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Growing together mixture of cultivars with contrasting level of resistance to disease has been shown as a way of reducing fungal aerial disease severityon crops. In order to improve the design of cultivar mixture for reducing splash dispersed diseases such as septoria tritici blotch, caused by Zymoseptoriatritici, our objective is to understand the role of the canopy architecture of wheat cultivar mixture. Two mechanisms related to the effect of canopyarchitecture on the epidemiological are studied here. The first one is the impact of architecture of each cultivar on the barrier effect provided by resistantplants among susceptible plants that reduce the dispersion of fungal spore. The second one is the possible modification of the microclimate within themixture compared to pure stand that could foster some epidemiological processes. We used a mechanistic modelling approach within an explicitdescription of canopy architecture and splash dispersal processes. Dispersal patterns in cultivar mixtures with either similar (70 cm height) or contrastedstraw height (120 cm and 70 cm) were compared. Spore interception on susceptible plants was lower when the susceptible cultivar was mixed with a tallresistant cultivar rather than with a resistant cultivar of the same height. This result was confirmed with field experiments with a reduction of AUDPCclose to 50%. Field experiments show also that within denser canopy the barrier effect is enhanced but on the other hand the leaf wetness durationincreased and could foster the disease. These results suggest that considering cultivar architecture in mixture design is as an additional lever to enhancemixture effects on foliar splash-dispersed diseases.

The study of climate change (CC) impact on pathosystems requires more attention. For several aerial fungal diseases of crop ecosystems facing climate change, the network ACCAF-Clif allowed a strong interaction between research and extension. In this framework, modelling of epidemiological risks under past or future climate was implemented in relation with crop adaptation resulting from climate change.Experimental results showed that taking into account the diversity of plant pathogens has to be priotarized. The balance between integration approach using modelling and experimental multifactorial comparison makes it possible to analyse and predict the behaviour of simple or a fortiori multiple pathosystems. Operational results include CC perception by agricultural sectors, modelling outputs on two pathosystems (potato mildew, wheat-airborne diseases) under climate change, and using scenarios of adaptation to abiotic stresses in external forcing of pathosystem models.Perspectives will involve (i) taking into account patterns of local adaptation of pathogens to climate, (ii) further developping adaptation of crop ecosystems to abiotic stresses and their impacts on crop diseases, and (iii) confronting pathosystem evolution under future climate to ecological niche evolution in relation to pathogen emergence.; La question de l’impact du changement climatique sur les maladies des agrosystèmes requiert une attention accrue. Pour un ensemble de maladies aériennes d’écosystèmes cultivés soumis au changement climatique, le réseau ACCAF-Clif a permis une forte interaction entre partenaires de la recherche et du développement agricole. Dans ce cadre, la modélisation des risques épidémiques sous l’action du climat passé ou futur a été mise en œuvre, en lien avec l’adaptation des cultures résultant du changement climatique.Les résultats expérimentaux montrent que la prise en compte de la diversité des agents pathogènes est une priorité. L’équilibre entre démarche d’intégration via la modélisation et la comparaison expérimentale multifactorielle de systèmes conditionne l’analyse et la prévision du comportement de pathosystèmes simples et a fortiori multiples. Les résultats opérationnels incluent la perception du changement climatique par les filières des cultures annuelles ou pérennes, la modélisation du pathosystème simple pomme de terre – mildiou et du pathosystème multiple blé-maladies aériennes en situation de changement du climat, et la mobilisation de scénarios d’adaptations aux stress abiotiques dans le forçage externe de la modélisation. Les perspectives consistent à (i) prendre en compte les patrons d’adaptation locale des pathogènes au climat, (ii) poursuivre les travaux réalisés sur l’adaptation des systèmes de culture étudiés aux stress abiotiques et leurs impacts sur les maladies, et (iii) confronter l’étude de l’évolution des pathosystèmes existants en climat futur, à celle de niches écologiques favorisant l’émergence ou la ré-émergence d’agents pathogènes

oral communication abstract; Using cultivar mixtures, i.e. growing several cultivars with different resistance traits in a same field, allows protection of susceptible cultivars and fungicide use reduction. Protective mixture effect against splash dispersed diseases such as septoria tritici blotch is variable depending on environmental conditions. Understanding disease reduction mechanisms is critical for improvement of mixture design and efficiency. Major mechanisms are related to modification of disease dispersal patterns within the mixture. Increased distance between two susceptible plants reduces spore transfer, while the presence of resistant plants provides a barrier to spore dispersal. Common mixture design recommendations include choice of cultivars with similar architecture in order to constitute homogeneous canopies which should minimize competition and ease agronomical management. However, no information is available on the possible impact of mixing cultivars with contrasted architecture on disease dispersal. We used a mechanistic modelling approach based on experimental results to characterize splash dispersal patterns in wheat cultivar mixtures with either uniform (homogeneous canopies) or contrasted straw height (heterogeneous canopies). We then performed numerical experiments to study the impact of variations in location of susceptible and resistant tissues within the canopy. Dispersal events were simulated based on field observations. Chosen rain dispersal events occurred during the post-flowering phase of wheat cycle, where disease develops on top leaves and reduces yield. At this stage, canopy structure is fully developed and fixed. Architectural measurements of individual plants were used to reconstruct static 3D mockups of pure stands and mixed canopies. Mockups provided information on resistant and susceptible tissue location within the canopies and were used to compute splash dispersal. Model inputs also included leaf disease severity and rain characteristics measured during studied dispersal events. Simulated spore dispersal was consistent with spore fluxes measured in the field. Disease reduction mechanisms that are specific to heterogeneous canopies were identified. Upper leaves of the tall cultivar acted as umbrellas by intercepting raindrops and reducing splash on diseased leaves at the bottom of the canopy. On the other hand, contaminated splash droplets produced at the same location were trapped by leaves of the lowest cultivar, thus reducing contamination of upper leaves of the tallest cultivar. Modelling results allowed quantification and hierarchisation of dispersal processes occurring in heterogeneous mixed canopies and outlined the importance of the location of resistant and susceptible organs within the canopy.

poster abstract; Crop canopy architecture affects the dispersal of airborne fungal spores of plant diseases, in particular in the case of septoria tritici blotch (STB) which is an important wheat disease mainly spread by rain splash. Therefore, the characteristics of canopy architecture (medium of dispersal of the pathogenic agent) can be taken into account to implement alternative disease control methods in order to slow down the vertical dispersal of STB in the field. And for the particular case of cultivar mixtures, different plant architectural traits can be used to improve the “barrier” effect on spore dispersal, which is provided by the most resistant components in the mixtures (see Vidal et al. in this issue). We investigated, by the mean of experiments under controlled conditions and modelling, the effects of the canopy architecture on one dispersal cycle of spores of Zymoseptoria tritici. The experiment was performed using a simulator of artificial rains on micro-canopies of wheat (1 m2), which were grown in a controlled greenhouse environment. A linear inoculum source of spores suspension was exposed to a simulated and calibrated rainfall event in order to get reproducible splash-dispersal towards four types of canopy differing by their architectures characterized by their leaf area densities (LAD). Splash droplets of the suspension were collected at different locations within the canopies to quantify spore fluxes and the resulting disease severity and incidence were assessed after the latency period. Based on a mechanistic modelling of spore dispersal and a 3D numerical reconstruction of the canopies, we quantified strong effects of the canopy structure on the spore dispersal. Denser canopies (i.e. with higher LAD) had a higher rate of spore interception that led, (i) for susceptible cultivars, to a higher disease severity, and (ii) for the resistant cultivars, to a higher spore trapping rate and therefore to a better “barrier” effect in the case of cultivar mixtures.

Mixing varieties with different levels of disease resistance provide a way to limit the progression of polycyclic epidemics. In such mixture configurations, susceptible varieties are protected by the presence of more resistant ones through two main mechanisms: barrier and dilution effects within the mixture. However, the effectiveness of these mixtures in terms of disease reduction can vary widely depending on the pathosystem, the dispersion mechanism and climatic conditions. Such variability has notably been pointed out in the case of the rainsplash dispersed disease, Septoria tritici blotch (STB, caused by Zymoseptoria tritici). Considering the impact of crop architecture on epidemic development within pure stands, the architectural lever, which consists of mixing plants, which differ in their architectural properties, appears as a candidate to improve mixture efficiency to control epidemics. The work presented here aimed at assessing if contrasted architecture between varieties could be an additional lever to design cultivar mixtures in addition to resistance. To this end, we conducted a micro-plot field trial in which we studied mixtures of cultivars with contrasted resistance to STB and either similar or contrasted architecture (difference in straw height). These cultivars were also grown in pure stands as a reference. Pathogen vertical dispersal gradients, STB severity at leaf scale, crop architecture and microclimatic conditions were monitored and compared between the different types of mixtures and pure stands during an annual epidemic. We highlighted the relative protection of susceptible short-strawed wheat in mixture with partially resistant tall-strawed wheat compared to the pure stand and the mixture with partially resistant short-strawed wheat. Mixed with a partially resistant tallstrawed wheat, severity of the three upper leaves of the susceptible cultivar was reduced by 53% compared to the conventional mixture and by 68% compared to the pure stand. The number of new lesions on the susceptible component was also reduced in mixtures with contrasted architecture of their components partly due to a stronger umbrella effect (raindrops interception by resistant leaves). This study outlines that mixtures efficiency to control STB progress can be improved by combining components of contrasted architecture in the design of cultivar mixtures in addition to resistance.

Les associations de variétés de blé permettent, sous certaines conditions, de réduire la progression de maladies foliaires telles que la septoriose. Les mécanismes impliqués reposent principalement sur une différence de niveau de résistance entre les variétés associées : une variété sensible peut ainsi être protégée par une variété résistante. Il est généralement recommandé d’associer des variétés de caractéristiques agronomiques proches afin de faciliter la gestion des cultures et de limiter la compétition entre variétés. Or, la structure des couverts a un impact sur la progression des épidémies, notamment via la dispersion des spores et le microclimat. En associant des variétés ayant des architectures contrastées, on constitue des couverts hétérogènes. Cette hétérogénéité pourrait être un levier supplémentaire pour le contrôle des maladies fongiques aériennes. Des associations de variétés différant par leurs niveaux de résistance et ayant des hauteurs de paille semblables (homogènes) ou très différentes (hétérogènes) ont été semées au champ afin de tester l'impact d'une hétérogénéité architecturale sur la progression d’épidémies de septoriose et d’analyser les mécanismes mis en jeu. Un suivi hebdomadaire de la sévérité, ainsi qu'un comptage de lésions montrent une réduction de la maladie chez la variété basse sensible (env. 0,8 m) associée à une variété haute résistante (env. 1,4 m) par comparaison avec la même variété basse en culture pure ou en association homogène. Ce constat est mis en relation avec des différences mesurées en termes de structure des couverts, de microclimat et de flux de spores. Par ailleurs, une modélisation biophysique permet de mieux identifier, quantifier et hiérarchiser les mécanismes physiques liés à la dispersion des spores dans les différents traitements, tels que les effets barrière, dilution et l'impact des différences de propriétés entre couches de couverts hétérogènes (notamment caractérisées par des proportions différentes de tissus résistants et sensibles). Nos résultats montrent que la diversité variétale et l'hétérogénéité du couvert résultante constituent un levier potentiel permettant l'amélioration de l'efficacité des associations variétales vis-à-vis de la septoriose du blé.

L’intérêt des associations variétales de blé pour freiner la propagation des maladies dispersées à longue distance par le vent est bien démontré, mais les références sont très limitées concernant les maladies dispersées à courte distance par la pluie. Des essais de recherche en épidémiologie réalisés au champ sur 5 ans montrent qu’une association de deux variétés de blé, l’une sensible et l’autre résistante à la septoriose, peut réduire de plus de moitié la sévérité de la maladie, mais de façon variable selon la pression de maladie de l’année. Les essais en vue de l’application agronomique réalisés de 2010 à 2012 sous des conditions de pression épidémique variables montrent que des associations de quatre variétés permettent de réduire les applications de fongicides d'environ 5 % tout en maintenant les rendements. Dans des essais menés sans protection fongicide, durant trois années et sur deux sites, le bénéfice d’une association de quatre variétés par rapport à la moyenne des rendements des variétés en culture monovariétale est estimé à 2,3 q/ha. Un modèle de simulation basé sur la dispersion de spores par éclaboussement de gouttes de pluie dans un couvert végétal hétérogène permet de déterminer les proportions optimales de variétés à associer en fonction de leur niveau de résistance partielle. Cette pratique culturale établie au semis, peut procurer un avantage en présence de maladies foliaires et n’est pas pénalisante en absence de maladie., The potential of wheat cultivar mixtures for reducing the spread of diseases by long-distance winddispersal is well documented, but the references are very limited for diseases spread by short-distance splash dispersal. Field epidemiological experimentations carried out over a 5-year period showed that a combination of a susceptible and a partially resistant wheat cultivar can reduce up to 40% the severity of septoria leaf blotch, which however depended on each year’s disease pressure. Extension services showed that the yield of mixtures of four wheat cultivars tested between 2010 and 2012 under different disease pressures had a 5% reduction of fungicide applications on average with the mean yield of the pure stands. In field trials without fungicide application over the 3-year period at two locations, the benefit of 4-cultivar mixtures compared to the mean of the pure stands was assessed to be 0.23 t/ha. A simulation model based on spore splash dispersal by raindrops in a heterogeneous canopy determined the optimal proportions of varieties in a two-way mixture as a function of the partial resistance level of the two varieties. This cropping system provided an advantage when foliar diseases were present and was not disadvantageous when diseases were not present.

Interactions between climate change and air pollution in the context of agriculture. Agroecosystems are sources and sinks of atmospheric pollutants and greenhouse gases. They are therefore involved in climate change and air pollution and their cross-relations. This contribution can be positive or negative. It results from complex processes, both direct and indirect, which is related to a range of topics: increase or decrease of emission and deposition, increase in fire frequency, change in plant protection etc. As for most of biological processes, there are large uncertainties and knowledge is lacking over a range of fields. However it is necessary to have a global overview of the involved processes and drivers when trying to limit the contribution of agroecosystem both to climate change and air pollution, with attention to the economic sustainability of agriculture under global change.

Ce 50ème volume de la Revue Innovations Agronomiques regroupe les résultats d'un ensemble de projets soutenus par le CTPS (Comité Technique Permanent de la Sélection).; The potential of wheat cultivar mixtures for reducing the spread of diseases by long-distance winddispersal is well documented, but the references are very limited for diseases spread by short-distance splash dispersal. Field epidemiological experimentations carried out over a 5-year period showed that a combination of a susceptible and a partially resistant wheat cultivar can reduce up to 40% the severity of septoria leaf blotch, which however depended on each year’s disease pressure. Extension services showed that the yield of mixtures of four wheat cultivars tested between 2010 and 2012 under different disease pressures had a 5% reduction of fungicide applications on average with the mean yield of the pure stands. In field trials without fungicide application over the 3-year period at two locations, the benefit of 4-cultivar mixtures compared to the mean of the pure stands was assessed to be 0.23 t/ha. A simulation model based on spore splash dispersal by raindrops in a heterogeneous canopy determined the optimal proportions of varieties in a two-way mixture as a function of the partial resistance level of the two varieties. This cropping system provided an advantage when foliar diseases were present and was not disadvantageous when diseases were not present.; L’intérêt des associations variétales de blé pour freiner la propagation des maladies dispersées à longue distance par le vent est bien démontré, mais les références sont très limitées concernant les maladies dispersées à courte distance par la pluie. Des essais de recherche en épidémiologie réalisés au champ sur 5 ans montrent qu’une association de deux variétés de blé, l’une sensible et l’autre résistante à la septoriose, peut réduire de plus de moitié la sévérité de la maladie, mais de façon variable selon la pression de maladie de l’année. Les essais en vue de l’application agronomique réalisés de 2010 à 2012 sous des conditions de pression épidémique variables montrent que des associations de quatre variétés permettent de réduire les applications de fongicides d'environ 5 % tout en maintenant les rendements. Dans des essais menés sans protection fongicide, durant trois années et sur deux sites, le bénéfice d’une association de quatre variétés par rapport à la moyenne des rendements des variétés en culture monovariétale est estimé à 2,3 q/ha. Un modèle de simulation basé sur la dispersion de spores par éclaboussement de gouttes de pluie dans un couvert végétal hétérogène permet de déterminer les proportions optimales de variétés à associer en fonction de leur niveau de résistance partielle. Cette pratique culturale établie au semis, peut procurer un avantage en présence de maladies foliaires et n’est pas pénalisante en absence de maladie.

Climate change is increasingly perceived as one of the major constraints that limit agricultural productivity. Crop losses due to climate change could be direct, such as damages through flooding or storms, or indirect such as altered distribution of crop pests. The real impact of climate change at global level is yet uncertain and likely variable from one region to another. Within this context, it is difficult to predict effects of climate change, particularly when long-term datasets from the past are missing to develop and test predictive models for the future. Nevertheless, our knowledge of plant-disease interactions, population genetics of pathogens as well as crops, and examples of overwhelming establishment of new diseases in a given region provides insights into how climate change may affect disease incidence and severity. Here we report examples of pest populations which have been established across regions previously considered detrimental for their survival and yield losses associated to these pests. Faced with the uncertainty regarding the effects of changing climate on crop protection, here we propose a number of action points that, to our opinion, may help improve current plant protection strategies. Given this uncertainty, policy, research, and extension should be prepared to promote resilience vis-à-vis pests which, at the biophysical level, entails uncovering what currently makes cropping systems resilient, while at the organizational level, the capacity to adapt needs to be recognized and strengthened (Lamichhane et al 2014). Such action points include increase in human resources, development of resilient cropping systems, more focus on crop-weed competition, anticipating of risks and international monitoring, and more effort on breeding for resistance, development of biological control strategies and pest risks analysis. This diversification could be achieved by improving current plant protection practices which might help mitigate the effect of climate change in future crop protection, particularly in the EU, but also at global level. The vision presented here is that of the ENDURE European Research Group, which brings together some of Europe’s leading agricultural research, teaching, and extension institutes with a special interest in IPM.

La santé est soumise à divers aléas, notamment climatiques.Pour gérer la santé de demain, il est urgent de concevoir des modèles intégrant les variables du climat, les caractéristiques des écosystèmes ou se développent les maladies...sans oublier l'être humain!

National audience; L'association variétale – c'est-à-dire l'association de différentes variétés d'une même espèce simultanément au sein d'une parcelle agricole – offre la possibilité de diversifier les traits de résistance aux maladies fongiques et les caractéristiques agronomiques des plantes. Bien conçues, les associations variétales permettent ainsi de mieux maîtriser les maladies et de stabiliser la quantité (rendement) et la qualité (par ex. taux de protéines) de la production. Les résultats expérimentaux montrent que l'efficacité réelle des associations dépend fortement de certains facteurs clés tels que les conditions climatiques, la pression de maladies et les modes de dispersion des agents pathogènes. L'utilisation conjointe des expérimentations au champ et de la modélisation permet d'appréhender leur fonctionnement, et notamment les détails des mécanismes impliqués. L'optimisation de la conception des associations (nombre de variétés, choix des variétés selon leurs gènes de résistances majeurs et quantitatifs et d’autres traits, proportions et agencement de ces variétés) doit tenir compte des attentes et de l'environnement de production.