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Recently, biochar has shown to be an alternative to waste disposal and a source of nutrients, acting as a soil amendment. The effects of two types of biochar on soil properties and sugar beet production as well as potential for carbon (C) sequestration were evaluated: biochar produced from sewage sludge (SB) and biochar produced from a 1:1 mixture of sewage sludge and sugarcane bagasse (MB). A greenhouse pot experiment was conducted using a sandy loam soil from the Brazilian savanna under treatments of MB applications at 2.5%, 5.0%, 7.5%, and 10.0%, SB application at 5.0%, and a conventional fertilization (CF) using lime and mineral fertilizers, with no fertilization as a control. After incubation for 45 d, seedlings were transplanted into each pot and cultivated for 55 d. Biochar characterization showed that pyrolysis reduced the biomass volume drastically, but concentrated the trace elements per unit of biochar weight. The MB treatments increased soil total C (by 27.8%) and pH (by 0.6), reduced the concentrations of nutrients, except for potassium (K), and chromium (Cr), and did not significantly alter lead (Pb) and cadmium (Cd) concentrations. Results of stable isotopes showed that all biochar treatments increased the total soil C stock and stability, suggesting a potential for application in C sequestration, and improved overall soil fertility. However, the biochar treatments also increased the concentrations of trace elements in the soil and plants. The sugar beet yields at 10.0% MB and 5.0% SB corresponded to 55% and 29% of the yield obtained in the CF treatment, respectively. These results may be due to biochar nutrients not being bioavailable when required by plants or to biochar nutrient adsorption.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]INSPIRE; Accurate estimation of leaf chlorophyll content (Cab) from remote sensing is of tremendous significance to monitor the physiological status of vegetation or to estimate primary production. Many vegetation indices (Vls) have been developed to retrieve Cab at the canopy level from meter- to decameter-scale reflectance observations. However, most of these Vls may be affected by the possible confounding influence of canopy structure. The objective of this study is to develop methods for Cab estimation using millimeter to centimeter spatial resolution reflectance imagery acquired at the field level. Hyperspectral images were acquired over sugar beet canopies from a ground-based platform in the 400-1000 nm range, concurrently to Cab, green fraction (GF), green area index (GAI) ground measurements. The original image spatial resolution was successively degraded from 1 mm to 35 cm, resulting in eleven sets of hyperspectral images. Vegetation and soil pixels were discriminated, and for each spatial resolution, measured Cab values were related to various Vls computed over four sets of reflectance spectra extracted from the images (soil and vegetation pixels, only vegetation pixels, 50% darkest and brightest vegetation pixels). The selected Vls included some classical Vls from the literature as well as optimal combinations of spectral bands, including simple ratio (SR), modified normalized difference (mND) and structure insensitive pigment index (SIPI). In the case of mND and SIPI, the use of a blue reference band instead of the classical near-infrared one was also investigated. For the eleven spatial resolutions, the four pixel selections and the five VI formats, similar band combinations are obtained when optimizing VI performances: the main bands of interest are generally located in the blue, red, red edge and near-infrared domains. Overall, mND(blue)[728,850] defined as (R-440-R-728)/(R-440+R-850) and computed over the brightest green pixels obtains the best correlations with C-ab for spatial resolutions finer than 8.8 cm with a root mean square error of prediction better than 2.6 mu g/cm(2). Conversely, mND(blue)[728,8501 poorly correlates with variations in GF and GAI, thus reducing the risk of deriving non-causal relationships with Cab that would actually be due to the covariance between C-ab and these canopy structure variables. As mND(blue)[728,8501 can be calculated from most current multispectral sensors, it is therefore a promising VI to retrieve C-ab from millimeter- to centimeter-scale reflectance imagery. (C) 2017 Elsevier Inc. All rights reserved.

Background: Pseudomonas syringae is a very heterogeneous bacterial species, inhabiting various ecological niches, affecting numerous host plants and representing great phylogenetic diversity. In 2013, a leaf spot disease of sugar beet caused by P. syringae was detected for a first time in Serbia.Objectives: We aimed to determine the phylogenetic diversity of isolates from sugar beet and the potential host range in order to define status of isolates within P. syringae species complex and estimate the pathogenic diversity.Methods: Twenty representatives among 104 collected P. syringae isolates from commercial fields of sugar beet were tested. Sequencing of cts gene, sequence analysis by the Neighbor-joining method and comparison with 59 P. syringae strains from 13 phylogenetic groups was performed for all tested isolates. The host range was determined by leaf inoculation of 16 different plant species in controlled greenhouse conditions. The virulence and aggressiveness of tested isolates were measured.Results: Phylogenetic analysis showed that all tested P. syringae isolates from sugar beet belong to the 02b phylogroup within the P. syringae species complex, representing one of the most abundant P. syringae phylogroups in the environment. Host range tests revealed extremely aggressive isolates causing symptoms on every tested plant (70% of tested isolates) as well as weakly aggressive isolates (30% of tested isolates). These findings provide the first insight to status of collected isolates from Serbian sugar beet fields within P. syringae metapopulation and provide information about potential risk to other crops.

International audience

UMR BFP - Equipe Métabolisme; International audience; Yield formation in regions with intermittent drought periods depends on the plant's ability to recover after cessation of the stress. The present work assessed differences in metabolic recovery of leaves and roots of drought-stressed sugar beets with high temporal resolution. Plants were subjected to drought for 13 days, and rewatered for 12 days. At one to two-day intervals, plant material was harvested for untargeted 1H-NMR metabolomic profiling, targeted analyses of hexose-phosphates, starch, amino acids, nitrate and proteins, and physiological measurements including relative water content, osmotic potential, electrolyte leakage and malondialdehyde concentrations. Drought triggered changes in primary metabolism, especially increases in amino acids in both organs, but leaves and roots responded with different dynamics to rewatering. After a transient normalization of most metabolites within 8 days, a second accumulation of amino acids in leaves might indicate a stress imprint beneficial in upcoming drought events. Repair mechanisms seemed important during initial recovery and occurred at the expense of growth for at least 12 days. These results indicate that organ specific metabolic recovery responses might be related to distinct functions and concomitant disparate stress levels in above- and belowground organs. With respect to metabolism, recovery was not simply a reversal of the stress responses.

International audience; Remote sensing has gained much attention for agronomic applications such as crop management or yield estimation. Crop phenotyping under field conditions has recently become another important application that requires specific needs: the considered remote-sensing method must be (1) as accurate as possible so that slight differences in phenotype can be detected and related to genotype, and (2) robust so that thousands of cultivars potentially quite different in terms of plant architecture can be characterized with a similar accuracy over different years and soil and weather conditions. In this study, the potential of nadir and off-nadir ground-based spectro-radiometric measurements to remotely sense five plant traits relevant for field phenotyping, namely, the leaf area index (LAI), leaf chlorophyll and nitrogen contents, and canopy chlorophyll and nitrogen contents, was evaluated over fourteen sugar beet (Beta vulgaris L.) cultivars, two years and three study sites. Among the diversity of existing remote-sensing methods, two popular approaches based on various selected Vegetation Indices (VI) and PROSAIL inversion were compared, especially in the perspective of using them for phenotyping applications. Overall, both approaches are promising to remotely estimate LAI and canopy chlorophyll content (RMSE'10%). In addition, VIs show a great potential to retrieve canopy nitrogen content (RMSE=10%). On the other hand, the estimation of leaf-level quantities is less accurate, the best accuracy being obtained for leaf chlorophyll content estimation based on VIs (RMSE=17%). As expected when observing the relationship between leaf chlorophyll and nitrogen contents, poor correlations are found between VIs and mass-based or area-based leaf nitrogen content. Importantly, the estimation accuracy is strongly dependent on sun-sensor geometry, the structural and biochemical plant traits being generally better estimated based on nadir and off-nadir observations, respectively. Ultimately, a preliminary comparison tends to indicate that, providing that enough samples are included in the calibration set, (1) VIs provide slightly more accurate performances than PROSAIL inversion, (2) VIs and PROSAIL inversion do not show significant differences in robustness across the different cultivars and years. Even if more data are still necessary to draw definitive conclusions, the results obtained with VIs are promising in the perspective of high-throughput phenotyping using UAV-embedded multispectral cameras, with which only a few wavebands are available.

Efsa Panel On Genetically Modified Organisms (gmo)Scientific opinionRequestor: European Commission (DG SANTE)Question number: EFSA-Q-2017-00026; Following the submission of application EFSA-GMO-RX-006 under Regulation (EC) No 1829/2003 fromKWS SAAT SE and Monsanto Company, the Panel on Genetically Modified Organisms of the EuropeanFood Safety Authority (GMO Panel) was asked to deliver a scientific risk assessment on the datasubmitted in the context of the renewal of authorisation application for the herbicide-tolerantgenetically modified sugar beet H7-1. The data received in the context of this renewal applicationcontained a systematic search and evaluation of literature, updated bioinformatics analyses andadditional documents or studies performed by or on behalf of the applicant. The GMO Panel assessedthese data for possible new hazards, modified exposure or new scientific uncertainties identified duringthe authorisation period and not previously assessed in the context of the original application. Underthe assumption that the DNA sequence of the event in sugar beet H7-1 considered for renewal isidentical to the originally assessed event, the GMO Panel concludes that there is no evidence in thecontext of this renewal application for new hazards, modified exposure or scientific uncertainties thatwould change the conclusions of the original risk assessment on sugar beet H7-1.

La betterave sucrière est la deuxième plante en termes de production de sucre avec 19,6% du sucre produit dans le monde entre 2015 et 2016, derrière la canne à sucre. Cultivée dans les zones tempérées comme le nord de la France et la Belgique, elle est sensible au stress thermique modéré. En effet, une augmentation de 1°C de la température moyenne entraîne une perte de rendement de 29%. Dans le cadre du réchauffement climatique et afin de fournir aux agriculteurs des variétés ayant une meilleure résistance à la chaleur, la compréhension des réponses de la betterave sucrière au stress hyperthermique est nécessaire. Pour cela, une étude des réponses physiologiques et métaboliques a été effectuée avec trois hybrides : un hybride de type sucré avec 18% de sucre dans sa racine, un hybride de type lourd avec un meilleur rendement que la moyenne mais avec seulement 17% de sucre dans sa racine, et un hybride dit « résistant » au stress hyperthermique, ayant le meilleur rendement aux champs avec des températures plus élevées. Alors que la photosynthèse nette n’était pas modifiée en condition de stress, une croissance plus rapide de la rosette a été observée aux stades jeunes pour les trois hybrides. Une approche de modélisation suggère qu’une croissance de la rosette plus rapide contrecarre les effets du stress hyperthermique sur la production racinaire. Cette hypothèse est confirmée par le fait que l’hybride le plus performant a la croissance foliaire la plus rapide. Le stress hyperthermique provoque une forte diminution du stockage transitoire du carbone dans les feuilles matures. Dans les feuilles en cours de développement, le stockage transitoire du carbone, dont la moitié sous forme d’amidon, était seulement maintenu chez l’hybride le plus performant. Un calcul intégrant les besoins en carbone de la croissance foliaire suggère que ce maintien contribue significativement au maintien du rendement chez cet hybride. Par ailleurs, un marqueur putatif de la sensibilité au stress hyperthermique a été identifié lors de cette étude. Au final ce travail a permis de mieux comprendre comment la betterave sucrière répond à l’élévation de la température et ainsi proposer de nouvelles stratégies pour l’amélioration de cette espèce

The objective of the work reported here was to reduce the uncertainty on the greenhouse gas balances of biofuels using agro-ecosystem modeling at a high resolution over the Ile-de-France region in Northern France. The emissions simulated during the feedstock production stage were input to a life-cycle assessment of candidate biofuel pathways: bioethanol from wheat, sugar-beet and miscanthus, and biodiesel from oilseed rape. Compared to the widely-used methodology based on fixed emission factors, ecosystem modeling lead to 55–70% lower estimates for N2O emissions, emphasizing the importance of regional factors. The life-cycle GHG emissions of first-generation biofuels were 50–70% lower than fossil-based equivalents, and 85% lower for cellulosic ethanol. When including indirect land-use change effects, GHG savings became marginal for biodiesel and wheat ethanol, but were positive due to direct effects for cellulosic ethanol.

The varieties choice represents a major issue for sugar beet farmers because their income depends on it. The fast turnover of the commercialized varieties on the market makes this choice difficult. In order to help the farmers, the sugar beet institute (ITB) hopes to develop a varieties choice personalized tool. This choice takes the conventional evaluation criteria and the studied plots specificities into consideration. The aim is to propose a list of varieties that guarantees an optimal productivity under agro-pedo-climatic conditions of every farm. My mission was to define a multicriteria analysis method combining every evaluation criteria available then to propose an optimal solution of varieties; the restrained method enables to take quantitative and qualitative criteria into consideration. Two multicriteria analysis methods have been combined: (i) the DEXi method that permit to evaluate the leaves diseases risk according to agronomic practices and (ii) the Electre III method that gives a list of varieties derived from the combination of the evaluation criteria. Electre III needs a weighting stage. An additional analysis over those weights has, afterwards, permitted to determine the most sensitive criteria. The developed method has been tested upon different practical cases representing some specificities of the French sugar beet areas. We manage to emphasis the interest of such a method that proposes an optimal choice without highlighting the most performing varieties only on one criterion. The method does not take the economic aspect into account; some economic performance index has then been calculated for the yield and the soil tare.; Le choix variétal constitue un enjeu majeur pour les planteurs de betterave car leur revenu en dépend. Le rapide turn-over des variétés commercialisées sur le marché rend ce choix assez complexe. Afin d’aider les planteurs, l’Institut Technique de la Betterave (ITB) souhaite développer un outil personnalisé d’aide au choix des variétés. Ce choix prend en compte les critères classiques d’évaluation des variétés et les spécificités des parcelles étudiées. La finalité est de proposer une liste de variétés garantissant une productivité optimale dans les conditions agro-pédo-climatiques de chaque exploitation. Mon travail a été de définir une méthode d’analyse multicritère combinant tous les critères d’évaluation disponibles puis proposant une solution optimale de variétés ; la méthode retenue permet de prendre en compte des critères qualitatifs et quantitatifs. Deux méthodes d’analyse multicritère ont été combinées : (i) la méthode DEXi, permettant d’évaluer le risque de maladie foliaire en fonction des pratiques agronomiques et (ii) la méthode ELECTRE III, permettant de proposer une liste de variétés issue de l’agrégation des critères d’évaluation. ELECTRE III nécessite une étape de pondération. Suite à une enquête réalisée auprès d’experts de l’ITB, les poids ont été définis. Une analyse supplémentaire sur ces poids a ensuite permis de déterminer les critères les plus sensibles. La méthode développée a été testée sur différents cas pratiques représentant quelques spécificités des régions betteravières françaises. Nous avons pu mettre en avant l’intérêt d’une telle méthode qui propose un choix optimum sans pour autant faire ressortir les variétés performantes sur un seul critère. La méthode ne prenant pas en compte l’aspect économique, des index de performance économique ont ensuite été calculés pour le rendement racine et la tare terre.

Carbon metabolism in sugar beet leaves experiencing heat stress. Metabolomics 2016. 12. Annual Conference of the Metabolomics Society

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

International audience; Sugar beet is the second biggest world contributor to sugar production and the only one grown in Europe. Great efforts are currently being made to preserve and enhance its competitiveness. Within this context, one of the main bottlenecks identified is the lack of effective tools for assessing sugar content in unprocessed sugar beet roots. In the sugar industry, NIRS has been long used to monitor product quality on sugar processing lines in both sugar beet and cane industrial processes. The main work have been performed on beet brei although some authors studied the feasability of predicting sucrose content of intact and sliced beets. The results are of very good quality, however the beet peel is still a real problem to acquire signals of sufficient quality. Optical fibers are an essential component for remote optical measurements and have been extensively used to deliver and collect light in optical setups. By invasive but non destructive measurement, the fiber-optic probe could be an effective tools for rapid assessment of sugar content of intact beets and deal with the problem caused by the presence of beet peel. The objective of this work is to evaluate the use of a self-designed fiber-optic probe for the estimation of Soluble Solid Content (SSC) in intact sugar beets. Two geometries were tested : a single-fiber probe and a multiple-fiber probe. The impact of different components of the probe were analyzed, such as fiber diameter, distance between illumination and collection fiber in order to optimize optical setup of the probe. Total reflectance over the [400-2500 nm] spectral range, of 180 sugar beet samples, were measured with the two probes. Immediately after spectrum acquisition, Soluble Solids Content measurements were achieved for each sample. Partial Least Square (PLS) algorithm was used to calibrate the SSC estimation of the sugar beets With the single-fiber probes and for the two tested diameters, the results were not satisfactory. The better correlation coefficient and the ratio of sample standard deviation to standard error of prediction are respectively equal to 0.757 and 2.02. For this configuration, the measured signal is mainly composed by the specularly reflected light, which overlaps and therefore masks the information related to chemical absorbance of SSC. On the contrary, Partial Least Squares regression (PLSr) models showed good performance in the estimation of SSC with the multiple-fiber probes. For two different positions of the collecting fiber, results showed good correlation between SSC and reflectance spectra for intact sugar beets, with a correlation coefficient higher than 0.90 and a ratio of sample standard deviation to standard error of prediction higher than 3.30. These first results are very promising. However, further improvement are needed in order to achieve a satisfactory accuracy: •optimization of the distance between emitting and collecting fiber, •reducing the multiple scattering using several preatraitements, •increasing the number of samples in order to increase the robustness of the models.

Pour lutter contre le rhizoctone brun qui est problématique dans les rotations étudiées (pomme de terre, maïs et betterave), une stratégie de protection à l’échelle du système de culture s’impose. Dans un premier temps, le travail a permis de comprendre les processus épidémiologiques de R. solani AG3/pomme de terre et R. solani AG2-2/betterave, d’analyser les effets de la biofumigation sur les épidémies, et de donner des orientations pour le raisonnement de la protection intégrée. Dans un second temps, des expérimentations multi-sites ont montré que l’effet de la biofumigation seule est faible mais en complément avec d’autres techniques de lutte, elle peut apporter des gains de rendement et sans doute, à long terme, un maintien de la bonne qualité sanitaire des sols. Dans un troisième temps, un groupe d’expert des différentes cultures a permis d’élaborer des propositions pour l’amélioration des itinéraires techniques actuels et a conçu des systèmes plus intégrés., Black scurf (or root rot), Rhizoctonia solani, is a real pest to the studied crops (potato, maize and sugar beet), therefore its control strategy has to be investigated at the crop rotation level. In a first phase, studies have provided comprehensive elements about epidemiological processes of R. solani AG3/potato and R. solani AG2-2/sugar beet, analytical data about the effects of biofumigation on the epidemics, and the first contributions to implement integrated pest control methods. In a second step, multi-site experiments have shown that biofumigation by itself was not sufficient to control the soil borne fungus, whereas added to other control methods, could be beneficial to yield increase and most likely contributing to maintaining healthy soils in the long term. In the last part of the project, scientific and technical crop experts have collaborated to propose improvement of current R. solani control practices and to conceive more integrated cropping systems.

The French sugar beet industry seeks to increase productivity in order to obtain sugar yields economically satisfactory. Nitrogen fertilization is one of the main factors influencing yield of sugar beet. Many models are designed to simulate the yield of sugar beet but few take into account the effect of nitrogen nutrition conditions. In this context, the objectives of this work were: (i) to reflect leading to the choice of the type of modeling, (ii) to identify the plant characteristics in response to nitrogen nutrition for parameterization of the model and (iii) evaluate our model.The modeling approach has focused on the integration of the nitrogen nutrition effects on the leaf area development, and source-sink relationships within the plant. Two years field experiments have enabled us to acquire data necessary for the study of the sugar beet responses under contrasting nitrogen nutrition conditions and parameterization of the model. A compilation of a data set validation at the ITB makes it possible to take into account parameters variability. We found that sugar beet responded to nitrogen nutrition as the other C3 plants. The model simulates the differences in sugar yield based on nitrogen nutrition status as reported in the literature. The model can find growth stages of sugar beet without force them. Coupled to the supply nitrogen module of the STICS crop model, the model simulates the major trends in yields over the past thirty years.; La filière betteravière française cherche à gagner en productivité afin d'obtenir des rendements en sucre économiquement satisfaisants. La fertilisation azotée est l'un des principaux facteurs influençant le rendement de la betterave sucrière. De nombreux modèles ont pour but de simuler le rendement en sucre de la betterave mais peu prennent en compte l'effet des conditions de nutrition azotée. Dans ce contexte, les objectifs de ce travail étaient: (i) de mener une réflexion conduisant au choix du type de modélisation, (ii) d'identifier les caractéristiques de la plante en réponse à la nutrition azotée pour le paramétrage du modèle, et (iii) d'évaluer notre modèle. La démarche de modélisation s'est concentrée sur l'intégration des effets de la nutrition azotée sur l'élaboration de la surface foliaire, et sur les relations source-puits au sein de la plante. Des expérimentations au champ sur deux années nous ont permis d'acquérir les données nécessaires à l'étude des réponses de la betterave à des conditions contrastées de nutrition azotée et au paramétrage du modèle. Un travail de compilation de données de validation disponibles à l'ITB a permis de prendre en compte la variabilité des paramètres. Nous avons constaté que la betterave répondait à la nutrition azotée comme les autres plantes en C3. Le modèle simule les différences de rendement en sucre en fonction de l'état de nutrition azotée comme annoncé dans la bibliographie. Le modèle permet de retrouver sans les imposer les stades de croissance de la betterave. Couplé au module de fourniture d'azote du modèle STICS, le modèle permet de simuler les grandes tendances des rendements depuis les trente dernières années.

The French sugar beet industry seeks to increase productivity in order to obtain sugar yields economically satisfactory. Nitrogen fertilization is one of the main factors influencing yield of sugar beet. Many models are designed to simulate the yield of sugar beet but few take into account the effect of nitrogen nutrition conditions. In this context, the objectives of this work were: (i) to reflect leading to the choice of the type of modeling, (ii) to identify the plant characteristics in response to nitrogen nutrition for parameterization of the model and (iii) evaluate our model.The modeling approach has focused on the integration of the nitrogen nutrition effects on the leaf area development, and source-sink relationships within the plant. Two years field experiments have enabled us to acquire data necessary for the study of the sugar beet responses under contrasting nitrogen nutrition conditions and parameterization of the model. A compilation of a data set validation at the ITB makes it possible to take into account parameters variability. We found that sugar beet responded to nitrogen nutrition as the other C3 plants. The model simulates the differences in sugar yield based on nitrogen nutrition status as reported in the literature. The model can find growth stages of sugar beet without force them. Coupled to the supply nitrogen module of the STICS crop model, the model simulates the major trends in yields over the past thirty years.; La filière betteravière française cherche à gagner en productivité afin d'obtenir des rendements en sucre économiquement satisfaisants. La fertilisation azotée est l'un des principaux facteurs influençant le rendement de la betterave sucrière. De nombreux modèles ont pour but de simuler le rendement en sucre de la betterave mais peu prennent en compte l'effet des conditions de nutrition azotée. Dans ce contexte, les objectifs de ce travail étaient: (i) de mener une réflexion conduisant au choix du type de modélisation, (ii) d'identifier les caractéristiques de la plante en réponse à la nutrition azotée pour le paramétrage du modèle, et (iii) d'évaluer notre modèle. La démarche de modélisation s'est concentrée sur l'intégration des effets de la nutrition azotée sur l'élaboration de la surface foliaire, et sur les relations source-puits au sein de la plante. Des expérimentations au champ sur deux années nous ont permis d'acquérir les données nécessaires à l'étude des réponses de la betterave à des conditions contrastées de nutrition azotée et au paramétrage du modèle. Un travail de compilation de données de validation disponibles à l'ITB a permis de prendre en compte la variabilité des paramètres. Nous avons constaté que la betterave répondait à la nutrition azotée comme les autres plantes en C3. Le modèle simule les différences de rendement en sucre en fonction de l'état de nutrition azotée comme annoncé dans la bibliographie. Le modèle permet de retrouver sans les imposer les stades de croissance de la betterave. Couplé au module de fourniture d'azote du modèle STICS, le modèle permet de simuler les grandes tendances des rendements depuis les trente dernières années.

Nowadays it is still difficult to predict and control the spread of soilborne diseases that cause substantial damage in crop systems. The aim of this epidemiological interdisciplinary work is to propose models for the spatio-temporal spread of soilborne pathogens in order to point out key parameters for the control of soilborne diseases. This thesis considers the spread of Rhizoctonia solani on sugar beet as an example pathosystem and focuses on three main problems. First, we use experimental measures of the dispersal of the pathogen to parameterise a stochastic spatially explicit model and we show that host growth can trigger the development of epidemics by causing a switch from non-invasive to invasive behaviour. Second, using experimental data we build an age-varying model for the distribution of the incubation period that links hidden infections and above-ground observations of the disease. Then, we investigate the cryptic behaviour of epidemics by using a hierarchical model that considers a realistic incubation period. Third, we use a spatially-implicit model to estimate rates of infection from temporal disease data, and, to analyse the effects of biofumigation on epidemics. These parameters are integrated into an individual-based model to predict the stochastic development of epidemics. Our results confirm that biofumigation only permits a partial control and suggest that this biological control reduces uncertainty of the cryptic development of the disease. To finish with, we discuss the results of the thesis and we present the perspectives of this work.; Il est encore difficile de prédire et de contrôler le développement des maladies telluriques qui sont à l'origine de nombreux dégâts dans les systèmes de culture. Ce travail interdisciplinaire en épidémiologie a pour objectif de comprendre et de modéliser le développement spatio-temporel des épidémies telluriques afin d'identifier des leviers de gestion pour ces maladies. En se basant sur le pathosystème betterave sucrière - Rhizoctonia solani, la thèse se focalise sur trois problèmes. Dans un premier temps, en alliant mesures expérimentales de la dispersion du pathogène et simulations d'un modèle stochastique spatialement explicite, nous montrons que la croissance de l'hôte peut induire un changement dans le comportement du système qui, dans certains cas, devient invasif alors qu'il était initialement non-invasif. Dans un second temps, sur la base de mesures expérimentales nous proposons un modèle âge-dépendant de la distribution de la période d'incubation qui est utilisé pour relier les infections cachées et les observations de maladie. Le comportement cryptique des épidémies est ensuite étudié par simulation d'un modèle spatial hiérarchique qui intègre la période d'incubation. Dans un troisième temps, un modèle spatialement implicite est utilisé pour estimer les taux d'infection à partir de données temporelles de maladie et pour analyser les effets de la biofumigation sur les épidémies. Ces paramètres sont ensuite utilisés pour prédire le développement stochastique des épidémies à partir d'un modèle spatial individu-centré. Les résultats confirment que la biofumigation ne permet qu'un contrôle partiel des épidémies mais suggèrent que ce contrôle biologique diminue l'incertitude autour du développement cryptique de la maladie. Pour finir, les résultats de ces travaux sont discutés et les perspectives qu'ils suscitent sont présentées.

CT1 ; CT3 ; EnjS1 ; EnjS4 ; Base de données Agroclim; International audience; The results of published Life Cycle Assessments (LCAs) of biofuels are characterized by a large variability, arising from the diversity of both biofuel chains and the methodologies used to estimate inventory data. Here, we suggest that the best option to maximize the accuracy of biofuel LCA is to produce local results taking into account the local soil, climatic and agricultural management factors. Methods We focused on a case study involving the production of first-generation ethanol from sugar beet in the Picardy region in Northern France. To account for local factors, we first defined three climatic patterns according to rainfall from a 20-year series of weather data. We subsequently defined two crop rotations with sugar beet as a break crop, corresponding to current practice and an optimized management scenario, respectively. The six combinations of climate types and rotations were run with the process-based model CERES-EGC to estimate crop yields and environmental emissions. We completed the data inventory and compiled the impact assessments using Simapro v.7.1 and Ecoinvent database v2.0. Results Overall, sugar beet ethanol had lower impacts than gasoline for the abiotic depletion, global warming, ozone layer depletion and photochemical oxidation categories. In particular, it emitted between 28 % and 42 % less greenhouse gases than gasoline. Conversely, sugar beet ethanol had higher impacts than gasoline for acidification and eutrophication due to losses of reactive nitrogen in the arable field. Thus, LCA results were highly sensitive to changes in local conditions and management factors. As a result, an average impact figures for a given biofuel chain at regional or national scales may only be indicative within a large uncertainty band. Conclusions Although the crop model made it possible to take local factors into account in the life-cycle inventory, best management practices that achieved high yields while reducing environmental impacts could not be identified. Further modelling developments are necessary to better account for the effects of management practices, in particular regarding the benefits of fertiliser incorporation into the topsoil in terms of nitrogen losses abatement. Supplementary data and modelling developments also are needed to better estimate the emissions of pesticides and heavy metals in the field.

The effects of biofumigation using a Brassica juncea (mustard) cover crop on the dynamics of rhizoctonia root rot of sugar beet were recorded in two field trials in 2007 and 2008, and analysed using epidemiological modelling. Differences between partial biofumigation, involving the pulling up of mustard plants, and complete biofumigation, involving the crushing and incorporation of mustard residues into the soil, were compared with bare soil treatment. An epidemiological model was used that includes rates of transmission of primary and secondary infection, pre-emergence damping off, and expression of wilting symptoms (above-ground disease) due to infected roots (below-ground disease). The model indicated that biofumigation reduces the transmission of primary infections but affects secondary infections in a variable pattern between field trials. Likewise, the proportion of infected plants expressing wilting was significantly reduced, by 28%, in the partial and complete biofumigation treatments compared with bare soil in the trial of 2007 but not in 2008. It is suggested that the effects of biofumigation on secondary infection and the expression of disease are more variable than those on primary infection, and that this is probably due to an interplay between pathogen, antagonists, host, and environmental factors. These interactions may or may not offset the benefits afforded by a reduction in primary infection and account for the overall variable success of biofumigation to control disease.

Sugar beet is a biennial plant with an absolute requirement of vernalization, corresponding to the acquisition of the competence to bolt and flower after a prolonged exposure to low temperatures. The cold duration needed to induce bolting and flowering varies depending on the genotypes, reflecting their bolting tolerance, which is an essential agronomic trait. This work aimed at (i) investigating a possible epigenetic control of bolting induction in bolting sensitive and bolting resistant sugar beet genotypes, (ii) identifying sequences targeted by DNA methylation and expression remodeling, and (iii) characterizing candidate sequences which could be used in marked-assisted selection for plant breeding. Our data suggest that the time course and amplitude of DNA methylation variations are critical points for the induction of sugar beet bolting and represent an epigenetic component of the genotypic bolting tolerance. In addition, we identified differentially methylated sequences exhibiting variations of gene-body DNA methylation and expression during cold exposure and/or between genotypes. Among them, two RNA METHYLCYTOSINE TRANSFERASES, in association with RNA methylation such as BvFL1 mRNA, a floral repressor, were shown to play a role in floral transition. Finally, using microarrays we identified an integrative network of genes including response to environment, phytohormone signalling and flowering induction. The activation kinetics of these genes could define the bolting tolerance level of sugar beet genotypes., La betterave sucrière est une plante bisannuelle dont le besoin de vernalisation est absolu. Ce processus correspond à l’acquisition de l’aptitude à la montaison et à la floraison et résulte d’une exposition prolongée à de basses températures. La durée de froid requise pour induire la montaison puis la floraison varie suivant les génotypes et reflète leur tolérance à la montaison, qui constitue donc un caractère agronomique essentiel. Cette thèse visait à (i) mettre en évidence un éventuel contrôle épigénétique (méthylation ADN) de l‘induction de la montaison chez des génotypes de betterave sucrière résistants ou sensibles à la montaison, (ii) identifier les séquences ciblées par des remaniements de méthylation de l’ADN et d’expression associés, et (iii) caractériser certaines séquences candidates en vue de leur utilisation comme marqueurs de la montaison. Nos travaux ont montré que l’amplitude et la cinétique des variations de méthylation de l’ADN observées au cours de la vernalisation semblent être des éléments critiques de l’induction et de la tolérance à la montaison. Par une approche ciblée, des séquences dont la méthylation de l’ADN est remaniée ont été identifiées. L’implication dans la transition florale de deux BvRNMT (RNA METHYLTRANSFERASES) et de la méthylation des ARN, tels que l’ARNm de BvFL1, un répresseur floral, a ainsi été mise en évidence chez la betterave sucrière. Enfin, grâce à une approche génomique, un réseau de gènes intégratif incluant la réponse à l’environnement, la signalisation hormonale et l’induction de la floraison a été identifié. La cinétique d’activation de ces gènes définirait le niveau de tolérance à la montaison des différents génotypes de betterave sucrière.

L’éthanol est un composé à usages très variés allant de la chimie à l’agroalimentaire. Cependant, la croissance actuelle du marché se fait essentiellement autour de l’utilisation de l’éthanol en tant que carburant. L’objectif de ce projet est d’intensifier la production d’éthanol à partir du sirop basse pureté, produit de la seconde cristallisation des jus d’extraction de betterave, afin de diminuer les consommations en énergie et en eau pour la production d’éthanol. Pour ce faire, en partenariat avec l’UNGDA et l’ADEME, nous avons mené des travaux de recherche sur les fermentations à haute densité afin d’obtenir des vins à teneur plus élevée en éthanol. A l’issu d’un état de l’art et de quatre visites dans des ateliers de production, une stratégie de recherche en trois points a été établie. Le premier point a consisté en la recherche d’une composition de milieu de fermentation permettant d’augmenter la concentration finale en éthanol. Le second point a eu pour but de déterminer si les besoins en nutriments se limitaient uniquement à la phase de croissance ou au contraire si l’apport de ces nutriments était bénéfique tout au long de la fermentation. Le dernier point a quant à lui utilisé l’ensemble des résultats obtenus pour définir une conduite de procédé, permettant d’obtenir la concentration finale en éthanol la plus élevée possible. Ces résultats montrent qu’il est possible de réaliser des fermentations haute densité à partir de sirop basse pureté et d’obtenir 15,2 % (v/v) d’éthanol en fin de fermentation. L’application de ces travaux dans les ateliers de production permettrait d’économiser par litre d’éthanol pur, entre 20 et 30 % d’énergie pour la distillation, entre 35 et 49 % d’eau pour la réalisation des milieux de fermentation à partir de SBP et de diminuer de 23 à 38 % le volume de déchet produit après distillation. Ethanol is a compound with a wide usage range from chemistry to food. However, the current market growth mainly concerns the use of ethanol as fuel. The objective of this project was to intensify ethanol production from low purity syrup 2, which is a substrate from sugar beet, in order to reduce the consumptions of energy and water for its production. To do this, in partnership with UNGDA and ADEME, we have conducted research on high-gravity fermentations in order to increase the ethanol concentration at the end of the fermentation. With the coming of a state of the art and four visits in production facilities, a three points research strategy has been established. The first point consisted of fermentation medium composition finding in order to increase the final ethanol concentration at the end of the fermentation. The second point was to determine if the nutrients requirements were limited only during the growth phase or, on the contrary, if nutriments were beneficial throughout the fermentation. The latter point was to use the overall results to define a fermentation process, to obtain a final ethanol concentration as high as possible. These results show that it is possible to achieve high gravity fermentation from low purity syrup and reach a final ethanol concentration of 15.2 % (v/v). The application of this work in production facilities could save per liter of pure ethanol between 20 and 30% energy for distillation, between 35 and 49 % water for the production of fermentation media from SBP and decrease from 23 to 38 % of the volume of waste produced after distillation.

Many aspects of the association of Polymyxa betae with beet necrotic yellow vein virus during transmission have not been elucidated. In order to study the specificity of virus acquisition by the vector and its transmission to the host, thin sections were made through sugar beet roots infected both by the virus and the fungus. Immunogold labelled virus was identified at different stages of the fungus (plasmodia, zoosporangia and mature zoospores). However, specifically labelled clusters of virions have not yet been observed in mature resting spores., De nombreuses questions relatives à l’association entre Polymyxa betae et le virus de la rhizomanie qu’il transmet restent sans réponse. Dans le but de mieux appréhender la spécificité de l’acquisition du virus par son vecteur ainsi que sa transmission à la plante hôte, des coupes ultra-fines ont été réalisées dans des radicelles de betterave sucrière infectées à la fois par le virus et le champignon, puis soumises au marquage immunocytochimique. Du virus marqué à l’or colloïdal a été détecté dans différents stades du champignon (plasmodes, zoosporanges, zoospores bien différenciées). Cependant, des amas caractéristiques de BNYVV n’ont pu être mis en évidence dans les cystosores et les spores de repos, probablement en raison de la difficulté de pénétration des résines dans de tels tissus.

This thesis aims at giving a better understanding of present Life Cycle Assessment (LCA) results for biofuels in order to identify their potential and breathing spaces from an energy consumption and GreenHouse Gases (GHG) emissions point of view. To this end, LCA methodology and existing studies on first generation biofuels were reviewed; then a sensitivity analysis on methodological and data parameters allowed identifying the roots of the discrepancies of results. Methodological choices appeared to be very crucial elements for final results and recommendations were made for LCA carrying out for biofuels. The close relationship between LCA results and local specificities of production were also underlined. A simplified process simulation was then performed to evaluate the impacts of technological and by-products uses alternatives on LCA results. Energy use of by-products shows the most important potential savings per MJ although its economic profitability is only ensured for high oil prices and reasonable agricultural prices and its GHG savings per used hectares are lower than in the reference cases. Finally LCA methodology was completed by integrating soil quality, especially their role as carbon sinks, within the system boundaries. This led to suggest a more specific temporal framework for comparisons of scenarios and to define a dynamic method of GHG weighting consistent with current uses of Global Warming Potentials and according to their emission year. Application of GHG weighting on two case studies of land-use changes was done and showed the need for assessments of biofuels of defining efficient land use criteria in addition to the GHG savings criteria from Directive 2009/28/CE.; Cette thèse vise à clarifier le panorama actuel des résultats d'Analyse de Cycle de Vie (ACV) pour les carburants issus de cultures végétales, en vue d'identifier le potentiel et les marges de manœuvre de ces filières, pour la consommation d'énergie et les émissions de Gaz à Effet de Serre (GES). A cette fin, après une analyse bibliographique de la méthodologie d'ACV, les études existantes sur les carburants végétaux de première génération sont revues et les causes de leurs disparités identifiées par une analyse de sensibilité portant sur les paramètres méthodologiques et les données. Il apparaît que les choix méthodologiques ont un impact prépondérant sur les résultats finaux, et des recommandations sont formulées quant à la réalisation de ces études d'ACV. Le lien étroit entre résultats d'ACV et localisation de la production est également relevé. Une simulation simplifiée des procédés a ensuite été effectuée pour mesurer l'impact sur les bilans d'ACV de variantes technologiques ou de modes de valorisation des co-produits. Si la valorisation énergétique des co-produits montre le potentiel d'économies le plus important, sa rentabilité n'est assurée que pour des prix du baril élevés et des cours des marchés agricoles modérés, et les économies de GES réalisées par hectare mobilisé sont moindres que dans les cas de référence. Enfin la méthodologie de l'ACV est complétée en intégrant le rôle des sols en tant que puits de carbone au sein des frontières du système. Ceci a conduit à proposer un cadre temporel de comparaison des scénarios plus précis, ainsi qu'à définir une méthode dynamique de pondération des GES en fonction de leur année d'émission, cohérente avec les usages actuels des pouvoirs radiatifs des gaz. Son application à deux cas d'étude de changements d'usage des sols démontre la nécessité de définir, pour la production de carburants végétaux, des critères d'efficacité d'usage des sols en plus de ceux relatifs aux économies de GES de la directive 2009/28/CE.

By Natacha MOTISI.Regulation of soil-borne diseases by a Brassica cover crop: mechanisms of action and effectiveness within a sugar beet-wheat rotation.Prepared within UMR1099 INRA-Agrocampus Ouest "Biology of Organisms and Populations Applied to Plant Protection". Supported on February 3, 2009, before the review panel : President: Philippe Leterme, Professor, Agrocampus Ouest, RennesRapporteur: Françoise Lescourret, DR INRA, AvignonRapporteur: Pierre Ricci, DR INRA, Sophia AntipolisThesis supervisor: Philippe Lucas, DR INRA, Rennes, FranceMembers: Grégory Dechamp-Guillaume, Professor ENSA Toulouse, Marc Richard-Molard, Director of Technical Institute of Sugar beet (ITB), ParisThierry Doré, Professor AgroParisTech, ParisAbstract. Biofumigation, a technique aiming at controlling soil-borne plant pathogens, relies on the toxicity of crop residues (notably Brassicaceous crop residues that release isothiocyanates). The insertion of a biofumigant cover crop during the intercrop period is considered to be a contribution to possible alternatives of the use of pesticides. However, field studies have generated conflicting assessments of the efficiency of biofumigation at the field scale. We hypothesized that the factors responsible for the variable efficacy may take place at two scales: (i) the biofumigant crop scale (during the period of biofumigant crop growth and the period when crop residues are pulverised and incorporated into the soil); and, (ii) the pathogen scale, considering its ecological and epidemiological characteristics (survival of primary inoculum and transmission of primary and secondary infections). Within this framework, the general objective of this thesis is to analyse the mode of action of a brown mustard (B. juncea) cover crop according to the different phases of crop management (residue incorporation and/or crop growth) on the different components of the epidemic (primary inoculum and apparent transmission rate of the epidemic) of Rhizoctonia solani on sugar beet, and to investigate the possible factors responsible for the variable efficacy of a biofumigant crop at the field scale to infer the effectiveness of biofumigation efficacy. With an epidemiological approach, this work combines: (i) controlled condition experiments to better understand the underlying biological mechanisms; (ii) field experiments to investigate the factors which affect the biofumigation efficacy and the impact this has on the epidemic of R. solani on sugar beet; and, (iii) modelling to analyse the field disease progress curves in order to deduce the epidemiological parameters that are affected by the biofumigant crop. The field study showed that growing the biofumigant crop significantly reduced disease incidence compared to the control field (without mustard). Incorporating crop residues further reduced the disease incidence and additionally reduced the conditional disease severity (severity calculated for diseased beets only). Results from modelling showed that the mustard growth phase and incorporation of the residues acted primarily on the transmission of primary infections. It was concluded that the epidemiological mechanisms were affected by the biofumigant crop in different ways during the two phases of interest (the growth phase and incorporation of the residues); the density of primary inoculum can be reduced in both phases but the residues bring further control by reducing pathogen activity. Results from controlled experiments showed that the mustard residues have a more longterm impact on the pathogen than the initial release of toxic compounds. It was further concluded that biological regulation of pathogens may be very important in the longer term control of disease. In another way, efficacy of growing mustard with respect to the control showed more variability over the 3 years of the study than mustard efficacy after incorporation of the residues which in this study showed little variability from one year to the next. The length of the mustard growth period and mustard biomass seemed to be the most relevant factors that can explain variability of efficacy of growing mustard. However, incorporation of the residues may regulate this variability, regardless of the factors commonly cited in literature (crop biomass, size of crushed residues and timing of irrigation linked to residue maceration). Until now, little effort has been directed towards understanding the differential mode of action of a biofumigant crop on soil-borne pathogens, according to the phases of crop management and the epidemiological mechanisms which are affected by biofumigation. Targeting these two areas offers an innovate tool to reduce the variability of biofumigation in cropping systems.; Par Natacha MOTISI.Réguler les maladies d'origine tellurique par une culture intermédiaire de Brassicacées : mécanismes d'action et conditions d'expression dans une rotation betterave-blé. Préparée au sein de UMR1099 INRA-Agrocampus Ouest « Biologie des Organismes et des Populations appliquée à la Protection des Plantes ». Soutenue le 3 février 2009, devant la commission d'examen : Président : Philippe Leterme, Professeur, Agrocampus Ouest, RennesRapporteur : Françoise Lescourret, DR INRA, AvignonRapporteur : Pierre Ricci, DR INRA, Sophia AntipolisDirecteur de thèse : Philippe Lucas, DR INRA, RennesMembres : Grégory Dechamp-Guillaume, Professeur ENSA Toulouse, Marc Richard-Molard, Directeur de l’Institut Technique de la Betterave, ParisThierry Doré, Professeur AgroParisTech, ParisRésumé. La biofumigation est une méthode de lutte phytosanitaire utilisant la toxicité de molécules issues des résidus de cultures (notamment les Brassicaceae, à l’origine de la production d’isothiocyanates) pour lutter contre de nombreux agents pathogènes telluriques. L’insertion d’une culture intermédiaire à objectif biofumigant pendant la période d’interculture est considérée comme une contribution à une alternative possible à l’utilisation de pesticides. Cependant, les niveaux d’efficacité de la biofumigation mis en évidence en conditions agricoles restent inégaux d’une étude à l’autre. Nos hypothèses de travail sont que les facteurs de variation de l’efficacité peuvent se situer à la fois au niveau de la culture biofumigante (pendant la phase de culture, et après enfouissement des résidus), et au niveau du pathogène et de ses caractéristiques écologiques et épidémiologiques (survie de l’inoculum primaire, transmission des infections primaires et secondaires). Dans ce contexte, l’objectif général de la thèse est (i) d’expliquer l’action d’une culture intermédiaire de moutarde brune (B. juncea) suivant différents modes de gestion (enfouissement des résidus et/ou culture simple) sur les différentes composantes de l’épidémie (inoculum primaire, vitesse apparente du cycle épidémique) de Rhizoctona solani sur betterave sucrière, et (ii) d’examiner les facteurs de variations possibles de l’efficacité de la culture biofumigante au champ pour en déduire les conditions d’expression de l’efficacité de la biofumigation. Avec une approche épidémiologique, ce travail combine (i) expérimentations en conditions semi-contrôlées, pour l’étude fine des mécanismes biologiques, (ii) expérimentations au champ, pour l’analyse des conditions d’expression de l’efficacité de la biofumigation sur une épidémie de R. solani sur betterave, et (iii) modélisation, pour l’analyse des courbes de progression de la maladie au champ permettant d’en déduire les paramètres épidémiologiques affectés par la culture biofumigante. L’étude au champ a permis de montrer que la moutarde en culture permettait de réduire significativement l’incidence de la maladie par rapport au témoin sans moutarde. Par comparaison, l’enfouissement des résidus permettait de réduire davantage l’incidence mais également de réduire la sévérité conditionnelle de la maladie (sévérité au sein des plantes malades). Les résultats de modélisation montrent que la seule moutarde en culture et les résidus réduisent principalement la transmission des infections primaires. La combinaison de ces deux types de résultats suggère que les mécanismes épidémiologiques affectés par la culture biofumigante sont différents suivant son mode de gestion : la seule moutarde en culture et l’enfouissement des résidus réduiraient la densité d’inoculum primaire mais les résidus apporteraient un contrôle supplémentaire en réduisant son activité pathogène. La confrontation de ces résultats à ceux obtenus en conditions semi-contrôlées, en particulier la mise en évidence d’une persistance d’effet des résidus de moutarde sur les agents pathogènes bien supérieure à la période de libération des composés organiques toxiques, indique que des mécanismes complexes de régulation biologique seraient, au-delà de l’effet toxique des résidus, très importants pour la réduction de l’expression de la maladie. Nos résultats montrent par ailleurs que l’efficacité de la moutarde en culture par rapport au témoin est plus variable que celle constatée après enfouissement des résidus qui, dans les conditions de cette étude, est régulière d’une année à l’autre. Après identification des facteurs de variation putatifs de l’efficacité de la biofumigation, la durée de culture de la moutarde et la biomasse produite semblent les plus pertinents pour expliquer la variabilité de l’efficacité de la moutarde en culture. En revanche, l’enfouissement des résidus permettrait de régulariser cette variabilité et ceci indépendamment des facteurs de variation de la conduite de la culture biofumigante couramment cités (biomasse produite, finesse de broyage des résidus et irrigation après enfouissement des résidus dans le sol). Ainsi, le mode d’action différentiel d’une culture biofumigante suivant son mode de gestion sur les pathogènes telluriques et les mécanismes épidémiologiques affectés par la biofumigation ont été jusqu’à présent peu étudiés en biofumigation, mais semblent être des voies de recherche pertinentes dans laperspective de réduire la variabilité d’efficacité de la biofumigation.

SUMMARYCarbohydrate remobilization from the sugar beet storage root to support leaf regrowth after release from water stress was demonstrated by experimental and modelling approaches. Experimental trials were carried out in northern France in 1994 and 1995 and in southern France in 2005, in conditions that involved a succession of soil moisture stresses and re-hydrations. Drought stress slowed leaf growth and the subsequent release of stress resulted in regrowth. A second trial showed that after total defoliation, sugar beet was able to produce new leaves. It was assumed that this leaf renewal, observed at drought stress release or after defoliation, relied on the possibility of remobilizing carbohydrates from storage roots to above-ground organs. This assumption was tested through a heuristic modelling approach, involving the STICS crop model and its existing sub-model on remobilization. The relevance of these formalizations for sugar beet was tested on the experimental data to validate the plant behaviour concerning remobilization. The model succeeded in reproducing leaf area index (LAI) dynamic trends and particularly leaf re-growth after drought stress release or defoliation, despite an over-estimation of the drought stress effect involving an inaccurate simulation of the changes in LAI. Nevertheless, the model's ability to forecast accurately above-ground and storage root dry weight, as well as trends in LAI dynamics, showed that the assumptions made about remobilization were able to explain sugar beet behaviour.

Trois champignons dont le pouvoir pathogène en culture artificielle ne se maintient pas de façon satisfaisante, ont été expérimentés : Pyrenochaeta lycopersici, Phytophthora infestans et Rhizoctonia violacea. Sauf pour P lycopersici, la conservation sous azote liquide est impossible ou très aléatoire; les techniques de maintien en condition anaérobie ne conviennent guère (et encore avec des réserves) qu’à P infestans. Pour les 3 parasites, nous avons utilisé avec succès la culture associée du champignon et de racines transformées. Cette technique permet, dans la majorité des cas, un léger gain d’agressivité. Plusieurs cultures de racines transformées ont été expérimentées : tomate, pomme de terre, carotte, betterave à sucre et endive. Après passages répétés sur ces cultures, nous n’avons observé ni préférence, ni adaptation parasitaire. L’intérêt des cultures associées en phytopathologie est discuté., Alternative means were sought to preserve 3 fungi, Pyrenochaeta lycopersici (tab I), Phytophthora infestans (tab II) and Rhizoctonia violacea (tab III) the pathogenicity of which is not maintained satisfactorily in artificial culture. With the exception of P lycopersici, preservation in liquid nitrogen is either not possible or very uncertain; maintenance in anaerobic conditions may suit P infestans only if at all. We successfully maintained the 3 pathogens in culture on transformed roots; with this method, the aggressiveness of the strains is maintained, and nearly always slightly increased, and it is not necessary to inoculate and reisolate from host plants in the greenhouse. Several cultures of transformed roots have been tested : tomato, potato, carrot, sugar-beet and endive. After repeated transfers on these cultures, no parasitic specialization was observed. The interest of mixed cultures is discussed.

Arabinan and galactan side chains of sugar beet pectins are esterified by ferulic acid residues that can undergo in vivo oxidative reactions to form dehydrodiferulates. After acid and enzymatic degradation of sugar beet cell walls and fractionation of the solubilized products by hydrophobic interaction chromatography, three dehydrodiferulate-rich fractions were isolated. The structural identification of the different compounds present in these fractions was performed by electrospray-ion trap-mass spectrometry (before and after (18)O labeling) and high-performance anion-exchange chromatography. Several compounds contained solely Ara (terminal or alpha-1-->5-linked-dimer) and dehydrodiferulate. The location of the dehydrodiferulate was assigned in some cases to the O-2 and in others to the O-5 of non-reducing Ara residues. One compound contained Gal (beta-1-->4-linked-dimer), Ara (alpha-1-->5-linked-dimer) and dehydrodiferulate. The location of the dehydrodiferulate was unambiguously assigned to the O-2 of the non-reducing Ara residue and O-6 of the non-reducing Gal residue. These results provide direct evidence that pectic arabinans and galactans are covalently cross-linked (intra- or inter-molecularly) through dehydrodiferulates in sugar beet cell walls. Molecular modeling was used to compute and structurally characterize the low energy conformations of the isolated compounds. Interestingly, the conformations of the dehydrodiferulate-bridged arabinan and galactan fragments selected from an energetic criterion, evidenced very nice agreement with the experimental occurrence of the dehydrodiferulated pectins. The present work combines for the first time intensive mass spectrometry data and molecular modeling to give structural relevance of a molecular cohesion between rhamnogalacturonan fragments.

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*INRA Unité d'Agronomie de Laon-Péronne Diffusion du document : INRA Unité d'Agronomie de Laon-Péronne Diplôme : Dr. Ing.

International audience

International audience; Knowledge of the incubation period of infectious diseases (time between host infection and expression of disease symptoms) is crucial to our epidemiological understanding and the design of appropriate prevention and control policies. Plant diseases cause substantial damage to agricultural and arboricultural systems, but there is still very little information about how the incubation period varies within host populations. In this paper, we focus on the incubation period of soilborne plant pathogens, which are difficult to detect as they spread and infect the hosts underground and above-ground symptoms occur considerably later. We conducted experiments on Rhizoctonia solani in sugar beet, as an example patho-system, and used modelling approaches to estimate the incubation period distribution and demonstrate the impact of differing estimations on our epidemiological understanding of plant diseases. We present measurements of the incubation period obtained in field conditions, fit alternative probability models to the data, and show that the incubation period distribution changes with host age. By simulating spatially-explicit epidemiological models with different incubation-period distributions, we study the conditions for a significant time lag between epidemics of cryptic infection and the associated epidemics of symptomatic disease. We examine the sensitivity of this lag to differing distributional assumptions about the incubation period (i.e. exponential versus Gamma). We demonstrate that accurate information about the incubation period distribution of a pathosystem can be critical in assessing the true scale of pathogen invasion behind early disease symptoms in the field; likewise, it can be central to model-based prediction of epidemic risk and evaluation of disease management strategies. Our results highlight that reliance on observation of disease symptoms can cause significant delay in detection of soil-borne pathogen epidemics and mislead practitioners and epidemiologists about the timing, extent, and viability of disease control measures for limiting economic loss.

International audience; Two approaches can be distinguished for crop production forecasting : statistical methods, which are sitespecific and can hardly allow to assess exceptional events, and crop growth models which allow dynamic diagnostic and prognostic. However, the use of process models at regional scale is limited by the lack of spatialized information on model parameters. Here, we propose an approach where remote sensing information is used to calibrate a crop growth model for regional application topics. As an illustration, we present a study performed over a sugar beet factory basin where the most variable in space within crop parameters are those related to the crop implantation at the beginning of the crop life, and those related to roots behavior during water stress episodes. In this study, not only the spatial variability of the crop growth parameters, but also that of the radiative transfer model parameters, was taken into account. High spatial resolution airborne and SPOT data were used to calibrate the crop model for each field of the region. Then the crop model was used to predict the sugar production on a number of fields representative of the basin. Both parameters estimates and final sugar production estimates were consistent with validation ground measurements.

Deux populations (Schach 0 et Schach 1) du nématode à kyste de la betterave, #Heterodera schachtii$, sont utilisées pour sélectionner de nouvelles virulences contre des gènes de résistance transférés de #Beta$ section #Procumbentes$ à #B. vulgaris$ (Hs1(web-7) et d'autres caractères de résistance localisés sur le chromosome 7). Les deux populations du nématode ont produit quelques kystes sur des plantes résistantes et se sont multipliées sur ces mêmes plantes pendant six générations successives. Les deux populations en résultant, sélectionnées à partir de Schach 0 ou de Schach 1, montrent une très grande virulence à l'égard de quatre lignées d'addition monosomique avec le chromosome web-7 ou pro-7. Cependant, la population sélectionnée à partir de Schach 0, ne surmonte pas la résistance des lignées de translocation portant le gène de résistance Hs1 du chromosome pro-1, pro-7, ou web-7, alors que la population issue de Schach 1 conserve sa virulence à l'égard de Hs1. Il est conclu qu'un gène de résistance Hs2(web-7), ayant un effet épistatique sur Hs1(web-7), existe sur le chromosome 7. Les deux nouveaux pathotypes virulents sont nommés Schach 2 et Schach 1,2. (Résumé d'auteur)

La fiche 'sucre' présente la production et les superficies mondiales, les rendements, la consommation mondiale, les échanges internationaux, les prix mondiaux, les principaux operateurs et les perspectives du commerce mondial

The effects of tillage on the energy balance and temperature of bare soil were studied using three plots that had different soil structures due to different times of seedbed preparation and soil compaction. The experiment was performed on a loamy soil (Gleyic luvisol) in northern France during the establishment of sugar beet in spring 1992. Temperature, water content, heat capacity and thermal conductivity of the ploughed layer, surface albedo and roughness, net radiation, soil heat flux, sensible heat flux and evaporation were all measured over a spring-tilled soil, an autumn-tilled soil and a compacted soil. Differences in soil heat fluxes were related to soil evaporation and thermal conductivity. Differences in soil temperatures were related to heat capacity. In spite of a considerable evaporation, the compacted soil had the highest soil heat flux because of its high thermal conductivity. Nevertheless, the spring-tilled soil was the warmest because of its low heat capacity, and sugar beet germinated more rapidly with spring soil tillage. (© Inra/Elsevier, Paris.), Une expérimentation a été conduite dans un sol limoneux (Gleyic luvisol) dans le Nord de la France pendant la phase d’implantation d’une culture de betterave sucrière au printemps 1992 pour étudier les effets du travail du sol sur le bilan d’énergie et sur le régime thermique du sol. La température, l’humidité, la capacité calorifique, la conductivité thermique au sein de la couche labourée, l’albédo et la rugosité de la surface, le rayonnement net, le flux de chaleur dans le sol et dans l’air et le flux de chaleur latente ont été mesurés dans un sol travaillé au printemps, dans un sol travaillé à l’automne ou dans un sol fortement compacté. Les différences de flux de chaleur dans le sol entre traitements étaient liées aux niveaux d’évaporation et à la conductivité thermique ; les différences de température étaient liées à la capacité calorifique. Le sol fortement compacté avait le flux de chaleur le plus élevé malgré un niveau d’évaporation important, à cause de sa forte conductivité thermique. Mais c’était le sol travaillé au printemps qui était le plus chaud à cause de sa faible capacité calorifique, entraînant une germination des betteraves sucrières plus rapide. (© Inra/Elsevier, Paris.)