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Introduction La forte croissance démographique du Mali entraîne un développement rapide de la demande alimentaire des populations rurales et urbaines. Jusqu’à présent, le renforcement de la production céréalière résulte principalement de l’expansion des surfaces cultivées. Toutefois, la saturation progressive des zones rurales limite cette évolution, et une augmentation durable de la productivité des systèmes de cultures sera nécessaire. Le changement climatique affectera probablement la répa...

This work was conducted to study the performance of eight sorghum varieties that contrasted with intensified practices in the Sudano-Sahelian zone of Mali. Two experiments were carried out in 2018 and 2019 rainy seasons at Sotuba Agricultural Research Station in Mali. The experimental design used was a Split-split-plot with three replications and three factors including two plant densities (D1: 26666 plants ha-1 and D2: 53333 plants ha-1) as the main plot, three nitrogen levels (0, 41 and 82 kg N ha-1) as the subplot and varieties as the sub-subplot. Measurements focused on growth and physiological parameters, grain yield and yield components. The results showed that sorghum grain yield was positively correlated with straw yield, leaf area index, grain number per panicle, panicle number per m2, panicle weight per m2 in N0D1 (0 kg N ha-1 and 26666 plants ha-1) and N2D2 (178 kg N ha-1 and 53 333 plants ha-1). Furthermore, straw yield was positively correlated with the leaf area index and panicle weight m-² in N0D1 and in N2D2. Analysis of variance showed that plant density, nitrogen and variety effect on grain and straw yields were significant. The interaction density x nitrogen x variety effect was also significant on grain and straw yields. Grain and straw yields were high in the N2D2 treatment for eight varieties compared to the N0D1 treatment. GRINKAN, C2_075-15 and C2_007-03 varieties had the highest grain and straw yields in N0D1. These caudatum-type varieties could be recommended in less intensive sorghum production areas in Mali. The FADDA variety produced high grain and straw yields in N2D2. Guinea-type hybrid FADDA may be recommended for grain and straw production in intensive sorghum production areas in Mali.

Le futur de l’Afrique de l’Ouest dépend de la capacité du secteur de l’agriculture à s’adapter pour garantir la sécurité alimentaire dans un contexte de changement climatique et de croissance démographique. Pour faciliter cette adaptation, la recherche a déployé d’importants efforts pour améliorer les connaissances sur les mécanismes climatiques et leurs impacts sur les systèmes agropastoraux. Or, ces avancées issues de la recherche ne sont que rarement prises en compte dans la planification et la prise de décision. Partant de ce constat, un projet de recherche « Agriculture et gestion des risques climatiques : outils et recherches en Afrique », soutenu par le ministère français des Affaires étrangères et du Développement international est mené entre 2016 et 2018 dans plusieurs pays d’Afrique de l’Ouest. Il a pour objectif d’élaborer des outils efficaces de gestion du risque climatique pour les agriculteurs, en co-construisant avec des réseaux de chercheurs et d’acteurs directement impliqués dans l’accompagnement de l’agriculture des stratégies innovantes basées sur les résultats de la recherche. Cet ouvrage restitue les principales avancées de cette recherche-action sur trois thématiques prioritaires : les services climatiques pour l’agriculture, la gestion des ressources en eau et l’intensification écologique. Il permet aux acteurs du secteur agricole (organisations paysannes, filières, secteur privé agricole, banques de développement agricole, fournisseurs d’intrants, services agricoles et de météorologie) de s’approprier de nouvelles connaissances et de nouveaux outils pour une meilleure prise en compte des risques climatiques dans la gestion des systèmes de production.

Introgression of bmr genes from less adapted donor parent to well adapted high yielding biomass varieties with poor nutritional value is very important for sustainable cattle feeding during pasture scare time in the Sahel. The main objective of this work was to introgress bmr6 and bmr12 genes in Nigerien and Malian sorghum varieties background for dual purpose grain and biomass potential. The plant material was composed of two improved sorghum varieties (Sepon82 and Kalla Kene) and El mota a farmer preferred variety as recurrent parents. bmr donor parents were redlan bmr6, Tx630 bmr12 and Wheatland bmr12. The hand emasculation technique was used to introgress bmr genes in recurrent parents to produce F3 and BC1F3 populations at Sotuba research Station in Mali from January 2016 to June 2017. Anthocyanin pigment and heterosis effects were key phenotypic traits to identify F1 and BC1F1 plants during the population development. Anthocyanin allowed the identification of F1 plants in a cross involving anthocyanin (purple plant) and tan plants, while for both tan plants cross, heterosis effect was major key to discriminate F1 from parental lines and bmr segregation in F2 to ascertain successful crosses. The χ2 test was used to analyze bmr segregation ration. Segregation ratios of bmr plants in F2 and BC1F2 showed a good fit of a single recessive gene (3:1). bmr 6 and 12 genes were successfully transferred to three recurrent parents varieties which are at F4 and BC1F3 generation for grain and biomass yields potential tests in Niger during the 2017 cropping season.

To face global warming and fossil fuel depletion crisis, plant biomass will provide a renewable source of energy, materials and chemicals. Accordingly, agriculture will have to adapt not only to avoid competition between food-feed and non-food non-feed uses but also to ensure the economical and environmental sustainability of these productions. In this context, we are developing an integrative strategy merging genetics, breeding, material sciences, energy production, animal nutrition and socio economic analyses to accelerate the development of multipurpose sorghum value chains for both Mediterranean and tropical semi-arid conditions (West Africa). As a first step, new products (biocomposites) and uses (biomethane production) are being developed. Then the plant traits impacting the production and quality of the different end-products and uses are being identified taking advantage of the genetic diversity of sorghum. As a third step, the set-up of these key traits in the plant is being analyzed in order to describe their patterns of development / accumulation, their susceptibility to environmental constraints and provide some insights regarding their molecular determinism. Taking advantage of these functional information, the genomic regions impacting the key traits are being deciphered and used to develop new breeding tools and breeding strategies. In parallel, to maximize the probability to convert scientific results in local impacts, the different stakeholders of the value chains are being mobilized and territorial analyses aiming to assess the relevance of the different value chains are performed.

Although the main targets of sorghum breeding programmes remain grain yield and quality in order to ensure human (in Africa) and animal (in other parts of the world) nutri$on needs, the yield and quality of the vegeta$ve biomass has been gaining more and more aHen$on as its interests in animal nutri$on, bioenergy and biomaterial increase. In this context, there is a cri$cal need to deepen our understanding of these traits in order to op$mize the efficiency of the development of new varie$es. A Backcross Nested associa$on mapping (BCNAM) design was developed to maximize the mapping resolu$on of the genomic regions of interest and provide the sorghum community with relevant gene$c materials for breeding in the context of the Sudano-sahelian region. The specific aim of this study was to iden$fy the genomic regions controlling stem yield and its biochemical composi$on.

Sorghum is among the world's most important cereals in terms of human and animal nutrition. It is also currently identified as a promising crop to support the emerging bio-economy value chains that include energy production, biomaterials and molecules for food-feed and non-food-feed applications. In this context, the development of varieties adapted to the different end-uses is critical to provide the industries with relevant feedstock. Breeding sorghum for existing and emerging markets requires several steps, from the definition of “Industrial Ideotypes” down to the identification of “Molecular Ideotypes” in order to speed up the breeding process and optimize the genetic gains per unit of time. Firstly, expectations of the industrials in terms of composition and properties of the sorghum biomass for the different applications (“Industrial ideotypes”) have to be defined. Secondly, “Industrial ideotypes” have to be translated in “Biological ideotypes” which refers to the properties of the raw sorghum material in terms of composition and structure. Third, high-throughput phenotyping tools compatibles with genetic analyses and breeding constraints have to be developed. Fourth, strategies to disentangle the genetic determinism of the “Biological Ideotypes” have to be set up. And fifth, relevant breeding schemes able to provide new hybrids and relevant parents have to be initiated. We will illustrate this process through two examples related to the production of sorghum biocomposites and the optimization of sorghum biogas production. For both targets, we will show how, through the use of the sorghum genetic diversity, traits affecting the final product properties were identified. We will then illustrate the efforts that are currently developed to tackle the challenges linked to high-throughput phenotyping. We will finally show how these phenotyping tools are used on diverse association panels and multiparental designs to identify the genomic regions affecting the traits of interest and develop new hybrids and elite parents. Funding acknowledgement: This research is supported through the Biomass For the Future project (funded by ANR) and the BIOSORG project supported by the Agropolis (Labex Agro) and Cariplo foundations.

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)

The development of multi-purpose sorghum varieties suitable not only for food, but also for feed and other applications became a priority for most of the breeding programs. However, a better understanding of the genetic determinism of stover quality is required. A BCNAM design involving 3 recurrent parents (RP) and 29 donor parents (DP) has been developed in order to provide the sorghum community with a high resolution mapping design and a relevant breeding scheme towards the development of varieties suitable for the soudano sahelian region. The aim of this study was to characterize the parental lines of a BCNAM multiparental design for their main stem composition and histological properties in order to: • Assess the relevance of this genetic design to reach a better understanding of the genetic bases of these traits • Evaluate the effect of the sowing dates, and height diversity on the biochemical composition of the stems • Have a first image of the relationships between stem histological and biochemical traits

En Afrique sub-saharienne, 90% des semences de mil et sorgho sont autoproduites par les agriculteurs. La recherche de variétés plus productives et rustiques a conduit une association d'organisations paysannes (AOPP) à tester des variétés améliorées en conditions paysannes. L'AOPP participe maintenant à la multiplication et à la diffusion de semences certifiées et s'insère dans une démarche de sélection participative associant recherche, ONG et Organisations Paysannes (OP). Dans le cadre de deux projets sur la gestion de l'agrobiodiversité, une variété de sorgho, Keninkeni Dieman, a été inscrite au catalogue malien en 2012. De plus, une coopérative, GDBA-Mali, a été créée en associant ONG et OP travaillant sur cette thématique. Elle prendra en charge des programmes de sélection participative et la diffusion de semences. À travers ces projets et l'inscription de variétés avec des OP, on peut mesurer l'évolution des systèmes semenciers en Afrique de l'Ouest, de systèmes informel d'un côté ou étatique de l'autre, à un système plus complexe et international.

Sorghum breeding in Mali mostly focuses on varieties for human consumption. Even if most of breeding efforts concentrate on productivity and adaptation, grain quality is a very important aspect to consider for improved material to be adopted and successful. One major traditional use of sorghum in West-Africa is the tô, a thick porridge prepared from sorghum flour. We evaluated several important technological traits involved in tô quality (pericarp thickness, dehulling yield, endosperm texture, grain roundness and size, amylose content, presence or not of anthocyan) in two F3 populations of 400 families each. Near infrared reflectance spectroscopy (NIRS) was investigated as an indirect method to evaluate some of these traits on sorghum grain rather than on flour. QTLs for these traits were detected and the interaction between QTLs evaluated. The consistency and color of tô were evaluated on mini-tô prepared from 200 families. QTLs for tô consistency were compared with those for technological traits. Several QTLs were detected including major QTLs, explaining 92% of the variation for the presence of anthocyan, 55% for pericarp thickness, and 22% for dehulling yield. A QTL explaining 19% of grain roundness and 11% for endosperm texture was also found. These QTLs are being used together with QTLs for grain yield, flowering time, plant and panicle morphology, to select varieties adapted for making good tô and combining productivity and grain quality through integrated marker assisted recurrent selection.

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.

Le mil constitue, avec le sorgho, la base de l’alimentation d’une part importante des populations indiennes et africaines. Au Niger, deuxième pays producteur en Afrique, cette culture représente les trois quarts de la production céréalière et occupe plus de la moitié des terres cultivées. C’est en Afrique de l’Ouest que se situent les zones d’origine et de diversification des mils cultivés (Penniselum glaucum subsp. glaucum) et l’on peut encore y trouver des populations de la forme sauvage (P. glaucum subsp. monodii). Mieux conserver, évaluer et valoriser ces ressources génétiques, tels sont les enjeux exposés lors de l’atelier « Ressources génétiques des mils et plantes associées en Afrique de l’Ouest » organisé à Niamey en 2002. L’IRD et ses partenaires y ont présenté une synthèse des résultats de recherches pluridisciplinaires (génétique, agronomie, anthropologie) sur le rôle des pratiques paysannes dans la dynamique de la diversité génétique des mils sauvages et cultivés au Niger. Cet atelier a également permis de confronter les expériences et conclusions d’autres équipes et a contribué à la réflexion sur les stratégies de conservation (in et ex situ) et de valorisation des ressources génétiques des mils et de quelques autres plantes cultivées dans les agrosystèmes sahéliens. Pearl millet is, along with sorghum, the staple food for a large part of Indian and African populations. In Niger, the second producing country in Africa, this crop accounts for three quarters of the cereals production and more than half of cultivated land. Regions of origin and diversification of pearl millet (Pennisetum glaucum subsp. glaucum) are located in West Africa, where wild millet populations (P. glaucum subsp. monodii) can still be found. A better conservation, evaluation and valorisation of this diversity is therefore an important challenge, that was adressed during a workshop on genetic resources of pearl millet and associated crops in West Africa, held in Niamey in 2002. IRD and its partners presented there a synthesis of their multidisciplinary research (genetics, agronomy, anthropology) on the role of farmers' practices in the dynamics of genetic diversity of wild and cultivated millets in Niger. The workshop allowed exchanges and comparisons of experience and conclusions of other teams and contributed to the debate on strategies of conservation (in and ex situ) and utilisation of genetic resources of pearl millet and other crops in Sahelian agrosystems. © IRD Éditions, 2004

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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)

In addition to being the fifth cereal in terms of grain production, the interest of sorghum as a feed and energy crop is increasingly underlined. Selection of sorghum genotypes for fodder and energy production relies on an in-depth understanding of stem tissue organization and cell wall characteristics variability. Although histological analyses of two genotypes harboring contrasting stem diameter revealed similar tissue organizations and cell sizes, their kinetics of biomass degradation when treated with enzymatic cocktails were different, the largest stem diameter genotype presenting a faster degradation with a lower percentage of monosaccharide solubilised, suggesting differences in soluble sugar content and cell wall polymer content and accessibility. According to these results we then focus our attention on the cell wall composition. From a previous characterization of 410 sorghum accessions using near infrared reflectance spectroscopy, a panel of 13 genotypes maximizing the diversity of cell wall properties were subjected to FTIR analyses, klason lignin and p-hydroxycinnamic acids contents measurement, and determination of lignin monomeric composition. In parallel, saccharification efficiency of the cell walls was evaluated. These analyses revealed a significant genetic variability of cell wall saccharification yield which has been associated with the variability of the lignin content in the cell wall, the S monomers content in the uncondensed lignin part and the concentration in esterified p-coumaric acid. Finally, addition of an Alkali pre-treatment before the enzymatic treatment showed significant improvement of cell wall saccharification yield but contrasting responses of the genotypes analyzed in terms of final yield and degree of improvement.

Sweet sorghum (Sorghum Bicolor (L) Moench) is a potential alternative to sugarcane for dry areas and may serve as substrate for bio-alcohol production (Tuck et al. 2006) while producing grain for human consumption and/or feed. Moreover sorghum is drought and heat resistant and thus well adapted to conditions brought about by climate fluctuations (Borrell et al. 2000). Recent research indicated that many West African sorghum cultivars produce a large stock of sucrose that is not mobilized for grain filling; diverse germplasm is available for desirable traits for dual purpose sorghums (sugar X grain, Reddy et al. 2007). However, sorghum sweetness is a complex trait, highly prone to GxE (Genotype x Environment) interactions that are still poorly understood, as well as its competition with grain filling. A study was recently initiated to provide a functional analysis of the GxE control of sucrose accumulation in sorghum stems and its competition with grain filling. The present study focuses on the analysis, on contrasted or manipulated (pruned, sterile) genotypes, the variability in sorghum ability to accumulate sucrose while maintaining grain.