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LEAFY (LFY) protein is a key regulator of floral development. Its gradually increased expression governs the sharp floral transition and LFY subsequently controls the patterning of flower meristems by inducing the expression of the floral homeotic genes APETALA1 (AP1), APETALA3 (AP3) et AGAMOUS (AG). According to some theories of evolution, LFY should have also played a central role in the appearance of flowering plants (Angiosperms). Despite a wealth of genetic data, how LFY functions at the molecular level is poorly understood. LFY is the only member of a transcription factor family specific of plant kingdom and its primary sequence looks like no other. The most important breakthrough of my PhD work, the obtention of the 3-D structure of LFY C-terminal domain (LFY-C) from Arabidopsis thaliana bound to two of its target genes, AP1 and AG, now helps us to better understand how this original protein works. LFY-C adopts a novel seven-helix fold and forms basespecific contacts in both the major and the minor grooves of DNA. LFY-C binds DNA as a cooperative dimer mediated by two basic residues. This cooperativity could partly explain LFY's effectiveness in triggering sharp flowering transition. The structure reveals also an unexpected similarity between LFY and HTH proteins such as homeodomain transcription factors or paired protein involve in animal development. Finally, allowing us to study LFY orthologues from all terrestrial plants in a novel way, these data provide a unique framework to elucidate the molecular mechanisms underlying the evolutionary history of flowering plants.; La protéine LEAFY (LFY) est un régulateur clé du développement floral. L'augmentation graduelle de son expression conduit à la transition florale, phénomène très soudain, suite à laquelle LFY intervient dans la mise en place des organes floraux par l'activation directe de l'expression des gènes homéotiques APETALA1 (AP1), APETALA3, et AGAMOUS (AG). Selon des théories de l'évolution, LFY serait également l'acteur majeur à l'origine de la naissance des plantes à fleur (Angiospermes). Malgré l'abondance des données génétiques concernant LFY, les bases moléculaires relatives au mode d'action de la protéine sont très peu comprises. LFY est l'unique membre d'une famille de facteur de transcription spécifique au règne végétal et sa séquence ne ressemble à nulle autre. Mon travail de thèse, marqué par l'obtention de la structure 3-D du domaine de liaison à l'ADN de LFY (LFY-C) d'Arabidopsis thaliana lié aux séquences régulatrices d'AP1 et AG, fournit une importante source de compréhension du mode de fonctionnement de cette protéine originale. LFY-C adopte un nouveau repliement globulaire à 7 hélices ! et forme des contacts base-spécifiques avec le petit et le grand sillon de l'ADN. Après avoir montré par approche biochimique classique que LFY-C liait l'ADN de façon coopérative sous forme de dimère, la structure du complexe LFY-C/ADN révèle que ce mécanisme résulte de contacts entre les monomères de LFY-C mettant en jeu deux résidus basiques. Cette coopérativité pourrait en partie expliquer la capacité de LFY à déclencher la transition florale. Les données cristallographiques indiquent également des similarités structurales inattendues avec les protéines HTH comme les facteurs de transcription à homéodomaine ou paired impliqués dans le développement animal. Enfin, en permettant d'étudier sous un nouvel angle les orthologues de LFY tout au long du règne végétal, ces données alimentent l'espoir de parvenir un jour à comprendre comment sont apparues les fleurs sur Terre.

Le photoperiodisme des varietes locales de sorgho permet la synchronisation de la floraison avec la fin de la saison des pluies. La prise en compte de ce caractere par les programmes d’amelioration est tres recente. L’integration du photoperiodisme dans un modele de culture et l’utilisation d’un systeme d’information geographique (SIG) permettent d’identifier les zones optimales de culture des differents cultivars en combinant les caracteristiques varietales, l’incertitude climatique et les pratiques culturales des paysans. Une variete est consideree adaptee a une zone si elle fleurit dans les 20 jours qui precedent la date moyenne de fin de saison. L’analyse prend en compte la grande incertitude sur les dates de semis qui peuvent s’etaler sur plus d’un mois a partir de l’installation des pluies. L’etude du comportement de 52 varietes locales et ameliorees au Mali et au Burkina Faso montre que les varietes precoces possedent une large adaptation geographique mais necessitent de maitriser la date de semis. Les varietes photoperiodiques sont specifiquement adaptees a une zone geographique mais tolerent une large gamme de dates de semis, ce qui est un caractere primordial pour les paysans africains. Les cartes d’adaptation issues de ce travail peuvent aider les selectionneurs a definir des ideotypes adaptes a la diversite des situations agroclimatiques d’Afrique soudano-sahelienne.

The thermogenesis and flowering biology of Colocasia gigantea (Blume) Hook. f. were studied from December 2005 to February 2006 on Espiritu Santo, Vanuatu (South Pacific). Endogenous thermogenesis was measured in two ways: (1) continuously over 5-day periods, and (2) over 3 h during maximum heating. The study showed that heat was generated by the male part of the spadix and probably the lower zone of the sterile region. The temperatures of the male part peaked twice: (1) between 0625 and 0640 (during the female phase) and (2) 24 h later (during the male phase). The average maximum temperature was 42.25 +/- 0.14 degrees C during the female phase (16.63 degrees C above the ambient temperature) and 35.14 +/- 0.22 degrees C during the male phase (10.61 degrees C above the ambient temperature). In the lower zone of the sterile region, thermogenesis was documented only during the female phase. The average maximum temperature was 35.44 +/- 0.41 degrees C (9.82 degrees C above the ambient temperature). Thermogenic heating appeared to be closely associated with the activities of pollinating insects.

Citrus is the most economically important fruit crop in the world. Citrus fruits are classified as hesperidiums, berries of very special organization characterized by a juicy pulp made of vesicles within segments. Besides the typical fruit components, citrus fruit contain many organic compounds necessary for human diet and an extraordinary number of metabolites displaying valuable properties for health. In citrus, the concept of fruit quality comprises several other aspects intimately related to human health apart from physical attributes and diet components. Citrus also possess a rare combination of intriguing biological characteristics including an unusual reproductive biology, a non‐climacteric fruit ripening and several specific tree‐traits. The combination of these characteristics suggests that the study of fruit growth regulation in citrus may reveal original mechanisms based on explicit molecular differences and on exclusive genes. Citrus is, therefore, an excellent model to study fruit quality because of its peculiar fruiting, singular biochemistry and economical relevance. In this chapter, the progress that has been carried out in the research on the molecular determinants related to development and fruit quality of citrus is reviewed. The review also intends to provide a physiological frame for the implementation of the information generated during the past years. Molecular background is provided on the current status of principal reproductive processes related to fruit quality mainly flowering, fruiting, ripening, and abscission. We also have focused on main characteristic secondary bioactive compounds, as major contributors of aroma and flavour and finally, on the abiotic stresses influencing development and fruit growth.

International audience; Although species of arid environments share physiological and morphological strategies to reduce plant transpiration and protect leaves from excessive radiation and wind desiccation, they differ significantly in growth form, aboveground architecture, and rate of leaf turnover. We studied shoot growth pattern and leaf phenology in relation to rainfall and air temperatures during the growing season in Mulinum spinosum, a cushion shrub having a broad distribution in the Patagonian steppe, a windy, temperate region with summer water deficit. The partitioning of aerial biomass in plants with different basal areas was also studied. Shoot formation began in late summer when annual shoots (AS) produced temporary short shoots which restarted extension again in spring. AS exhibited continuous leaves senescence during the mid and late growing season. Delayed branching of AS was related to total leaves senescence on parent shoots in late summer. Fast leaf turnover reduces the transpiring area and would allow plant re-hydration from soil water reserves, thus facilitating branching initiation. Plant annual biomass was reduced to a thin external layer, which became denser in plants of higher basal area, protecting buds and leaves in this arid and windy environment.

Little is known about the effect of flowering on leaf photosynthesis. To understand why net photosynthesis (A(net)) is lower in Mangifera indica L. leaves close to inflorescences than in leaves on vegetative shoots, we measured nitrogen and carbohydrate concentrations, chlorophyll a fluorescence and gas exchange in recently matured leaves on vegetative terminals and on floral terminals of 4-year-old trees. We used models to estimate photosynthetic electron fluxes and mesophyll conductance (g(m)). Lower A(net) in leaves close to developing inflorescences was attributable to substantial decreases in stomatal conductance and g(m), and also in photosynthetic capacity as indicated by the decrease in the light-saturated rate of photosynthetic electron transport (J(max)). The decrease in J(max) was the result of decreases in the amount of foliar nitrogen per unit leaf area, and may have been triggered by a decrease in sink activity as indicated by the increase in the hexose:sucrose ratio. Parameters measured on leaves close to panicles bearing set fruits were generally intermediate between those measured on leaves on vegetative shoots and on leaves close to inflorescences, suggesting that the changes in A(net) associated with flowering are reversible.

National audience

la pagination du document est réalisée pour l'impression recto-verso; Mon activité de recherche, appuyée par l'encadrement d'étudiants, s'est développée autour d'une thématique centrale, l'analyse architecturale de l'arbre fruitier. Mes travaux, sur pommier essentiellement, ont tout d'abord montré l'intérêt de l'architecture comme outil de caractérisation de la variabilité génétique existante (cultivars). J'ai mis en évidence que les différences variétales de comportement architectural et fruitier pouvaient être bien expliquées par deux caractères discriminants non analysés jusque-là : la mortalité physiologique des rameaux, appelé phénomène d' « extinction », et l'aptitude au retour à fruit d'une année à la suivante sur le même rameau. Une relation positive a été mise en évidence entre ces deux phénomènes : les cultivars à forte extinction ont en général une forte aptitude au retour à fruit. Par ailleurs il a été montré que la longueur d'un rameau conditionne la probabilité de floraison terminale et, en cas de floraison, la taille de l'inflorescence et son aptitude à la nouaison. La succession temporelle des évènements joignant la formation d'un méristème à son fonctionnement pluri-annuel apparaît donc comme un système hautement intégré et à déterminisme précoce. Nos résultats suggèrent une régulation fonctionnelle et dynamique entre le nombre de bourgeons en croissance dans une architecture et leurs potentiels organogénétiques individuels. Ils nous ont conduit à formuler des hypothèses sur les effets de manipulations expérimentales (ex. taille, arcure) sur l'architecture de l'arbre entier (ex. durée et rythmicité de croissance, probabilité de floraison) et à les tester in horto. Ces travaux constituent la base de collaborations scientifiques pluridisciplinaires sur deux axes principaux. Le premier est l'analyse de l'impact de manipulations sur le climat lumineux intra-arbre et la contribution des différents types de rameaux à l'interception de la lumière. Le second est l'étude des relations entre architecture et ravageurs-maladies. Il permet de hiérarchiser les facteurs, directement ou indirectement liés à l'architecture, explicatifs du développement des bioagresseurs. Ces deux axes de recherche sont le moteur de mon implication dans différents programmes nationaux et internationaux, ainsi que dans des réseaux informels en France et à l'étranger. Mes travaux s'étendent à d'autres espèces, comme le manguier en collaboration avec le CIRAD où le couplage architecture(spatial)/phénologie(temporel) est approfondi. Mon programme scientifique actuel se recentre sur ce qui est à la base de l'édification architecturale de l'arbre, la croissance du rameau et la distribution et la nature de sa ramification axillaire. Il s'appuie sur des collaborations pluridisciplinaires. Dans une première phase la recherche porte sur des rameaux arqués. L'objectif est de mieux appréhender les mécanismes déterminant certains aspects de la ramification à l'interface entre biomécanique (ex. : contraintes liées à l'arcure) et hydraulique (ex. : lien entre conductance hydraulique des tissus xylémiens reliés au bourgeon et organogenèse). Des résultats récents permettent de formuler des hypothèses sur les rôles respectifs des effets mécaniques et environnementaux sur le patron de ramification observé.

The effect of two contrasting methods of conduct (vs. Central Leader. Driving Centrifugal) was studied on three apple cultivars architecturally distinct 'Scarletspur Delicious', 'Golden Delicious' and 'Granny Smith'. Trees are digitized using a 3D electromagnetic tool to scale shoots twice during the first year and before the second harvest year. The shoots are described and classified according to their length and their typology (vs. fruiting. Vegetative). The timber carrier is also described in the second year focusing on the strategy of size (carved wooden carrier vs. Uncut). Virtual experiments are carried out through the reconstruction of the foliage, creating 3D models and simulation of light interception at the tree-level, types of shoots and individual shoots. A simplified model for the estimation of light interception by isolated trees is proposed, using parameters of canopy structure. Demographics and the sequence of shoots are mainly affected by cultivar, with a weak influence of driving style. A similar trend is observed across the tree for the parameters of canopy structure and light. The spatial distribution of shoots and leaf area density differ depending on driving style. 'Scarletspur Delicious' tree is a reduced-form and compact compared to other two cultivars of trees that have more open and larger. The effect of control systems results in a greater proportion of vegetative shoots long and repeated (R-LVS) on trees in Central Leader. The latter exhibit a heterogeneous distribution of leaf area and light interception of two kinds of shoots caused by R-LVS which increase the mutual shading of the shoots. These differences vary with cultivars and are more trenches at Granny Smith. The parameters studied show that the control system could have a direct impact on development and spatial positioning of shoots. This significantly affects flowering and production, although growth and structure of the tree depends mainly on cultivar; L'effet de deux méthodes de conduite contrastées (Central Leader vs. Conduite Centrifuge) est étudié sur trois cultivars de pommiers architecturalement distincts ; 'Scarletspur Delicious' , 'Golden Delicious' et 'Granny Smith'. Les arbres sont digitalisés en 3D en utilisant un outil électromagnétique à l'échelle des pousses deux fois en cours de première année et avant la récolte en deuxième année. Les pousses sont décrites et classifiées selon leur longueur et leur typologie (fructifères vs. végétatives). Le bois porteur est également décrit en deuxième année en mettant l'accent sur la stratégie de taille (bois porteur taillé vs. non taillé). Des expérimentations virtuelles sont réalisées à travers la reconstruction du feuillage, la création de maquettes 3D et la simulation de l'interception de la lumière, à l'échelle de l'arbre, des types de pousses et des pousses individuelles. Un modèle simplifié pour l'estimation de l'interception de la lumière par les arbres isolés est proposé, en utilisant des paramètres de structure du feuillage. La démographie et la séquence des pousses sont principalement affectées par le cultivar, avec une faible influence du mode de conduite. Une tendance similaire est observée à l'échelle de l'arbre pour les paramètres de structure du feuillage et de la lumière. La distribution spatiale des pousses et la densité de surface foliaire se différencient selon le mode de conduite. 'Scarletspur Delicious' est un arbre de forme réduite et compacte par rapport aux deux autres cultivars qui possèdent des arbres plus ouverts et plus grands. L'effet des systèmes de conduite se traduit par une plus grande proportion de pousses végétatives longues et réitérées (R-LVS) sur les arbres en Central Leader. Ces derniers présentent une distribution hétérogène de la surface foliaire et de l'interception de la lumière des deux types de pousses causées par les R-LVS qui augmentent l'ombrage mutuel des pousses. Ces différences varient en fonction des cultivars et sont plus tranchées chez Granny Smith. Les paramètres étudiés montrent que le système de conduite pourrait avoir un impact direct sur le développement et le positionnement spatial des pousses. Ceci affecte notablement la floraison et la production, même si la croissance et la structure de l'arbre dépendent essentiellement du cultivar

Effective flowering time in Gossypium hirsutum cotton plants was studied with the aim of enhancing decision making on the best varieties to plant according to the planting date under rainfed cropping conditions. Trials were conducted at two sites in a cotton-growing area of Benin in 2002 and 2003. A split-split plot design with three replicates was used to compare 10 cotton varieties, with different growth cycle lengths and morphology, at three stand densities (42 000, 125 000, 167 000 plants ha−1) and two planting dates (standard planting in June and late planting). The flowering period was characterized by the mean first flower opening date (FF), which is an indicator of flowering earliness, and by the opening date of the last flower giving rise to a first-position boll on fruiting branches (LFP1). Effective flowering time (EFT) was calculated as the difference between LFP1 and FF. EFTs differed markedly in the 10 cotton varieties tested and this parameter could not be predicted on the basis of flowering earliness. Late planting and high planting rates delayed first-flower opening, accelerated last-boll development and reduced the effective flowering time. This latter factor should be taken into account in cotton breeding programmes so that varieties adapted to local rainfall constraints can be recommended to growers while also enhancing crop management sequences.

Reproductive phenology was observed over three years in a Eucalyptus grandis seed orchard in Madagascar to determine the impact of geographic differences of parental selections on the expected genetic composition of seed crops. Pollen flow (observed pollen cloud) was deduced from a paternity assignment based on sampling from one year's seed production. The two approaches were used to verify whether knowledge of phenology is sufficient to predict the genetic quality of the seeds collected. Despite the high flowering level, with a constant cycle over three years, the results demonstrated wide reproductive phenological differences associated with the parents' origin, suggesting putative pollination disequilibrium. From both observed and expected pollen clouds, the results showed preferential mating among different provenances, which has consequences for seed crop composition. Phenological observations, which can be made inexpensively, can be used to promote methods of effective seed orchard management in order to improve the genetic quality of seeds.

Citrus is the main fruit tree crop in the world and therefore has a tremendous economical, social and cultural impact in our society. In recent years, our knowledge on plant reproductive biology has increased considerably mostly because of the work developed in model plants. However, the information generated in these species cannot always be applied to citrus, predominantly because citrus is a perennial tree crop that exhibits a very peculiar and unusual reproductive biology. Regulation of fruit growth and development in citrus is an intricate phenomenon depending upon many internal and external factors that may operate both sequentially and simultaneously. The elements and mechanisms whereby endogenous and environmental stimuli affect fruit growth are being interpreted and this knowledge may help to provide tools that allow optimizing production and fruit with enhanced nutritional value, the ultimate goal of the Citrus Industry. This article will review the progress that has taken place in the physiology of citrus fruiting during recent years and present the current status of major research topics in this area. Citrus é a principal fruteira no mundo, tendo, portanto, profundos impactos econômicos, sociais e culturais em nossa sociedade. Nos últimos anos, o conhecimento sobre a biologia reprodutiva de plantas tem aumentado consideravelmente, principalmente em função de trabalhos desenvolvidos com plantas-modelo. Todavia, a informação produzida nessas espécies nem sempre pode ser aplicada a citrus, fundamentalmente porque citrus é uma cultura arbórea perene com uma biologia reprodutiva muito peculiar e incomum. A regulação do crescimento e desenvolvimento do fruto em citrus é um fenômeno complexo e dependente de muitos fatores externos e internos que podem operar tanto seqüencialmente como simultaneamente. Os elementos e mecanismos pelos quais estímulos ambientes e endógenos afetam o crescimento do fruto vêm sendo interpretados, e esse conhecimento pode auxiliar a prover ferramentas que permitiriam otimizar a produção per se, além da obtenção de frutos com maior valor nutricional, o objetivo precípuo da Industria de Citrus. Neste artigo, revisam-se os avanços que vêm ocorrendo na fisiologia da frutificação de citrus durante os últimos anos; apresenta-se, também, o status atual de pesquisas mais relevantes nessa área.

In this paper, the long term observation of plants originating from control and cryopreserved stabilized polyembryonic cultures (SPCs) of six elite oil palm clones was carried out. Survival of plantlets in the nursery was monitored, then a series of vegetative and floral characteristics of over 440 palms were studied for up to 12 years after field transfer in Côte d'Ivoire. The six clones tested showed an average recovery of 34% after freezing in liquid nitrogen. The average survival in the nursery of plantlets originating from pretreated and dehydrated and from cryopreserved SPCs was higher than that of control SPCs. Palm trees originating from control SPCs were found to flower earlier than those originating from pretreated and dehydrated and from cryopreserved SPCs. This delay in flowering disappeared progressively and all palms had flowered 3 years after planting regardless of the SPC treatment. Abnormal palms were observed in one clone only. With this clone, the percentage of abnormal palms originating from cryopreserved SPCs was significantly lower (5%) than that measured on palms originating from control SPCs (29%).

Des records de précocité de floraison pour le département de l'Hérault dans le sud de la France ont été relevés en janvier 2007 pour l'espèce d'orchidée Ophrys lupercalis. Le rôle du réchauffement global et les conséquences éventuelles sur les populations de ces orchidées sont discutés.

International audience; In bread wheat (Triticum aestivum L.), the simultaneous improvement of both yield and grain protein is difficult because of the strong negative relationship between these two traits. However, some genotypes deviate positively from this relationship and this has been linked to their ability to take up nitrogen (N) during the post-flowering period, regardless of their N status at flowering. The physiological and genetic determinants of post-flowering N uptake relating to N satiety are poorly understood. This study uses semi-hydroponic culture of cv. Récital under controlled conditions to explore these controls. The first objective was to record the effects of contrasting N status at flowering on post-flowering nitrate (NO₃⁻) uptake under non-limiting NO₃⁻ conditions, while following the expression of key genes involved in NO₃⁻ uptake and assimilation. We found that post-flowering NO₃⁻ uptake was strongly influenced by plant N status at flowering during the first 300-400 degree-days after flowering, overlapping with a probable regulation of nitrate uptake exerted by N demand for growth. The uptake of NO₃⁻ correlated well with the expression of the gene TaNRT2.1, coding for a root NO₃⁻ transporter, which seems to play a major role in post-flowering NO₃⁻ uptake. These results provide a useful knowledge base for future investigation of genetic variability in post-flowering N uptake and may lead to concomitant gains in both grain yield and grain protein in wheat.

The genus Prosopis contains many valuable, long-lived, multi-purpose legume trees, some of which are also invasive species. The time of first flowering is important for increasing production of sweet, protein-rich pods in plantations, especially under short rotations, and affects the rate of spread as a weed. Trees generally begin flowering at 3–5 years of age. However, seedlings from a small seedlot collected from an introduced population in southern Mauritania were observed to begin flowering at 3–4 months after germination. This is unknown in the native range of any Prosopis species, and appears to represent a major evolutionary event triggered after naturalization. This paper reports a detailed investigation with seed collected from Aleg, Brakna region, Mauritania, in 1998 (Prosopis sp. ‘Aleg’). Two experiments were established, in glasshouses at Cirad, Montpellier, France, and Coventry University, UK. Flowering began at the two sites 104 and 169 days after sowing, respectively, and 97.5% of plants had flowered at Coventry after 306 days. Flowers produced abundant pollen with 50–60% viability indicated by FDA staining and 40–50% germination on an artificial medium. No pods were formed. All plants analysed were diploid. Morphologically, these juvenile plants were similar to American species of section Algarobia, and exhibited leaf characters typical of P. pallida. However, due to the large variation in morphology within this section of the genus, further studies are required to confirm the actual species. This is the first record of precocious flowering in Prosopis, and has been found only in a single, introduced population. Implications for genetic improvement of tropical Prosopis, and particularly the spread of these species as invasive weeds, are discussed. Such a life history shift in the increased reproductive ability of a species following introduction, with potentially significant environmental effects, may not be restricted to Prosopis and merits further detailed investigation.

Cette mission en république d'Haïti avait essentiellement pour objet d'apporter une analyse critique et un appui au SNS en ce qui concerne les aspects variétaux et l'état sanitaire des différentes ignames cultivées en Haïti. Une tournée dans une des principales zones de culture d'ignames (Grande anse, Sud, Sud-est et Ouest) a permis de se faire une idée de la diversité variétale des ignames et d'y rechercher, notamment, des plantes florifères particulièrement intéressantes pour utilisation en création variétale. Une forte érosion génétique, expliquée en partie par la forte présence des principales maladies (anthracnose sur Dioscorea alata, viroses), a été constatée. Une stratégie visant à accompagner et relancer la production d'igname de qualité est proposée. Elle passe notamment par la sauvegarde et la valorisation des ressources génétiques locales et par l'introduction de ressources exogènes sous forme de clones élites ou de graines non sélectionnées.

Parents and progenies genetic diversity, and male and female contributions to the seed crop were assessed in three experimental Prunus avium seed orchards. Collected data were used to compare different effective population sizes, based on phenological, seed crop and paternity analysis. Our results did not show any difference of genetic diversity between parents and progenies. A limited pollen pollution was detected. We showed that distance and coflowering among clones had a significant effect on effective pollination, and a significant effect of the production of flowers was revealed in one of the seed orchards. Our study also revealed a quite low number of effective size of fathers per mother, but high effective sizes of mothers, fathers and parents at the level of the seed orchard. Finally, the calculation of effective size of mothers, fathers and parents was not highly modified when having the complete information based on the paternity analysis., La diversité génétique des parents et de leurs descendants, ainsi que les contributions mâle et femelle à la récolte de graines ont été estimées dans trois vergers à graines expérimentaux de Prunus avium. Les données collectées ont été utilisées pour comparer différentes tailles de population efficace, en se basant sur l'analyse de la phénologie, de la récolte de graines et de la paternité. Nos résultats n'ont pas montré de différence de diversité génétique entre les parents et les descendants. Une pollution pollinique limitée a été mise en évidence. Nous avons montré un effet significatif de la distance et de la cofloraison entre clones sur la pollinisation efficace, ainsi qu'un effet significatif de la production de fleurs dans l'un des vergers à graines. Notre étude a aussi révélé un faible nombre efficace de pères à l'échelle de chaque mère, et un nombre efficace de mères, de pères et de parents important à l'échelle du verger à graines. Enfin, le calcul des tailles efficaces de pères et de parents à l'échelle du verger à graines n'a pas été fortement influencé par le fait d'avoir l'information totale de contribution donnée par l'analyse de paternité.

Le décalage entre les floraisons mâle et femelle (ASI) est lié génétiquement à la perte de rendement en déficit hydrique, puisque les génotypes présentant les ASI les plus élevés en déficit hydrique sont ceux qui maintiennent le moins bien le rendement. Le présent travail montre tout d’abord que les variations d’ASI sont liées à des variations de vitesse de croissance des soies. L’analyse spatiale et temporelle des divisions et de l’extension des cellules dans les soies suggère une base biologique à l'ASI : elle correspond à la durée entre la fin des divisions cellulaires dans les soies, synchrone avec la déhiscence des anthères, et le début de l'arrêt de la croissance dans la partie apicale des soies, synchrone avec la sortie des soies. Une méthode de mesure in situ de la croissance des soies a été mise au point. L’analyse des cinétiques de vitesse de croissance des soies indique une forte similitude avec les cinétiques de croissance foliaire. La réponse de la croissance des soies à la température, au déficit hydrique du sol et de l’air a été quantifiée, et la variabilité des paramètres des courbes de réponse, selon le génotype, a été examinée. Les résultats obtenus suggèrent que les mécanismes impliqués dans le contrôle de l’extension des tissus en réponse au déficit hydrique du sol et de l’air sont communs aux feuilles et aux soies, avec un rôle central des processus hydrauliques. Ils confortent l’hypothèse d’un déterminisme génétique commun aux deux tissus pour le maintien de la croissance en conditions de sécheresse., Drought tolerance in maize is associated to the maintenance of a short anthesis-to-silking interval (ASI) under water stress. The present study firstly shows that the variations of ASI in response to soil and air water deficits are explained by variations of silk elongation rate. A spatial and temporal analysis of cell division and elongation in silk tissues suggests a biological basis for ASI : it corresponds to the duration between the end of cell division in the silk, coinciding with anthesis, and the arrest of cell growth in the apical part of the silk, coinciding with silking. A non-destructive method was developed to continuously record silk elongation rate. Kinetics of silk elongation rate shared strong similarities with those of leaf growth. The response of silk growth to drought was quantified as a function of temperature, soil water potential and air evaporative demand. The variability of the parameters was examined across genotypes with contrasted ASI or leaf growth under water deficit. Our results suggest that the mechanisms involved in the control of tissue elongation in plants subjected to soil and air drying could be common to leaves and silks, and mainly relevant to hydraulics. They reinforce the hypothesis of a common genetic determinism for the maintenance of elongation in both tissues under drought

Acorn production is often too low and irregular to satisfy the needs in Forest Reproductive Materials for planting. Yet, oak flowers rather regularly. The paper describes the reproduction cycle of white oak, analyzes the causes of failure of acorn production and shows the results of fertilization trials set up in selected stands of sessile and pedonculate oak. On average, this simple treatment resulted in a 100% increase in acorn production without any losses in quality., L'irrégularité notoire des glandées induit une pénurie chronique des semences nécessaires aux plantations de chêne. Or, les floraisons sont assez régulières. L'article décrit le cycle reproducteur des chênes blancs, analyse les causes d'échec de la fructification et présente les résultats d'essais de fertilisation réalisés dans quatre peuplements classés de chênes sessile et pédonculé. Ce traitement simple a permis de doubler la production de glands, sans perte de qualité.

Thermal time models express the temperature dependence of plant or organ development and are mostly used to predict phenological events over time. The most general thermal time model is the accumulation of daily mean temperatures above a threshold temperature [theta] during a development phase. The predictive quality of the model depends on the value of the parameter [theta]. However, the physiological and mathematical bases for [theta] estimation are sometimes forgotten, leading to questionable interpretation. Threshold temperatures [theta] have been estimated for the flowering to harvest phase of two tropical fruit species. For strawberry guava, a large and variable set of data, collected in orchards at different elevations, was available, and [theta] was estimated by five different statistical methods. For mango, few data were available and [theta] was estimated as a parameter of the fruit growth curve. Estimated [theta] values were - 3.9°C for strawberry guava and 20.0°C for mango. For strawberry guava, discrepancies between the model and data were significantly correlated with orchard elevation, fruit set ratio and flowering to harvest duration, but not with the mean temperature of the phase. These results are discussed with a special emphasis on three points which could improve thermal time models and their use: the significance of the threshold temperature [theta], the domain of validity of the model, and the influence of factors other than temperature on plant development. (Resume d'auteur)

Grapevine (Vitis vinifera L.) is naturally affected by flower abscission in various extents depending on cultivars, meaning that flowers abort during their development. This abscission may be caused by both physiological and environmental factors. In this context, we focused on the analysis of carbon metabolism in the inflorescence during flower development using the sensitive Gewurtzraminer (GW) and the low sensitive Pinot noir (PN) cultivars grow in vineyards. In parallel, we optimized a protocol to obtain flowers under controlled conditions enabling to get inflorescences that mimic vineyard grown inflorescence development. Numerous differences were detected between GW and PN i.e. male and female organs develop more precociously in PN than in GW. Carbohydrate (starch, sucrose, glucose and fructose) levels in inflorescences differ between the two cultivars during the whole of floral development, especially between stages 15 and 17, corresponding to the key male and female meiosis. At this stage, one of the main differences consist in the presence of starch in the ovules of PN, in the contrary of GW. The assay of carbohydrate related enzyme activities confirmed that between stages 15 and 17 PN and GW metabolize sugars differently. Besides, we have shown that photosynthesis occurs in the inflorescence with different intensities in PN and GW, in particular between stages 15 and 17. The greater tolerance of PN to flower abscission may thus result in different carbohydrate metabolism enabling to avoid sugar starvation during meiosis when environmental stress occurs. In order to confirm the impact of sugar physiology during flower development, we did perturb carbohydrate metabolism acting on reserve accumulation in perennial organs and using both vineyard grown plants and fruiting cuttings. Our results indicate in both cvs. that reserve restoration during the year n conditions the number of inflorescences per plant and the number of flowers per inflorescence developing during the year n+1.; La vigne (Vitis vinifera L.) est naturellement affectée par l'abscission et la chute des fleurs (coulure) durant le développement des inflorescences. Ce phénomène est dépendant de facteurs physiologiques et environnementaux et tous les cépages y sont sensibles à un degré plus ou moins important. Les causes exactes de la coulure demeurent encore inconnues à ce jour. Dans ce contexte, nous nous sommes focalisés sur le métabolisme des sucres dans les inflorescences durant le développement des fleurs en utilisant des cépages de sensibilité différente à la coulure. Nous avons travaillé sur des plantes cultivées au vignoble et nous avons optimisé un système expérimental mimant le développement floral en conditions contrôlées à partir de boutures fructifères.De nombreux critères de différenciation existent entre le Gewurztraminer (GW), cépage sensible à la coulure et le Pinot noir (PN), cépage peu sensible. Ainsi, les structures reproductrices mâles et femelles de PN se développent plus précocement que celles de GW. De plus, les teneurs en glucides (amidon, saccharose, glucose et fructose) des inflorescences diffèrent entre les deux cépages lors du développement floral, notamment entre les stades 15 et 17, période des méioses polliniques et ovulaires et stades clés dans le développement reproducteur. Les différences constatées se manifestent, entre autres, par la présence d'amidon dans les ovules de PN, contrairement à ceux du GW. La mesure des activités enzymatiques du métabolisme glucidique ont confirmé que, durant la période 15-17, les deux cépages utilisent les sucres de manière différente. Nous avons par ailleurs démontré l'existence d'une photosynthèse nette positive dans les inflorescences des deux cépages, avec des intensités fluctuantes, notamment entre les stades 15 et 17. La tolérance plus importante à la coulure du PN pourrait donc résulter d'un métabolisme glucidique différent, permettant d'éviter toute carence glucidique lors de la méiose en cas de stress environnementaux. Afin de confirmer l'impact de la physiologie des glucides dans le développement floral, nous avons tenté de perturber le métabolisme carboné en agissant sur la mise en réserve dans les organes pérennes, au vignoble et sur boutures fructifères. Les résultats obtenus démontrent dans les deux cépages l'importance de la mise en réserves de l'été n sur la floraison de l'année n+1 et ce, à la fois sur le nombre d'inflorescences par pied et sur le nombre de fleurs par inflorescence.

http://www.sciencedirect.com/science?ₒb=IssueURL&_tockey=%23TOC%235880%232005%23999509996%23596026%23FLA%23&ₐuth=y&view=c&ₐcct=C000056834&_version=1&_urlVersion=0&_userid=2292769&md5=87e7f8be94f92a8574da566c600ce631; International audience; Models that combine Markovian states with implicit geometric state occupancy distributions and semi-Markovian states with explicit state occupancy distributions, are investigated. This type of model retains the flexibility of hidden semi-Markov chains for the modeling of short or medium size homogeneous zones along sequences but also enables the modeling of long zones with Markovian states. The forward-backward algorithm, which in particular enables to implement efficiently the E-step of the EM algorithm, and the Viterbi algorithm for the restoration of the most likely state sequence are derived. It is also shown that macro-states, i.e. series-parallel networks of states with common observation distribution, are not a valid alternative to semi-Markovian states but may be useful at a more macroscopic level to combine Markovian states with semi-Markovian states. This statistical modeling approach is illustrated by the analysis of branching and flowering patterns in plants.

Ideally, the Forest Reproductive Materials (FRM) are genetically consistent with the Basic Materials (BM) they come from. Therefore, seed orchards should have a panmictic reproduction regime, which means that all the genotypes should produce the same number of gametes and that all the gametes should mate at random. However, deviations to panmixis always exist ; they may result in reduced genetic diversity and, finally, in a diminution of both adaptability and genetic gains. This study aims at quantifying these deviations, assessing the impact of seed orchard management and describing the seed lot rating schemes used abroad.According to the literature, genetic variability of male and female fertility has a greater influence on FRM genetic quality than flowering asynchrony. This factor was studied in several orchards in several years. In fact, the gap between FRM and BM genetic composition, quantified using the effective number of parents (Ne), proved to be smaller than expected. Moreover, the deviation to panmixis can be reduced by flower stimulation. These treatments and, particularly, the most sophisticated ones, tend to homogenize parental gametic contributions. The first part ends with a presentation of the advantages and drawbacks of various methods likely to be used for the characterization of orchard seed lot genetic quality. Then, this report describes the seed lot rating schemes used in British Columbia (Canada), New Zealand and Australia in order to assess the genetic quality, in terms of performances and diversity, of the seed lots available on the market. Their interest in the French context is discussed., Idéalement, les Matériels Forestiers de Reproduction (MFR) sont génétiquement conformes aux Matériels de Base (MB) dont ils dérivent. Pour cela, les vergers à graines devraient avoir un régime de reproduction panmictique, ce qui signifie que tous les génotypes produisent le même nombre de gamètes et que ces gamètes s'apparient au hasard. Or, il existe toujours des écarts à la panmixie ; ils peuvent conduire à une réduction de la diversité génétique et, par suite, à une diminution des capacités d'adaptation et des gains génétiques. Cette étude vise à quantifier les écarts à la panmixie, à évaluer l'impact des pratiques de gestion en vergers et à présenter des systèmes de certification de MFR utilisés à l'étranger.D'après la bibliographie, la variabilité génétique de fertilité mâle et femelle a un impact plus important que les décalages phénologiques sur la qualité génétique des MFR. Ce facteur a été étudié dans plusieurs vergers et au cours de plusieurs années de floraison. Il s'avère que les distorsions entre les compositions des MFR et des MB, quantifiées en utilisant l'indicateur Ne (taille de la population efficace), sont moins importantes qu'on ne l'imaginait initialement. D'autre part, nous démontrons que les écarts à la panmixie peuvent être réduits en mettant en ½uvre des techniques d'induction florale. Ces traitements tendent en effet à homogénéiser les contributions gamétiques parentales. Cette première partie s'achève par une présentation des avantages et inconvénients des méthodes envisageables pour caractériser la qualité génétique de récoltes en vergers. Ce rapport se poursuit par une description des systèmes de certification mis en place en Colombie-Britannique (Canada), en Nouvelle-Zélande et en Australie pour estimer la qualité génétique, en termes de performances et de diversité, des lots de graines disponibles sur le marché. Nous discutons ensuite leur pertinence dans le contexte des vergers à graines français.

L'activité thermogénétique des inflorescences de populations sauvages d'Alocasia macrorrhizos (L.) G. Don a été enregistrée à Espiritu Santo (Vanuatu, Pacifique Sud), entre décembre 2002 et février 2003, puis entre février 2004 et mars 2004. Les températures ont été mesurées à l'aide de six thermocouples cuivre-constantan (type T) de taille infra-millémétrique, reliés à une centrale d'acquisition automatique Campbell Scientific 10X. La période thermogénétique dure de 36 à 42 heures et ne fut détectée que sur la partie mâle et sur l'appendice stérile. On enregistre les plus hautes températures sur les appendices stériles. Ces températures commencent à monter lentement avant minuit, et atteignent un pic entre 05h45 et 06h00, lorsque l'odeur de l'inflorescence devient plus intense. La température maximale moyenne des 59 inflorescences mesurées était de 43,9 ± 0,6 °C. Le maximum absolu fut de 47,4 °C. L'écart maximal à la température ambiante fut de 25,6 °C. L'activité thermogénétique de la partie mâle démarrait 10 à 15 heures avant que l'inflorescence ne devienne très odorante, et s'arrêtait 2 à 3 heures après la libération du pollen. Deux pics furent enregistrés: le premier apparaissait 15 min après celui de l'appendice stérile, alors que le deuxième apparaissait au moment de la libération du pollen. Les insectes visiteurs les plus abondants étaient des perce-oreilles (Labidura truncata Kirby, Labiduridae, Dermaptera). La production de graines était extrêmement rare.

• Background and Aims Tillering is an essential factor when estimating yield, but investigations rarely include both the temporal and spatial changes that occur in tillers. This study analyses the morphology and development dynamics of each tiller, based on its topological location, the timing of appearance and main stem development stage. • Methods An indica cultivar of rice, ‘Ir64’, glasshouse-grown (25/20 °C, 12 h photoperiod), was used to examine the emergence, phenology and morphology of each axis starting at the third leaf stage up to heading. • Key Results Little variability was observed in the structural and morphological characteristics of the tillers, and the rice population appeared to be hierarchical. Blade length initially increased with leaf rank and then decreased sharply for the last three leaves. The number of phytomers per axis decreased with branching order and rank. An analysis of plant dynamics showed synchronous emergence of the leaves on the main stem and on the tillers up to flowering. Axillary bud development into tillers depended on their topological location and plant developmental stage. • Conclusions The timing and frequency of flowering tillers complied with rules of priority depending on their order, rank and emergence time. Precise description of plant topology in grasses is a useful tool that can be used to quantify growth events and predict tillering in terms of location, structure and fate according to growing conditions.

Grapevine (Vitis vinifera L.) is naturally affected by flower abscission in various extents depending on cultivars, meaning that flowers abort during their development. This abscission may be caused by both physiological and environmental factors. In this context, we focused on the analysis of carbon metabolism in the inflorescence during flower development using the sensitive Gewurtzraminer (GW) and the low sensitive Pinot noir (PN) cultivars grow in vineyards. In parallel, we optimized a protocol to obtain flowers under controlled conditions enabling to get inflorescences that mimic vineyard grown inflorescence development. Numerous differences were detected between GW and PN i.e. male and female organs develop more precociously in PN than in GW. Carbohydrate (starch, sucrose, glucose and fructose) levels in inflorescences differ between the two cultivars during the whole of floral development, especially between stages 15 and 17, corresponding to the key male and female meiosis. At this stage, one of the main differences consist in the presence of starch in the ovules of PN, in the contrary of GW. The assay of carbohydrate related enzyme activities confirmed that between stages 15 and 17 PN and GW metabolize sugars differently. Besides, we have shown that photosynthesis occurs in the inflorescence with different intensities in PN and GW, in particular between stages 15 and 17. The greater tolerance of PN to flower abscission may thus result in different carbohydrate metabolism enabling to avoid sugar starvation during meiosis when environmental stress occurs. In order to confirm the impact of sugar physiology during flower development, we did perturb carbohydrate metabolism acting on reserve accumulation in perennial organs and using both vineyard grown plants and fruiting cuttings. Our results indicate in both cvs. that reserve restoration during the year n conditions the number of inflorescences per plant and the number of flowers per inflorescence developing during the year n+1., La vigne (Vitis vinifera L.) est naturellement affectée par l'abscission et la chute des fleurs (coulure) durant le développement des inflorescences. Ce phénomène est dépendant de facteurs physiologiques et environnementaux et tous les cépages y sont sensibles à un degré plus ou moins important. Les causes exactes de la coulure demeurent encore inconnues à ce jour. Dans ce contexte, nous nous sommes focalisés sur le métabolisme des sucres dans les inflorescences durant le développement des fleurs en utilisant des cépages de sensibilité différente à la coulure. Nous avons travaillé sur des plantes cultivées au vignoble et nous avons optimisé un système expérimental mimant le développement floral en conditions contrôlées à partir de boutures fructifères.De nombreux critères de différenciation existent entre le Gewurztraminer (GW), cépage sensible à la coulure et le Pinot noir (PN), cépage peu sensible. Ainsi, les structures reproductrices mâles et femelles de PN se développent plus précocement que celles de GW. De plus, les teneurs en glucides (amidon, saccharose, glucose et fructose) des inflorescences diffèrent entre les deux cépages lors du développement floral, notamment entre les stades 15 et 17, période des méioses polliniques et ovulaires et stades clés dans le développement reproducteur. Les différences constatées se manifestent, entre autres, par la présence d'amidon dans les ovules de PN, contrairement à ceux du GW. La mesure des activités enzymatiques du métabolisme glucidique ont confirmé que, durant la période 15-17, les deux cépages utilisent les sucres de manière différente. Nous avons par ailleurs démontré l'existence d'une photosynthèse nette positive dans les inflorescences des deux cépages, avec des intensités fluctuantes, notamment entre les stades 15 et 17. La tolérance plus importante à la coulure du PN pourrait donc résulter d'un métabolisme glucidique différent, permettant d'éviter toute carence glucidique lors de la méiose en cas de stress environnementaux. Afin de confirmer l'impact de la physiologie des glucides dans le développement floral, nous avons tenté de perturber le métabolisme carboné en agissant sur la mise en réserve dans les organes pérennes, au vignoble et sur boutures fructifères. Les résultats obtenus démontrent dans les deux cépages l'importance de la mise en réserves de l'été n sur la floraison de l'année n+1 et ce, à la fois sur le nombre d'inflorescences par pied et sur le nombre de fleurs par inflorescence.

En: XIII GREMPA Meeting on almonds and pistachios = XIIIème Réunion du GREMPA sur l'amandier et le pistachier . Zaragoza : CIHEAM-IAMZ, 2005. Eds: Oliveira M.M., Cordeiro V.-- Meeting of the Mediterranean Research Group for Almond and Pistachio, 2003/06/01-05, Mirandela (Portugal).-- 6 pages, 4 tables., [EN] The correlations between seed germination or leafing time and flowering time in almond [P. dulcis (Mill.) D.A. Webb] were studied in a population of 502 seedlings from 13 families. The aim of the study was to discover the possibilities of an early selection of those seedlings with late flowering in relation to germination of seeds or leafing time in the following year. The crosses were conducted in 1997. The seeds obtained were germinated by conventional stratification at 7°C, and the number of weeks necessary for the germination of each seed recorded. The trees were planted in 1998. Between 1999 and 2002 their leafing time was recorded, and in 2001 and 2002 also their flowering time. The results indicated that these characteristics bear a relation when considering the population globally, but with a high variability. However, within each family, the correlations between these characteristics were not important and, in most cases, not significant. In the case of germinationflowering, the lack of correlation seems to be the consequence of the germination depending mainly on the female parent. In the case of leafing-flowering, the lack of correlation was due to the positive or negative correspondence between leafing and flowering and to the genotype x environment interaction. In our opinion, to obtain seedlings with an extra-late flowering time, the selection of parents with very late flowering time is essential, with subsequent selection of the seedlings during their first flowering. An early selection regarding the leafing period could be applied with a certain degree of success when, for any reason, interested in selecting late-flowering trees coming from parents with very late and very early-flowering periods. In such cases, the high variability expected could compensate, to a certain degree, for the differences between leafing and flowering., [FR] "Sélection précoce d'amandiers à floraison tardive". Les corrélations entre la germination de la graine ou la date de débourrement et la date de floraison chez l'amandier [P. dulcis (Mill.) D.A. Webb] furent étudiées dans une population de 502 plantes issues de 13 familles. L'objectif de l'étude était de découvrir les possibilités d'une sélection précoce de ces plantes ayant une floraison tardive en relation avec la germination des graines ou la date de débourrement dans l'année suivante. Les croisements furent réalisés en 1997. Les graines obtenues ont germé selon une stratification conventionnelle à 7°C, et le nombre de semaines nécessaires à la germination de chaque graine est enregistré. Les arbres furent plantés en 1998, et leur date de débourrement enregistrée entre 1999 et 2002, ainsi que leur date de floraison en 2001 et 2002. Les résultats indiquèrent que les caractéristiques ont mis en évidence une relation si l'on considère la globalité de la population, mais avec une forte variabilité. Cependant, dans chaque famille, les corrélations entre ces caractéristiques se sont avérées peu importantes et dans de nombreux cas, non signifiantes. Dans le cas de la germination-floraison, la faible corrélation semble être la conséquence du fait que la germination soit contrôlée principalement par le parent femelle. Dans le cas du débourrement-floraison, la faible corrélation serait due à une asynchronie positive ou négative entre le débourrement et la floraison, et aussi à l'interaction entre le génotype et l'environnement. Selon nous, afin d'obtenir des sélections aux dates de floraison très tardives, la sélection de parents avec une date de floraison très tardive est essentielle, avec la sélection de plantes pendant leur première floraison. Une sélection précoce prenant en compte la période de débourrement pourrait être appliquée avec un certain taux de réussite quand, quelle que soit la raison, nous voulons obtenir des sélections très tardives à partir d'un croisement entre un géniteur très précoce et un autre très tardif. Dans ce cas, la grande variabilité attendue pourrait compenser, à un certain degré, des différences entre le débourrement et la floraison., This work has been financed by the project AGL2001-1054-C03-01 ("Mejora Genética del Almendro") from the Spanish Ministry of Science and Technology. The authors also acknowledge the support of the Spanish Ministry of Science and Technology for the contract of Dr. P. Martínez-Gómez.

Summary The key parameters of photosynthetic capacity (maximum carboxylation rate ( V cmax ), electron transport capacity ( J max ) and dark respiration rate ( R d )) and the slope ( m ) of the stomatal conductance model of Ball et al. [Progress in photosynthetic research, Martinus Nijhoff, Dordrecht, 1987] were measured for a whole growing season in fully expanded leaves of 12-year-old mango trees cv. Cogshall in La Reunion island. Leaf nitrogen partitioning into carboxylation ( P c ) and bioenergetic ( P b ) pools were computed according to the model of Niinemets and Tenhunen [Plant Cell Environ 1997;20: 845–66]. V cmax , J max , R d , P c and P b remained relatively stable over the whole study period, with the exception of the period of linear fruit growth when J max , R d and P b were slightly lower, and leaf non-structural carbohydrate content higher. During the pre-floral and floral periods, m decreased by more than 50%, indicating an increase in photosynthetic water use efficiency and m increased again during the period of linear fruit growth. Our results show that, in tropical orchard conditions characterized by mild seasonal climatic changes and non-limiting water supply, leaf nitrogen partitioning is rather stable. Our results also advocate for more studies on the effect of phenology on m and photosynthetic water use efficiency, which is of paramount importance for building coupled biochemical models of photosynthetic carbon assimilation.

8 pages, 3 figures.-- Short communication.-- Printed version published Nov 2004., Flower and fruit production of the abundant, tall, long-lived, dioecious, surface-pollinating seagrass species Enhalus acoroides (L.) Royle were estimated at seven sites in the reef flats off Bolinao (NW Luzon, The Philippines) featuring different fragmentation of the seagrass meadows. Fragmentation of the seagrass meadow was quantified as cover of E. acoroides and all seagrass species present in 20×20 m plots. E. acoroides and overall seagrass cover were correlated positively. The proportion of female flowers of E. acoroides that developed a fruit increased sharply as overall seagrass cover was around 50%. Apparent sex ratio bore no relationship with overall seagrass cover. This threshold-type of relationship suggests that fragmentation of seagrass meadows can have a major effect on the reproductive output of this species. A possible mechanism underlying these results would be a non-linear increase of the efficiency of trapping the surface-dispersed pollen with increasing seagrass canopy density. This provides the first evidence based on real data that fragmentation can affect the population dynamics of seagrass species., This work was funded by the INCO-DEV program of the European Commission (project ERBIC18CT980292). C. Billot and F. Alberto acknowledge fellowships from Fundação para a Ciência e Tecnologia (FCT), Portugal.

International audience; Rubus alceifolius Poiret (Rosaceae) was introduced to the island of Réunion in the southeastern Indian Ocean about 1850 and is now highly invasive. This bramble, native from southeastern Asia and Malaysia, has invaded a wide variety of habitats (lowland rainforest, mountain and submountain rainforest, Acacia heterophylla rainforest) from sea level to 1700 m. It is suspected to be monoclonal so, its remarkable success may be due in part to great phenotypic plasticity. On Réunion, bud, flower, fruit and seed production, the duration of the flowering period and the importance of the seed bank were found to be negatively correlated with elevation (50-1500 m a.s.l.). At a lowland site, fruit production in mature stands averaged between 30 and 80 fruits/m2 during 1999 and 2000. No fruit set occurred above 1100 m. This fruit production pattern was similar over two years. Although the number of leaves per unit area is similar along the whole gradient studied, decrease of fruit set in upland areas might be compensated for by an increase in vegetative growth. Temperature variation is very sharp along the elevation gradient and may control the fruit and the seed production. Fruit production allows establishment of new populations all around the island via bird dissemination. Once established, R. alceifolius maintains dense patches that can grow vegetatively. Our results may be relevant for eradication programs that should take into account variation in reproductive strategy in lowland vs. highland habitats.

Strawberry guava naturally bears a heavy crop at the end of the hot and rainy season, with poor fruit quality as a consequence. Nitrogen triggers a floriferous flush in that species, leading to a better off-season production. Because phenological constraints, nitrogen is usually applied just after the heavy natural crop, and the triggered flush is weak and not very floriferous. As carbohydrate availability seems to play a role in the triggered flush, fruit thinning on the natural production thus appeared to be a means to overcome the low response to nitrogen. Two treatments were compared, thinned and unthinned trees, for their effect on the fruit quality of the natural production, and on the characteristics of the triggered flush. Results showed that fruit thinning had a positive effect on the fruit quality of the natural cycle: the mean fruit weight was improved (7.1 g for thinned trees versus 5.4 g for unthinned trees), but total soluble solids were not affected. Fruit thinning also had a positive effect on the intensity and the floriferous quality of the triggered flush, leading to a heavier off-season crop. The overall annual production was not affected by the treatments and was more evenly distributed between the natural and the triggered production cycles on thinned trees, whereas alternate bearing occurred on unthinned trees. The positive effect of thinning on yield steadiness continued during five consecutive production cycles.

L'effet de stress hydriques, exercés durant des phases déterminées à différents moments du cycle de l'arachide a été étudié sur la mise en place des organes reproducteurs. La contrainte affecte l'apparition de ces organes. Les stress hydriques intervenant avant ou au tout début de la formation des gousses retardent leur apparition et limitent temporairement la croissance végétative. En revanche, un stress hydrique au cours de la période d'apparition des gousses arrête de façon irréversible l'accroissement de la biomasse végétative et stoppe l'élaboration de nouvelles gousses. De façon générale, il apparaît qu'une compensation du nombre de gousses par rapport au témoin est possible après la levée de la contrainte si la période d'apparition des gousses est retardée (stress hydriques avant le début de formation des gousses). Elle est impossible dans le cas où les contraintes appliquées ne modifient pas le calendrier de développement des gousses.

Empirical observation seemed to indicate that NPK fertilisation induced a rapid floriferous flush in strawberry guava (Psidium cattleianum), modifying thus its natural phenological cycle. Factors affecting the plant response to fertilisation have been investigated: identification of the nutrient(s) responsible for the flush; effect of the amount of fertiliser and of the plant phenological stage. A complete NPK fertilisation is followed after 30 to 50 days by the emergence of a floriferous flush. Nitrogen was the trigger of this flush, enhancing the rate of flushing branches. The amount of fertiliser or the leaf nitrogen content had no effect on the flush characteristics. The phenological stage had a strong influence on the plant response, with a more intense and less variable flush when fertilisation was applied after a 3 months resting period than just after a harvest. This suggested that the carbohydrate availability was involved in the plant response, in particular its floriferous status. The possibility of triggering production cycles by nitrogen has interesting agronomic consequences, such as off-season production.

Understanding stomatal functioning and its role is important since stomata control both photosynthesis, i.e. the production potential, and transpiration, which in turn influences irrigation management. Moreover, it is well known that stressing conditions which induce stomatal closure are needed for flowering in mango. The first striking feature is that mango seems to be well protected against excessive losses of water through transpiration. Stomatal frequency is high but stomata are small, which allows for quick responses to relevant stimuli. Transpiration curves show that a loss of less than 2% of water can lead to complete stomatal closure. Stomatal conductance, g,, is also very sensitive to the ambient concentration of CO 2 of the air. This is consistent with the close linear relationship we observed between g s and net photosynthesis, A net , all year round. High water availability and humidity of the air, plus the presence of an intense sink activity are needed to achieve the highest g s values. Interestingly measurements of chlorophyll fluorescence did not reveal any photoinhibition in high photosynthetically photon flux density and low gs conditions. The practical consequences of these observations are discussed.

Summary Effect of photoperiod-sensitivity on yield and yield components of three sorghum varieties grown in West Africa West African sorghums are highly photoperiod-sensitive because this character has given them a great evolutionary advantage under the continental climate of the area, with large inter-annual variation in the amount and distribution of rainfall. This adaptation must be maintained in improved varieties for the region. But with the exception of variation in the duration of the vegetative cycle, few studies have examined physiological aspects of photoperiod-sensitivity in tropical cereals and this trait has been generally discarded until now. An ecophysiological study has been carried out on three sorghum varieties representative of material cropped in West Africa to quantify their physiological photoperiod-sensitivity. Experiments were done at Samanko, Mali, under natural environment over 2.5 years. Original conclusions on the development and growth of photoperiod-sensitive sorghum have been found, mainly due to the highly contrasting behaviour of the guinea race variety, which originated from West Africa: - The triggering of panicle initiation depends on both the photoperiod and the rate of change in daylength or of its components the time of sunrise or sunset. - The rates of apical leaf production varies with photoperiod and its variation at emergence, either the rate of change of daylength or the change in the time of sunrise or sunset. Initial developmental rates acquired at emergence remain constant until a sudden slowdown occurring around the date of the initiation of the 23rd leaf. This coincides with the onset of stem elongation, which occurs before panicle initiation. - Internode elongation is triggered by the sufficient availability of biosynthates related with a fast inherent LAI increase. All the developmental and growth rates slow down simultaneously probably as a consequence of the stem trophic competition and in respect with the co-ordination relationships between phytomers that organize the plant architectural cohesion. - When more than 23 leaves are produced trophic competition between organs is minimum and the biomass repartition driven by the demand of organs. On the contrary, when less than 23 leaves are produced, the panicle competes with stem for biosynthates during its development and the first part of its growth. - Panicle size has shown little variation with sowing date due to the antagonistic evolution of the duration and rate of its development varying in a contrary way in relation to photoperiod at emergence. A growth model integrating this knowledge and hypotheses has been developed, calibrated and tested for each of the three varieties. Its utilization, coupled with the acquired physiological knowledge, suggests that tillering and height reduction are probably not the right ways to improve the yield potential of photoperiod-sensitive sorghum. Emphasis has to be put on the de-correlation of the current relation between the potential panicle size and the flowering date of the variety., Résumé Le rôle du photopériodisme dans l'élaboration du rendement de trois variétés de sorgho cultivées en Afrique de l'Ouest Les sorghos d'Afrique de l'Ouest sont très photopériodiques parce que ce caractère leur confère un important avantage évolutif en raison du climat continental de la zone, caractérisé par de fortes variations inter-annuelles du régime pluviométrique. Cette adaptation doit être maintenue dans les variétés améliorées pour la région. Mais en dehors de la variation de la durée du cycle de la phase végétative, les réponses physiologiques à la photopériode ont été peu quantifiées chez les céréales chez lesquelles ce caractère a été contre-selectionné jusqu'à présent. Une étude écophysiologique a été conduite sur 3 variétés de sorgho représentatives du matériel cultivé en Afrique de l'Ouest afin de quantifier la physiologie du photopériodisme. Les expérimentations ont été réalisées en conditions naturelles à Samanko, Mali, pendant 2 années et demi. Plusieurs conclusions originales sur le développement et la croissance des sorghos photopériodiques ont pu être tirées, grâce en particulier aux réponses très marquées de la variété de race guinea, originaire de la région, dont les principales sont : - Le déclenchement de l'initiation paniculaire est sous la double dépendance de la photopériode et du sens de variation de la durée du jour ou de ses composantes, les heures de lever et de coucher du soleil. - Le rythme de production des feuilles par l'apex varie en relation avec la photopériode et ses variations quotidiennes au moment de la levée, durée ou heures de l'aurore et du crépuscule. Il conserve ensuite la valeur initialement acquise jusqu'à un brusque ralentissement aux environs de la date de production de la 23ème feuille, lorsque débute la montaison spontanée en l'absence d'initiation paniculaire. - Le déclenchement de l'élongation des entre-nœuds à cette date est probablement la conséquence de la rapide augmentation du LAI et par conséquent de la biosynthèse. Tous les autres rythmes de développement et de croissance ralentissent simultanément en raison de la concurrence trophique et des relations de coordination entre phytomères qui organisent la cohésion architecturale de la plante. - Lorsque plus de 23 feuilles sont produites la concurrence trophique entre organes est minimale et la répartition de la biomasse est pilotée par la demande potentielle de chacun d'eux. En revanche, en dessous de 23 feuilles la panicule est en concurrence avec la tige pendant son développement et une part de sa croissance. - La taille de la panicule est peu variable en raison de l'évolution antagoniste de la durée et de la vitesse de son développement sur lesquels la photopériode exerce une influence inverse. Un modèle de croissance synthétisant ces connaissances et hypothèses a été calibré et testé pour chacune des variétés. Son utilisation couplée aux connaissances physiologiques acquises permet de conclure à destination des équipes de sélection que le tallage et la réduction de taille ne sont probablement pas de bonnes voies vers l'amélioration du potentiel de rendement des sorghos photopériodiques. L'effort doit essentiellement porter sur la décorrélation de la relation qui lie actuellement la taille potentielle de la panicule à la date de floraison de la variété.

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Results are presented about the effects of fruiting and flowering on leaf nitrogen content and photosynthetic capacity in mango. The relationship between leaf photosynthetic capacity and the total amount of nitrogen per unit leaf area, Na, seems to be a robust one in mango, but the presence of inflorescences changes the origin and slope of the linear relationship between mitochondrial respiration rate and Na. The presence of developing fruits has a positive effect on Na of leaves experiencing the same light regime than control leaves. This effect was found to be mediated mainly by an increase in the mass-to-area ratio of leaves, Ma. On the contrary, the leaf-to-fruit ratio per se has a negative effect on Na by decreasing the leaf nitrogen concentration per unit mass, while Ma remains constant. The possibility of incorporating such effects in a biochemical model of leaf photosynthesis is discussed.