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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 (

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)

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.