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International audience; CONTEXT: More diversified crop rotations are a key factor in reducing weed, disease and pest pressure while reducing the use of phytosanitary products. The increase in available data calls for the development of new methods and indicators to characterize crop rotations.OBJECTIVES: This paper presents an application of network analysis to assess the diversity of crop rotations from the Land Parcel Identification System, which now provides field boundaries and type of crops grown in a given year for farmers receiving subsidies from the European Common Agricultural Policy. Different indicators are presented to compare the diversity of crop rotations for the 22 regions of mainland France (corresponding to the boundaries of former administrative regions) and the influence of some methodological choices are discussed. METHODS: Using LPIS data, previous-following crop pairs have been identified for two thirds of the French fields for three crop successions (from 2017 to 2018, from 2018 to 2019 and from 2019 to 2020). These data were used to build crop rotation networks for each region. Crop rotations were simulated from those networks in order to estimate the return time of soft winter wheat, which is the most cultivated crop in the country.RESULTS AND CONCLUSION: Crop rotation networks were similar between the three crop successions compared, but differed among regions. Ignoring the most uncommon previous-following crop pairs, the mean number of precedents per crop ranged from three to nine depending on the region. The estimated return times for winter wheat increase when taking into account grasslands in crop rotation networks, but in any case the use of phy-tosanitary products was negatively correlated with the return time. SIGNIFICANCE: The methodology developed in this article provides some initial guidelines for developing relevant agronomic indicators from crop rotation network analysis. It has been shown that the estimated return time could be an indicator of the intensity of use of phytosanitary products, and could therefore be used to guide public policies aimed at reducing the use of these products.; LE CONTEXTEDes rotations de cultures plus diversifiées sont un facteur clé pour réduire la pression des mauvaises herbes, des maladies et des ravageurs tout en réduisant l'utilisation de produits phytosanitaires. L'augmentation des données disponibles nécessite le développement de nouvelles méthodes et indicateurs pour caractériser les rotations culturales.OBJECTIFSCet article présente une application de l'analyse de réseau pour évaluer la diversité des rotations de cultures à partir du Land Parcel Identification System, qui fournit désormais les limites des champs et le type de cultures cultivées au cours d'une année donnée pour les agriculteurs recevant des subventions de la politique agricole commune européenne. Différents indicateurs sont présentés pour comparer la diversité des assolements pour les 22 régions métropolitaines (correspondant aux limites des anciennes régions administratives) et l'influence de certains choix méthodologiques est discutée.MÉTHODESA partir des données du SIPA, des couples de cultures précédent-suivant ont été identifiés pour les deux tiers des champs français pour trois successions de cultures (de 2017 à 2018, de 2018 à 2019 et de 2019 à 2020). Ces données ont été utilisées pour construire des réseaux de rotation des cultures pour chaque région. Des rotations de cultures ont été simulées à partir de ces réseaux afin d'estimer le temps de retour du blé tendre d'hiver, qui est la culture la plus cultivée dans le pays.RÉSULTATS ET CONCLUSIONLes réseaux de rotation des cultures étaient similaires entre les trois successions de cultures comparées, mais différaient selon les régions. En ignorant les paires de cultures précédentes-suivantes les plus rares, le nombre moyen de précédents par culture variait de trois à neuf selon la région. Les temps de retour estimés pour le blé d'hiver augmentent avec la prise en compte des prairies dans les réseaux de rotation des cultures, mais dans tous les cas l'utilisation de produits phytosanitaires est corrélée négativement avec le temps de retour.IMPORTANCELa méthodologie développée dans cet article fournit quelques premières lignes directrices pour développer des indicateurs agronomiques pertinents à partir de l'analyse des réseaux de rotation des cultures. Il a été montré que le temps de retour estimé pouvait être un indicateur de l'intensité d'utilisation des produits phytosanitaires, et pouvait donc être utilisé pour orienter les politiques publiques visant à réduire l'utilisation de ces produits.

Shoot architecture is a key component of the interactions between plants and their environment. We present a novel model of grass, which fully integrates shoot morphogenesis and the metabolism of carbon (C) and nitrogen (N) at organ scale, within a three-dimensional representation of plant architecture. Plant morphogenesis is seen as a self-regulated system driven by two main mechanisms. First, the rate of organ extension and the establishment of architectural traits are regulated by concentrations of C and N metabolites in the growth zones and the temperature. Second, the timing of extension is regulated by rules coordinating successive phytomers instead of a thermal time schedule. Local concentrations are calculated from a model of C and N metabolism at organ scale. The three-dimensional representation allows the accurate calculation of light and temperature distribution within the architecture. The model was calibrated for wheat (Triticum aestivum) and evaluated for early vegetative stages. This approach allowed the simulation of realistic patterns of leaf dimensions, extension dynamics, and organ mass and composition. The model simulated, as emergent properties, plant and agronomic traits. Metabolic activities of growing leaves were investigated in relation to whole-plant functioning and environmental conditions. The current model is an important step towards a better understanding of the plasticity of plant phenotype in different environments.

With global production exceeding 750 million tons in 2017, wheat is considered a staple food for the world's population. Wheat mapping and monitoring could then be a very effective tool for achieving the Sustainable Development Goals (SDG2-Zero Hunger). In Lebanon, wheat receives technical and financial support, yet many errors occur in estimating the wheat acreage due to absence of reliable agricultural census and lack of wheat mapping using satellite images. In addition, identifying the best rotation type and agricultural practices leads to identify the most efficient wheat-based cropping system in terms of productivity (protein production and net profit), efficiency (water and nitrogen use), as well as the economic risk on the farmer. Thus, The aim of the current study, which is conducted in the Bekaa plain of Lebanon, is to utilize remote sensing technology and crop modelling for supporting policy makers and end-users in making strategic decisions regarding one of the most food security-driving crop in the Mediterranean (i.e. winter wheat).The first part of the thesis evaluates the potential of optical data for early winter wheat mapping by allowing the transfer of knowledge from one year to another (2016 and 2017 in this study). For its high spatial and temporal resolutions, Sentinel-2 data are employed. Results show that when the developed approach was applied on Sentinel-2 time series of 2017 in using 2016 ground truth data, the overall accuracy reaches 87.0%, whereas, when implemented using 2017 ground truth data, the overall accuracy is 82.6% on 2016 data. The outputs are executed up to six weeks before harvest, as well as distinguishing winter wheat from similar cereals (barley and triticale).The second part of the thesis examines the ability of the SAR (Synthetic Aperture Radar) C-band data of the new radar satellite (Sentinel-1) regarding its ability to monitor winter wheat crop by identifying the economically important phenological phases that cannot be detected relying solely on NDVI derived from optical satellite Sentinel-2. Results show that VV polarization at incidence angle of 32°-34° is best for predicting heading, VH polarization at incidence angle of 43°-45° for predicting soft dough, and the ratio VV/VH at incidence angle of 32°-34° for predicting germination and harvesting.The third part of the thesis is dedicated to test, in contrasted biophysical and management conditions, the hypothesis that promoting wheat-fava bean rotation leads to a significantly better productivity and resources use efficiency, as well as, reducing economic risk than the promoted intensive wheat-wheat and wheat-potato rotations. The cropping simulation model “CropSyst” is used after being calibrated and validated by using experimental data for different wheat-based rotations combining different soil, climate and management options. The results show that there is no particular optimal scenario that can simultaneously ensure high productivity, reduce economic risk, and achieve high wheat- water- and nitrogen-use efficiency. However, the wheat-fava bean rotation cultivated with no wheat fertilization appears to be a better substitute to the wheat-wheat rotation in terms of protein production in both (low and high) Water Holding Capacity (WHC) soils (0.93 t/ha versus 0.8 t/ha in low WHC and 1.34 t/ha versus 1.17 t/ha in high WHC). This cropping system could achieve a higher net profit, showing high resource-use efficiency and good economic sustainability. Moreover, a very high profit could only be attained with the wheat-potato rotation (8640 US DOLL./ha and 12170 US DOLL./ha), yet with low input-efficiency and high economic risk., Avec une production mondiale dépassant 750 millions de tonnes en 2017, le blé est considéré comme un aliment de base pour la population mondiale. Sa cartographie et sa surveillance pourraient alors se révéler être un outil très efficace pour atteindre les objectifs de développement durable (ODD2-Faim zéro). Au Liban, en vue d’assurer la sécurité alimentaire nationale, le blé reçoit un soutien financier et technique du gouvernement. Cependant, de nombreuses erreurs dans l'estimation de la superficie en blé à travers le pays sont dues principalement aux déclarations peu fiables des agriculteurs. De plus, le choix du système de culture basé sur le blé (en termes de type de rotation et de pratiques agricoles) peut avoir un impact considérable sur la productivité du système (protéines et rentabilité), l'efficacité d'utilisation des ressources (efficacité d'utilisation de l'eau et utilisation de l’azote), ainsi que sur le risque économique pour les agriculteurs. La présente étude menée dans la plaine de la Bekaa au Liban a pour objectif d'utiliser la télédétection et la modélisation de la croissance des cultures pour fournir aux décideurs politiques et aux utilisateurs finaux les informations dont ils ont besoin sur le blé d’hiver.La première partie évalue le potentiel des images optiques pour la cartographie du blé d'hiver précoce en permettant le transfert de connaissances d'une année à l'autre (2016 et 2017) Les résultats montrent que, lorsque l'approche développée est appliquée à la série chronologique Sentinel-2 de 2017, en utilisant les données de vérité au sol 2016, la précision globale atteint 87,0%, tandis que, lorsqu'elle est mise en œuvre avec les données de vérité au sol 2017, elle est de 82,6% en 2016. Les classifications pour distinguer le blé d'hiver de céréales similaires (orge et triticale) sont réalisées jusqu'à six semaines avant la récolte.La deuxième partie examine la capacité des images radar en bande C du nouveau satellite Sentinel-1 à surveiller la culture de blé d'hiver en identifiant les stades phénologiques économiquement importants qui ne peuvent pas être détectés en utilisant uniquement les indices issus de l’optique (Sentinel-2). Les résultats montrent que la polarisation VV (incidence de 32°-34°) et VH (incidence de 43°-45°) sont respectivement préférables pour estimer les stades de l'épiaison et de pâteux mou. De plus, le rapport VV/VH (incidence de 32°-34°) est préférable pour détecter la germination et la récolte.La troisième partie a pour objectif de vérifier si la rotation blé-féverole, nécessitant des intrants agricoles extensifs (eau et azote), a une performance nettement meilleure que la rotation intensive blé-blé en termes de productivité, d’utilisation rationnelle des ressources, et de minimisation du risque économique à l’échelle parcellaire. Le modèle de croissance des cultures «CropSyst» a été adopté après avoir été calibré et validé sur notre zone d'étude. Les résultats montrent qu’il n’existe pas un scénario de système de culture optimal permettant d’assurer une productivité élevée, de réduire le risque économique et d’obtenir une efficacité élevée de l’utilisation de l’eau et de l’azote. Cependant, le scenario de rotation blé-féverole sans fertilisation du blé semble être un meilleur substitut à la rotation blé-blé en termes de production de protéines. Pour un sol avec une faible capacité de rétention, la production de protéines est de 0,93 t/ha et de 0,8 t/ha respectivement pour les rotations blé-féverole et blé-blé. Pour un sol avec capacité de rétention élevée, la production de protéines est de 1,34 t/ha pour blé-féverole contre 1,17 t/ha pour blé-blé. De plus, ce système de culture blé-féverole pourrait générer un bénéfice net plus élevé que celui du blé-blé. Enfin, la rotation blé-pomme de terre peut générer des bénéfices nets très élevés (8640 US DOLL./ha et 12170 US DOLL./ha) mais avec une faible efficacité des intrants et un risque économique élevé

International audience; Smallholder farmers play a critical role in supporting food security in developing countries. Monitoring crop phenology and disturbances to crop growth is critical in strengthening farmers' ability to manage production risks. This study assesses the feasibility of using crowdsourced near-surface remote sensing imagery to monitor winter wheat phenology and identify damage events in northwest India. In particular, we demonstrate how streams of pictures of individual smallholder fields, taken using inexpensive smartphones, can be used to quantify important phenological stages in agricultural crops, specifically the wheat heading phase and how it can be used to detect lodging events, a major cause of crop damage globally. Near-surface remote sensing offers granular visual field data, providing detailed information on the timing of key developmental phases of winter wheat and crop growth disturbances that are not registered by common satellite remote sensing vegetation indices or national crop cut surveys. This illustrates the potential of near-surface remote sensing as a scalable platform for collecting high-resolution plot-specific data that can be used in supporting crop modeling, extension and insurance schemes to increase resilience to production risk and enhance food security in smallholder agricultural systems.

Nitrogen (N) deficiency and weed infestation are the main factors limiting the yield and quality of organic soft winter wheat (Triticum aestivum L.). If forage legumes are associated with wheat, simultaneously or successively, they can help to reduce the impact of limiting factors through the ecological services they provide. The aim of this study was to evaluate two intercropping strategies to increase soft winter wheat yield and protein content and improve the provided ecological services (mainly N provisioning and weed control) by white clover (Trifolium repens L.). White clover (Trifolium repens L. cv Aberdai) was intercropped with soft winter wheat (Triticum aestivum L. cv Renan) under organic conditions. Two strategies were compared, simultaneous intercropping versus relay intercropping using three field experiments. A control treatment with sole wheat crop was included in the three field experiments. Fertilization management on organic wheat was also tested (0 versus 100 kg N applied at spring time) to evaluate its incidence on cash and cover crop yields and protein content. White clover shoot dry matter (DM) was significantly higher in simultaneous intercropping compared to relay intercropping at wheat harvest (2.2 vs. 0.1 Mg DM ha−1) and at cover destruction (4.5 vs. 3.1 Mg DM ha−1). Wheat grain yield was not affected by the intercropping strategy while the protein content was significantly lower under simultaneous intercropping system (9.1% of the grain DM) compared to relay intercropping or in wheat as sole crop (10.0% of the grain DM). At cover destruction, both simultaneous and relay intercropped white clover significantly decreased weed shoot DM compared to sole wheat crop (−1.4 Mg DM ha−1 for relay intercropping and −1.8 Mg DM ha−1 for simultaneous intercropping). In comparison to relay intercropping strategy, N accumulation in white clover shoot DM was higher under simultaneous intercropping strategy at wheat harvest (52 vs. 2 kg N ha−1) and at cover destruction (123 vs. 83 kg N ha−1). In conclusion, our study has highlighted the positive effect of combining a simultaneous intercropping strategy with high N availability to guarantee a sufficient level of legume shoot DM as rapidly as possible to increase both N accumulation and weed control services, thus reducing the risk of impairing winter wheat yield and protein content.

Understanding the drivers of yield levels under climate change is required to support adaptation planning and respond to changing production risks. This study uses an ensemble of crop models applied on a spatial grid to quantify the contributions of various climatic drivers to past yield variability in grain maize and winter wheat of European cropping systems (1984–2009) and drivers of climate change impacts to 2050. Results reveal that for the current genotypes and mix of irrigated and rainfed production, climate change would lead to yield losses for grain maize and gains for winter wheat. Across Europe, on average heat stress does not increase for either crop in rainfed systems, while drought stress intensifies for maize only. In low-yielding years, drought stress persists as the main driver of losses for both crops, with elevated CO2 offering no yield benefit in these years., Drivers of crop yield variability require quantification, and historical records can help in improving understanding. Here, Webber et al. report that drought stress will remain a key driver of yield losses in wheat and maize across Europe, and benefits from CO2 will be limited in low-yielding years.

Plant nitrogen (N) information has widely been estimated through empirical techniques using hyperspectral data. However, the physical model inversion approach on N spectral response has seldom developed and remains a challenge. In this study, an N-PROSAIL model based on the N-based PROSPECT model and the SAIL model canopy model was constructed and used for retrieving crop N status both at leaf and canopy scales. The results show that the third parameter (3rd-par) retrieving strategy (leaf area index (LAI) and leaf N density (LND) optimized where other parameters in the N-PROSAIL model are set at different values at each growth stage) exhibited the highest accuracy for LAI and LND estimation, which resulted in R2 and RMSE values of 0.80 and 0.69, and 0.46 and 21.18 µg·cm−2, respectively. It also showed good results with R2 and RMSE values of 0.75 and 0.38% for leaf N concentration (LNC) and 0.82 and 0.95 g·m−2 for canopy N density (CND), respectively. The N-PROSAIL model retrieving method performed better than the vegetation index regression model (LNC: RMSE = 0.48 − 0.64%; CND: RMSE = 1.26 − 1.78 g·m−2). This study indicates the potential of using the N-PROSAIL model for crop N diagnosis on leaf and canopy scales in wheat.

National audience

Impact of the climate change on the distribution of the grains of the spike in winter wheat. 2. Agriculture and Climate Change Conference

International audience; Leaf area index and Fraction of Absorbed Photosynthetically Active Radiation are important land biophysical parameters that enable monitoring and quantitative assessment of vegetation state. Remote sensing data from space can be used to estimate these parameters at regional and national scale. High temporal satellite imagery is usually required to capture main parameters of crop growth. In this paper, we assess efficiency of using satellite images at high spatial and temporal resolution acquired within the SPOT-5 Take 5 initiative for mapping biophysical parameters.

International audience; A stumbling block to the adoption of silvoarable agroforestry systems is the lack of quantitative knowledge on the performance of different crops when competing for resources with trees. In North-Western Europe, light is likely to be the principal limiting resource for understorey crops, and most agronomic studies show a systematic reduction of final yield as shade increases. However the intensity of the crop response depends on both the environmental conditions and the shade characteristics. This study addressed the issue by monitoring winter wheat (Triticum aestivum L.) growth, productivity and quality under artificial shade provided by military camouflage shade-netting, and using the Hi-sAFe model to relate the artificial shade conditions to those applying in agroforestry systems. The field experiment was carried out over two consecutive years (2013–14 and 2014–15) on the experimental farm of Gembloux Agro-Bio Tech, Belgium. The shade structures recreated two shade conditions: periodic shade (PS) and continuous shade (CS), with the former using overlapping military camouflage netting to provide discontinuous light through the day, and the latter using conventional shade cloth. The experiment simulated shading from a canopy of late-flushing hybrid walnut leaves above winter wheat. Shading was imposed 16 (2013–14) and 10 (2014–15) days before flowering and retained until harvest. The crop experienced full light conditions until the maximum leaf area index stage (LAImax) had been reached. In both years, LAI followed the same dynamics between the different treatments, but in 2013–2014 an attack of the take-all disease (Gaeumannomyces graminis var. tritici) reduced yields overall and prevented significant treatment effects. In season 2014–15 the decrease in global radiation reaching the crop during a period of 66 days (CS: – 61% and PS: – 43%) significantly affected final yield (CS: – 45% and PS: – 25%), mainly through a reduction of the average grain weight and the number of grain per m2. Grain protein content increased by up to 45% under the CS treatment in 2015. Nevertheless, at the plot scale, protein yield (t/ha) did not compensate for the final grain yield decrease. The Hi-sAFe model was used to simulate an agroforestry plot with two lines of walnut trees running either north-south or east-west. The levels of artificial shade levels applied in this experiment were compared to those predicted beneath trees growing with similar climatic conditions in Belgium. The levels used in the CS treatment are only likely to occur real agroforestry conditions on 10% of the cropped area until the trees are 30 years old and only with east-west tree row orientation.

Uncertainty in simulating N uptake and N use efficiency in the crop rotation systems across Europe . International Crop Modelling Symposium

International audience; The strong negative correlation between grain protein concentration (GPC) and grain yield (GY) in bread wheat complicates the simultaneous improvement of these traits. However, earlier studies have concluded that the deviation from this relationship (grain protein deviation or GPD) has strong genetic basis. Genotypes with positive GPD have an increased ability to uptake nitrogen (N) during the post-flowering period independently of the amount of N taken up before flowering, suggesting that genetic variability for N satiety could enable the breakage of the negative relationship. This study is based on two genotypes markedly contrasted for GPD grown under semi-hydroponic conditions differentiated for nitrate availability both before and after flowering. This allows exploration of the genetic determinants of post-flowering N uptake (PANU) by combining whole plant sampling and targeted gene expression approaches. The results highlights the correlation (r(2) = 0.81) with GPC of PANU occurring early during grain development (flowering-flowering + 250 degree-days) independently of GY. Early PANU was in turn correlated (r(2) = 0.80) to the stem-biomass increment after flowering through its effect on N sink activity. Differences in early PANU between genotypes, despite comparable N statuses at flowering, suggest that genetic differences in N satiety could be involved in the establishment of the GPC. Through its strong negative correlation with genes implied in N assimilation, root nitrate concentration appears to be a good marker for evaluating instantaneous plant N demand, and may provide valuable information on the genotypic N satiety level. This trait may help breeders to identify genotypes having high GPC independently of their GY.

Weed control is generally considered to be essential for crop production and herbicides have become the main method used for weed control in developed countries. However, concerns about harmful environmental consequences have led to strong pressure on farmers to reduce the use of herbicides. As food demand is forecast to increase by 50% over the next century, an in-depth quantitative analysis of crop yields, weeds and herbicides is required to balance economic and environmental issues. This study analysed the relationship between weeds, herbicides and winter wheat yields using data from 150 winter wheat fields in western France. A Bayesian hierarchical model was built to take account of farmers’ behaviour, including implicitly their perception of weeds and weed control practices, on the effectiveness of treatment. No relationship was detected between crop yields and herbicide use. Herbicides were found to be more effective at controlling rare plant species than abundant weed species. These results suggest that reducing the use of herbicides by up to 50% could maintain crop production, a result confirmed by previous studies, while encouraging weed biodiversity. Food security and biodiversity conservation may, therefore, be achieved simultaneously in intensive agriculture simply by reducing the use of herbicides.

In organic agriculture, weeds and nitrogen deficiency are the main factors that limit crop production. The use of relay-intercropped forage legumes may be a way of providing ecological services such as weed control, increasing N availability in the cropping system thanks to N fixation, reducing N leaching and supplying nitrogen to the following crop. However, these ecological services vary considerably depending on the forage legume biomass. The aim of this study was to identify factors that affect forage legume establishment and growth to help farmers adjust the management of the cover crop. Sixteen field experiments were conducted over a period of five years. In each experiment, winter wheat was grown as sole crop or intercropped with one of two species of forage legumes; Trifolium repens L. or Trifolium pratense L. After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Climatic conditions, and the accumulation of legume and weed biomass were monitored from when the legume was sown to destruction of the cover crop. Our results showed that a minimum threshold of about 500 kg ha−1 biomass in the aboveground parts of the cover crop was needed at the end of intercropping to obtain the minimum biomass of 2000 kg ha−1 in September necessary to guarantee ecological services. To obtain sufficient legume biomass at the end of intercropping period, a thermal time greater than 1900 °Cd and more rainfall than 300 mm are required for legume growth. Moreover, a legume density of at least of 300 plants per square meter at the wheat flowering stage was a good indicator of legume biomass at the end of the intercropping period. Rainfall was a limiting factor of legume growth between the end of the intercropping period and September. Legume density at wheat flowering and climatic conditions during the intercropping period thus appear to be good indicators to predict to capacity of cover crop to produce sufficient biomass in September. These indicators can be used by farmers as a management tool for the cover crop.

International audience; This paper aims to evaluate the contribution of multitemporal polarimetric synthetic aperture radar (SAR) data for winter wheat and rapeseed crops parameters [height, leaf area index, and dry biomass (DB)] estimation, during their whole vegetation cycles in comparison to backscattering coefficients and optical data. Angular sensitivities and dynamics of polarimetric indicators were also analyzed following the growth stages of these two common crop types using, in total, 14 radar images (Radarsat-2), 16 optical images (Formosat-2, Spot-4/5), and numerous ground data. The results of this study show the importance of correcting the angular effect on SAR signals especially for copolarized signals and polarimetric indicators associated to single-bounce scattering mechanisms. The analysis of the temporal dynamic of polarimetric indicators has shown their high potential to detect crop growth changes. Moreover, this study shows the high interest of using SAR parameters (backscattering coefficients and polarimetric indicators) for crop parameters estimation during the whole vegetation cycle instead of optical vegetation index. They particularly revealed their high potential for rapeseed height and DB monitoring [i.e., Shannon entropy polarimetry (r2=0.70) and radar vegetation index (r2=0.80), respectively]

Eyespot is a major fungal disease of winter wheat, mostly affecting the base of the stem. The development of biological control approaches, using organisms such as earthworms, represents a potential alternative strategy for eyespot control. In a greenhouse experiment, we analyzed the response of two wheat cultivars (Soissons and Aubusson) to the presence of the pathogenic fungus Oculimacula yallundae and the anecic earthworm Lumbricus terrestris, alone and in combination. We assessed necrosis frequency, necrosis severity, wheat biomass, resource allocation and soil mineral concentrations. Disease incidence was lower in the presence of earthworms: the frequency of necrosis was 44% lower for Soissons and 70% lower for Aubusson. Necrosis severity was also lower for both cultivars (50% lower for Soissons and 80% lower for Aubusson) in the presence of earthworms. Earthworms had no detectable effect on the shoot and root biomasses of plants exposed to the fungus, but they modified resource allocation between plant organs and nutrient translocation within the plant. Our results suggest that earthworms are a potentially effective biocontrol agent for eyespot, and we discuss the possible underlying mechanisms. (C) 2015 Elsevier B.V. All rights reserved.

EA SPE EcolDur EJ2 CT3; National audience; Contexte - Cet article fait suite à une description, dans Phytoma n° 678, de l'évolution de la flore adventice du blé d hiver en France depuis quarante ans, basée sur le travail de Barralis & al. dans les années 1970 et celui du réseau Biovigilance Flore de 2002 à 2010. Il cherche à expliquer ces évolutions. Évolution de la flore - Ce travail a permis de confirmer et évaluer l'influence, sur la flore globale et sa diversité, de la zone géographique, des facteurs pédo-climatiques, du type d'agriculture et des pratiques culturales : notamment IFT herbicide (mesure de l'IC, indice de contrôle) et travail du sol. Analyse par espèce - Une analyse statistique des évolutions de seize espèces d'adventices communes et de seize messicoles rares permet : de préciser les pratiques culturales sélectionnant (influençant l'évolution de) la flore : pression herbicide, type de travail du sol, combinaison précédent/ date de semis ; de différencier sept groupes d'espèces selon leurs réponses aux pratiques culturales en lien avec leurs traits de vie (taille, cycle, vigueur germinative, etc.).

EA SPE EcolDur; National audience

Background Certain temperate species require prolonged exposure to low temperature to initiate transition from vegetative growth to flowering, a process known as vernalization. In wheat, winter cultivars require vernalization to initiate flowering, making vernalization requirement a trait of key importance in wheat agronomy. The genetic bases of vernalization response have been largely studied in wheat, leading to the characterization of a regulation pathway that involves the key gene VERNALIZATION1 (VRN1). While previous studies in wheat and barley have revealed the functional role of histone modification in setting VRN1 expression, other mechanisms might also be involved. Here, we were interested in determining whether the cold-induced expression of the wheat VRN-A1 gene is associated with a change in DNA methylation. Results We provide the first DNA methylation analysis of the VRN-A1 gene, and describe the existence of methylation at CG but also at non CG sites. While CG sites show a bell-shape profile typical of gene-body methylation, non CG methylation is restricted to the large (8.5 kb) intron 1, in a region harboring fragments of transposable elements (TEs). Interestingly, cold induces a site-specific hypermethylation at these non CG sites. This increase in DNA methylation is transmitted through mitosis, and is reset to its original level after sexual reproduction. Conclusions These results demonstrate that VRN-A1 has a particular DNA methylation pattern, exhibiting rapid shift within the life cycle of a winter wheat plant following exposure to particular environmental conditions. The finding that this shift occurs at non CG sites in a TE-rich region opens interesting questions onto the possible consequences of this type of methylation in gene expression.

International audience; Weed species are not homogeneously distributed into field elements (Cordeau et al. 2012)*.In a field, weed species are mainly competing with the crop and constrained by management practice (i.e.disturbances). In the crop edge, less unfavorable conditions for weed development (i.e.absence of direct crop competition,l ess frequent disturbances could explain the greater diversity of weeds.To understand this observation, a functional approach base dont raits known to respond both to disturbances and to competitive or facilitative interactions can be used.Our assumptions are that(i)the crop edge is likely to all owawi derrange of ecological strategies thus promoting species coexistence while (ii) in the field, disturbances should lead to are duction in the range of ecological strategies.

Eds. Risto Sievänen, Eero Nikinmaa, Christophe Godin, Anna Lintunen & Pekka Nygren; A parameterisation of wheat architecture was developed, having high flexibility to simulate contrasted genotypes and growth conditions with a reasonably low number of parameters. Field measurements at 4-5 dates allowed to simulate crops from emergence to maturity with a good agreement between simulated and measured ground cover and GAI. Dynamics of leaf angles were shown to impact strongly ground cover.

The present work analyzes the effects of different water application levels on agronomic parameters and water use efficiency of a durum wheat (Triticum durum Desf. Var. Karim.) cultivar under the Mediterranean climatic conditions in central Tunisia. The objective of this work was to identify an appropriate irrigation strategy associated with high crop water use efficiency. Field experiment was conducted at the Higher Institute of Agronomy of Chott Meriem during the growing season 2011-2012. The irrigation strategy consisted in maintaining fixed the irrigation intervals and changing the volumes of water applied as a percentage of the crop water requirements. The effects of three irrigation treatments were investigated. The irrigation treatments were full irrigation (T1) corresponding to 100% of predetermined irrigation water levels, (T2) 75% of full irrigation and (T3) 50% of full irrigation. Results concerning water use efficiency revealed that T1 and T3, with respectively 1.72 and 1.6 kg/m3, were classified in the same group. T2, with 1.43 kg/m3, resulted in lowest water use efficiency. Comparing the effects of water supply on yield components, the best results were registered for T1 while the lowest yield components were obtained for T3. LAI from T1 was significantly higher than in the other treatments. According to the study results, each increase in irrigation regime increased days to maturity. The results achieved in this study showed that irrigating winter wheat with continuously providing only 50% of the crop water requirements in semi arid climate in Tunisia could result in high efficient irrigation water use.

Agronomic practices modify crop architecture in ways that may facilitate or hamper disease development. The processes involved are complex and mechanistic models simulating plant-pathogen interaction should help clarifying them. Virtual Plants, i.e. models in which the three-dimensional structure of the plant is explicitly described, appear specially promising to express the effects of the plant architecture on the epidemic development. The objective of this study is to examine the ability to simulate the effect of plant architecture on disease development using a Virtual Plant model.The work focuses on the pathosystem wheat-Septoria tritici, in which architecture plays an important role because spores of Septoria are propagated from infected leaves to upper healthy leaves by rain splash. We build on a pre-existing model of Septoria epidemics, Septo3D. Wheat architecture was examined for a range of sowing date and density treatments. Differences of phyllochron between treatments were in a range sufficient to likely modify epidemic development; they were well represented by a descriptive model depending on photoperiod and final leaf number. A detailed description of architectural variables at the organ and canopy scale provided an original and comprehensive documentation of the plastic response of wheat, which was used for parameterising the wheat description in Septo3D. Overall, the investigated treatments resulted in strong differences in the time course of vegetation density. Septoria dynamics were monitored in a subset of three treatments of contrasted densities. Simulated disease kinetics were consistent with field measurements. Although, the approach needs further validation, results support that virtual plant modelling provides new insights into the processes and plant traits that impact epidemics. We conclude with prospects for further improvements and applications.; Les pratiques culturales modifient l'architecture des couverts de manière à augmenter ou diminuer le développement des épidémies mais les processus mis en jeu sont complexes ; des modèles mécanistes simulant l'interaction entre plante et pathogène devraient aider à les clarifier. Les modèles de Plantes Virtuelles, qui permettent de décrire explicitement la structure tridimensionnelle de la plante, semblent particulièrement prometteurs pour exprimer les effets de l'architecture de la plante sur le développement des épidémies. L'objectif de cette étude est d'examiner la possibilité de simuler l'effet de l'architecture des plantes sur le développement de la maladie en utilisant un modèle Plante Virtuelle. Dans ce travail, nous nous intéressons au pathosystème blé-Septoria tritici, dans lequel l'architecture joue un rôle important. En effet, les spores de Septoria tritici sont propagées par les éclaboussures de pluie depuis les feuilles infectées du bas du couvert vers les nouvelles feuilles saines. Notre travail s'est appuyé sur un modèle pré-existant d'épidémie de la septoriose, Septo3D. L'architecture du blé a été étudiée pour une gamme de densités et de date de semis. Les différences de phyllochrone entre traitements ont été dans une gamme susceptible de modifier le développement de la septoriose. Ces variations ont été représentées par un modèle descriptif qui tient compte du nombre de feuilles final et de la photopériode. Une description détaillée des variables d'architecture à l'échelle des organes et du couvert a fourni une documentation originale et complète sur la plasticité de l'architecture du blé. Ces données ont été utilisées pour paramétrer la description du blé dans Septo3D. Globalement, les traitements étudiés ont conduit à de fortes différences de la densité de végétation au cours du temps. Les dynamiques de développement de la septoriose ont été suivies pour trois traitements de densités contrastées. Les cinétiques de la maladie simulées par le modèle étaient conformes aux mesures expérimentales. Bien que, l'approche nécessite davantage de validation, les résultats confirment que l'approche Plante Virtuelle apporte un nouvel éclairage sur les processus et les caractéristiques des plantes qui impactent les épidémies. En conclusion, nous proposons quelques perspectives en vue de nouvelles applications et améliorations de l'approche.

National audience; In a previous paper [Bedoussac L, Justes E (2009) Plant Soil, doi: 10.1007/s11104-009-0082-2], we showed that intercropping of durum wheat and winter pea increased the yield and protein concentration of durum wheat when early N availability was less than 120 kg N ha−1. The aim of the present work was to understand these results by analysing intercrop species dynamics for growth, light and N acquisition. A 2-year field experiment was carried out in southwest France with different fertilizer-N levels in order to compare wheat (Triticum turgidum L.) and pea (Pisum sativum L.) grown as sole crops and as an intercrop in a row substitutive design. The advantages of intercropping in low N conditions were due mainly to: (1) better light use (up to 10%), thanks to species dynamic complementarity for leaf area index and height; (2) growth complementarity over time (higher growth rate of wheat until pea flowering and then of pea until wheat flowering); and (3) dynamic complementary N acquisition associated with better wheat N status throughout growth. Disadvantages, underlining poorer complementarity within the intercrop stand, were observed with ample available N in early growth. This induced higher cereal growth during winter, which led to increase interspecies competition by reducing pea light absorption and, consequently, its biomass production.

International audience

*INRA, systèmes agraires et développement, Saint-Laurent-de-la-Prée (FRA) Diffusion du document : INRA, systèmes agraires et développement, Saint-Laurent-de-la-Prée (FRA) Diplôme : Dr. Ing.