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Citation suggérée : Anses. (2022). Analyse comparative des avis de l’Anses et de l’EFSA relatifs aux demandes d’autorisation de mise sur le marché de plantes génétiquement modifiées au titre du règlement (CE) n° 1829/2003. Identification, description et analyse des sources d’écart entre les avis formulés par l’Anses au cours du processus décisionnel européen et les avis adoptés parl’EFSA. Saisine n° 2020-SA-0063. Maisons-Alfort : Anses, 84 p.; L’Anses a décidé de lancer un travail de fond sur ses méthodes d’évaluation des risques liés à l’utilisation des plantes génétiquement modifiées (PGM) en alimentation animale et humaine, afin de les adapter aux développements des innovations biotechnologiques. Ces travaux s’inscrivent en complémentarité de ceux réalisés par ailleurs par l’EFSA.Chaque demande d’autorisation de mise sur le marché d’une PGM au titre du règlement (CE) n° 1829/2003 est évaluée par l’EFSA, qui rend un avis à la Commission européenne. Au cours de cette procédure d’évaluation, les États membres sont invités à formuler des commentaires sur les dossiers initiaux (dans un délai de trois mois), que l’EFSA peut intégrer dans sonévaluation. C’est dans ce cadre que la DGCCRF, autorité compétente française sur ces produits, saisit l’Anses sur le volet sanitaire des dossiers. L’évaluation réalisée donne lieu à un avis initial, qui est publié sur le site de l’Anses.Pendant le processus d’évaluation, l’EFSA peut faire des demandes d’informations complémentaires auprès du pétitionnaire avant de rendre son avis. Dans ce contexte, la DGCCRF peut saisir l’Anses pour qu’elle évalue ces données complémentaires concernant le volet sanitaire. Cette demande intervient entre la publication de l’avis de l’EFSA et le vote des États membres sur le projet de décision d’autorisation au Comité permanent des végétaux, des animaux, des denrées alimentaires et des aliments pour animaux (CPVADAAA), section OGM. L’évaluation des risques sanitaires réalisée par l’Anses donne lieu à un aviscomplémentaire, qui est également publié sur le site de l’Agence.Cette autosaisine a pour origine le constat suivant : sur les mêmes dossiers, les avis de l’EFSA sont majoritairement favorables, alors que les avis de l’Anses comportent fréquemment des réserves (environ ⅔ des cas) et se terminent alors par des conclusions négatives (telles que définies au paragraphe 2.3.1). Dans la mesure où le collectif d’experts de l’Anses (groupe de travail « Biotechnologie ») s’appuie sur le même référentiel d’expertise que l’EFSA, il apparaît nécessaire d’analyser la nature des écarts entre les avis des deux agences en vue d’engager des discussions avec l’EFSA.Ces échanges pourront aboutir à des évolutions du référentiel d’expertise mentionné supra. En effet, ces travaux s’inscrivent dans le prolongement de ceux menés dans le cadre de la saisine n° 2013-SA-0035 (Anses, 2019c), relative à des propositions pour améliorer l’évaluation de la sécurité sanitaire des PGM, et ont aussi pour objectif de permettre à l’Anses de formuler de nouvelles propositions pour améliorer l’évaluation de la sécurité sanitaire des PGM.

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.

International audience; Thousand grain weight is one of the components determining wheat grain yield. It represents the average value of individual grain weights which depends on position within the ear and on positon within the spikelet. Our objective was to quantify the influences of individual floret anthesis date, of carpel weight at anthesis and of rate and duration of grain filling, on variation in individual final grain weight. Two bread wheat cultivars were grown in a greenhouse and their ears were sampled from anthesis through to harvest. Each ear was divided into three parts-basal, central and apical-where the two proximal grains were dissected from each of two spikelets. We analysed (i) the flowering time shift within the ear and within the spikelet; and (ii) the growth kinetics during grain filling in relation to position along the ear. For both cultivars, florets located in the central part of the ear were the first to reach anthesis followed by those in the apical part and then the basal part. Within a spikelet, the floret located nearest the rachis flowered first followed by the more distal ones. We found no significant systematic effect of flowering time-shift on final grain weight. Nevertheless, grains in the central part were heavier than the basal ones (9.75% smaller) and than the apical ones (18.25% smaller). These differences were explained mainly by differences in mean grain filling rates. Analysis of growth kinetics enabled an improved explanation of the variability of individual grain weight along the ear.

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.

The aim of this study was to develop a white bread with improved nutrient contents and reduced levels of potentially harmful Maillard reaction products such as N(ε)-carboxymethyllysine (CML) and 5-hydroxymethylfurfural (HMF). Assays were carried out through a full factorial experimental design allowing the simultaneous analysis of four factors at two levels: (1) wheat flour extraction rates (ash content: 0.60%-0.72%), (2) leavening agents (bakers' yeast - bakers' yeast and sourdough), (3) prebaking and (4) baking conditions (different sets of time and temperature). The baking conditions affected HMF and CML as well as certain mineral contents. A reduced baking temperature along with a prolonged heat treatment was found to be favourable for reducing both the CML (up to 20%) and HMF concentrations (up to 96%). The presence of sourdough decreased the formation of CML (up to 28%), and increased the apparent amounts of calcium (up to 8%) and manganese (up to 17.5%) probably through acidification of the dough. The extraction rate of flours as well as interactions between multiple factors also affected certain mineral content. However, compounds like folate, thiamine, copper, zinc, iron and phytic acid were not affected by any of the factors studied.

UNLABELLED: Magnesium (Mg), an indispensable mineral for plant growth, is concentrated in the peripheral layers (PLs) of the mature grain of wheat. The supply of Mg was interrupted from plant heading to maturity and a proteomic approach was used to investigate the PLs at three stages of development. Two genotypes with contrasting concentrations of Mg in the grain were studied: Apache (low Mg) and MgHL (high Mg). The concentration of Mg was significantly reduced in the roots (10-21%), straw (18-50%) and grain (24-10%), respectively. Mg deficiency altered enzymes involved in photosynthesis, glycolysis, respiration, amino acid synthesis, cell division, protein degradation and folding at early stages, especially in MgHL. This latter had smaller grain by reducing grain potential size and dry matter accumulation. By contrast in Apache, few proteins were affected at early stages and proteins related to stress/defense and arginine/proline metabolism were up accumulated resulting in lower number of grains per ear (24.9%). This study showed that Mg in PLs plays an important role in cell division, ATP generation, carbohydrate and amino acid metabolism, and hence may influence grain potential size and assimilates in grain, which determines grain weight. These results should help wheat breeders improve Mg content and hence grain yield. BIOLOGICAL SIGNIFICANCE: Magnesium (Mg) is an abundant cation and is involved in many cell activities. Its role in determining wheat productivity remains unclear. This study is the first to investigate how Mg deficiency influences the physiological characters of wheat and dry matter in the grain in two genotypes with contrasting Mg content. Moreover, Mg is concentrated in peripheral layers of grain, which are known to play a critical role in grain development. In this study, we investigated proteins in the peripheral layers expressed differentially in three development stages to identify the mechanism by which Mg influences grain development. This study revealed that the supply of Mg influences grain yield and that Mg regulates proteins related to cell metabolism and stress defense in grain.

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 can vary considerably depending on the growing conditions. The aim of this study was to identify early indicators to assess these two ecological services, thereby giving farmers time to adjust the management of both the cover crop and of the following crop. Nine field experiments were conducted over a period of three 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 Two levels of fertilization were also tested (0 and 100 kg N ha(-1)). After the intercropping stage, the cover crop was maintained until the end of winter and then destroyed by plowing before maize was sown. Legume and weed biomass, nitrogen content and accumulation were monitored from legume sowing to cover destruction. Our results showed that a minimum threshold of about 2 t ha(-1) biomass in the aboveground parts of the cover crop was needed to decrease weed infestation by 90% in early September and to ensure weed control up to December. The increase in nitrogen in the following maize crop was also correlated with the legume biomass in early September. The gain in nitrogen in maize (the following crop) was correlated with legume biomass in early September, with a minimum gain of 60 kg N ha(-1) as soon as legume biomass reached more than 2 t ha(-1). Legume biomass in early September thus appears to be a good indicator to predict weed control in December as well as the nitrogen released to the following crop. The indicator can be used by farmers as a management tool for both the cover crop and following cash crop. Early estimation of available nitrogen after the destruction of the forage legume can be used to adjust the supply of nitrogen fertilizer to the following crop.

Bulk Cr, Cu, Ni, Pb and Zn contents were analyzed in a Cr–Ni rich basalt, derived andic soil and in grass subaerial and aerial components to assess natural trace metal mobility in soil. Phytoavailability and relative mobility of elements were quantified by three different approaches: selective extractions, calculation at mineral scale after XRD, SEM-EDS and EMP analyses and measurement of pools at profile scale. Pool variations from rock to soil horizons give a view of the long-term mobility, while selective extractions and comparisons of pools measured in plants and top soil provide estimations of the current mobility and bioavailability. Major amounts of trace metals were held in the solid constituents of the soil. Examination of the solid residues following extractions clarified the potential mobility of these metal containing solids. Water soluble and exchangeable fractions never exceed 3% of the total trace metal amounts, which is of similar magnitude to pools found in grass roots and shoots. Zinc is the most easily extracted element followed by Cu, Ni and Cr. Over the short term, Zn also occurs in greater amounts in grass. Its involvement in organic matter turnover explains its greater accumulation in the soil profile over the long term. Chromium and Ni which are predominantly held in stable minerals (spinels) are less available for plants in the short term. They are both relatively depleted in soil, compared to initial pools in rock, over the long term. From a methodological point of view, the results demonstrate the necessity of comparing selective extraction data with other quantitative methods for assessing both short-term and long-term trace metal mobility and bioavailability.

Agronomic plant species may display physiological and biochemical responses to oxidative stress caused by heavy metals and metalloids. Zea mays plants were grown hydroponically for eight days at different concentrations of As (0, 134 and 668 μM) and at different pH (4, 7 and 9). Metabolic variations in response to As toxicity were measured using physiological parameters and antioxidant enzymatic activities. A significant decrease in SOD activity was observed in the leaves and roots of Z. mays with the majority of As treatments. As decreased G-POX activity less in leaves than in roots. An increase in the concentration of As increased APX activity in leaves and roots, except As(V) at pH 4 and pH 9 in the leaves and As(III) at pH 9 in the roots, when there was a significant decrease in APX activity at low As concentrations. After exposure to As(V), CAT activity was the same as in the control. As(III) led to an increase in CAT activity in leaves and to a decrease in roots. With increasing concentrations of As(III), CAT activity increased in both leaves and roots whatever the pH. To obtain more detailed knowledge on the effects of arsenate and arsenite exposure on Vicia faba and Z. mays, root meristems were also examined. Roots were fed hydroponically with 134, 334, 534 and 668 μM arsenate or arsenite and 4 × 10(-3)M of maleic hydrazide as positive control, at three different pH. Physiological parameters, the mitotic index and micronuclei frequencies were evaluated in root meristems. At all three pH, the highest As(V) and As(III) concentrations induced a substantial modification in root colour, increased root thickness with stiffening, and reduced root length. High concentrations also caused a significant decrease in the mitotic index, and micronucleus chromosomic aberrations were observed in the root meristems of both species.

Agrostis tenuis is known to be able to metabolise arsenate (As(V)) and arsenite (As(III)) which are toxic salts for most plants. A proteomic approach was developed to identify proteins expressed in response to treatments with these salts. A. tenuis plants were grown hydroponically in the presence of 134 and 668 μM As(V) or As(III) for 8 days at pH 7. During arsenic treatments, leaves showed chlorotic symptoms but fresh and dry leaf weights were not reduced, except in the presence of 668 μM As(III). On the contrary, a slight increase in biomass was observed with high As(V) concentrations. Thus, A. tenuis was more sensitive to As(III) than to As(V) and biomass was affected. Proteomic analysis enabled identification of a set of A. tenuis leaf proteins differentially expressed in response to arsenic exposure including a major functionally homogeneous group of enzymes such as oxygen-evolving enhancer protein, RuBisCO small and large subunits, RuBisCO activase and ATP synthase involved in the Calvin or Krebs cycle. The adaptative response to treatments resulted in partial disruption of the photosynthetic processes with prominent fragmentation of the RubisCO. Other proteins expressed differently from controls were identified and are possibly involved in the tolerance mechanisms of A. tenuis to arsenic treatments.

The Auvergne is an agricultural region with twenty six thousand square kilometres and one million five thousand hectares of useable farm area. There are two farming systems which need organic products to manage the organic matter status of soils: - the crops in the plain of Limagnes - and the animal farming in the mountains region. In the context of the spreading refusal or the demand of departure for the law, the objectives of the project are to determine the impact of sludge spreading in real crop conditions on productivity and metallic trace element (MTE) contents. Our works confirm the interest of sludge use on agricultural soils in increasing the final dry matter production and playing on different stages of yield since of the first year of spreading. At this stage, they don't reveal direct risk of MTE plant contamination by the sludge spreading according to the regulation conditions. The variability of results relating to the impact of the sludge on the productivity and on the MTE soil/plant transfer from year to year and from site to site has led to constitute a data base of MTE with a threshold contents by species. In the future, the data base must be extended to more annual crops. The final objective is to plan the cultural practices and particularly the organic matter management in respect of quality and environmental plant production., L'Auvergne est une région agricole avec 26 000 km2 et 1,5 million d'hectares de surface agricole utile. Elle comprend deux systèmes de production qui nécessitent des produits organiques pour assurer le niveau de matière organique des sols cultivés : les grandes cultures en plaine de Limagnes et le système polycultures/élevage en montagne. Dans le contexte de refus d'épandre ou de demande de dérogation à la réglementation des boues urbaines, les objectifs du projet sont de déterminer l'impact de l'épandage des boues en conditions agricoles réelles sur la productivité et sur les teneurs en éléments traces métalliques (ETM). Nos travaux confirment l'intérêt de l'apport de boues sur les sols agricoles en augmentant la production finale de matière sèche et en jouant sur les différents stades d'établissement du rendement dès la première année d'épandage. À ce stade, ils ne révèlent pas de risque direct de contamination métallique des plantes par l'épandage de boues réalisé dans les conditions réglementaires. La variabilité des résultats relatifs à l'impact des boues sur la productivité et sur le transfert sol/plante des ETM d'une année à l'autre et d'un site à l'autre a conduit à constituer une base de données en ETM avec un seuil de teneurs par espèce et par élément. Dans le futur, les données devront être étendues à d'autres espèces annuelles. L'objectif final est de raisonner les pratiques agricoles et particulièrement la gestion des apports organiques dans le respect de la qualité de la production végétale et de son environnement.

As the increase in cultivated areas can only be limited, increasing yield is the main way to meet the growing demand for wheat production. Part of this increase may come from the selection of more efficient varieties. They will have to be able to maintain a high level of performance in more unfavourable conditions related to global change. Thousand grain weight is one of the main yield components. It is estimated at the plot scale and represents the average value of a large number of grains. However, there is a large variability in the individual mass of the grains according to their position within the ear. Observing only average values could hide a source of genetic variability that would allow breeding for wheat varieties better adapted to the new climatic constraints imposed by global change. The objective of this work is therefore to identify the ecophysiological determinism of the variability of the individual grain mass as a function of their position within the ear.This study is based on two experiments: the first, conducted in the field at two levels of nitrogen fertilization in 2014, allowed to characterize the mass distribution, to define a methodology for studying this distribution, and to identify contrasting genotypes in order to give a generic character to the results obtained. Two varieties were chosen to test in the second experimentation under controlled conditions, several hypotheses that could be at the origin of the variability of the final dry mass of the grains.Results showed a parabolic distribution of final dry mass of the grains along the ear. Moreover, the proximal grains were heavier than the distal grains within a spikelet. The ablation of spikelets did not highlight physical constraints between spikelets that could explain the variability in final dry matter of the grains. The delay in flowering dates and the duration of grain filling did not seem to explain the variability observed. Similarly, no correlation between the size of ovaries at flowering and the final dry mass of the grains was showed. The differences in final dry mass observed along the ear was finally related to differences in grain growth rate. This work highlighted differences in sink strength within the ear, and enabled to identify parameters that could affect these differences. We hypothesize that the allocation of assimilates between grains is the emerging property of relative sink strength that would express themselves differently between spikelets and between grains of the same spikelet. The next step after this work would therefore be to validate this hypothesis, and to determine all the parameters influencing the final dry mass in order to define, test and validate rules for the allocation of carbon within the grain according to its position in the ear. The underlying objective is to create a mechanistic and dynamic model capable of simulating the impacts of environmental and genetic factors on individual grain dry mass.; L’accroissement des surfaces de culture ne pouvant être que limité, l’augmentation des rendements est la principale voie pour répondre à la demande croissante de la production de blé. Une partie de cette augmentation peut être due à la sélection de variétés plus performantes qui devront être capables de maintenir un niveau de rendement élevé, dans des situations plus défavorables liées au changement global. Le poids de mille grains est une des principales composantes du rendement. Elle est calculée à l’échelle de la parcelle et représente la valeur moyenne d’un grand nombre de grains. Cependant, il existe une forte variabilité de la masse individuelle des grains selon leur position dans l’épi. Observer uniquement les valeurs moyennes pourrait cacher une source de variabilité génétique qui permettrait de sélectionner des variétés de blé mieux adaptées aux nouvelles contraintes climatiques imposées par le changement global. L’objectif de ce travail est donc d’identifier le déterminisme écophysiologique de la variabilité de la masse individuelle des grains en fonction de leur position au sein de l'épi.Cette étude est basée sur deux expérimentations : une première, menée au champ avec deux niveaux de fertilisation azotée en 2014, a permis de caractériser la distribution des masses, de définir une méthodologie d’étude de cette distribution, et d’identifier des génotypes contrastés pour apporter un caractère générique aux résultats obtenus. Deux variétés ont ensuite été choisies pour tester, en conditions contrôlées, plusieurs hypothèses pouvant être à l’origine de la variabilité de masse sèche finale des grains.Les résultats montrent une distribution parabolique de la masse sèche finale des grains le long de l’épi. De plus, les grains proximaux sont plus lourds que les grains distaux au sein d’un épillet. L’ablation d’épillets n’a pas mis en évidence de contraintes physiques inter-épillets pouvant expliquer la variabilité de la matière sèche finale des grains. Le décalage des dates de floraison ainsi que la durée de remplissage des grains n’expliquent pas non plus la variabilité observée. De même, aucune corrélation entre la taille des ovaires à floraison et la masse sèche finale des grains n’est observée. En revanche, les différences de masse sèche finale observées le long de l’épi sont liées à des différences de vitesse de croissance des grains.Ces travaux ont permis de mettre en évidence des différences de forces de puits au sein de l’épi, et d’identifier des paramètres pouvant jouer sur les différences de masse sèche finale. Nous faisons l’hypothèse que l’allocation des assimilats entre grains est la propriété émergente de forces de puits relatives qui s’exprimeraient de manière différente entre épillets et entre grains d’un même épillet. La suite de ce travail consisterait donc à valider cette hypothèse, et à déterminer l’ensemble des paramètres influant sur la masse sèche finale pour à terme définir, tester et valider des règles d’allocation du carbone vers le grain en fonction de sa position dans l’épi. L’objectif sous-jacent est de créer un modèle mécaniste et dynamique capable de simuler les impacts des facteurs environnementaux et génétiques sur la masse sèche individuelle des grains.

As the increase in cultivated areas can only be limited, increasing yield is the main way to meet the growing demand for wheat production. Part of this increase may come from the selection of more efficient varieties. They will have to be able to maintain a high level of performance in more unfavourable conditions related to global change. Thousand grain weight is one of the main yield components. It is estimated at the plot scale and represents the average value of a large number of grains. However, there is a large variability in the individual mass of the grains according to their position within the ear. Observing only average values could hide a source of genetic variability that would allow breeding for wheat varieties better adapted to the new climatic constraints imposed by global change. The objective of this work is therefore to identify the ecophysiological determinism of the variability of the individual grain mass as a function of their position within the ear.This study is based on two experiments: the first, conducted in the field at two levels of nitrogen fertilization in 2014, allowed to characterize the mass distribution, to define a methodology for studying this distribution, and to identify contrasting genotypes in order to give a generic character to the results obtained. Two varieties were chosen to test in the second experimentation under controlled conditions, several hypotheses that could be at the origin of the variability of the final dry mass of the grains.Results showed a parabolic distribution of final dry mass of the grains along the ear. Moreover, the proximal grains were heavier than the distal grains within a spikelet. The ablation of spikelets did not highlight physical constraints between spikelets that could explain the variability in final dry matter of the grains. The delay in flowering dates and the duration of grain filling did not seem to explain the variability observed. Similarly, no correlation between the size of ovaries at flowering and the final dry mass of the grains was showed. The differences in final dry mass observed along the ear was finally related to differences in grain growth rate. This work highlighted differences in sink strength within the ear, and enabled to identify parameters that could affect these differences. We hypothesize that the allocation of assimilates between grains is the emerging property of relative sink strength that would express themselves differently between spikelets and between grains of the same spikelet. The next step after this work would therefore be to validate this hypothesis, and to determine all the parameters influencing the final dry mass in order to define, test and validate rules for the allocation of carbon within the grain according to its position in the ear. The underlying objective is to create a mechanistic and dynamic model capable of simulating the impacts of environmental and genetic factors on individual grain dry mass.; L’accroissement des surfaces de culture ne pouvant être que limité, l’augmentation des rendements est la principale voie pour répondre à la demande croissante de la production de blé. Une partie de cette augmentation peut être due à la sélection de variétés plus performantes qui devront être capables de maintenir un niveau de rendement élevé, dans des situations plus défavorables liées au changement global. Le poids de mille grains est une des principales composantes du rendement. Elle est calculée à l’échelle de la parcelle et représente la valeur moyenne d’un grand nombre de grains. Cependant, il existe une forte variabilité de la masse individuelle des grains selon leur position dans l’épi. Observer uniquement les valeurs moyennes pourrait cacher une source de variabilité génétique qui permettrait de sélectionner des variétés de blé mieux adaptées aux nouvelles contraintes climatiques imposées par le changement global. L’objectif de ce travail est donc d’identifier le déterminisme écophysiologique de la variabilité de la masse individuelle des grains en fonction de leur position au sein de l'épi.Cette étude est basée sur deux expérimentations : une première, menée au champ avec deux niveaux de fertilisation azotée en 2014, a permis de caractériser la distribution des masses, de définir une méthodologie d’étude de cette distribution, et d’identifier des génotypes contrastés pour apporter un caractère générique aux résultats obtenus. Deux variétés ont ensuite été choisies pour tester, en conditions contrôlées, plusieurs hypothèses pouvant être à l’origine de la variabilité de masse sèche finale des grains.Les résultats montrent une distribution parabolique de la masse sèche finale des grains le long de l’épi. De plus, les grains proximaux sont plus lourds que les grains distaux au sein d’un épillet. L’ablation d’épillets n’a pas mis en évidence de contraintes physiques inter-épillets pouvant expliquer la variabilité de la matière sèche finale des grains. Le décalage des dates de floraison ainsi que la durée de remplissage des grains n’expliquent pas non plus la variabilité observée. De même, aucune corrélation entre la taille des ovaires à floraison et la masse sèche finale des grains n’est observée. En revanche, les différences de masse sèche finale observées le long de l’épi sont liées à des différences de vitesse de croissance des grains.Ces travaux ont permis de mettre en évidence des différences de forces de puits au sein de l’épi, et d’identifier des paramètres pouvant jouer sur les différences de masse sèche finale. Nous faisons l’hypothèse que l’allocation des assimilats entre grains est la propriété émergente de forces de puits relatives qui s’exprimeraient de manière différente entre épillets et entre grains d’un même épillet. La suite de ce travail consisterait donc à valider cette hypothèse, et à déterminer l’ensemble des paramètres influant sur la masse sèche finale pour à terme définir, tester et valider des règles d’allocation du carbone vers le grain en fonction de sa position dans l’épi. L’objectif sous-jacent est de créer un modèle mécaniste et dynamique capable de simuler les impacts des facteurs environnementaux et génétiques sur la masse sèche individuelle des grains.