Anticipating and responding to biological complexity in the effects of climate change on agriculture

The effects of climate change on biological systems are complex. This is particularly apparent for multispecies systems such as plant diseases and plant-herbivore interactions where climate can affect each species individually as well as influencing the interactions between species. Climate change-driven shifts in agricultural patterns and practices add another layer of complexity (Savary et al., Field Crops Res., 2005, 91:263-271). Plant diseases and insect pests have important impacts on agricultural systems; for example, agricultural losses to plant disease are estimated at over 10% (Savary et al., Ann. Rev. Phytopathol., 2006, 44:89-112). Thus, as a first step it will be important to develop an adequate conceptual framework for anticipating the biological complexity of the responses of these systems to climate change. Secondly, an adequate conceptual framework for the effects of different adaptation and mitigation scenarios, with their own complexities, will be needed to evaluate appropriate responses. Our objective is to develop frameworks to help meet this need, and here we outline a modeling structure for these components, with an emphasis on plant disease. The impact of climate, through weather patterns, on plant disease has been studied in detail for several important plant diseases (Garrett et al., Ann. Rev. Phytopathol., 2006, 44:489-509). It is possible to predict with reasonable confidence whether disease will become more or less important within a field as a function of weather variables

Spatio-temporal distribution of Erysiphe necator genetic groups and their relationship with disease levels in vineyards

International audienceThe discovery of genetically distinct Erysiphe necator groups (A or B), with high phenotypic similarities, raises important questions about their coexistence. For plant pathogens, niche partitioning, allowing the coexistence on the same host (i.e. the same resource), might result from separation in space and/or time. We used a landscape genetic approach to study the geographic distribution of genetic groups of E. necator (distinguished by a SNP in the β-tubulin gene) at the spatial scale of the Languedoc-Roussillon region (southern France) and to assess the temporal succession of groups along the course of the 2007 epidemic. Spatial distribution revealed a high heterogeneity between vineyards: from 100% B to 100% A, with 62% and 38% of vineyards showing a majority of A and B isolates, respectively. Temporal isolation seems to be the major mechanism in the coexistence of the two genetic groups: all isolates collected towards the end of the epidemic belonged to group B, whatever the initial frequency of genetic groups. Our results confirm that both A or B isolates can lead to flag-shoot symptoms, and showed that group A isolates tend to disappear during the course of the epidemic, whereas group B isolates may be active during the entire epidemic and involved in further production of cleistothecia, when recombination takes place. For the first time, the relationship between the frequency of genetic groups and disease levels on leaves and clusters at the end of the epidemic was evaluated. We showed a strong relationship between the disease severity and the genetic composition of E. necator populations: the damage was more important when the epidemic was initiated by B isolates

Effect of weather factors on the release of ascospores of Uncinula necator, the cause of grape powdery mildew, in the Bordeaux region

International audienceAu cours de 5 années consécutives (1993-1997), la projection des ascospores d'Uncinula necator (Schweiniz) Burrill a été suivie par piégeage en conditions naturelles dans la région bordelaise. La projection des ascospores débute toujours après le débourrement et se termine généralement avant la floraison. Les périodes de capture des ascospores sont toujours associées à une pluviométrie (supérieure à 2 mm avec une majorité à 6 mm ou plus), une durée d'humectation (2,5 h, généralement supérieure à 8 h), une température moyenne généralement supérieure à 11°C et un cumul des températures moyennes journalières depuis le 1 novembre jusqu'à la libération des ascospores supérieur à 1100°C. Il n'a pas été observé de relation entre la précocité, le nombre de projections et la gravité des attaques sur grappes (Vitis vinifera L. cv. Merlot). Le poids de l'inoculum initial ne semble pas être déterminant sur le développement de la population d'oïdium. Par contre les conditions climatiques du mois d'avril (pluviométrie et température) semblent influencer fortement l'intensité de la maladie sur baies en permettant l'installation du parasite sur feuilles. Les informations recueillies pourront être utilisées pour déterminer les dates optimales des premières interventions contre l'oïdium de la vigne en fonction des conditions climatiques

Modelling and mapping potential epidemics of wheat diseases—examples on leaf rust and Septoria tritici blotch using EPIWHEAT

Policy makers and researchers need to develop long-term priorities using reliable, quantitative tools to assess the risks associated with plant diseases over a range of plant pathogens and over space. EPIWHEAT is a generic simulation model designed to analyse potential disease epidemics in wheat, i.e., epidemics that depend only on the physical environment, and that are not constrained by any disease control. The model is developed on a core structure involving healthy, latent, infectious, and removed sites, and accounts for lesion expansion. It simulates in a simple way host dynamics (growth and senescence). The model involves as few parameters as possible, and a few driving functions. Here, EPIWHEAT is populated with parameters for brown rust (leaf rust; Puccinia triticina) and Septoria tritici blotch (Zymoseptoria tritici). Simulated epidemics are compared to observations at the field, national (France), and European scales. The model appears to represent a sound basis for predicting potential epidemics of wheat foliar diseases at large scales. Areas for model development are documented and discussed. EPIWHEAT appears to provide a simple, generic, transparent, flexible, and reliable platform to modelling potential epidemics caused by leaf pathogens of wheat

A review of principles for sustainable pest management in rice

This review addresses four principles on which sustainable pest management in rice is to be grounded. The goal of modern pest management is to contribute to agricultural sustainability, with its different facets (food security, balanced relations between man-made and natural ecosystems, conservation of ecosystem services). The four principles are considered in turn within the classic Human - Pest - Environment - Crop framework. Biodiversity, as a first principle, is fundamental to the functioning of food webs. The second principle, host plant resistance (HPR), is a pro-poor, and an often highly efficient element that critically contributes to sustainable crop protection. HPR needs to account for the other principles in its implementation in order to sustain durable resistances over time and space. The third principle, landscape ecology, encompasses inter-linked levels of spatial hierarchies governing the performance of systems (pests, host plants, plant genotypic make-ups, plant and crop physiology, trophic chains, and the physical environment). The fourth principle, hierarchies, concerns the different levels of hierarchy in a landscape, from biological to social. This principle concerns the very fabric of human societies, which involve perceptions, knowledge, and attitudes, which translate into decision-making at several scales, from the individual farmer to policy-makers. This principle thus addresses psychological, policy, and decision-making dimensions. In this review, all organisms that may be harmful to rice are referred to as 'pests', including pathogens and animal pests. We do not address all rice pests, but proceed through a few key examples, nor do we enter into the specifics of pest management strategies covering the range of rice production situations. This is because of the very large range of rice pests, of the corresponding diversity of rice production situations worldwide, of the unprecedented rate of diversification of rice production in response to environmental, climatic, social, and economic drivers, and lastly because plant protection in rice faces emerging crop health challenges that continually call for new solutions in new contexts. The review shows that the considered framework - Human - Pest - Environment - Crop - applies, with each of its summits having a different bearing depending on the pest considered. The review further underlines the need for basic research across a range of disciplines, with novel approaches and methods, as well as the need for connecting hierarchy levels, from farmers, to consumers, to societies, the environment, and to policies. © 2011 Elsevier Ltd

Simulation modelling of yield losses caused by wheat stem rust

Stem rust, or black rust, of wheat, caused by Puccinia graminis f. sp. tritici, has recently re-emerged in several parts of the world, with epidemics occurring in eastern Africa, as well as northern and southern Europe. Damage mechanisms from disease dynamically affect the physiology of the crop as it grows and develops, and as the epidemic progresses, leading to yield losses in the stem rust-diseased wheat stand. Process-based agrophysiological models that include disease-induced damage mechanisms can help to better understand the physiological processes leading to yield losses, and to inform strategic decisions such as breeding strategies. Such models have not been developed for wheat stem rust so far. Two damage mechanisms for stem rust, light stealing and assimilate diversion, were incorporated in the agrophysiological simulation model WHEATPEST. The model, tested from experimental field data retrieved from the literature, provides a satisfactory representation of the system, although consistently underestimates relative yield losses by about 6.9%, resulting in relative yield losses between 17% and 56%. Analyses highlight the importance of the diversion of assimilates toward the pathogen in the magnitude of yield loss. Considering only the reduction of green leaf area would underestimate damage from stem rust by at least threefold. The analysis also shows the importance of the dynamic interplay between disease and crop growth, especially the dynamics of leaf area, on yield loss. Directions to consider additional damage mechanisms are proposed, and perspectives for future research, especially in relation to plant breeding strategies under climate change, are offered