Agritrop

    Ecologie et taxonomie intégrative des moucherons piqueurs du genre Culicoides Latreille (Diptera : Ceratopogonidae) en région Afrotropicale

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    Dans un contexte d'émergence ou de réémergence des maladies à transmission vectorielle, certaines espèces de Culicoides (Diptera : Ceratopogonidae) sont impliquées dans la transmission de certains virus (Reoviridae : Orbivirus) et de nématodes (Onchocercidae : Mansonella) en région Afrotropicale. Cependant, le schéma systématique et taxonomique ainsi que la bio-écologie des espèces d'intérêt vétérinaire restent à explorer. Ce travail de taxonomie intégrative a pour objectifs de réaliser (i) une révision systématique et taxonomique des espèces appartenant à des sous-genres et des groupes d'intérêt à partir de phylogénie moléculaire multi-marqueur et de délimitation d'espèces, et (ii) de développer des outils moléculaires pour l'étude de la bio-écologie des espèces d'intérêt vétérinaire et de la dynamique de leurs populations d'immatures. Nos résultats mettent en évidence (i) la présence de trois clades monophylétiques le groupe d'espèces Imicola, le groupe d'espèces Milnei et le sous-genre Remmia, (ii) une nouvelle espèce pour la science nommée C. sp. #22 et affiliée au sous-genre Avaritia, groupe Imicola, (iii) la présence d'une nouvelle espèce non - décrite nommée C. sp. #54 appartenant au groupe d'espèces Dasyops, sous-genre Avaritia, (iii) d'affilier les groupes d'espèces Similis et Neavei au sous-genre Synhelea et, (iv) de poser l'hypothèse d'une présence d'espèces cryptiques au sein de C. oxystoma (sous-genre Remmia). D'un point de vue bio-écologique, le travail réalisé combinant suivi entomologique et identification moléculaire avec une librairie de séquences barcodes a permis de décrire le comportement trophique de C. imicola , C. kingi et C. oxystoma ainsi que leurs habitats larvaires dans des environnements équins de la zone des Niayes au Sénégal. L'ensemble de ce travail permet de compléter le corpus de connaissances sur le genre Culicoides en région Afrotropicale afin d'améliorer la compréhension de l'épidémiologie des pathogènes transmis et proposer des pistes de recherches pour mieux contrôler les populations immatures et adultes des espèces vectrices afin de mieux anticiper et prévenir des événements sanitaires. (Résumé d'auteur

    Nod factor-independent nodulation in Aeschynomene evenia required the common plant-microbe symbiotic toolkit

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    Nitrogen fixation in the legume-rhizobium symbiosis is a crucial area of research for more sustainable agriculture. Our knowledge of the plant cascade in response to the perception of bacterial Nod factors has increased in recent years. However, the discovery that Nod factors are not involved in the Aeschynomene-Bradyrhizobium spp. interaction suggests that alternative molecular dialogues may exist in the legume family. We evaluated the conservation of the signaling pathway common to other endosymbioses using three candidate genes: Ca2+/Calmodulin-Dependent Kinase (CCaMK), which plays a central role in cross signaling between nodule organogenesis and infection processes; and Symbiosis Receptor Kinase (SYMRK) and Histidine Kinase1 (HK1), which act upstream and downstream of CCaMK, respectively. We showed that CCaMK, SYMRK, and HK1 are required for efficient nodulation in Aeschynomene evenia. Our results demonstrate that CCaMK and SYMRK are recruited in Nod factor-independent symbiosis and, hence, may be conserved in all vascular plant endosymbioses described so far. (Résumé d'auteur

    Formaliser ou sécuriser ? Leçons de l'expérience sénégalaise dans la vallée du Sénégal

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    L'objet de cette communication est d'analyser les mécanismes mis en oeuvre au Sénégal pour améliorer la situation foncière. Il est cependant impossible d'effectuer ce type d'analyse sans la mettre en perspective avec une grille d'évaluation des intérêts et résultats de ces mécanismes. Or, qui dit grille d'évaluation dit " valeur " attribuée aux différents effets potentiels, recherchés ou non désirés. La première partie de notre communication s'attachera donc à identifier les différents " pourquoi " potentiels à l'origine des " comment " mis en oeuvre. C'est grâce à cette première partie que nous pourrons ensuite analyser les mécanismes mis en oeuvre, en situant leurs objectifs et leurs effets par rapport aux différents " pourquoi " possibles. (Résumé d'auteur

    Overexpression of EcGSH1 induces glutathione production and alters somatic embryogenesis and plant development in Hevea brasiliensis

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    Oxidative stress occurring during in-vitro culture is detrimental for clonal propagation by somatic embryogenesis in particular in Hevea brasiliensis. In previous work, overexpression of the gene encoding the cytosolic reactive oxygen species detoxification enzyme HbCuZnSOD led to reduce somatic embryo regeneration in Hevea. In this study, the role of antioxidant was tested by overexpression of the E.coli GSH1 gene involved in glutathione biosynthesis in rubber embryogenic callus lines. Transgenic lines were successfully established and some plants were regenerated. Overexpression of EcGSH1 gene led to glutathione over-accumulation, and affected dramatically the somatic embryogenesis process and plant development. Upon a water deficit treatment, these plants displayed the greatest drop in photosynthetic nitrogen use efficiency, higher proline content, and higher glutathione reductase activity. Changes induced in transgenic lines overexpressing HbCuZnSOD and EcGSH1 were discussed as well as possible applications on plant material propagation, overcoming loss of natural rubber production through Tapping Panel Dryness, and tropical soil remediation. (Résumé d'auteur

    Coupled effect of torrefaction and blending on chemical and energy properties for combustion of major open burned agriculture residues in Thailand

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    Thailand is an agriculture-based country. It produces large amounts of open burned agricultural residues. A strategy to use them as biofuel all year round is to enhance their fuel properties by coupling blending and thermochemical pre-treatment. In this study, the pyrolytic behaviour of major residues (napier grass , rice straw, cassava stalks and corn cob) exposed to a high torrefaction temperature (300°C) was investigated for various blending ratios, i.e. 100:0, 50:50 and 70:30. The release of chlorine was quantified for each biomass blend, including, a new fouling risk index ratio. Also, the synergistic effects of both ignition and burnout temperatures were analysed. Rice starw and napier grass were found to be characterised by a high ash content and so large amounts of solid yield after torrefaction. Raw biomasses and untreated biomass blends were found to be less suitable as biofuel than torrefied biomasses. The ratio K2O:SiO2, indicator of fouling risk during combustion, was found to be low for all torrefied blends. The HHV:Cl ratio, indicator of combustion quality, indicated that NG mixed with RS (50:50 proportion) is the most promising blend. Significant synergetic effects were observed for biomasses mixed before torrefaction. The burnout temperatures for raw and torrefied biomasses were identified in the range 773-787 °C and 786-795 °C. (Résumé d'auteur

    Agrumes (dossier)

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    A socio-geographical approach to the diversity of urban agriculture in a West African city

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    There is a substantial body of literature addressing urban agriculture (UA) and its diversity. But the reasons for this diversity and the perseverance of UA in today's cities are complex, and few studies have been conducted on a regional scale that focuses on the UA dynamics involved. We took this approach in a multi-scale and space-time analysis of UA in the African city of Bobo-Dioulasso (Burkina Faso). In order to identify determinants of the transformations in agriculture within the city and its urban fringe we analyzed interactions from two main perspectives: (i) between urban and agricultural dynamics in both the city and on a regional scale, and (ii) between land status and actor strategies at the intra-urban scale. The analysis is centered on three areas of urban fringe that have been subjected to various land use changes over time and illustrate the different ways that farmers have adapted to urbanization. On a regional scale, results show how agricultural and regional market dynamics foment UA development by providing commercial outlets and producing agricultural inputs. At the local (city) scale, results show how and why different forms of UA have emerged in specific locations that reflect the socio-economic profile of farmers (ranging from autochthonous urban farmers to relatively wealthy urban dwellers), their access to resources, the possibility of intensifying farming activities, and the formal or informal land negotiations and transactions between the various categories of actors. We conclude with a discussion of the theoretical implications of this research and its relevance to public policy. Our analysis underlines the pertinence of comprehensive and qualitative approaches for analyzing the complexity of UA dynamics and enhancing the position of agriculture in land planning for geographically-specific urban contexts. (Résumé d'auteur
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