likely as plant insect pests to be the subject of a published CLIMEX niche model. We explore key factors that may account for this disparity, including inconsistent experimental paradigms and lack of cross-disciplinary (i.e., plant pathology and modelling) expertise.     

Extremwetterlagen und Auswirkungen auf Schaderreger – extreme Wissenslücken

Climate Change is likely to increase the frequency, intensity, spatial extent, duration and timing of weather and climate extremes and can result in unprecedented extremes. Managed systems like agriculture are not immune to them. Studying the rapidly growing body of climate change literature it has been noted that there are only a few papers concerning the influences of extreme weather on agriculture. Projections of future impacts of extreme weather cannot always be made with a high level of confidence. Pests (weeds, insect pests and plant pathogens) represent a major constraint to crop production. The present paper analyses scientific literature published since 1945 concerning the knowledge about the influences of extreme weather on incidence of pests in wheat, barley, maize, beet, potato, rape, forage crops and grassland. Only 63 papers were found. Insect pests and plant pathogenic fungi of maize and wheat are most investigated. The most papers describe the influences of drought, dryness heat and heavy down pours. There are enormously knowledge gaps. On the basis of this it is not possible to assess the influences of weather extremes in a changing climate on pests and yield loss current. More research in this field is needed urgently.     

Current knowledge on plant/canopy architectural traits that reduce the expression and development of epidemics

To reduce the use of pesticides, innovative studies have been developed to introduce the plant as the centre of the crop protection system. The aim of this paper is to explain how architectural traits of plants and canopies induce a more or less severe epidemic and how they may be modified in order to reduce disease development. In particular, it focuses on three key questions: i) which processes linked to epidemics can be influenced by architecture ii) how can architecture be characterized relative to these modes of action, and iii) how can these effects be explored and exploited? The roles of plant/canopy architecture on inoculum interception, on epidemic development via the microclimate and on tissue receptivity are discussed. In addition, the concepts of disease avoidance, canopy porosity and an ideotype unfavourable for disease development are described. This paper shows that many advances have already been made, but progress is still required in four main fields: microclimatology, mathematical modelling of plants, molecular genetics and ideotype conception.     

Extremwetterlagen und Schaderreger – extreme Wissenslücken

Here we reviewed the possible impacts of weather extremes on pests (weeds, insect pests and plant pathogens) of wine, hope, apple and asparagus by analyzing scientific literature published since 1945, concerning the knowledge about the influences of extreme weather on incidence of these pests. A weather extreme event is generally defined as the occurrence of a value of a weather variable above or below a threshold value near the upper or lower tails of the range of observed values of the variable (IPCC). Although there are still many open scientific questions, climate change will likely lead to increase the frequency, intensity, spatial extent, duration and timing of weather and climate extremes and can result in unprecedented extremes. After considering all the results of derivative analysis, we concluded that the knowledge gap is enormously. Only 13 papers were found. These few papers concerning the influence of storm, hail, flooding, dryness or heavy down pours on the pests of apple (10 papers), asparagus (2 papers) or wine (1 paper). Thus projections of future impacts of extreme weather on plant pests and yields cannot be made with a high level of confidence. More research to get more primary results and data is needed urgently.     

Plant—pathogen Interactions: Genetic and Comparative Analyses

The interactions between plants and pathogens can be shifted to favor either plant of pathogen by small changes in the environment, primarily temperature and plant nutrition, and it leaves a quandary as to whether the plant on pathogen is most affected by the change in the environment. The stage of development of a plant can affect the resistance or susceptibility to a pathogen. A plant may be susceptible to a given pathogen a one stage of development but resistant at another stage of development. The view of the gene-for-gene hypotheses as a one-for-one relationship is not supported by experiments that ask whether avirulence genes and resistance genes function alone. The term genomics has been intemreted several different ways, but its most useful impact on studies of host-pathogen interactions will, most likely, be to find all the pieces to the puzzle of how plants and pathogens communicate.     

@RISK在有害生物定量风险评估中的应用

定性风险评估和定量风险评估是有害生物风险分析的主要方法,@RISK是进行定量风险评估的重要软件工具之一。本文在回顾有害生物定性风险评估与定量风险评估概念、关系及优缺点的基础上,综合分析了国内外使用@RISK软件针对植物病原物和害虫进行定量风险评估的发展现状,并就@RISK的未来应用提出了相关建议。     

Effect of light and dark on the growth and development of downy mildew pathogen Hyaloperonospora arabidopsidis

Disease development in plants requires a susceptible host, a virulent pathogen, and a favourable environment. Oomycete pathogens cause many important diseases and have evolved sophisticated molecular mechanisms to manipulate their hosts. Day length has been shown to impact plant–oomycete interactions but a need exists for a tractable reference system to understand the mechanistic interplay between light regulation, oomycete pathogen virulence, and plant host immunity. Here we present data demonstrating that light is a critical factor in the interaction between Arabidopsis thaliana and its naturally occurring downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa). We investigated the role of light on spore germination, mycelium development, sporulation, and oospore formation of Hpa, along with defence responses in the host. We observed abundant Hpa sporulation on compatible Arabidopsis under day lengths ranging from 10 to 14 hr. In contrast, exposure to constant light or constant dark suppressed sporulation. Exposure to constant dark suppressed spore germination, mycelial development, and oospore formation, whereas exposure to constant light stimulated these three stages of development. A biomarker of plant immune system activation was induced under both constant light and constant dark. Altogether, these findings demonstrate that Hpa has the molecular mechanisms to perceive and respond to light and that both the host and pathogen responses are influenced by the light regime. Therefore, this pathosystem can be used for investigations to understand the molecular mechanisms through which oomycete pathogens like Hpa perceive and integrate light signals, and how light influences pathogen virulence and host immunity during their interactions.     

A systematic review of the literature reveals trends and gaps in integrated pest management studies conducted in the United States

Integrated pest management (IPM) is a broad‐based approach for addressing pests that negatively affect human and environmental health and economic profitability. Weeds, insects and disease‐causing pathogens (diseases) are the pests most often associated with IPM. A systematic review, widely used in other scientific disciplines, was employed to determine the most commonly studied IPM topics and summarize the reasons for these trends and the gaps. In a field synopsis of the literature, 1679 relevant published papers were identified and categorized into one of the following five broad areas: IPM and organic (organic), climate change and pests (climate), rural and urban IPM (rural and urban), next‐generation education (education) and advanced production systems (technology). Papers were examined in greater detail for at least one of the three main pests in a systematic review. A majority (85%) of IPM papers have been in the area of rural and urban IPM, primarily addressing agriculture (78%). Professionals, landowners and the general public were the focus of a majority (95%) of IPM papers on education. Technology is an increasing area of focus in the literature. Over the past 40 years, IPM papers have primarily (75%) addressed insects and been limited mostly to rural and urban settings. Climate change, technology and education specific to pest management studies are increasingly being published and will help broaden the focus that could result in increased adoption and development of IPM. © 2017 Society of Chemical Industry     

Sensorik für einen präzisierten Pflanzenschutz

Precision agriculture is a management concept depending on information technologies related to within-field variability. Site-specific plant production requires the use of technologies, such as global positioning systems, sensors, and information management tools to assess variations in soil, crop canopy and micro-climate. Crop protection is an important production factor, which at present is applied in high-input cropping systems homogeneously in the field despite of site-specific heterogeneity in the incidence and distribution of weeds, pests and pathogens. The spatial and temporal heterogeneity of pests in the field is assessed using remote sensing techniques linked to global positioning systems. The generation and management of information on pest incidence with high spatial resolution and its conversion into precise control systems will enable a targeted and resource-preserving integrated pest management system under high productivity conditions, which is economically successful, environmentally sound and socially acceptable. The recording of disease-related weather data and the assessment of spatial heterogeneity of micro-climate in the field as well as the detection of disease specific symptoms with remote and near range sensors (multispectral and hyperspectral cameras, thermography, chlorophyll fluorescence etc.) have the potential to make crop protection more precise in space and time. Innovative approaches are discussed in detail.     

Risk of establishment of non-indigenous diseases of citrus fruit and foliage in Spain: An approach using meteorological databases and tree canopy climate data

Based on macroclimate comparisons of monthly means of temperature and rainfall, the Mediterranean-type climate might be considered unfavorable for the establishment of the quarantine pathogens of fruit and foliage of citrus regulated by the EC Council Directive 2000/29. The presence of free water on the canopy during periods with temperatures favorable for disease development seems to be limited by the characteristic rainless summer. However, our field study showed that due to the formation of dew, rainfall and rain days were not positively correlated with canopy wetness. Dew periods were quite frequent during summer nights with temperatures over 15°C and even 20°C. Nevertheless, wetness periods were seldom continuous and they were usually interrupted by dry periods approximately 10–14 h long. In contrast to some endemic foliar pathogens such asAlternaria alternata, no data are currently available on the performance of these non-indigenous pathogens under interrupted wetness conditions. Due to the lack of rain during the summer in semi-arid areas, the natural spread of rain-disseminated citrus pathogens, such asElsinoë spp. andXanthomonas axonopodis pv.citri, might be rather limited. However, windborne pathogens, such asGuignardia citricarpa andPseudocercospora angolensis, would have considerable potential for dissemination under the Mediterranean climate. We consider that more information about the effect of microclimate on the epidemiology of these diseases is needed to estimate accurately their risk of establishment in Spain and in other citrus-growing countries of the Mediterranean Basin.     

Detailing Köppen–Geiger climate zones at sub‐national to continental scale: a resource for pest risk analysis

The widely used Köppen–Geiger climate classification system can inform judgements of establishment during pest categorizations and systems of simplified pest risk assessment. Such processes allow national plant protection organizations to quickly identify plant pests of potential regulatory concern. Judging whether a pest can establish is a key factor in determining whether a pest satisfies the definition of a quarantine pest. Climate is often a significant factor influencing where species can establish. Here, we provide a resource that reports the Köppen–Geiger climate classification at a range of spatial scales from sub‐national to continental for the period 1986–2010 in an accessible table. The data is provided as a resource for pest risk analysis to inform and support rapid decision‐making. An online appendix is provided showing the number of grid cells in each of the 31 Köppen–Geiger climate types in 417 regions across the globe at country level or less. Thirteen climate types occur within the European Union (EU), the most common is ‘temperate oceanic’ occupying 48% of EU grid cells. Twenty‐four of 31 climate types occur within the EPPO region; the most common is ‘continental, uniform precipitation with cold summer’, occupying 35% of EPPO grid cells.     

气候变化下山东稻区水稻重大害虫灾变规律及其防控评价——以郯城为例

山东稻区是我国典型的单季中熟水稻种植区。近年来,随着气候变化加剧、主栽品种更新换代及栽培制度变迁等,该区水稻害虫表现出新的灾变特点。以山东水稻主栽区临沂市郯城县1994—2009年水稻害虫监测预警与防控的历史虫情资料为基础,结合同期气象数据分析气候变化下水稻害虫发生及其危害损失,并评估植物保护措施的控害保产效果。结果显示年均温和年降雨量与二化螟和稻飞虱的发生危害面积和水稻产量损失之间相关不显著,但与稻纵卷叶螟的发生危害面积和水稻产量损失之间相关显著甚至极显著。可见,通过积极开展水稻害虫的准确监测和及时防控,可有效提高气候变化下水稻害虫的管理水平,从而确保粮食安全生产,进而保障农民增产增收。     

Plant architecture, its diversity and manipulation in agronomic conditions, in relation with pest and pathogen attacks

Plant architectural traits have been reported to impact pest and disease, i.e., attackers, incidence on several crops and to potentially provide alternative, although partial, solutions to limit chemical applications. In this paper, we introduce the major concepts of plant architecture analysis that can be used for investigating plant interactions with attacker development. We briefly review how primary growth, branching and reiteration allow the plant to develop its 3D structure which properties may allow it (or not) to escape or survive to attacks. Different scales are considered: (i) the organs, in which nature, shape and position may influence pest and pathogen attack and development; (ii) the individual plant form, especially the spatial distribution of leaves in space which determines the within-plant micro-climate and the shoot distribution, topological connections which influence the within-plant propagation of attackers; and (iii) the plant population, in which density and spatial arrangement affect the micro-climate gradients within the canopy and may lead to different risks of propagation from plant to plant. At the individual scale, we show how growth, branching and flowering traits combine to confer to every plant species an intrinsic architectural model. However, these traits vary quantitatively between genotypes within the species. In addition, we analyze how they can be modulated throughout plant ontogeny and by environmental conditions, here considered lato sensu, i.e. including climatic conditions and manipulations by humans. Examples from different plant species with various architectural types, in particular for wheat and apple, are provided to draw a comprehensive view of possible plant protection strategies which could benefit from plant architectural traits, their genetic variability as well as their plasticity to environmental conditions and agronomic manipulations. Associations between species and/or genotypes having different susceptibility and form could also open new solutions to improve the tolerance to pest and disease at whole population scale.     

Impacts of climate change on plant diseases—opinions and trends

There has been a remarkable scientific output on the topic of how climate change is likely to affect plant diseases. This overview addresses the need for review of this burgeoning literature by summarizing opinions of previous reviews and trends in recent studies on the impacts of climate change on plant health. Sudden Oak Death is used as an introductory case study: Californian forests could become even more susceptible to this emerging plant disease, if spring precipitations will be accompanied by warmer temperatures, although climate shifts may also affect the current synchronicity between host cambium activity and pathogen colonization rate. A summary of observed and predicted climate changes, as well as of direct effects of climate change on pathosystems, is provided. Prediction and management of climate change effects on plant health are complicated by indirect effects and the interactions with global change drivers. Uncertainty in models of plant disease development under climate change calls for a diversity of management strategies, from more participatory approaches to interdisciplinary science. Involvement of stakeholders and scientists from outside plant pathology shows the importance of trade-offs, for example in the land-sharing vs. sparing debate. Further research is needed on climate change and plant health in mountain, boreal, Mediterranean and tropical regions, with multiple climate change factors and scenarios (including our responses to it, e.g. the assisted migration of plants), in relation to endophytes, viruses and mycorrhiza, using long-term and large-scale datasets and considering various plant disease control methods.     

Gesunde Pflanzen unter zukünftigem Klima

Predicted changes in average values of global climate variables (increased temperatures, altered precipitation patterns, increased concentrations of atmospheric CO₂) and changes in the frequency, duration, and degree of extremes (frost, heat, drought, hail, storms, floods, etc.) will affect agricultural crops, agroecosystems, and agricultural productivity. Although forecasts of regional climate changes are still imprecise, mean temperature increases in Europe are expected to be greater in the north (2.5–4.5°C) than in the south (1.5–4.5°C). Regional forecasts for precipitation changes are also very far from precise; however, problems with drought are expected to increase, especially in Mediterranean countries. Overall, shortage of water will be the predominant factor affecting plant growth. As higher temperatures are known to enhance plant development and especially the grain-filling duration of cereals, grain yield losses are possible in a warmer climate. On the other hand, elevated atmospheric CO₂ concentrations are known to stimulate photosynthesis and enhance growth and yield (“CO₂ fertilization”); concomitantly, leaf transpiration is reduced, resulting in improved water use efficiency. Total biomass and yield were enhanced by 20–30% in experiments with elevated CO₂ exposure (550–700 ppm) under more or less ideal growth conditions. Elucidating the interactions between positive and negative effects of climate change is of crucial importance for any prediction of future crop yields. The present paper is a brief summary mainly of the potential effects of elevated temperatures and atmospheric CO₂ on crop growth, quality, and yield. Also, adaptation measures, possible interactive effects of different climate variables, and interactions of climate change components with other growth variables (pathogens, air pollutants) are briefly described.     

Simulation model of Oulema melanopus in the winter-wheat ecosystem1

Simulation system sonches (Simulation of Nonlinear Complex Hierarchical Ecological Systems) is a tool for computer-aided experimental investigation of the dynamic behaviour of ecological systems. A winter-wheat agroecosystem was modelled with the help of sonches . The whole model consists of several submodels. One of them is the growth-development model of winter wheat itself. The others are pest models. The model of cereal leaf beetle (Oulema melanopus) was investigated. The main driving force in the model is daily mean temperature. The temperature inside the plant canopy is different from the temperature outside it (at the meteorological station). A microclimate model was used to modify the measured temperature values. Simulation experiments were carried out to show the effect of using microclimate data instead of standard meteorological data. The difference between the temperature inside and outside the canopy depends on radiation. The days of the vegetation period were classified by sunshine duration: clear, cloudy and overcast days. Winter wheat treated with different amounts of nitrogen fertilizer has a different canopy structure. The microclimate inside the canopy alters according to density. Results of simulation experiments in the form of population dynamics are presented.