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La chenille légionnaire d'automne, Spodoptera frugiperda (Lepidoptera, Noctuidae), est un ravageur invasif d'introduction récente qui cause d'importants dégâts sur les cultures de maïs en Afrique. Des stratégies de gestion durable du ravageur basées sur les principes de la lutte intégrée ont été recommandées pour limiter les externalités négatives liées au recours systématique aux insecticides de synthèse, tant sur la santé des écosystèmes que sur la biodiversité. Une des approches proposées repose sur l'établissement de seuils économiques d'intervention fixant la densité de population du ravageur à partir de laquelle une décision d'intervention doit être prise pour contenir les dégâts dont l'incidence économique serait supérieure au coût d'une intervention. Nous présentons ici les premiers résultats d'une expérimentation au champ qui avait pour objectif de déterminer les relations entre les dégâts causés par les chenilles à différents stades phénologiques d'une culture de maïs doux et les pertes de production. Pour cela, nous avons transféré des chenilles sur des plants de maïs à différents stades du cycle de développement, puis évalué les dégâts sur les feuilles (échelle de Davis) au stade végétatif, ou sur les épis au stade reproductif. A la récolte, la longueur des épis ainsi que les dégâts directs sur les épis ont été évalués. Seules les attaques très précoces des plants de maïs au stade végétatif une ou deux semaines après la levée ont un impact significatif sur la longueur et le nombre d'épis produits, tandis que les attaques au stade reproductif ont plutôt un effet sur la qualité organoleptique des épis. Les analyses en cours doivent permettre de déterminer les niveaux de dégâts foliaires et de dégâts sur les épis susceptibles de provoquer des pertes de rendement. En conclusion, il apparaît que des attaques spectaculaires de la CLA dans les champs de maïs ne nécessitent pas forcément des interventions phytosanitaires, en raison de la capacité de compensation de la plante en fonction des conditions du milieu.

The rate of leaf appearance is related to early vigor, crop duration, and its environment. This experiment aimed to measure the variability of the leaf appearance rate and its response to two watering systems within the rice indica race. The GRISP Global Rice Phenotyping Network assembles a multi-environment, multi-trait phenomics resource for rice diversity panels. Our team specifically examined the dynamics of leaf appearance of 304 indica accessions of the modified PRAY panel that were either transplanted and flooded or direct-seeded and grown in aerobic conditions. In rice, the leaf appearance rate is fast for the first 4-5 embryonic leaves, slows down for the next leaves until about leaf 12, and slows down again for the last leaves. This pattern was confirmed in all plants with crop duration over 110 days. In earlier varieties, a proportion of the plants showed only two distinct phases intermediated by leaf 5. The earlier the variety, the higher this proportion was. The rates of leaf appearance and the durations of the second and third phases were strongly correlated: all late varieties had slow rates of leaf appearance and late transition to third phase. Meanwhile, the rate of appearance of the embryonic leaves was independent from the other four parameters. Differences in the leaf appearance kinetics between aerobic and flooded conditions were also related to the variety's crop duration. In varieties with duration over 105 days, the second phase is characterized by faster leaf appearance rate in flooded conditions. On the third phase, the rates equalize for both conditions. On the contrary, earlier varieties showed a reversed pattern: equal and then faster rate in flooded conditions, before and after the second transition, respectively. The transition from the second to the third phase was earlier by 0 to 14 days in aerobic than in flooded conditions for varieties with 80 to 105-day duration, and equal to 14 days for later varieties. All parameters of the leaf appearance kinetics are thus strongly correlated with the crop duration of the indica rice varieties except the rate of appearance of the embryonic leaves that can be bred independently.

International audience; Air temperature is one of the most critical climatic factors controlling rice growth, development, and production in current and future climatic scenarii predicting increasingly frequent situations of extreme and/or fluctuating temperatures. With its large spectrum of geographical origins and cropping areas, one can credit tropical japonica rice subspecies of a probable genetic diversity of its response to air temperature, which is of major interest for the breeding of better adapted rice varieties. A panel of 195 rice accessions (175 japonica plus 20 reference cultivars) was studied in controlled environment to estimate cardinal (base, optimum, and maximum) temperatures based on the monitoring of the elongation rate (LERmax) of the sixth leaf on the main stem in response to six fixed thermal treatments ranging from 16 to 35 degrees C. A dedicated statistical framework was elaborated for estimating LERmax, cardinal temperature and related uncertainties. Developed statistical framework enhanced the precision of cardinal temperatures estimated compared to previously reported methods, especially for base temperature. Maximum temperature was trickier to estimate and will require further studies. A significant genotypic variability for base and optimal temperature was pointed out, suggesting tropical japonica subspecies represents a relevant genetic pool to breed for rice genotypes adapted to various thermal situations. These results also suggested that using genotype-dependent cardinal temperature values should enhance the way crop growth models account for genotype x environment interactions hence their predictive value in current and future climatic conditions.

In sub-Saharian countries, simple micro-gin, without seed-cotton cleaner nor lint-cleaner, is often used as a reference device for characterizing the performance of industrial gin plants for fiber quality preservation. It is however useful to check if this micro-gin itself is properly set and maintained. Reference seed-cotton materials, well homogenized with known variability level, and available in large quantities, may serve the purpose of monitoring the performance of the micro-gin in order to detect any malfunction or any drift. Therefore, it is expected that any deviation in SITC results on ginned reference seed-cotton materials from predetermined data would alert on altered ginning conditions. This experiment demonstrates the feasibility of setting mean values and confidence intervals on measured SITC characteristics on fiber samples, to later detect any malfunction or drift that may occur in practices, settings, or degradation in a micro-gin.

CIRAD's Omega3 project, which operated from 2008-2012, aimed at (i) gaining knowledge on ecological pest and disease regulation processes that can be mobilized via plant species diversity (PSD) deployment in agroecosystems, as an alternative to conventional practices based on pesticide use, and (ii) generating tools and methods to design and evaluate innovative pest and disease-resilient cropping systems based on PSD. Some biological models (="pathosystems") representing a range of spatial scales of PSD deployment, across the pest/pathogen life history traits the most amenable to manipulation via by PSD (namely dispersal ability and host specificity), were selected, with a view to robustness and generality of expected results. At a metric scale, we studied the effects of sanitizing plants on soil borne white grubs and parasitic weed Striga affecting upland rice in Madagascar, and on tomato bacterial wilt (TBW) in Martinique. At the field level, we studied the luring effects of trap plants, combined (i) with barrier effects and conservation biological control on tomato fruitworms (TFW) and sap-feeding pests on vegetable crops in Martinique and Niger and, (ii) with a food attractant mixed with a biological insecticide on cucurbit fruit flies in Reunion. We also studied the effect on cocoa plant bugs and black pod rot (BPR) of intercropping cocoa trees with other perennial plants using different spatial designs in Cameroon. At the landscape scale, we studied the effects of the arrangement of various land uses on the incidence of coffee leaf rust (CLR) and the abundance of coffee berry borer (CBB) in Costa Rica. Our examples stressed the need for trade-offs to manage conflicts or exploit synergies in underlying PSD-based processes. For instance, against TBW or upland rice white grubs, the tradeoff between high biomass production for indirect regulation via alteration of microbial communities vs low biomass production but direct regulation via biocidal/allelopathic effect. Or the trade-off between the prevention or encouragement of infestation of the main vegetable crop by early occurring/little damaging sap-feeding pests, in perspective with a positive or adverse effect on regulation of later occurring/highly damaging fruit pests (e.g. TFW), via top-down pathways. Or the trade-off to account for conflicting interactions between cocoa and plant bugs and BPR in relation with shade and natural enemies (entomopathogenic fungi and ants) on the one hand, and between CBB and CLR (and their natural enemies) on coffee in relation with landscape fragmentation/connectivity, on the other hand. Specifically, a spatially-explicit individual-based model including three interacting modules was developed, to be used as a generic tool to improve our understanding of system functioning in our field-level case studies, by assessing relative attractiveness of the commercial vs trap crops, the spatiotemporal planting design of the crops, and the insect behavioural traits. (Texte intégral)

Bt cotton was introduced in Burkina Faso (West Africa) in 2008, while countries that adopted Bt cotton earlier have been facing increasing pressure by sucking pests. We conducted a three year comparative study in Bt and non-Bt cotton fields of South-West Burkina Faso to assess hemipteran populations and to detect potential insect outbreaks as observed in other countries such as China and USA. Hemipteran insect sampling was carried out three times per year and insect abundance was evaluated on the base of families. The study was complemented with a three year damage assessment on leaves and bolls and a boll production analysis in 2010. Cicadellidae (Typhlocibinae), Pyrrhocoridae, Pentatomidae, Coreidae and Miridae had the highest incidence in cotton fields. The dominant trend in their population dynamics shows higher insect frequencies in Bt cotton and an increase over time in both cultivars (Bt or non-Bt). Leaf and boll damages were significantly higher in Bt cotton than in non-Bt cotton. Our study suggests different and additive possible causes of the hemipteran outbreak that should further be investigated in depth: 1 - the reduction of insecticide spray numbers in Bt-cotton fields, 2 - the loss of genetically inherited resistance (leaf hairiness), 3 - the decreasing efficacy of insect control programs in non-Bt cotton and (particularly) 4 - the emergence of insecticide resistance in some hemipteran populations, especially in non-Bt fields. The authors also draw the attention of the Burkinabe cotton sector stakeholders on the importance of a quick implementation of IPM measures to guarantee the sustainability of Bt-cotton cultivation in Burkina Faso.

La présente étude analyse les perceptions qu'ont les producteurs des changements climatiques, leur cohérence avec les observations climatiques et les mesures d'adaptation adoptées par les producteurs sur le plateau d'Allada au sud du Bénin. A cet effet, les données liées à la pluviométrie, la température et les vents ont été analysées entre 1951 et 2010. Les perceptions et mesures d'adaptation des producteurs ont été collectées à l'aide d'un questionnaire structuré auprès de 201 producteurs sur le plateau d'Allada en 2010. Lors de l'analyse, les producteurs ont été classés en trois groupes selon leur âge : i) moins de 41 ans, ii) entre 41 et 55 ans et plus de 55 ans. Le test de ² a été utilisé pour vérifier si les perceptions des producteurs sont indépendantes de leur âge. Pour chaque groupe, le nombre de personnes ayant adopté une mesure d'adaptation donnée à été calculé. Le tableau de contingence obtenu a été soumis à une analyse factorielle des correspondances. Les perceptions des producteurs et les observations climatiques ne convergent pas toujours. En outre, l'âge influence les perceptions des producteurs et détermine l'adoption des mesures d'adaptation. Il importe de comprendre la cause des divergences entre perceptions et observations climatiques.

En Martinique, le flétrissement bactérien (R. solanacearum) affecte les cultures de solanacacées (la tomate en particulier) et de cucurbitacées. La gestion de cette maladie repose principalement sur le concept de lutte intégrée combinant différentes méthodes. L'introduction des plantes assainissantes dans les systèmes de culture maraîchères en association ou en rotation culturale doit réduire le potentiel infectieux du sol en R. solanacearum tout en préservant la diversité microbienne des sols. Le potentiel assainissant de six espèces végétales (Fabacées et Alliacée) sur la régulation du flétrissement bactérien (R. solanacearum) de la tomate a été tout d'abord évalué en conditions semi-contrôlées (serre) puis au champ au cours de 2 saisons successives. Ces essais ont été couplés à une étude des communautés microbiennes du sol. Les résultats obtenus en serre (2011) ont révélé (i) un effet assainissant significatif de C. juncea et C. spectabilis après la phase culturale (77% de réduction de maladie); (ii) un effet assainissant significatif de C. juncea après la phase de décomposition (55% de réduction de maladie) ; (iii) une tendance à la réduction de la maladie après une culture d'A. fistulosum, quelle que soit la phase testée (54% de réduction de maladie). Les résultats obtenus au champ (saisons 2012 & 2013) ont révélé un effet assainissant significatif après un précédent cultural de C. spectabilis (69% de réduction de maladie). Un effet assainissant a également été obtenu avec A. fistulosum (37% de réduction de maladie). Parallèlement, les résultats de tous les essais ont montré que les plantes de service introduites en précédent cultural stimulent les communautés microbiennes du sol. Ces résultats ont permis d'identifier trois espèces végétales–modèle capable de réduire l'impact du flétrissement bactérien au champ : Crotalaria juncea, Crotalaria spectabilis et Allium fistulosum. La gestion culturale de chaque espèce végétale–modèle doit être optimisée en conditions réelles sur différents types de sols. (Texte intégral)

La prévision de récolte de canne à sucre est une étape cruciale dans l'organisation logistique et la rentabilité de l'ensemble de la chaine de production de sucre. Nous présentons une méthode d'estimation de la récolte simple, robuste automatisable et de faible coût. Son principe repose sur l'ajustement d'un modèle de régression linéaire multivariée entre des variables de croissance simulées par un modèle de croissance de la canne et un historique de production. La performance de cette méthode est évaluée en l'appliquant à la production de canne à sucre de l'île de La Réunion. Elle est basée sur la modélisation de la croissance des parcelles de canne par le modèle de culture MOSICAS qui fournit des variables explicatives à des régressions linéaires de plusieurs variables ajustées sur un historique de production de 11 années des cinq bassins de production de La Réunion. Pour cela, la performance des méthodes de régression Stepwise et Least angle sont comparées. La précision des prévisions issues des deux modèles de régression a été calculée par validation croisée. Des prévisions de rendement sont simulées jusqu'à quatre mois avant le début de la récolte. Sont comparées, la précision des prévisions fournies par les deux modèles de régression, les prévisions à dire d'expert, et la moyenne des productions réelles, aux échelles du bassin de production, de l'usine, et de l'ile entière. Les résultats ont montré que les deux modèles de régression ont les meilleures performances à toutes les échelles. A l'échelle des bassins de production, la méthode de Least angle, avec une erreur quadratique moyenne de 7%, est légèrement meilleure que la méthode Stepwise (7.4%), et plus précise que la variation interannuelle moyenne du rendement (9.2%). Cette erreur descend à 3.6% à l'échelle de l'ensemble de l'ile. La précision à l'échelle du bassin est très satisfaisante même quatre mois avant le début de la récolte (erreur maximale de 10%). Cette méthodologie de prévision de récolte a l'avantage d'être semi-automatisable. Les prévisions de rendement peuvent ainsi être actualisées en temps quasi-réel à condition de disposer d'un réseau de stations météorologiques automatiques.

Fiber length, fiber strength, micronaire, uniformity, reflectance and yellowness measured on standardized instrument for testing cotton (SITC) are often used on cotton bales produced in the world for trading purposes with full respect of agreed commercial tolerances in order to limit the frequency of claims. In Africa, almost no trading on SITC data is made because we lack the study of within-bale variability of the given characteristics to deduce sampling and testing protocols insuring the respect of the same agreed commercial tolerances. We then conducted this study of the within-bale variability of fiber length and its uniformity, fiber strength, micronaire, reflectance and yellowness. We took eight samples per bale within 455 cotton bales produced in 14 African countries during two crop seasons. Our representative sample is then composed of over 3640 fiber samples which were analyzed in controlled conditions by SITC in a laboratory fully respecting the international recommendations. We then achieved an estimation of the within-bale variability of cotton fiber technological characteristics in most of the African cotton producing countries. The results indicated the variability per country, per bale in some situations and it was noted that even the gins (saw and roller) have also some effects in relation to within bale variability.

Most of the cotton bales produced in the world are sold according to the analysis of their technological characteristics using standardized instrument for testing cotton (SITC). In the United States of America, periodical studies of the results variability allow to accompany the results with commercial tolerances in order to limit the frequency of claims. In Africa, no such study was conducted to our knowledge. Therefore, we studied the within-bale variability of fiber length and of its uniformity, of fiber strength, of micronaire, of reflectance and of yellowness. We took 8 samples per bale within over 400 cotton bales produced in 13 African countries during two crop seasons. Our representative sample is then composed of over 3200 fiber samples which were analyzed in controlled conditions by SITC in a laboratory fully respecting the international recommendations. We then achieved an estimation of the within-bale variability of cotton fiber technological characteristics in most of the African cotton producing countries.

The ANR DELICAS project will address the problem faced in sugarcane for identifying molecular markers with a strong effect on traits of agronomic interest. The genetic control of cane and sugar yield traits in sugarcane typically involves numerous QTLs with small individual effects (Hoarau et al. 2002; Aitken et al. 2006). The lack of markers has been so far one of the most important constraints to a wider contribution of genomics to sugarcane breeding and for the development of marker assisted selection in this crop. Phenotypic traits for production potential interact strongly with the environment, and represent the outcome of multiple processes difficult to measure and to tag at the genetic level. Plant growth modelling can describe yield formation dynamically as a set of interactive equations using only a small number of genotypic parameters. The different parameters participating in phenotype expression can be considered as synthetic component traits, presumably controlled by fewer genes than the complex agronomic traits and can be expected to be closer to gene or QTL effects, in the sense that Genotype x Environment `noise' is reduced (Hammer et al. 2002, Dingkuhn et al. 2005). In such a `heuristic' approach, parameter variation among genotypes can be interpreted as an expression of allelic diversity, and analyzed accordingly in QTL or association studies. Model assisted phenotyping has been applied to maize (Reymond et al. 2003) or peach tree (Quilot et al. 2004). The DELICAS project, which associates the breeding company eRcane and Cirad, aims at identifying molecular markers associated with genes implied in the elaboration of sugarcane yield by using ecophysiological models. To achieve the objectives of the project, we will: (i) elaborate methods and tools for model assisted ecophysiological phenotyping of sugarcane, and (ii) phenotype a core collection with two ecophysiological models, Mosicas (Martine, 2003) and EcoMeristem (Luquet et al. 2006), and detect associations between genetic markers and model parameters.

To sustain the future world demand in sugar, bioenergy and biofuels, sugarcane crops with higher productivity are needed. This relies in first place on the creation of varieties with higher yield potential. New approaches exist that use known linkages between genome regions and agronomic traits of interest (Yin et al., 1999). In this respect, the DELICAS ANR project aims at identifying molecular markers associated with genes involved in the elaboration of sugarcane yield (Nibouche et al. poster, same session). The success of such an approach relies on the identification of simple process based traits constituting yield formation, more simple genetically and less prone to genotype by environment interactions (GxE, Hammer et al., 2005). As growth models mimic dynamically elemental processes of yield formation, related process based parameters could be considered as finer phenotypic traits and used in a phenotyping approach. Since a few years, model assisted phenotyping has been used on various plants with simple models (Yin et al., 1999). On Sugarcane, modelling studies mainly dealt with crop growth model (Canegro, Apsim, Qcane, Mosicas) applied to very few varieties in not too contrasted E. This did not provide to date a clear view of the genetic variability of their crop parameters. Also, O'Leary (2000) and Singels et al. (2005) underlined the need to explore the genetic variability that can be accounted for by the parameters in existing sugarcane crop models, this, to consequently adapt those models to support breeding purposes. The objective of this study is to determine the genetic and environmental variability of the crop parameters of two dynamic sugarcane crop growth models applied to 18 sugarcane genotypes in two contrasted environments in La Réunion Island: 1/ Mosicas [ Martiné & Todoroff, 2002] a population level model used widely for agronomic purposes, 2/ and Ecomeristem [Luquet et al., 2006], simulating rice and sorghum plant growth in its stand and adapted to sugarcane in the context of DELICAS project(see Luquet et al. in this session). This study being underway, this paper gives an overview of applied methodologies and first experimental results regarding elemental processes of canopy development.

Daily calibration of the FMT3 machine is required to compensate the effects of sample preparation by different technicians and the ageing of the apparatus. As this calibration involves the use of a limited stock of standard reference cotton, the problem of replacing the standards arises when the latter are exhausted. The standards are described by two values called PL and PH. This study covers the stability of measurements in time, the incidence of two types of calibration, the validity of the corrections made by calibration and the evaluation of the PL and PH values of new standards by several technicians. The USDA ICCS standards used are very homogeneous and supplied in 225-g rolls. The differences between technicians and the heterogeneity of the rolls are taken into account using a randomized experimental design and a linear model. It is simple to use and requires little material and technician time. A daily calibration by regression ensures a greater stability of FMT3 measurements and compensates any technician effect.

Introduction: The ecosystems of Southern Larzac (France) have experienced an evolution of pastoral practices which progressively led to a change of landscape structure. With the disappearance of transhumance and the decrease of grazing, the landscape tends to close up and it ancestral equilibrium is changed. Thus, the role of dung beetles (Coleoptera: Scarabaeoidea) and the organization of their communities are strongly modified. The aim of this work is to analyse the structure of these communities and their diversity according to this global evolution. Methods: The study was carried out during the year 2005. The insects were collected with attractive baited pitfall traps in six sites during four periods of the year. The Motomura model was used to analyse the diversity and the organization of communities. The distribution of the main species was described with correspondence analysis taking into account climatic parameters and pastoral practices. Results: 4582 insects were collected. The study of the communities showed a wide range of 46 species belonging to four families (Aphodiidae, Scarabaeidae, Geotrupidae, Trogidae). The functional groups differed depending on the seasons, the pedoclimatic characteristics and their breeding requirements. Conclusion: These preliminary results on the seasonal and spatial structure of the populations of dung beetles highlight the significant role of dung beetle communities in Larzac ecosystems. From a Biological Conservation point of view, our results can help to take decisions for a sustainable management of these ecosystems. (Texte intégral)

Des expérimentations comparant des systèmes de culture intensifs ont été menées au Brésil et à Madagascar, dans les zones tropicale et subtropicale. Des systèmes sans labour à couverture permanente (NT) ont été comparés au labour classique (CT), ou à un témoin en jachère. Sur la ferme ABC au Brésil, des traitements intermédiaires permettent en plus de constituer une échelle de quatre niveaux de travail du sol. La teneur en carbone organique du sol (SOC) a été mesurée tous les mois jusqu'à 10 cm de profondeur, 15 ans après le début de l'expérimentation ABC. Les variations saisonnières considérables de SOC indiquent un flux et une transformation continus de carbone. Sous le système sans labour (NT), le stock de carbone organique, suivant les saisons, était de 4 à 15 tonnes supérieur à celui mesuré avec labour (CT). Une fraction stable du carbone organique, associée à des agrégats de 53 à 210 µm, était toujours supérieure en masse sous le système sans labour. Le bilan de carbone était aussi le plus favorable sous le système sans labour (NT), non seulement à cause de son apport plus grand en carbone organique, mais aussi à cause d'une minéralisation plus lente. Cette tendance est clairement illustrée à l'aide d'un modèle simple de bilan carboné. Dans l'expérimentation ABC, les taux de minéralisation étaient significativement différents entre systèmes de culture, et leur progression suivant le niveau de travail du sol montre qu'une minéralisation plus lente est associée à la fois à un sol moins perturbé et à un apport supérieur de biomasse protectrice.