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Background and Aims Daylength determines flowering dates. However, questions remain regarding flowering dates in the natural environment, such as the synchronous flowering of plants sown simultaneously at highly contrasting latitudes. The daily change in sunrise and sunset times is the cue for the flowering of trees and for the synchronization of moulting in birds at the equator. Sunrise and sunset also synchronize the cell circadian clock, which is involved in the regulation of flowering. The goal of this study was to update the photoperiodism model with knowledge acquired since its conception. Methods A large dataset was gathered, including four 2-year series of monthly sowings of 28 sorghum varieties in Mali and two 1-year series of monthly sowings of eight rice varieties in the Philippines to compare with previously published monthly sowings in Japan and Malaysia, and data from sorghum breeders in France, Nicaragua and Colombia. An additive linear model of the duration in days to panicle initiation (PI) and flowering time using daylength and daily changes in sunrise and sunset times was implemented. Key Results Simultaneous with the phyllochron, the duration to PI of field crops acclimated to the mean temperature at seedling emergence within the usual range of mean cropping temperatures. A unique additive linear model combining daylength and daily changes in sunrise and sunset hours was accurately fitted for any type of response in the duration to PI to the sowing date without any temperature input. Once calibrated on a complete and an incomplete monthly sowing series at two tropical latitudes, the model accurately predicted the duration to PI of the concerned varieties from the equatorial to the temperate zone. Conclusions Including the daily changes in sunrise and sunset times in the updated photoperiodism model largely improved its accuracy at the latitude of each experiment. More research is needed to ascertain its multi-latitudinal accuracy, especially at latitudes close to the equator.

AGAP; International audience; In West Africa Sudano-Sahelian zone, sorghum sensitivity to photoperiod is a major trait for flowering adjustment toward the end of the rainy season. This trait ensures that conditions for crop development are optimal. Improving the understanding of the genetic control of flowering time in sorghum is thus an important step toward breeding climate resilient varieties for meeting the challenge of climate smart agriculture. In the wake of green revolution, most sorghum breeders eliminated photoperiod sensitivity to develop early maturing varieties. The evidence is now that simultaneous improvement of production, yield stability and grain quality requires the development of photoperiod-sensitive varieties. A segregating sorghum population derived from a cross between two photoperiod sensitive elite parents was evaluated in three different locations and five environments. CERES crop model was applied to decompose the flowering time of each genotype into basic vegetative phase, critical photoperiod and photoperiod sensitivity. Phenology and model derived variables were used for genetic analysis. The three model parameters were controlled by specific genomic regions. A major QTL affecting critical photoperiod was identified, whereas only independent minor QTLs were found for basic vegetative phase and photoperiod sensitivity. Candidate gene analysis in the major QTL region allowed us to propose a candidate gene (ELF3) involved in the circadian clock as a key regulator of flowering time in photoperiod-sensitive sorghum. Our findings provide critical information supporting the development of photoperiod-sensitive genotypes specifically adapted to climate variability encountered in Sudano-Sahelian zone.

Phenology and time of flowering are crucial determinants of rice adaptation to climate variation. A previous study characterized flowering responses of 203 diverse indica rices (the ORYTAGE panel) to ten environments in Senegal (six sowing dates) and Madagascar (two years and two altitudes) under irrigation in the field. This study used the physiological phenology model RIDEV V2 to heuristically estimate component traits of flowering such as cardinal temperatures (base temperature (Tbase) and optimum temperature), basic vegetative phase, photoperiod sensitivity and cold acclimation, and to conduct a genome-wide association study for these traits using 16 232 anonymous single-nucleotide polymorphism (SNP) markers. The RIDEV model after genotypic parameter optimization explained 96% of variation in time to flowering for Senegal alone and 91% for Senegal and Madagascar combined. The latter was improved to 94% by including an acclimation parameter reducing Tbase when the crop experienced low temperatures during early vegetative development. Eighteen significant (P

The combined production of grain and sugar by sorghum requires efficient leaf C acquisition (source) and allocation to productive sinks, namely the stem and the panicle. Photoperiod sensitivity, which regulates plant phenology and growth, is also likely to be a key regulator of such C source-sink relationships, while it is crucial to drought adaptation. This study set out to evaluate the contribution of plant leaf area and stem growth to the production of grain and sugar by sweet, photoperiodic sorghum depending on the sowing date and post-flowering water availability. Twelve West African accessions were studied in the field in Senegal during two consecutive rainy seasons, comparing two sowing dates and post-anthesis water regimes (irrigated, or not). Plant growth and development were monitored weekly up to flowering. Organ size and biomass, stem juiciness and sweetness were characterized at flowering and maturity. At flowering, early sowing enhanced plant leaf area, stem dry weight and sugar production, and plant leaf area expressed per unit of stem dry weight was positively correlated to stem sweetness, suggesting that a high pre-flowering source-to-sink ratio favors early sugar accumulation. Overall, a late sowing date reduced sugar and grain production more than post-anthesis drought, whereas early sowing enhanced both types of production. No post-anthesis competition was found between grain filling and stem sugar accumulation. However, under drought conditions, the maintenance of combined production was better for the most leaf stay-green accessions. It is suggested that the combined production of sugar and grain by sweet, photoperiodic sorghum in response to the sowing date and post-anthesis drought is firstly sink-driven but that source (plant leaf area) dynamics can enhance stem sugar accumulation and its maintenance under drought conditions. These results provide further insight into the traits to be combined in dual-purpose ideotypes dedicated to drought-prone environments.

The effects of light at different wavelengths and photoperiod on growth and ochratoxin A production of Aspergillus carbonarius and Aspergillus westerdijkiae were studied: far-red (740 nm), red (625 nm), blue (445 nm), and UV-A (366 nm). Fungal growth was not significantly affected by photoperiod or light wavelength; the only exception was A. westerdijkiae which showed reduced growth under UV-A light (366 nm). Short-wavelength blue light (445 nm) and UV-A light caused a reduction in ochratoxin A production of both fungal species. However, long-wavelength red light (625 nm) and far-red light (740 nm) reduced ochratoxin A production only in A. westerdijkiae but not in A. carbonarius. It is believed that this difference in reactivity to light is due to differences in the melanin content of the two fungal species: A. carbonarius is a black fungus with higher melanin content than A. westerdijkiae, a yellow fungus. Other possible explanations for the reduction of ochratoxin A production by light were also discussed.

In Sub-Saharan Africa, Genotype-Environment interaction plays a key role in formulating strategies for crop improvement. Multi-location trials have created enabling structure to determine varieties yield performance and stability. Crop modeling led to prediction of long-term and spatial effects of climate variability. Three improved varieties were compared to three landraces. Optimum cultivation areas minimizing the risk of crop failure were delineated by comparing predicted flowering dates and end of rainy seasons. Agronomic values were determined in trials from three climatically different zones in 27 farms. Yield stability was determined using linear regression depending on each environmental mean and the AMMI model. Photoperiod sensitive varieties have wider optimal cultivation areas whereas early-maturing varieties (photoperiod insensitive) are subjected to strong constraints on sowing date. In low productivity conditions, landraces and improved varieties are not distinct. As the environmental cropping conditions increase, improved lines become significantly superior to landraces. Photoperiod insensitive landrace is subservient to climate conditions of its area of origin and its productivity drops sharply when moved to a wetter area. Varieties studied combined productivity and stability traits. These findings are important steps toward breeding climate resilient varieties for meeting the challenges of climate smart agriculture and sustainable intensification. Key words: Mali, sorghum, GxE, photoperiodism, climate change, yield stability.

Sweet sorghum is highly coveted to contribute and take up food and energy challenges. A collection of 84 West Africa landraces mostly from Senegal and four control cultivars were screened to identify relevant accessions and trait combination for multi-purpose (sugar/grain/biomass). The implication of photoperiod sensitivity was particularly addressed. A total of 20 traits related to phenology, morphology, grain and sugar production were assessed in two sowing dates (July and August) at CNRA Bambey in Senegal. Late sowing resulted in shortened vegetative phase and a significant decrease in traits related to plant size, stem sugar, biomass and grain productions. Broad-sense heritability was moderate to high for most of the phenology, morphology, grain and sugar-related traits, suggesting their interest for breeding. All the traits related to plant size were positively correlated with plant sugar production except plant height. A cluster analysis identified three groups contrasting in their ability to combine sugar, grain or fodder production based on 18 traits measured for the early sowing. Clusters I and III were suitable for one purpose: grain and sugar, respectively. Cluster II was the most suitable for multi-purpose, showing the best trade-off among grain, sugar and vegetative biomass production. The best accessions for stem sugar yield belonged to durra, caudatum and their intermediate types. The relationship between internode size and sweetness should be further studied, in particular exploring their relationship with internode tissue anatomy. Further studies are also needed to evaluate the role that stay-green can play in sugar yield maintenance under post-flowering drought. (Resume d'auteur)

Leaf appearance and leaf elongation rates in rice play an essential role in determining the development of the plants' architecture which affects their adaptability to varying environments. This study aimed to characterize the rates of leaf appearance and elongation on all leaves of the main culms of rice plants for 11 contrasting varieties and to determine if the decrease in the leaf appearance rate was related to a simultaneous decrease in the rate of leaf elongation. Forty four 13-L pots were sown with one plant from one genotype and laid out in 4 randomized complete blocks. The experiment, conducted inside a greenhouse, was repeated twice. The increase in length of the leaves expanding on the main stems was monitored daily until flag leaf. Data were used to estimate the rates of leaf appearance and leaf elongation. Significant variability in the rate of leaf appearance, rate of leaf elongation, and leaf length was found across varieties. The kinetics of leaf appearance had linear phases intermediated by a curvilinear phase, without sharp changes in the phyllochron duration. Maximal leaf elongation rate (LER) of all genotypes (except for one) increased linearly with leaf rank until it reached its maximum value at leaf 8 to 10 (11 - 12 for Azucena) where it stabilized before decreasing linearly with leaf rank for the last leaves. Finally, both rates of leaf appearance and leaf elongation evolved with time more smoothly than expected so no sharp decrease in LER occurred at the time of the decrease in leaf appearance rate of the last leaves. However, the trilinear model fits the data well enough to remain useful in efficiently comparing the leaf appearance kinetics of contrasting varieties.

Better defining niches for the photoperiod sensitive sorghum (Sorghum bicolor L. Moench) varieties of West Africa into the local cropping system might help to improve the resilience of food production in the region. In particular, crop models are key tools to assess the growth and development of such varieties against climate and soil variability. In this study, we compared the performance of three process-based crop models (APSIM, DSSAT and Samara) for prediction of diverse sorghum germplasm having widely varying photoperiod sensitivity (PPS) using detailed growth and development observations from field trials conducted in West Africa semi-arid region. Our results confirmed the capability of each selected model to reproduce growth and development for varieties of diverse sensitivities to photoperiod. Simulated phenology and morphology organs during calibration and validation were within the closet range of measured values with the evaluation of model error statistics (RMSE and R2). With the exception of highly sensitive variety (IS15401), APSIM and Samara estimates indicate the lowest value of RMSE (

Matching phenology with prevalent abiotic and biotic conditions is a prerequisite for varietal adaptation to the environment. That is particularly important in the context of climate change because an increase in temperature is most likely to modify the precocity of the varieties. The forecast of flowering time in photoperiod- sensitive sorghum is complex as flowering depends on temperature, day length and soil fertility. The objectives of this work were to quantify effects of latitude on the development of selected sorghum varieties and to verify the precision of our models to predict sorghum maturity. A field experiment at three locations along the latitudinal gradient in Mali with staggered sowing dates (SDs) was conducted. Seven sorghum cultivars covering a wide range of the diversity of cultivated sorghums in Mali were sown on the 10 of June, July and August in 2009 and 2010. Duration of the vegetative phase strongly decreased with latitude. Although the maximum day length difference between locations was < 8 min, for some varieties, we observed a reduction in crop duration of up to 3 weeks. Some varieties were photoperiod insensitive at one location but became photoperiod sensitive at another. The effect of latitude on the phenology is underestimated by the existing models. To determine the optimal areas for the varieties in West Africa and to forecast the effects of climate change, a correction of the simulation coefficients taking account of latitude is proposed. But, in the end, it will be necessary to develop a new model that will be able to predict the effects of both SD and latitude. More research is needed to understand physiological response mechanisms of the pronounced latitude effects on sorghum phenology. (Resume d'auteur)

Climate variability is a characteristic feature of the tropics where the summer monsoon starts from May/June and ends mostly in October, thus producing an unpredictably variable length December 9, 2011 of growing season. This results in serious challenges for the mainly substituent small holder farmers in the arid to semi-arid zones of the tropics. A study was conducted to determine the attainable grain yield and yield stability of 10 well characterized and extensively cultivated tropical sorghum accessions across 18 environments comprised of 3 dates of sowing at 3 sites (along a latitudinal gradient covering 3 agro-ecological zones) over 2 years in Mali. For each year and site combination, sorghum accessions and dates of sowing were arranged in a split plot and tested in a Randomized Complete Block (RCB) design. Appropriate cultural practices and timing were used to minimize effects of biotic factors. In addition to Grain yield, yield penalty associated with delayed sowing was determined. Two static and five dynamic indices were used to assess the stability of grain yield for genotypes across environments. Mean grain yield ranged from 0 to 248 g m-2 across environments, from 74 to 208 g m-2 across the 10 genotypes and generally reduced with delayed sowing. A genotype combining photoperiod sensitivity and stay-green traits was revealed as the most stable. The similarities and differences were observed among the stability indices used in terms of ranking of the genotypes. Implications of these for adaptation to climate change are discussed. (Resume d'auteur)

Effects of photoperiod (PP) on panicle initiation (PI) of West African sorghums are essential for the crop's agro-ecological adaptation, but not well understood. Conventional models based on fixed PP thresholds (qualitative response) or additive signal accumulation (qualitative response) are able to predict flowering for only a limited range of conditions. Recently, an alternative concept was proposed based on thresholds that vary with plant age. Using this concept, this study develops a generic model of PP response of sorghum called “ Impatience ” because it implements decreasing day length requirements during prolonged wait states, or appetence, during the photoperiod sensitive phase (PSP). The model was applied to experimental field data obtained from sowing date experiments in Mali, in order to validate it and evaluate the range of genotypic response that can be explained with it. It predicted accurately the observations that (1) PI does not occur at any genotype specific day length, but instead, on increasingly long days as the PSP is extended; (2) PI occurs predominantly when day length decreases, or after summer solstice; (3) the duration of PSP increases linearly (but not always proportionally) when crops are sown earlier in the year; (4), a genotype specific sowing date exists in winter (cool season) or spring (hot dry season) after which PSP suddenly increases by up to 160 days (“break point”); (5), the largest variance of PSP occurs near the break point. Most genotypic variations of this complex pattern could be simulated by fitting only one of the four model parameters while using default values for the three other parameters. However, the model tended to underestimate the duration of PSP when it fell into the cool season, which might be explained by specific thermal effects or a specific inhibitory effect of increasing day length on PI in some genotypes. The ability of the model to discriminate among genotypes was used to devise a simple, model assisted phenotyping methodology. Genotypic parameters were determined by fitting two model parameters to measured dates of flag leaf ligule appearance for three sowing dates. Thus parameterized, the model predicted accurately the phenological patterns of contrasting materials observed in different experiments. The authors discuss the physiological probability of the model's underlying concepts, the need for further studies to develop them into a comprehensive theory, and possible applications in crop simulation and varietal selection.

Un projet de sélection participative du mil a été initié pour comprendre les raisons de la faible diffusion des variétés améliorées dans la zone soudano-guinéenne du Mali. Un diagnostic et une prospection des variétés locales ont été réalisés en 2007 dans cinq villages de la région de Sikasso. Un essai comportant deux dates de semis (18 juin et 16 juillet 2007) a été réalisé à la station agricole de Sotuba. La durée du cycle de 29 variétés locales a été mesurée. Toutes les variétés prospectées sont photopériodiques, leur cycle diminue lorsque le semis est retardé. Les nouvelles variétés proposées aux paysans sont précoces, peu sensibles à la photopériode. Les chercheurs et les paysans sont convaincus que des variétés plus précoces que les cultivars locaux permettront d'éviter les sécheresses de fin de cycle. En réalité, les variétés locales résultent d'une sélection massale ancestrale et sont souvent spécifiquement adaptées à leurs environnements d'origines. La floraison des variétés locales est naturellement synchrone avec la date moyenne de fin de la saison des pluies. Ce caractère permet aux variétés locales de surmonter la principale incertitude climatique de la zone : la variabilité du début de la saison des pluies. La faible prise en compte des qualités propres aux variétés locales par les programmes d'amélioration des plantes explique le rejet des nouveaux cultivars par les paysans. Les programmes de sélection s'appuient maintenant sur le germoplasme local et un volet essentiel de l'expertise paysanne devient accessible à l'analyse des chercheurs.

La vitesse de développement des sorghos fortement photopériodiques et par conséquent tardifs adaptés aux savanes d'Afrique de l'Ouest est ralentie pendant les phases de montaison et de développement de la panicule. Cette lenteur du développement, exprimée par un long phyllochrone, ou temps écoulé entre l'apparition de deux feuilles successives, est en relation avec la taille limitée des panicules des sorghos tardifs. Par conséquent, une modification de la vitesse de développement de la plante pourrait être une voie pour augmenter le potentiel de rendement de ce type de variétés. La variabilité pour ce caractère a été recherchée dans la mini core collection de sorgho du Centre de coopération internationale en recherche agronomique pour le développement (Cirad) et n'a pas été décelée. Au contraire, les vitesses de développement sont apparues homogènes au sein de l'espèce. Aucune variation du phyllochrone initial, depuis la levée, n'a été montrée et en dépit de la grande variabilité du phyllochrone secondaire, exprimé pendant la montaison, il n'a pas été mis en évidence de différence significative entre variétés de même maturité. Le phyllochrone secondaire, fortement corrélé à la durée de la phase végétative, est apparu comme l'une des fonctions affectées par la réponse photopériodique.

Il est couramment admis que la sécheresse en Afrique de l'Ouest a entraîné l'adoption par les paysans de variétés de sorgho plus précoces que les cultivars traditionnels. Pour mesurer l'évolution récente du cycle des sorghos du Mali, nous avons étudié la phénologie de deux collections de variétés locales prospectées à 20 ans d'intervalle en 1978 et en 2000. Les dates de début et de fin de saison des pluies ont été calculées pour tous les villages échantillonnés. La sensibilité des cultivars à la photopériode a été mesurée à l'aide d'un essai comportant deux dates de semis. Un modèle permet d'étudier l'adaptation des variétés au climat en tenant compte de la latitude et du régime des pluies de leurs zones d'origines. Le déficit pluviométrique n'a pas entraîné un raccourcissement important des cycles végétatifs. En 20 ans, le cycle moyen des cultivars locaux s'est raccourci de 5 jours. Pour des latitudes inférieures à 14° N, la grande majorité des cultivars sont photopériodiques, la floraison des variétés se produit dans les 20 jours qui précèdent la date moyenne de fin de la saison des pluies. Ce caractère permet d'optimiser l'alimentation en eau des cultures et d'éviter de nombreuses contraintes biotiques. Pour des latitudes supérieures ou égales à 14° N, la floraison moyenne coïncide avec la fin de saison. On note la présence simultanée de variétés tardives et précoces. Dans ces régions, la culture du sorgho dépend moins de la pluviométrie car les systèmes traditionnels valorisent des situations diversifiées et les reports d'eau sur les toposéquences. Cette diversité des cycles contribue à sécuriser la production agricole en zone aride. Ce travail permet de guider les programmes de sélection dans la définition d'idéotypes spécifiquement adaptés à la gamme d'environnements climatiques rencontrés dans la région.

The GRiSP Global Rice Phenotyping Network seeks to assemble a multi-environment, multi-trait phenomics resource for rice (Oryza sativa L.) diversity panels in order to understand existing genetic diversity and identify genes/alleles conveying adaptation and yield potential. Phenology is central to plant adaptation and productivity in different agro-ecologies. We studied a panel of 209 accessions, including 189 indica types and 20 acc. representing other genetic groups. The panel was field-phenotyped under flooded conditions for duration to flowering (F) for 6 sowing dates in Senegal (capturing different thermal and day length regimes) and during two years at two altitudes (mid, 857 m asl; high, 1497 m asl; with similar latitude) in Madagascar. The experiments had an augmented design in Senegal (6 blocks × 6 dates as subplots and 209 acc. as sub-subplot) with 4 replicated check varieties; and a complete block design with 3 replications at 2 sites × 2 years in Madagascar. To dissociate different traits contributing to variation of F, five genotypic Index Variables were calculated. Among them, PCA identified three as describing 98% of diversity: Estimated basic vegetative phase (BVP), photoperiod (PP) sensitivity, and altitude response. Three clusters were identified within the indica group and related to genotype origin, agronomic type and ecosystem of adaptation. Cluster C1 was PP-sensitive, C2 had short BVP and C3 had long BVP. Within C1, a sub-cluster was highly altitude sensitive, and within C3 two sub-clusters were comparatively altitude insensitive. Harvest index (HI), aboveground dw and stem height observed in the most favorable environment (Senegal wet season) showed distinct patterns among clusters, with C2 having high HI and C1 being tall. The phenomics resources will be further analyzed using a crop model and genome-wide association (GWA) studies. (Resume d'auteur)

En Afrique de l’Ouest, l’igname est traditionnellement une culture itinérante, installée après défriche-brûlis d’une jachère longue. L’état actuel des connaissances sur le fonctionnement de la culture est insuffisant pour permettre d’élaborer des alternatives durables à ce mode de conduite pénalisant pour l’environnement. Des études récentes montrent que la variabilité du rendement entre plantes d’une même parcelle constitue un verrou majeur à l’amélioration de la culture d’igname. Actuellement, la cause de cette variabilité reste inexpliquée et freine les tentatives d’intensification des systèmes de culture. Dans ce contexte, l'objectif de la thèse était d’étudier la variabilité interplante des deux espèces majeures d’igname en Afrique de l’Ouest (Dioscorea alata et D. rotundata), et plus particulièrement : de la quantifier, d’en identifier les causes et d’en estimer les conséquences physiologiques, agronomiques, et économiques. Une série de 11 expérimentations menées de 2006 à 2009 sur deux sites au Bénin nous a permis de démontrer que la variabilité de rendement entre plantes d’igname était nettement supérieure à celle des autres cultures à tubercules, telles que la pomme de terre (CV > 40% et CV < 20%, respectivement) et s’exprimait dès les premiers stades de croissance. Les causes de cette variabilité ont été identifiées et leurs effets directs et indirects ont été quantifiés en utilisant un modèle graphique de type réseau bayésien. Ces résultats montrent qu’aux densités de plantations traditionnelles en Afrique de l’Ouest (0,4 à 1 plante m-²), il n’y a pas de compétition entre plantes. En revanche, le matériel de plantation utilisé introduit une forte variabilité initiale entre individus via la taille des semenceaux et la date d’émergence. Nous avons mis au point un modèle à l’échelle de la plante permettant de simuler la croissance de l’igname en fonction des facteurs responsables de la variabilité du rendement, et son développement en fonction de la photopériode et de la température. Le modèle prédit bien les rendements individuels observés. Les observations ainsi que les prédictions montrent clairement que les plantes émergées plus tardivement, ou issues de semenceaux de faible qualité, auront une croissance ralentie, une tubérisation initiée trop rapidement et finalement, un rendement plus faible. En comparaison avec l’utilisation d’un matériel de plantation théorique, plus homogène, calqué sur celui de la pomme de terre, ces pertes sont estimées, en moyenne, à 22 et 27% du rendement pour D. alata et D. rotundata respectivement. En tenant compte du prix de vente saisonnier et du coût des semenceaux, cette perte de rendement se traduit par une réduction du profit de l’agriculteur de 30 et 40%, respectivement. Pour la culture d’igname en Afrique de l’Ouest, les conséquences agronomiques et économiques de la variabilité de la croissance et du développement entre plantes d’une même parcelle, plaident en faveur du développement d’une filière de production de semenceaux de qualité., In West Africa, shifting cultivation using the slash and burn technique is the traditional yam cropping system. Current knowledge is insufficient to elaborate and recommend sustainable alternatives to this cropping system, which threatens the environment. Recent studies have shown unexplained interplant yield variability to be an important brake on the improvement of yam production system that hinders intensification attempts. In this context, the objective of the thesis was to study yield interplant variability of the two main yam species (Dioscorea alata and D. rotundata) and more specifically to quantify this variability, to identify its causes and to estimate its physiological, agronomic and economic consequences. A set of 11 experiments carried out between 2006 and 2009 at two locations in Benin, enabled us to demonstrate that interplant variability of yam yield is much higher than that of similar tuber crops, such as potato (CV > 40% and CV < 20%, respectively) and that it appears at an early growth stage. Causes of this variability were identified and their direct and indirect effects were quantified using a Bayesian network. At common planting densities (0.4-1 plants m-²), these results showed that there was no competition between plants. In contrast, the use of traditional planting material introduced important initial variability between individual plants, especially in the observed emergence date and seed-tuber weight. We developed a plant model to simulate yam growth as a function of factors affecting yield variability and yam development as a function of daily photoperiod and temperature. The model gives good estimates of observed plant yield. Observations and simulations both demonstrate that delayed emergence and lower seed-tuber quality (lower weight) lead to a slower vegetative growth, unduly early tuber initiation and finally a lower yield. In comparison with the use of a theoretical planting material based on the potato, the use of traditional planting material resulted in a 22 and 27% yield loss for D. alata and D. rotundata respectively. Taking into account the seasonal selling price of the crop and the cost of the seed tubers, the yield loss represents a decrease of 30 and 40% in profit for the producer. Agronomic and economic consequences of the interplant yield variability would suggest the development of a quality seed-tuber production system to the benefit of yam cropping in West Africa.

Dans la zone soudano-sahélienne la variabilité climatique inter et intra saisonnière est importante et conditionne le potentiel de production des cultures. L'incertitude principale porte sur les dates de début et de fin des pluies. Le photopériodisme des variétés locales de mils et sorghos permet la synchronisation de la floraison avec la date moyenne de fin des pluies. La détermination des zones d'adaptation des génotypes nécessite la connaissance du développement phénologique qui dépend étroitement de la durée du jour et de la latitude du lieu de culture. Les modèles de croissance des plantes prennent insuffisamment en compte les effets de la latitude sur l'expression du photopériodisme. Un indice simple d'adaptation variétale basé sur l'écart entre les dates d'épiaison et de fin de la saison des pluies permet de générer des cartes d'adaptation variétale. Une prospection variétale a été réalisée sur des transects latitudinaux dans 20 villages des zones d'adaptation de la variété de mil Bofoué et de la variété de sorgho Ceblen, deux variétés vulgarisées au Mali. Les variétés prospectées dans ces villages montrent un comportement phénologique similaire aux deux variétés témoins. Ce résultat valide les limites latitudinales des bandes d'adaptation variétale au niveau des agrosystèmes villageois. Le concept de " précocité " des accessions est relatif et spécifique à chaque latitude. Nos résultats donnent une idée plus précise de la complexité des interactions Génotype x Environnement x Technique culturale et permettent de comprendre les stratégies et techniques d'adaptation aux risques environnementaux adoptés par les paysans. Les outils cartographiques développés ouvrent de nouvelles perspectives en définissant le concept " d'adaptation spécifique " à chaque environnement dans les agrosystèmes villageois. Ces cartes permettent d'extrapoler notre connaissance de la variabilité du développement des variétés dans divers systèmes de cultures, et d'aider au processus de création et de diffusion de variétés aux niveaux local, national et régional. (Texte intégral)

Rice is an increasingly important cereal in West Africa, where it is grown in a wide range of hydrological conditions in high rainfall, humid forest to low rainfall, savanna agro-ecological zones. In order to identify cultivars that are well adapted to these diverse environments, and the traits that are needed in new cultivars to ensure adaptation, the effects of photoperiod and temperature on duration from emergence to flowering (f) need to be quantified. The objectives of this study were: to phenotype duration to flowering of a diverse set of rice cultivars representing types grown in West Africa using data from carefully selected photothermal controlled environments (CEs); to examine how basic vegetative phase (BVP) and photoperiod-sensitivity varied among the different species and ecotypes; and to assess the usefulness of this simplified approach for characterising genotypes and lines for plant breeding and association and functional genomics. Twenty-two genotypes of rice representing the diversity found in West Africa, and including Oryza sativa indica and japonica, Oryza glaberrima and O. sativa×O. glaberrima progenies, were grown in a controlled environment (CE) under flooded (lowland) and free-drained (upland) hydrologies at 11 and 13 h photoperiods combined with mean temperatures of 22 and 28 °C. A simple model describing f in terms of a BVP, photoperiod-sensitive phase (PSP) and post-PSP was used to analyse variation in f. Hydrology had no effect on f but did affect plant height in some genotypes. Flowering occurred earliest in the 11 h photoperiod regimes (between 41 and 87 days after emergence (DAE)) and latest at 13 h/22°C (between 68 and >150 days). The earliest genotypes to flower were all O. glaberrima and these all had a very short BVP (mean 276°C days: Tb=10°C) but were strongly photoperiod-sensitive (mean PSP 364°C days h-1). In contrast traditional O. sativa japonica cultivars were all late flowering due to a long BVP (mean 1006°C days) and strong photoperiod-sensitivity (mean 342°C days h-1). Improved japonicas, indicas and O. sativa×O. glaberrima progenies all had shorter BVPs (447-662°C days) than traditional japonicas. Photoperiod-sensitivity was also less in the progenies and improved japonicas (about 200°C days h-1). There were good correlations between values for BVP and PSP estimated in CE and the field (r=0.86 and 0.68, respectively). We conclude that diverse genotypes can be successfully phenotyped for f using a simple model and three or four carefully chosen photoperiod and temperature regimes in a CE facility. © 2003 Elsevier Science B.V. All rights reserved.

Au Sahel, les agriculteurs pratiquent la sélection massale en produisant leurs semences de sorgho dans les champs de culture. Dans un tel agroécosystème, du fait de l'allogamie partielle du sorgho, les variétés peuvent s'intercroiser naturellement entre elles. Dans la zone soudano-sahélienne du Mali, on note la diffusion récente d'une variété améliorée " Jakumbé ", peu photopériodique, de morphologie proche des variétés locales mais nettement plus précoce. Le taux de diffusion de Jakumbé est très imprécis allant, selon les études, de 20 à 90%. L'objectif de ce travail qui combine des résultats d'enquête et des caractérisations phénologiques est d'estimer la diffusion réelle de Jakumbé dans deux villages et les conséquences de cette adoption sur le devenir des variétés traditionnelles. Comme Jakumbé est plus précoce que les variétés locales photopériodiques, la durée du cycle est utilisée pour distinguer les différents cultivars. Les variétés cultivées dans deux villages de la région de Ségou au Mali, Bouawéré et Kagnan, ont été étudiées en 2009 et 2010, quelques années après la vulgarisation de Jakumbé. En 2009, les variétés provenant de 29 champs du village de Bouawéré ont été étudiées avec une date de semis précoce le 8 juin. En 2010, les variétés provenant de 19 champs du village de Kagnan ont été étudiées avec deux dates de semis le 18 juin et le 19 juillet. Les résultats montrent qu'une faible proportion des champs peut être considérée comme composée uniquement de Jakumbé (11 % à Bouawéré comme à Kagnan). La plupart des champs présente une distribution bimodale de la précocité qui identifie un mélange entre les variétés locales et Jakumbé (71% à Bouawéré et 47 % à Kagnan). Le reste des champs porte des variétés locales uniformément plus tardives que Jakumbé (18 % à Bouawéré et 42 % à Kagnan). Comme la morphologie de Jakumbé est proche de celle des variétés locales, les paysans ne sont pas capables d'identifier la présence de mélanges. Sans le savoir, les paysans cultivent donc majoritairement un mélange de variétés traditionnelles et de Jakumbé plus précoce. Cette diffusion rapide de Jakumbé montre l'intérêt des paysans pour les nouvelles variétés précoces proposées par la recherche. Toutefois, la culture de mélanges de variétés pourrait avoir un impact négatif en contribuant au développement de la Cécidomyie (Stenodiplosis sorghicola), un important ravageur du sorgho en Afrique sub-saharienne mais encore peu présent au Mali.

Responses of #Neoceratitis cyanescens# (Bezzi) (Diptera: Tephritidae) females to visual stimuli were studied in a laboratory flight chamber. A bright orange sphere was used to investigate the effects of age, mating status and time of day on their responses. In no-choice assays, four parameters were considered : mean time before leaving the release vial, percentage of flies that visited the sphere, mean number of flights and mean time before landing on the sphere. Naive mated females first became strongly responsive to the orange sphere 6 days post-adult emergence (>40%). The percentage of females that visited the sphere increased significantly with egg load. There were no significant differences in behavioural responses between virgin and mated mature females. In a choice situation between a yellow and an orange sphere, starved females displayed a greater propensity than well-fed females to land on the yellow sphere. Mature females were more responsive to the orange sphere when tested in the afternoon than earlier in the day. In a no-choice situation, females visited the yellow sphere as often as the orange sphere. However, the mean delay before landing was significantly greater for the yellow sphere. The results emphasize the importance of physiological condition on responses of #N. cyanescens# females to host-simulating visual stimuli. (Resume d'auteur)

Sorghum [Sorghum bicolor (L.) Moench] is an important cereal crop grown in a wide range of tropical and temperate environments. This study was conducted to characterise the photothermal flowering responses of sorghum genotypes and to examine relationships between photothermal characteristics and environment of origin in order to better understand the phenological basis of adaptation to environment in sorghum. Twenty-four germplasm accessions and one hybrid from 24 major sorghum-growing areas were grown in a wide range of environments varying in temperature and photoperiod in India, Kenya and Mali between 1992 and 1995. Times from sowing to flowering (f) were recorded, and the responsiveness of 1/f to temperature and photoperiod was quantified using photothermal models. Times from sowing to flowering were accurately predicted in a wide range of environments using a multiplicative rate photothermal model. Significant variation in the minimum time to flower (Fm) and photoperiod sensitivity (critical photoperiod, Pc, and photoperiod-sensitivity slope, Ps) was observed among the genotypes; in contrast there was little variation in base temperature (Tb). Adaptation of sorghum to the diverse environments in which it is grown was largely determined by photoperiod sensitivity and minimum time to flower; photoperiod sensitivity determines broad adaptation to latitude (daylength), while variation in the minimum time to flower determines specific adaptation within smaller ranges of latitude, e.g. within the humid and sub-humid tropics.

La reproduction du Coq peut être dans une large mesure contrôlée par la durée quotidienne d’éclairement. Ce sont les variations de cette durée qui permettent le mieux de maîtriser la précocité de la production de spermatozoïdes, tandis que la persistance de cette production peut, sauf cas particulier, être la plus satisfaisante en jours courts. Cette condition est donc contradictoire à la fois avec une production de spermatozoïdes précoce, qui nécessite des jours croissants, et avec le maintien d’une intensité de ponte élevée, car on ne sait l’obtenir qu’en jours longs. Comme palliatif, on utilise donc dans la pratique un large effectif de coqs dont l’alimentation est par ailleurs rationnée afin de maintenir leur libido. L’insémination artificielle serait sans doute plus satisfaisante, en permettant d’adopter des conditions d’élevage spécifiques des coqs tout en réduisant leur nombre au minimum. Largement employée dans les autres espèces avicoles, son utilisation pour produire des poussins de chair bute encore sur des habitudes, sur la nécessité d’employer plus de personnel, plus qualifié et plus motivé, et sur une structure de filière où l’éleveur est encore parfois client de l’accouveur., The reproductive capabilities of the cockerel are strongly influenced by daylength. Its variations strongly influence the age at which testicular development occurs, and consequently the age at sexual maturity. Both are advanced by increasing the daily photoperiods in growing cockerels. However the sperm production markedly declines after sexual maturity in cockerels submitted to long days, though they are known to allow high egg laying rates in the hen. By contrast, the adult sperm production may be well maintained under short constant days (e.g. 8L:16D), which induce delay in sexual maturity. Therefore there is an antagonism between photoschedules required to reach precocious sexual maturity and those able to maintain sperm production. In the industry, adult broiler cockerels are raised under long days, together with the hens, to reproduce by natural mating. Many males (8 to 12 per 100 females) are used to compensate for the decline in their adult sperm production. They are furthermore submitted to restricted feeding, to prevent them from fattening and to stimulate their libido. However a number of deficient cockerels must often be replaced during the reproductive period. On an experimental basis, artificial insemination leads to a better management of males, through the use of specific photoschedules. It also permits the number of males to be reduced markedly by optimizing the use of semen to match the fertility requirements of hens. But artificial insemination is expensive and its technical requirements are rather hard to meet. It is therefore not in use for broiler production in countries where the cost of labour is high, even though it maximises profits in other domestic bird species.

Genetic diversity in Sahelian rice systems is very limited with more than 90% of the irrigated rice area planted to only three varieties. Recent liberalization and intensification of production require varieties that are better adapted to climatic constraints associated with evolving rice-rice and alternative rice-based cropping systems. Forty nine locally grown or introduced genotypes were characterized for their photothermal response in the field using a model described in a previous paper. Varietal constants Tbase, Topt, Tsum, BVP and CPP characterized thermal and photoperiodic effects on flowering and were validated using literature and field data from independent experiments. Photothermal constants were associated with seasonspecific, agronomic performance. Short-duration types with high plasticity of duration performed best in the dry season, and medium-duration types with high plasticity in the wet season. Short-duration types with low plasticity of duration performed well in both seasons. Locally grown varieties were mostly medium duration and comparatively thermo- and photoperiod-insensitive. Researchers' selections were markedly different from locally used materials. We conclude that photothermal response of phenology is an important character for breeding improved irrigated rice in arid environments.

Sugar accumulation in sorghum (Sorghum bicolor (L.) Moench) stems is a complex trait that is particularly plastic in response to photoperiod. This study investigated sucrose accumulation in a sterile (no grain filling) and fertile near-isogenic line of the photoperiod-sensitive cultivar IS2848 in two greenhouse experiments. Variable phenology was induced by applying a short (12-h PP) and a long (13-h PP) photoperiod. Dynamics of plant growth, phenology, sugar accumulation and related enzyme activities in internodes were investigated. Under 13-h PP, plants flowered 28 days later and attained threefold higher sucrose concentration at anthesis compared with those under 12-h PP. Sucrose accumulation in individual internodes was driven by organ physiological age, not by plant phenology. Competition with grain filling was marginal but greater under 12-h PP (i.e. when sucrose accumulation in internodes occurred after flowering). Enzyme activities showed marked developmental patterns but contributed little to explaining differences between treatments and genotypes. The study demonstrates that sucrose storage physiology in sweet sorghum resembles that of sugarcane (Saccharum spp.) but is more complex due to photoperiod effects on phenology. It confirms the field results on 14 sorghum genotypes contrasting for phenology and photoperiod sensitivity presented in a companion paper. Perspectives for developing sorghum ideotype concepts for food and fuel crops are discussed.

Matching phenology with favourable abiotic and biotic conditions is a prerequisite for good varietal adaptation. That is particularly important in a context of climate change because the temperature increase is likely to modify the precocity of the varieties. The forecast of the phenology of photosensitive cereals is complex because flowering depends on both temperature and day length. The effects of photoperiod and temperature can be studied by trials in phytotron, but, high cost prohibits the use of this technique where large numbers of varieties are handled. The day length varies with latitude. Multilocation field trials can be employed for creating a range of environments, but in this type of trials, the great variability of the environments (mainly photoperiod x temperature interaction) often masks the photoperiodic effect. The maturity of the photoperiodic varieties is especially very variable according to the sowing date. Trials comprising of several sowing dates facilitate the study of the effect of small variations of photoperiod on phenology. The objectives of this work are to compare these two last approaches by precisely measuring the effect of the latitude on the development of selected varieties of sorghum sown at staggered planting dates and to verify the precision of our models to predict sorghum maturity. A field experiment in Mali was conducted at the experimental sites of Cinzana (13°15' N), Sotuba (12°39' N) and Farako (11°13' N) in 2009 and 2010. Six sorghum cultivars representing the diversity cultivated sorghum in Mali were sown on three dates (10th June, July and August). The study is related to the phenology and the phyllochrone on the main stem. The effect of latitude on the phenology was underestimated by the existing models. Although the day length difference between Cinzana and Farako is less than 8 minutes, for some varieties we observed a variation in the duration of the crop cycle of up to two weeks. Thus comparable small latitudinal differences highly affected on photosensitivity. However, some varieties respond non-photosensitive in Farako and photoperiodic in Cinzana. To determine the optimal areas for the varieties in West Africa and to forecast the effects of climate change, it is necessary to develop a new model that is able to predict the effects of both, sowing date and latitude. Further research is needed to understand physiological response mechanisms of the pronounced latitude effects on phenology of sorghum. (Texte intégral)

Studies were conducted to characterize diverse sorghums varieties adaptation to climate change at the Institut d'Economie Rurale (IER) of Mali in three sites covering latitude and rainfall gradients. Experimental sites were Cinzana Agronomic Research Station (600 mm rain fall, latitude 13° 15 N, longitude 5° 58 W); Sotuba Research Station (900 mm rainfall, latitude 12° 39 N, longitude 7° 56 W) and Farako research Station (1000 mm, latitude 11°21 N, longitude 5°46 W). A split plot design with planting date as main factor and varieties as sub factor, in a randomized complete block design (RCBD) was used. 200kg/ha of "15N- 15P205-15 K20 were applied 2 weeks after seedling emergence while 50kg/ha of urea (46N-0-0) were side dressed 4 weeks after seedling emergence. Dates of phonological phases for each variety were scored from emergence to panicle initiation. Above ground biomass was also measured (stems, leaves, panicles). Results indicated that most varieties react to variation in sowing dates by reducing their cycle (emergence to maturity) from 7 to 20 days from north to south gradients (13°N to 11°N). This is a consequence of varieties sensitivity to day length (photoperiod). Total biomass was reduced (50 to 800g m-²) with vegetative phases shortening. There exists great variability among varieties within and between sites on total biomass produced. This variability is due to threshold differences in varieties sensitivity to photoperiod. These results justify well the early sowing practices of Sahelian farmers which support reasonable use of their biodiversity in order to better exploit early rain falls. These practices are to mitigate climate change effects. (Texte intégral)

Winter pea suffers from two main types of damage, due to the length of its cycle and climatic conditions (rainfall periods, leaf wetness duration and frost periods): frost and ascochyta blight (Mycosphaerella pinodes). New winter lines resistant to frost (later flowering varieties) are being bred. They can be sown early in autumn, lengthening the crop cycle and thereby increasing target yields. We analysed the reaction of this new type of winter pea (Hr genotype) to ascochyta blight under field conditions, by comparing epidemic disease development on this genotype with that on the classical cultivars Cheyenne and Dove. We also assessed the effect of sowing date (mid-September, mid-October) on ascochyta blight on these genotypes. Field experiments were carried out at five locations (Dijon, Estrees-Mons, Maisse, Rennes, Toulouse). Disease development, assessed on stipules and stems, differed between experimental locations, ranging from mild to very severe epidemics. Disease levels were highest for the first sowing date for each genotype. The Hr genotype had the lowest level of disease at each experimental site. Ascochyta blight was less affected by sowing date in the Hr genotype than in Cheyenne and Dove. Disease affected seed yield differently in the three genotypes. These results have potential implications for the management of disease on winter pea.

A great number of plants synchronize flowering with day length. In rice (Oryza sativa), photoperiod is the primary environmental cue that triggers flowering. Here, we show that the s73 mutant, identified in a γ-irradiated Bahia collection, displays early flowering and photoperiodic insensitivity due to a null mutation in the PHOTOPERIOD SENSITIVITY5 (SE5) gene, which encodes an enzyme implicated in phytochrome chromophore biosynthesis. s73 mutant plants show a number of alterations in the characteristic diurnal expression patterns of master genes involved in photoperiodic control of flowering, resulting in up-regulation of the floral integrator Heading date3a (Hd3a). Early heading date1 (Ehd1), an additional rice floral activator, was also highly expressed in the s73 mutant, suggesting that SE5 represses Ehd1 in wild-type plants. Silencing of Ehd1 in both Bahia and s73 backgrounds indicated that SE5 regulates Ehd1 expression. The data also indicate that SE5 confers photoperiodic sensitivity through regulation of Hd1. These results provide direct evidence that phytochromes inhibit flowering by affecting both Hd1 and Ehd1 flowering pathways.

Para estimar el índice de confort térmico (THI) y los periodos críticos (frecuencia, persistencia) en la cría de pollos de engorde, se generaron datos climáticos de temperatura y humedad diaria con una frecuencia de 10 minutos entre medidas, durante el periodo seco (febrero a marzo, 2006) en un galpón de producción comercial de pollos de engorde, localizado en la región central de Venezuela. El índice THI se determino para las 24 horas del día desde el ingreso hasta la salida de los animales, con cálculo de probabilidad de ocurrencia y persistencia del evento y aplicación de umbrales y ecuaciones de regresión desarrolladas para las aves para estimar la ganancia diaria de peso (GDP) de los animales. Los datos obtenidos se analizaron a través de estadísticos descriptivos, pruebas de medias, varianzas, tendencias y frecuencias y el índice THI fue comparado con valores referenciales de THI para su interpretación. Con los valores horarios estimados se calculo la probabilidad de ocurrencia y la duración del periodo diario. Los resultados en relación al ciclo diario del THI indicaron un efecto altamente significativo sobre el confort térmico de los animales, que permite confirmar la importancia de la hora del día sobre la presencia de estrés en los animales y su variación dentro del ciclo diario, donde se concluye que la condición normal del animal se presentó en horario de 4:30 y 8:30, peligro de 10:30 a 16:30 y alerta de 18:30 a 2:30. La condición de riesgo de estrés en el animal se intensificó con la edad debido al proceso de pérdida y ganancia de calor. Al estimar la GDP a través de la ecuación empírica utilizada se encontraron diferencias altamente significativas (P

Background and Aims: West African sorghum (Sorghum bicolor) varieties are generally highly photoperiod-sensitive, which is a necessary adaptation to the variable onset date of the rainy season and the variable dates of sowing in the savannah zone. Depending on sowing date, plants can produce from 12 to >40 leaves on the main culm, with height varying from 1 m to more than 5 m. The present study aimed to better understand the complex phenology of these variables.Methods: A 2-year series of monthly sowings of three West African sorghum varieties was conducted near Bamako, Mali. Drought stress was avoided by supplemental irrigation. Rate of initiation of primordia at the stem apex was recorded, together with rate of leaf emergence and increase in plant height.Key Results: Leaf initiation and appearance rates (plastochron-1 and phyllochron-1) were constant for a given sowing date in cases where less than 20 leaves were produced (generally observed with late sowing dates). In contrast, rates were bilinear for early sowing dates, for which plants produced more than 20 leaves. The secondary rates, which occurred from the 20th leaf onwards, were only half of the initial rate. Plastochron and phyllochron showed large variations among sowing dates, and were correlated with the rate of plant height increase. The initial plastochron and phyllochron were positively correlated with soil temperature and negatively correlated with both day length and day-to-day change of day length prevailing at plant emergence, but these factors explained only half of the variation observed.Conclusions: Although they belong to different genetic groups and have different height and photoperiod sensitivity, the three varieties studied exhibited similar response patterns of development rates among phenological phases and seasons, with the local landrace showing the greatest variation due to its longer vegetative phase and longer stem internodes. The possible adaptive advantages in African savannah environments of bilinear development rates and the associated limitation in height increase are discussed. (Resume d'auteur)

La reproduction chez les poissons est un phénomène cyclique, synchronisé pour beaucoup d'espèces avec les fluctuations saisonnières de l'environnement qui agissent sur la physiologie des poissons en stimulant ou en inhibant certains stades de la gamétogenèse ou de la ponte. Ces changements des conditions du milieu sont contrôlés par des processus endocriniens qui dépendent des facteurs externes comme par exemple la photopériode, la température ou le régime alimentaire. C'est le complexe hypothalamo-hypophysaire, l'organe pinéal et les gonades qui interviennent dans la réception des stimuli de l'environnement et qui, par le biais de messagers chimiques, les hormones, régulent de nombreuses fonctions vitales pour l'organisme, et notamment le comportement sexuel et la reproduction. Les principales hormones jouant un rôle dans la fonction reproductrice sont les gonadotropines, la Gn-RH et les stéroïdes sexuels. La température et la photopériode sont les deux facteurs majeurs d'action sur le métabolisme des poissons qui agissent respectivement à tous les niveaux du contrôle de la reproduction mais aussi via le métabolisme général ; de façon importante sur la gamétogenèse et souvent comme synchroniseurs des rythmes endogènes de l'animal. A ces deux facteurs principaux viennent s'ajouter une multitude d'autres facteurs dont les effets sur la reproduction des poissons ont été démontrés comme par exemple le régime alimentaire, les pluies, les crues et les facteurs sociaux. Le cas du tilapia est très intéressant puisqu'il représente un intérêt aquacole important pour les populations des pays du Sud. Il est donc nécessaire, par le biais d'études, d'essayer de comprendre l'action des facteurs environnementaux sur la biologie et la physiologie de ce poisson. Les résultats qui découleront de ces recherches permettront ainsi d'optimiser la production du tilapia.

Le photopériodisme des variétés locales du Mali a été étudié pour préciser les relations existant entre la phénologie des sorghos et le climat de leur zone d'origine. La répartition de la biomasse de trois variétés d'architecture et photosensibilité différentes a été mesurée. Nous comparons les productions d'une variété locale de grande taille (V1), sa descendance de taille réduite (V2) et une variété hybride de l'Icrisat très productive mais précoce. La sensibilité à la photopériode est une source de plasticité agronomique. La floraison des variétés locales débute en moyenne dans les 20 jours qui précèdent l'arrêt de la saison des pluies. La réduction de taille n'a pas influencé la production de feuilles et donc le potentiel photosynthétique n'a pas été influencé. En revanche, la production de tige de la variété locale V1 (14 t/ha) est très nettement supérieure aux variétés V2 et V3 (respectivement 7 et 5 t/ha). La variété hybride V3 a donné un rendement supérieur (5 t/ha) mais la récolte a nécessité une protection individuelle des panicules contre les oiseaux. Le rendement de la variété V2 (3 t/ha) a été supérieur à son parent V1 (1 t/ha). L'augmentation du rendement résulte du plus grand nombre de talles fertiles développé, ce qui a montré l'intérêt de la réduction de la taille des variétés photopériodiques. On a observé très peu de mobilisation des sucres dans les tiges vers le grain après floraison. L'essentiel de la biomasse racinaire s'est trouvé dans l'horizon 0-40 cm du sol. La réduction de taille des tiges a entraîné une diminution de la production de racines. Le modèle impatience de SARRA-H a été calibré pour prendre en compte le photopériodisme des sorghos du Mali. L'utilisation du modèle a permis de valider le fonctionnement du module de photopériodisme. Le modèle a permis d'intégrer spatialement le génotype, la variabilité climatique et les pratiques culturales des paysans.

Le semis très précoce du soja a été étudié dans l’objectif d’améliorer le potentiel de rendement et/ou de réduire les besoins en eau. Trois variétés, appartenant à différents groupes de maturité, ont été retenues afin d’identifier les traits variétaux d’intérêt pour le semis très précoce. Un ensemble d’essais multilocaux, comportant deux modalités de semis avec irrigation, a été réalisé au cours de 5 années culturales (2010-2014). Le rendement et les besoins en eau ont été déterminés; un suivi dynamique du développement et de la croissance a été réalisé pour la variété Santana. Les effets combinés des basses températures et de la photopériode en réponse au semis précoce se traduisent par une production de biomasse aérienne réduite en phase végétative et une augmentation de la durée de remplissage des graines. Les valeurs maximales de rendement sont observées pour le semis très précoce, mais en moyenne le rendement est sensiblement plus faible en semis très précoce (3,7 t/ha vs. 3,9 t/ha). L’irrigation pour conduire les cultures dans des conditions proches de l’ETM a été sensiblement plus faible en semis très précoce (170 mm vs. 182 mm). Une variété tardive (groupe de maturité II) apparaît mieux adaptée au semis très précoce qu’une variété de groupe de maturité I. Cette étude constitue une première référence agronomique d’évaluation du semis très précoce du soja et suggère que des types variétaux très tardifs pourraient améliorer le potentiel de rendement du soja en semis très précoce pour des conduites irriguées dans le Sud-Ouest de la France., This study was carried out on very early sowing of soybean in order to improve potential yield and/or reduce water requirements. Three varieties belonging to different maturity groups were selected to identify varietal traits of interest in very early sowing. A set of multi-location irrigated trials consisting in two sowing dates was performed from 2010 to 2014. Yield and water requirements were determined; crop development and growth was monitored on cv. Santana. The combined effects of low temperatures and photoperiod in very early sowing resulted in limited aboveground biomass production during vegetative period and increased grain filling duration. Maximal values for yield were observed in very early sowing modality, although yield was slightly lower in very early sowing compared to conventional one (3.7 t/ha vs. 3.9 t/ha). The amount of water brought by irrigation for meeting ETM conditions was slightly lower in very early sowing (170 mm vs. 182 mm). A late variety (maturity group II) appears better adapted to very early sowing compared to a maturity group I variety. This study stands as the first agronomical reference for evaluating early sowing of soybean and suggests that late-varietal type could improve soybean potential yield for early sowing in irrigated cropping conditions of South-Western France.