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National audience; En Agriculture de Conservation des Sols (ACS), la perturbation minimale du sol est l’un des trois prin-cipes. Si l’impasse se fait sentir mieux vaut repenser le système que de laisser le mur se rapprocher à grands pas. Trois types de gestion d’interculture (Labour, travail superficiel (TCS) et semis direct avec glyphosate (SD)) ont été comparés sur des parcelles conduites sans labour depuis 17 ans dont les 7 dernières années en ACS sur le domaine de l’INRA de Dijon avant implantation d’un blé, sur un dispo-sitif en bandes répétées sur quatre parcelles. Des relevés de flore adventice, rendement et compo-sante de rendement ont été faite. Les densités moyennes sont faibles pour le Labour et SD (environ 25 individus/m²). De forte hétérogénéité de densité adventice sont observées en TCS, avec des zones allant de quelques individus de vulpins des champs à plus 300 par m². L’ensemble des modalités pré-sentent du vulpin et du gaillet. Leurs densités sont très faibles en Labour comparées au SD et TCS. On observe six fois moins de vulpin en Labour (4 plantes/m² en moyenne) qu’en SD (21,4/m²) ou en TCS (24,5/m²). On observe 2 fois moins de gaillet en labour (2,5/m²) qu’en SD (4,7/m²) ou en TCS (4,9/m²). Le type de travail du sol mis en oeuvre a été à l’origine de changement drastique de flore (richesse, composition), malgré une conduite homogène durant 17 ans. Statistiquement, il n’y a pas eu de diffé-rences de rendement entre les modalités, même si la modalité SD produit 5 q/ha de moins que les modalités TCS et Labour. Aucune différence en termes de composantes de rendement n’est observée. Can tillage overcome a weed management deadend in conservation agriculture? A com-parison of tillage options Minimal soil disturbance is one of the fundamental pillars of conservation agriculture (CA). In case of weed management difficulties, reintegrating tillage in the system might be the most viable option. Three types of fallow management (ploughing (CT), superficial tillage (RT), no-till with glyphosate (NT)) were compared on four fields after 10 years of no-plough and 7 years of no-till at the INRA experi-mental farm in Epoisses. Weed density, crop productivity and yield components were assessed in the following winter wheat. Blackgrass and cleavers were the two most problematic species of the exper-iment. Weed density was low in CT and NT (~25 pl/m²) while highly variable weed densities were ob-served in RT, with densities of blackgrass varying from a few to 300 plants/m². Blackgrass density was six times lower in CT (4 pl/m²) than in NT or RT (21-25 pl/m²). Cleavers density was half as important in CT (2.5 pl/m²) than in NT or RT (~5 pl/m²). The reintegration of tillage after 17 years of CA proved be a major driver of weed communities (density and richness). No significant differences were observed in terms of yield or yield components, even if grain yield was 0.5 T/ha lower in NT than CT or RT.

Coffee is a key export commodity of East Africa, but average smallholders' yields are low. To guide sustainable yield improvements of smallholders' coffee systems, we investigated coffee yield components in three different types of coffee cropping systems along an altitude gradient (1100−2100 m.a.s.l.) during two production years (2015 and 2016). We selected 810 coffee trees distributed over 27 farms and monitored number of stems per tree, fruit load per branch, productive nodes per branch (on four branches of one stem per tree) and number of productive branches per stem (on one stem per selected tree) in both years. Additionally, we monitored productive stems per ha, coffee tree density and cherry weight in combination with pest and disease occurrence and management information from interviews. Coffee farms were classified as Coffee-Open (CO) (< 20 % shade cover), Coffee-Banana (CB) (coffee dominantly intercropped with bananas) or Coffee-shade Tree (CT) (coffee dominantly intercropped with shade trees). Coffee-Banana had larger yield per ha (green bean kg ha−1) (1086±736 kg ha−1) and yield per stem (green bean kg stem−1) (0.24±0.16 kg stem−1) than CO (670±457 kg ha−1 and 0.21±0.26 kg stem−1) and CT (428±259 kg ha-1 and 0.10±0.12 kg stem−1). Fruit loads, productive nodes, productive branches and cherry weight declined with shade cover, especially for shade cover>30 %. Additionally, the same yield components correlated negatively with number of stems per tree. Fertilizer and fungicide use were related to more productive branches and cherry weight respectively, and stem borer was identified as the most important pest in this area. Our results suggest that yield in the region could be increased, i) by maintaining shade at an intermediate level, particularly at low and mid altitude and by reducing the number of stems per coffee tree (< 4), and ii) by improving soil fertility and protection against pest and disease.

On evalue une methode de diagnostic des limitations au rendement du mais. L'evaluation repose sur une enquete conduite dans l'Ouest du Burkina-Faso, chez 437 agriculteurs au total, et repartie sur trois ans. On a releve des donnees du climat du sol de l'exploitation, du champ de mais (evenements culturaux, et sur deux placettes par champ, composantes du rendement). Le diagnostic est fonde sur l'analyse des composantes du rendement, comparees a des valeurs potentielles. Des indices de realisation des differentes phases du cycle sont definis pour quantifier les contraintes locales, et les situer dans le temps. On propose un traitement qui distingue des contraintes durables (de type fertilite), et des contraintes passageres (de type accidentel). Dans nos conditions, les contraintes durables etaient les plus frequentes. Elles dependent davantage des techniques culturales que des facteurs environmentaux. L'intensite des contraintes accidentelles depend aussi des pratiques culturales. La methode permet une analyse satisfaisante des differents types de situations etudiees. Le diagnostic est limite par les donnees sur les facteurs abiotiques sources des contraintes. (Resume d'auteur)

Double cropping of rice is constrained by tight cropping calendars. In mechanized production systems such as in the Senegal River delta of Africa, drainage date is important for yield, maturity and field trafficability. Randomized complete-block field experiments were conducted at the WARDA research station at Ndiaye in Senegal during the hot-dry and wet seasons to determine effects of drainage date on soil drying, grain yield and assimilate partitioning. The soil was a slightly acid, shrinking clay. Pre-germinated seed of I Kong Pao rice was sown broadcast and the plots kept flooded until drainage at four different dates after flowering (treatments). Topsoil and grain moisture content and the dry weight of panicles, stems, green leaves and dead leaves were measured on six dates between 1st flowering and 2 wk after maturity. Soil moisture content decreased more rapidly under a green canopy than with a mature crop. Grain yield was reduced by 34 to 36% in both seasons when plots were drained 3 to 4 days after flowering (DAF) (P < 0.01, compared to drainage at maturity) but were not affected when drained 12 to 14 DAF or later. Grain yield reduction was due one-third to poor grain filling and two-thirds to unfilled spikelets. Maturity (20% grain moisture content) was advanced 10 to 11 d by early drainage (3 to 4 DAF), compared to drainage at maturity. Apparent mobilization of reserves based on dry weight decrease of vegetative organs after flowering was 32 to 42% and constituted 46 to 84% of panicle growth, depending on treatment. Early drainage reduced dry matter production during ripening but did not proportionally affect grain yield because of compensatory mobilization of stem reserves. Models are proposed on the buffering effect of reserves if assimilation during grain filling is variable.

Introduction. Au Cameroun, le plantain joue un role important pour la securite alimentaire. Une augmentation de la production serait necessaire pour satisfaire la demande. Depuis avril 2002, le CARBAP maintient un observatoire de la production de plantain. L'objectif principal est d'etudier en priorite les contraintes de production et de caracteriser les strategies de commercialisation, afin d'ameliorer la rentabilite de cette culture pour les petits exploitants. Materiel et methodes. Dix-huit parcelles de terrain ont ete identifiees dans des fermes representatives de la diversite agro-ecologique et socio-economique de la region. Ces parcelles ont ete considerees comme unite d'echantillonnage pour l'analyse agronomique et celle des contraintes parasitaires. Les fermes ont ete considerees comme unite elementaire utilisee pour l'analyse des contraintes socio-economiques. Pour chaque parcelle, un suivi regulier de 50 plants de banane et des pratiques agronomiques a ete effectue. Grâce a la participation des petits exploitants, un suivi de chaque ferme a ete egalement mis en place pour l'analyse des conditions de production. Resultats. Il est possible de distinguer les petits exploitants a partir de differents niveaux de diversification des cultures par rapport a la production de plantain. Les resultats agronomiques dans les parcelles examinees ont ete evalues grâce aux parametres de croissance, de rendement et d'infestation parasitaire. Les bons ou mauvais resultats sur jeunes ou vieilles parcelles ont ete fondamentalement identifies. Les differences individuelles sont influencees par des facteurs de depart (varietes disponibles lors de la plantation, culture anterieure sus la parcelle), les moyens disponibles (intrants) et les capacites techniques pour la culture du plantain. Conclusion. Le dispositif mis en place permet de detecter des indicateurs de diversification vis-a-vis de la culture de plantain et de verifier la durabilite de telles strategies. Il est possible de proposer des techniques de culture ameliorees. Elles pourront etre utilisees au cours d'etudes a venir visant l'amelioration de la production de plantain. (Resume d'auteur)

L'Etat de São Tomé et Principe tire une grande partie de ses ressources de l'exportation du cacao. La production actuelle ne asse pas 4.000 t. En 1999, à la suite d'un programme de redistribution des terres, la production de cacao est assuré par de petits agriculteurs, de moyens entrepreneurs et 6 grandes entreprises agricoles confiées à une gestion privée. Parmi elles, l'entreprise agricole Socatomé couvre une superficie totale de 2.500 ha. Pour pallier aux faibles rendements constatés, elle a décidé, en collaboration avec le CIAT, de procéder à la comparaison de 2 types d'itinéraires techniques, entre 1997 et 1999, sur les rendements. Le matériel végétal hybride est issu de différentes origines géographiques: Côte d'Ivoire, Cameroun, Gabon, Nigeria et São Tomé. Au sein de la plantation divisée en 2 sous-unités opérationnelles, 28 sites ou parcelles ont été sélectionnés pour tenir compte de la variabilité de ces origines géographiques. Dans chacun de ces sites, deux types de parcelles sont comparés: - Les parcelles Témoin dans lesquelles les entretiens courants (nettoyage, égourmandage, traitements phytosanitaires) sont réalisés au même rythme que celui défini pour l'ensemble des parcelles en production de l'entreprise. - Les parcelles Jardin dans lesquelles un itinéraire technique particulier et intensif est appliqué. Il met en oeuvre un ensemble des connaissances agronomiques et de défense de culture. Dans les 2 cas, les fruits sont récoltés mensuellement, pesés et toutes les pertes sont identifiées: elles concernent plus particulièrement les dégâts dus à Phytophthora spp, Selenothrips rubrocinctus, Bathycoelia thalassina et aux rongeurs. Les résultats mettent en évidence une amélioration significative des rendements en cacao marchand par hectare quand l'itinéraire technique type Jardin est utilisé. Les différences dépendent également de l'origine du matériel végétal et de l'environnement pédo-climatique. De plus, la fréquence élevée des traitements fongicides et insecticides réalisés dans les parcelles Jardin réduit considérablement le taux de pertes moyen qui passe de 40 à moins de 15%. L'influence des 2 itinéraires techniques sur le poids et le nombre de fruits par arbre ainsi que le poids de fèves par cabosse est également étudiée. Enfin, les coûts annuels d'entretien des parcelles jardin reviennent à 600 ¿ par hectare pour des gains de productions significatifs mais toutefois limités et non rentables compte tenu des cours du cacao en 1999. Des itinéraires techniques simplifiés basés sur la prise en compte de la réalité économique devraient permettre de trouver un compromis entre amélioration des rendements et rentabilité.

Ce rapport présente la plupart des données brutes obtenues en 2003 sur les parcelles expérimentales en milieu paysan et sur les sites expérimentaux de Pintchoumba, Winde Pintchoumba et Zouana, et le site de multiplication de semence de Pitoa. Dans ce document les données ne sont ni synthétisées ni analysées.

Multi-clonal tapping experiments set up in Côte d'Ivoire and in Thailand have confirmed that clonal yield potential of Hevea brasiliensis (Pmax) can be accurately estimated, when using reduced tapping frequencies like d/3 or d/4, as a linear combination of Po (Production observed without ethephon stimulation, representing metabolic component of the yield potential) and [SUCpo] (latex sucrose concentration without stimulation, representing the sugar loading component of the yield potential): Pmax = Po + [alpha][SUCpo]. Whereas the first yield component (Po) describes the clonal latex metabolic activity, also correlated to inorganic phosphorus latex concentration ([Pio]), the second yield component ([alpha][SUCpo]) reflects the capability of the clone to sustain any further intensification of exploitation, especially regarding its possible response to ethephon stimulation. Classification of Hevea brasiliensis clones in a 2 dimensions-matrix (Latex Clonal Typology) containing five different metabolic types (low, low-medium, medium, medium-high and high) and three different latex sugar loading types (low, medium and high) allows to describe the response of any clone to ethephon stimulation: stimulation intensity should increase when clonal latex metabolic activity decreases and/or when clonal latex sugar loading capacity increases. Conversely, stimulation intensity should decrease when clonal latex metabolic activity increases and/or when clonal latex sugar loading capacity decreases. Latex Clonal Typology therefore greatly simplifies stimulation recommendations, as only five different levels of stimulation intensity (very high, high, medium, low and very low) provide accurate stimulation recommendations to all physiological types of clones, depending on their respective position in the matrix. Stimulation recommendations based on this principle are currently applied on a large rubber plantation of North Sumatra, Indonesia. Latex Clonal Typology provides as well accurate information regarding clonal susceptibility to tapping panel dryness (TPD), clonal adaptation to different tapping frequencies (high or reduced) and clonal yield potential. It is also of major interest for rubber breeding programmes, in order to enhance integration of clonal physiological profiles in Hevea brasiliensis genetic selection schemes.

In northern Thailand, swidden cultivation of upland rice (Oryza sativa L.) is still an important component of remote highland farming sytems. Under no-external-input cropping systems, yields in farmers' fields are generally low (1-1.5 t ha-1), but quite variable. Yields of 3 and 4 t ha-1 for early- and late-maturing varieties, respectively, are observed in pockets in farmers' fields. But such yields are seldom achieved because of multiple and interacting permanent or transient limiting factors. Identifying and ranking these limiting factors is a prerequisite to setting research and extension priorities for improving current fanners' practices. An onfarm diagnostic survey was therefore carried out in a remote highland village of Fang District, Chiang Mai Province (600-800 mas1), to identify, date, and rank the environmental and cropping system variables causing major yield limitations in upland rice under actual farmers' circumstances and management practices. Data on the crop population status for two early- and late-maturing types of local cultivars, crop environmental conditions, and cropping practices were obtained by monitoring 432 squares in 63 Lahu fanners' fields on deep granitic Acrisol soils with a clay-loamy texture during four cropping seasons. An empirical model of yield buildup and phase realization indices were used to date and rank the periods of yield differentiation and principal component analyses with instrumental variables were carried out to identify the factors affecting yields and their components. For the reproductive phase, the analysis of rice yield buildup processes pinpointed panicle formation and spikelet differentiation as key periods of yield differentiation. During the vegetative period, poor crop biomass accumulation was more important than low plant density. Vegetative biomass accumulation per plant also influenced panicle and spikelet formation. The analysis of pooled data revealed strong negative relationships for (a) no. of panicles plant-1 and no. of spikelets panicle-1 vs rice root aphid infestation; (b) plant density vs late weed competition and late-maturing cultivars (sown at lower densities); and (c) percentage of filled spikelets and 1000-grain weight vs 1995 wet season, which was characterized by dry spells during the vegetative and the reproductive phases. Weak negative relationships were found for no. of panicles plant' vs slope angle, erosion, no. of successive upland rice crops, minimum tillage, and early weed stress. A weak positive correlation between the older secondary forest type of fallow and upland rice grain yield was also observed. Brown spot was the only disease having some limited effect on crop productivity, especially for late-maturing varieties. Rice root aphid infestation was identified as the single major limiting factor with a strong and consistent effect on final grain yields. Weed competition was found to be the second most important yieldlimiting factor, followed by soil erosion in sloping fields after shallow tillage. These results show that attention should be paid to the management of soil-borne pests when setting priorities for improving upland rice-based cropping systems in northern Thailand highlands.

Due to genetic correlations, selection on one trait might lead the plant breeders unexpected responses in non-selected characters. Or this can be used as a tool for further breeding activities. To study this phenomena, two rice crosses have been taken as material (Fero/Zenchuzry; Solnecnyt/Iz160). In each F2 population 10 plants have been selected for the following characters: the most productive; the shortest plant (their yield were over average); the longest panicle length; the highest tillering. Beside this, a randomly selected sub-population from each population have been selected and all have been transplanted next year as F3 generation. After routine observations or measurements (grain yield, number of days to flowering; culm length; panicle length; numbers of tillers; thousand kernel weight; total number of panicle; number of sterile spikelet and number of fertile spikelet per panicle), classical quantitative genetically parameters have been calculated. Thereafter expected and realized direct genetically responses and expected and realized correlated responses have been estimated. Expected and realized correlated responses were in the same (positive) direction for following selections in both hybrids: "Grain Yield - number of tiller", "Plant Height - thousand-kernel weight and panicle length", "Panicle Length - number of fertile spikelet per panicle", "Number of Tiller - grain yield". Those results are proving that, a successful selection of one economically important trait might cause a disappointment to the breeder due to unexpected correlated response in some traits. Therefore estimation of expected correlated responses might be quite useful to the breeders.

Introduction. Le plantain est une culture importante pour la securite alimentaire en Afrique sub-saharienne. Pour mieux hierarchiser les priorites de recherche en fonction des contraintes des producteurs, une cellule d'observation permanente a ete mise en place dans le cadre d'une demarche interdisciplinaire. Materiel et methodes. Un echantillonnage en bananeraies a couvert les zones de contextes agroecologiques distincts qui approvisionnent Douala. Les donnees ont ete obtenues par un suivi de parcelles et d'exploitations. A l'echelle des parcelles, les observations ont porte sur les pratiques culturales, les populations de nematodes et de charancons, et les rendements. A l'echelle des exploitations, les suivis ont porte sur les fonctions economiques du plantain. Resultats et discussions. La gamme de situations culturales etudiees correspond a une diversite de contextes et d'objectifs des exploitations agricoles. Les observations effectuees sur bananiers (rythme d'emission foliaire, circonference du pseudotronc, nombre de doigts et de feuilles vivantes, poids et longueur des doigts, poids du regime) ont permis d'expliquer comment se determinait le rendement. Celui-ci est surtout affecte par les pertes avant recolte, en relation avec l'etat sanitaire des racines et la presence de nematodes et de charancons. Ces pertes ont ete maximales a la fin de la saison seche. Le rendement est egalement lie au poids du regime determine par le nombre de doigts essentiellement lie a la croissance et a leur remplissage. Pour ce dernier caractere, les resultats obtenus ne mettent pas clairement en evidence l'incidence de la maladie des raies noires. Des ameliorations du protocole de suivi sont proposees.

The association among yield components, their direct and indirect influence on grain yield of rice was investigated. Eighty breeding lines derived from 11 different cross populations in F6 generation and their parents were used in the experiment in 1995. According to the results of first year, 49 breeding lines selected, they and their parents were tested in an experiment in 1996. The phenotypic correlation among the traits and path co-efficient were estimated in both years. Grain yield was significantly correlated with its components characters like the number of panicle per squarmetter, biological yield, harvest index, and the number of filled grains per panicle in both years. Path co-efficient analysis revealed that biological yield and harvest index had the highest direct effects on the grain yield in both years. According to the magnitude of direct effects on grain yield, the order of yield components was the number of filled grain per panicle > the number of panicle per squarmetter > 1000 grain weight. The improvement in grain yield could be efficient, If the selection is based on these component characters. The biological yield, harvest index and the number of filled grains per panicle may be utilized for pure line selection in late generations, however, both high biological yield and high harvest index should be taken into account together in this selection.

Participation aux réflexions pour identifier les actions urgentes à entreprendre au niveau régional, de manière concertée, pour améliorer la compétitivité de la filière cotonnière des pays AOC, et pour la sortir de la crise due 1- à l'effondrement des cours mondiaux, 2- la "concurrence déloyale" engendrée par les fortes subventions des pays riches (USA, U.E.) qui annihile la compétitivité du coton africain, 3- la mise en place douloureuse d'une libéralisation qui nécessite bien des évolutions institutionnelles et un ré-équilibrage des "rapports de force" entre les parties prenantes, (asymétrie d'information, capacité de négociation...). Il a été admis qu'il est urgent de s'impliquer de manière stratégique dans les négociations internationales sur l'agriculture. L'idée avancée par le CIRAD "d'exploiter" les règles de l'OMC et de proposer la constitution d'un fonds de compensation alimenté par les économies réalisées par la réduction des subventions les plus "distordantes ("boîte orange") a été retenue. Cela permettrait d'allier régulation du commerce et aide au développement. La mission a été également mise à profit pour apporter un appui à l'équipe locale de Résocot.

Strawberry guava (Psidium cattleianum) domestication is studied within a project of crop diversification in humid highlands o f Reunion Island. The number of fruit per plant and their individual weight determine the commercial yield. These characteristics are highly variable and do not seem to be linked to the genotype. An agronomic approach o f domestication is proposed for this species. It consists in identifying how are built-up these characteristics and their variability through the different steps of the production cycle and under the effect of environmental, physiological and genetic factors. The objective is to act on some of these factors using appropriate cultivation techniques. Main features of this approach are the genetic diversity and the lack of references on the species, as confirmed by a bibliographical analysis. Strawberry guava phenological cycle was studied on feral stands in Reunion Island. In cultivation, nitrogen modifies the natural phenological cycle by triggering a new production cycle. The setting of the study is a natural production cycle in an orchard, without interaction with triggered cycles. A model representing the process of fruit number and individual weight build-up is proposed, structured around five steps: number of flowers build-up, flowering, pollination, fecundation-fruit set, and fruit growth. The model outputs are the individual fruit weight and harvest dates distributions at the orchard level. Its functions are simulation and prediction in order to assist farmers in their technical choices. This work deals with the flowering, fecundation-fruit set and fruit growth steps. The plant genetic diversity induces a flowering asynchrony which is not taken into account by flowering model conceived for a monovarietal orchard. A general stochastic flowering model is then built. It describes flowering at different levels and considers the flowering asynchrony both within and between plants. A controlled pollination experiment showed that strawberry guava is partially self-compatible, and that self-compatibility level varies among plants. The distribution of seed number per fruit depends on the individual, on the pollen genetic origin and on the pollination conditions. The modelling of pollination and fecundation in a genetically heterogeneous population appears complex and further research is needed. A general approach to model the effect of growth factors on individual fruit growth curve is presented. It is then applied to strawberry guava fruit growth, with the seed number per fruit and the plant leaf: fruit ratio as growth factors. Statistical errors are associated to the prediction model in order to estimate the output variability. The distribution of harvest dates at the plant level is estimated from the plant leaf: fruit ratio and the mean number of seeds per fruit. The general approach used in this study and the results are discussed, and further research is outlined. Practical consequences of this work are underlined. Finally, the generalisation of the agronomic approach of domestication and of the models is discussed.

L'idée de ce dossier est née du constat suivant: de nombreuses informations sur les pratiques des agriculteurs ne sont ni capitalisées, ni traitées pour permettre aux vulgarisateurs de mieux les comprendre. Cet ouvrage n'est ni un manuel d'agronomie classique expliquant comment cultiver le riz pluvial, ni une présentation générale de la riziculture pluviale dans l'ouest de la Côte d'ivoire. Il s'agit d'un document voulant décrire comment des agriculteurs, en un lieu donné, cultivent le riz, comment ils le connaissent, comment ils en parlent, quelles justifications ils donnent à leurs pratiques et comment ils évaluent leurs résultats. Ce dossier pédagogique est conçu pour servir de support de formation à des agents chargés de programmes de vulgarisation et de conseil technique auprès d'agriculteurs. Après quelques présentations théoriques et méthodologiques, l'itinéraire technique pour la culture du riz pluvial est passé en revue sous forme de dix-sept fiches. Des tentatives de modélisation sont ensuite présentées. Enfin, le dispositif et les résultats du suivi agronomique sont détaillés. Le but de cet ouvrage est donc plus de susciter des questions chez le lecteur que d'apporter des solutions clés en main.

Cette etude analyse les effets d'un ombrage simule sur les interactions entre puits reproductifs, en utilisant des cotonniers elagues, ne presentant qu'une seule serie d'organes reproducteurs. Les plantes ont ete cultivees en milieu controle sous regime hydrique non limitant. Un ombrage, reduisant de 40% le niveau lumineux (600 micromol.m-2.s-1 chez le temoin), a ete impose a partir de la 7e anthese. Des suivis de la transpiration, de la distribution de matiere seche et de la phenologie ont ete realises. Un indice de competition apparente pour les assimilats (ICA) a ete calcule en divisant la charge en capsules par le taux de croissance de la plante. A l'echelle de l'inflorescence, l'ombrage affecte la cascade de processus determinant la capacite de puits, incluant la croissance des carpelles, le nombre de graines, l'abscission de la capsule, la masse finale de coton-graine par graine et la fraction de fibres. En plus d'une reduction de la capacite des puits (abscission, nombre de graines), l'ombrage augmente la duree de developpement de la capsule, etalant dans le temps la demande pour les assimilats. Ce phenomene provoque une reduction de la qualite des fibres. L'ombrage reduit egalement le taux d'apparition des capsules, limitant ainsi le nombres de puits en competition. Les taux d'apparition des capsules, de duree de developpement des capsules et d'abscission sont correles avec l'ICA. L'utilisation future de l'ICA dans l'etude des puits au sein de systemes de plantes complexes est discutee. (Resume d'auteur)

The genetics of current sugarcane cultivars ( Saccharum spp.) is outstandingly complex, due to a high ploidy level and an interspecific origin which leads to the presence of numerous chromosomes belonging to two ancestral genomes. In order to analyse the inheritance of quantitative traits, we have undertaken an extensive Quantitative Trait Allele (QTA) mapping study based on a population of 295 progenies derived from the selfing of cultivar R570, using about 1,000 AFLP markers scattered on about half of the genome. The population was evaluated in a replicated trial for four basic yield components, plant height, stalk number, stalk diameter and brix, in two successive crop-cycles. Forty putative QTAs were found for the four traits at P = 5 x 10(-3), of which five appeared in both years. Their individual size ranged between 3 and 7% of the whole variation. The stability across years was improved when limiting threshold stringency. All these results depict the presence in the genome of numerous QTAs, with little effects, fluctuating slightly across cycles, on the verge to being perceptible given the experimental resolution. Epistatic interactions were also explored and 41 independent di-genic interactions were found at P = (5 x 10(-3))(2). Altogether the putative genetic factors revealed here explain from 30 to 55% of the total phenotypic variance depending on the trait. The tentative assignment of some QTAs to the ancestral genomes showed a small majority of contributions as expected from the ancestral phenotypes. This is the first extensive QTL mapping study performed in cultivated sugarcane.

Une étude de la diversité des caractères agromorphologiques suivie d'une caractérisation physique, nutritionnelle et technologique ont porté sur une série d'écotypes et de lignées sélectionnées de sorgho guinea tan, comparées à deux variétés témoins. Au total 12 variétés réparties en 36 échantillons de grains entiers et en 12 échantillons de farines ont été étudiées. Les résultats de cette étude montrent que la productivité est bonne pour la plupart des variétés étudiées à l'exception d'une seule, la CG 34/4-3-2. Aussi les lignées sélectionnées présentent une diversité assez importante pour les caractères morphologiques et certains caractères agronomiques. Par ailleurs, les résultats des analyses physiques, nutritionnelles et technologiques des grains et farines montrent qu'aucune des variétés étudiées n'est tendre, elles sont vitreuses ou semi-vitreuses et aptes au décorticage à l'exception de l'écotype G 1636. Cependant la composition biochimique des farines montre que dix variétés sont susceptibles de donner des tô fermes par leur teneur suffisamment riche en amylose, c'est-à-dire supérieure à 24% MS et moyennement faible en cendres et protéines (Fliedel et al. 1989, 1994). Au terme de cette étude, 9 parmi les 12 variétés étudiées paraissent aptes pour une éventuelle diffusion/vulgarisation auprès des utilisateurs et producteurs.

In the Plain of Reeds, Vietnam, the characteristics, water levels, and water quality of acid sulphate soils are highly variable in space and time, in relation to micro-elevation, and hence, favourable conditions for crop production are met during a very short period. Yield components were analysed in recently reclaimed farmers' fields. A semi-quantitative model was developed, explaining rice growth and yield as a function of different biophysical conditions on severely acid sulphate soils. Intra-field variability of rice growth and yield was explained by the high short-range variability of soil and water, which was explained by micro-elevation. Long submersion and deep reduction were important agronomic problems in the beginning of the plant cycle and led to low plant, tiller, and panicle densities. Strong oxidation leading to acidification and solubilisation of aluminium was frequent at the end of the cropping season and was responsible for poor plant growth and grain filling. Inter-field variability of plant growth and yield was explained by differences in soil and water in relation to mean field level and number of years after reclamation. A typology of fields based on rice development is proposed as a guideline to extension in the Plain of Reeds.

Cette étude cherche à analyser les effets d'un ombrage sur le rendement et la qualité des fibres, en mettant en évidence les interactions entre puits reproductifs. Des cotonniers simplifiés, ne présentant qu'une seule série d'apparition successive d'organes reproducteurs, du cultivar DES 119 ont été cultivés au champ en Thaïlande et en conditions contrôlées. En parallèle, une expérimentation de répartition du 14C après 11h d'exposition à du CO2 marqué, a été réalisée. Un indice de compétition apparente pour les assimilats (ICA) a été calculé en divisant la charge en capsules par le taux de croissance de la plante. A l'échelle de l'organe reproducteur, l'ombrage va influer sur les composants d'une cascade de processus incluant la rétention de l'organe, la croissance en masse sèche des carpelles (qui peuvent éventuellement représenter une réserve pour la croissance du coton-graine), les composantes du rendement en fibres: le nombre de graines, la masse de coton-graine par graine et la fraction de fibres par coton-graine, et la qualité des fibres (degré d'épaississement des parois secondaires des fibres). Chacun de ces composants est sensible à la disponibilité en ressource durant des périodes particulières mises en évidence. La compétition ne joue pas exclusivement sur les paramètres quantitatifs mais aussi sur les durées de développement, comme le taux d'apparition des organes fructifères et la durée individuelle de leur développement. Une restriction en assimilats durant le développement reproducteur n'induit pas de différence de répartition entre parties végétative et reproductrice, ni entre organes reproducteurs. La demande d'un organe reproducteur est fonction de son âge et de son nombre de graines. Au sein de la capsule, sous ombrage, l'allocation aux carpelles durant leur croissance peut être réduite au bénéfice du coton-graine. Des perspectives d'utilisation des résultats sont données concernant la modélisation, et l'utilisation d'outil de diagnostic des contraintes.

This study analyzes the potential of conservation tillage (CT) for improving maize productivity under a range of soil and rainfall conditions in a semiarid zone of West-Central Mexico, evaluating the consequences of tillage practices on the crop's ability to take up and store water, on evapotranspiration, on crop physiology, and on grain yield, under cropping systems typical of small-scale farmers. Even with low use of crop residue mulching (0.2 kg/m2), CT has considerable potential for adoption in these areas, once technical issues such as supply of appropriate machinery, weed control, and the competing use of the maize residue for forage have been resolved. Even under wetter conditions, CT resulted in acceptable yields.

As water for agriculture becomes scarcer, some lowland areas will be forced to shift to upland rice cultivation. Rice generally yields less in aerobic systems. To obtain adequate yields, we need to understand the causes of reduced productivity in upland conditions and their genetic control. This chapter combines results from variety comparisons, a doubled-haploid line (DHL) mapping population, and near-isogenic lines (NILs) to address these questions. The development of leaf area index was greater in aerobic conditions for an upland variety, Azucena, and also a lowland variety, IR72. For both varieties, the percentage of sterile grain was greater and the 1,000-grain weight less in aerobic conditions, leading to a lower harvest index in the upland field. The reduction in harvest index was more severe in the lowland cultivar. We also compared yield components measured in sprinkler-irrigated upland, furrow-irrigated upland, and lowland conditions for 85 DHLs derived from a cross between another semidwarf indica lowland cultivar, IR64, and Azucena. Yields and most yield components were poorly correlated across upland and lowland environments. Common quantitative trait loci (QTLs) were identified across water levels for some traits, but QTLs for yield and yield components were generally specific to one environment. Additional studies examined the performance of NILs of IR64 that had chromosomal segments from Azucena introgressed through marker-aided selection. The introgressed segments were chosen because they contained QTLs for root traits (e.g., root thickness, length), but some yield component QTLs had also been mapped near those segments. When the NlLs were cultivated under lowland conditions, they produced fewer tillers per plant than did IR64, but some produced more tillers m-2 in the uplands. Preliminary yield data indicate that some NILs can outyield IR64 in lowland and/or upland conditions. These results provide insights into the genetic control of the development of rice yield components in aerobic and anaerobic environments.

The breeder is often confronted with the need to select individual trees in heterogeneous populations (farmers' fields, breeding trials), without availability of long term records on individual trees. In breeding trials, preference is to be given to selection within progenies that have good average performance. Within the CFC/ICCO/IPGRI project such preselection of adult trees is proposed for the local clone selection plots and for population breeding. The objective of this proposal is to indicate important selection traits that can be quite simply observed to increase efficiency of individual tree selection.

Growth and yield characteristics of two different clones of banana plants (#Musa# ¿AAA' cv. ¿Grande naine') originating from four months old embryogenic cell suspensions were studied. These characteristics were compared with those plants produced by the conventional #in vitro# budding multiplication method. Two types of variants were observed during the acclimatization phase among 500 embryogenic cell suspension derived plants. The first type related to banana plants with 'variegated or deformed leaves' were also observed in #in vitro# budding derived plants. The second type concerned 'fasciated-leaféd' plants. During the field growth, these two variant types produced plants morphologically similar to the other plants. Thus, none of the cell suspension derived plants exhibited off-type traits in the field. A Fisher block model was used to compare the field performances of the two clones produced through the two #in vitro# propagation techniques.The analysis of variance showed that there were no significant differences between the plants produced by either micropropagation techniques for the plant height and circumference, the length of the reference leaf, the number of nodal clusters of the inflorescence and of fruits, the bunch weight, the period of time between planting and flowering, and between planting and harvesting. This study showed that banana plants with an agronomical behaviour similar to those produced by the conventional #in vitro# budding method could be regenerated from embryogenic cell suspension.

Pearl millet is an important crop in the sub-Saharan West Africa. In Senegal, the instability in millet production is caused mainly by soil water deficit and nitrogen deficiency. For this reason, this study was conducted in a sandy soil in Senegal for three years during the dry and rainy seasons, to assess the effect of interaction between drought and N deficiency on the agrophysiological responses of millet. The experimental design incorporated two watering regimes (water stressed and well irrigated control) and three level of N fertilization (0.00, 17.13, and 68.5 kg N ha-1). When water stress was applied at early vegetative stage and during flowering - grain filling phases, high fertilizer application reduced grain yield and grain N yield more than zero fertilizer input. Yield components analysis showed that higher grain and grain N yields in zero fertilizer input were due to dry matter partitioning in favour of the grains resulting from the attainment of higher water status. The lower leave area index (LAI) combined with zero fertilizer input induced lower water losses (evapotranspiration) which became beneficial in terms of soil water stock when water stress was applied. Associated with deep rooting, these responses were responsible for the higher water potential, stomatal conductance, rates of transpiration and photosynthesis under zero N fertilization. The implications of these drought responses on the performance of millet under N deficiency are discussed on the basis of cropping systems and climatic risks.

Chez le bananier, la mise en place graduelle des fleurs femelles, hermaphrodites et mâles semble obéir à un certain déterminisme encore mal connu. En préliminaire à des études plus approfondies sur les mécanismes impliqués dans la transition florale, des observations sur l'enchaînement et le développement des fleurs ont été faites chez plusieurs variétés de bananiers. Trois cultivars du sous-groupe 'Plantain' ('AAB'), un cultivar du sous-groupe 'Cavendish' ('AAA') et une variété sauvage ('BB') ont été observés. La composition florale des assises florifères, le nombre de mains et de doigts, le niveau d'apparition de la transition florale sur l'inflorescence et la fréquence d'expression de la main hermaphrodite ont été notés. Un coefficient a été utilisé pour quantifier les séquences observées. La transition florale chez les bananiers s'opère soit directement (TrD) en passant des assises florifères femelles à des assises mâles, soit progressivement (TrP) en formant des assises hermaphrodites intermédiaires. Pour une population donnée, le rapport entre le nombre de TrD et le nombre de TrP semble surtout dépendre de la variété. Le type de matériel planté pourrait aussi influencer ce rapport. La mise en place des différents types de fleur au cours de la morphogenèse florale du bananier serait le lieu d'interactions de divers flux hormonaux et/ou d'un désordre physiologique dont l'amplitude déterminerait le mode et le niveau de la transition florale. L'étude des influences hormonales sur la mise à fleur du bananier devrait être encouragée.

In spite of the fact that cowpea (#Vigna unguiculata# (L.) Walp.) is one of the most drought-tolerant crops, its production in dry Sahel environment is affected by very intense water deficit that usually occur in the course its growth cycle. The objective of this work was to compare with the help of agromophorlogical criteria, the degree of sensitivity to water deficit of the early maturing, erect cowpea varieties and the late maturing, semi-erected or crawling varieties. The effect of severe water deficit applied at the vegetative phase until the beginning of floral initiation was studied during the dry season in 1999 at Bambey (Senegal). The agronomical observations were focused on the soil water status, the dynamism of vegetative development and root growth, yield and yield components. The sensitivity of the varieties to water stress were assessed by water stress index (ls) and water use efficiency (WUE) for the pods, grains and the total biomass productions, respectively. The results obtained showed that the early maturing, erect varieties were more sensitivity to drought than the other varieties. This sensitivity was deduced from very high Is for the grains (0.61), the pods (0.54) and a lower WUE for grain production (3.27 kg ha-1 mm-1) under water stress as against 6.41 kg ha-1 mm-1 under optimal water conditions. It was observed that under water deficit at pre-floral phase at the three varieties, an increase in the mean grain weight correlated with the reduction in grain number per m2. At the plant population level, the results obtained could serve in the definition of drought tolerance criteria relevant to varietal selection. (Texte intégral)

The feasibility of using Quantitative Trait Loci detection in sugarcane, despite the handicap of a high ploidy, is being tested. One difficulty is to have a well saturated map of this polyploid genome. For this purpose, advantage was taken of AFLP technology as a powerful source of markers. For field trait evaluation, a population of 300 progeny obtained by selfing the cultivar R570 was planted in a complete block design with five replications. The basic plot was a 1.5m row. Similarly a second experiment involving a subset of 80 progeny was planted and was more finely evaluated. Several yield components were measured in plant cane and in first ratoon: brix, pol, fibre, plant height, stalk diameter and tillering. Rust resistance was also assessed. All 300 progeny were genotyped using 38 AFLP primer combinations yielding more than 1200 segregating bands of which about 80% were simplex markers. Over 950 simplex markers have been included in 105 co-segregation groups of the genetic map drawn with Mapmaker at a LOD score of 5. This AFLP map covers more than 6500 centimorgans. We attempted a first QTL detection on the basis of an analysis of variance. Numerous marker-QTL associations at P

Hace nueve años que se implanto una red internacional de ensayos varietales en el Cono Sur. Estos ensayos de diez variedades son fuentes de varios estudios entre los cuales están los trabajos de mapeo de plantas. A partir de uno de ellos realizado en Bolivia, se hizo un análisis de correlaciones entre 13 variables de mapeo y un análisis en componentes principales cual destaco dos poblaciones de variedades. Se observo correlaciones negativas y significativas entre ciertas variables componentes de la producción del tallo principal y otras variables componentes de la producción sobre las ramas vegetativas. Estos resultados sugieren que puede existir un fenómeno de compensación, sobre las vegetativas, de las perdidas de producción que pueden ocurrir sobre el tallo principal. Estos resultados preliminares deberán ser profundizados con el estudio del conjunto de los ensayos de la red del Cono Sur.

Cet ouvrage présente une revue bibliographique de 187 références, centrée sur le maïs en zones tropicales et l'utilisation de matériel exotique, en particulier par introgression, dans les programmes de sélection variétale. La comparaison avec les zones tempérées est faite systématiquement en abordant les aspects climatiques, notamment le rayonnement ; le déroulement du cycle du maïs avec la température ; le fonctionnement du couvert végétal, l'élaboration du rendement et la partition des assimilats. Une synthèse des carctéristiques génotypiques susceptibles d'être travaillées pour augmenter le rendement des maïs tropicaux est présentée. L'utilisation de matériel exotique est développée avec trois objectifs : la recherche de bonnes combinaisons hétérotiques ; le transfert de caractères précis par back-cross ; l'élargissement de la variabilité génétique et l'intérêt pour les recombinants par les techniques d'introgression.

La culture du palmier à huile est implantée de longue date au sud du Bénin. La pluviométrie y est le principal facteur limitant. Le régime pluviométrique comporte deux saisons des pluies et deux saisons sèches. Au cours des 70 dernières années, l'importance de la petite saison sèche tend à se réduire en faveur de la grande saison. Si la hauteur totale des précipitations annuelles reste stable à long terme, on note des fluctuations marquées. Le palmier subit un déficit hydrique fluctuant entre 400 mm et 700 mm avec des pointes à 900 mm. Il en résulte une entrée en production tardive, une production réduite et soumise à des variations saisonnières importantes. Les épisodes les plus secs provoquent des dégâts végétatifs pouvant aller jusqu'à la mort. Du point de vue agronomique, la culture du palmier en conditions sèches impose un choix rigoureux des zones destinées à la culture du palmier, et des pratiques agricoles adaptées. L'ablation des inflorescences à l'entrée en production améliore l'installation du système racinaire. La réduction de la densité de plantation et l'allégement des couronnes réduisent la mortalité au détriment de la production. Le matériel génétique doit cumuler productivité et tolérance à la sécheresse. Si des différences de mortalité sont constatées, leur déterminisme et les sources de tolérance doivent être étudiés plus systématiquement. Les principaux facteurs à prendre en compte sont l'alimentation hydrique, l'utilisation optimale de l'eau disponible, la répartition des cycles de production et les mécanismes cellulaires de tolérance.

The effects of different nitrogen supplies on the performance of the short-day cultivar M9D3 of pearl millet (Pennisetum glaucum L. R.Br.) and their interaction with sowing time were analysed in a two-year experiment in Mali. The first sowing dates coincided with the beginning of the rainy season. The second sowings were 20 days later. The sowing date affected only the emergence - earing duration independently of nitrogen application. The linear reduction in straw yield, caused by the shortening of the cycle, was not combined with a reduction in grain yield. The application of even low levels of nitrogen to millet crops always increased the grain yield, as a consequence of a higher number of productive panicles, while the straw production was positively affected only when the rainy season started early. The non-agreement between the high productive potential of the first sowing crops and their grain yield, in comparison with the plants of the second sowing date, could be ascribed, first of all, to the more marked asynchrony between the time corresponding to LAImax and the grain filling phase, characterised by the maximum sink demand and, second, to a longer time interval during which stem growth and panicle growth are in direct competition.