Le Cirad en Amazonie

Ce document recense et présente l'ensemble des activités menées par le Cirad en Amazonie depuis une vingtaine d'années. Ces activités concernent la connaissance et la gestion des ressources naturelles, l'analyse des dynamiques en cours et la participation à l'élaboration d'une agriculture durable. Pour chaque thème sont présentés la problématique générale, les différents volets de recherche entrepris par le Cirad, une bibliographie et les missions effectuées par les chercheurs. (Résumé d'auteur

Time-Resolved characterization of InAsP/InP quantum dots emitting in the C-band telecommunication window

The dynamic response of InAsP quantum dots grown on InP(001) substrates by low-pressure Metalorganic Vapor Phase Epitaxy emitting around 1.55 $\mu$m, is investigated by means of time-resolved microphotoluminescence as a function of temperature. Exciton lifetime steadily increases from 1 ns at low temperature to reach 4 ns at 300K while the integrated photoluminescence intensity decreases only by a factor of 2/3. These characteristics give evidence that such InAsP/InP quantum dots provide a strong carrier confinement even at room temperature and that their dynamic response is not affected by thermally activated non-radiative recombination up to room temperature

Different outcome of sarcoglycan missense mutation between human and mouse

Sarcoglycanopathies are rare autosomic limb girdle muscular dystrophies caused by mutations in one of the genes coding for sarcoglycan (α, β, δ, and γ-sarcoglycans). Sarcoglycans form a complex, which is an important part of the dystrophin-associated glycoprotein complex that protects sarcolemma against muscle contraction-induced damages. Absence of one of the sarcoglycan at the plasma membrane induces the disappearance of the whole complex and perturbs muscle fiber membrane integrity. We previously demonstrated that point mutations in the human sarcoglycan genes affects the folding of the corresponding protein, which is then retained in the endoplasmic reticulum by the protein quality control and prematurely degraded by the proteasome. Interestingly, modulation of the quality control using pharmacological compounds allowed the rescue of the membrane localization of the mutated sarcoglycan. Two previously generated mouse models, knock-in for the most common sarcoglycan mutant, R77C α-sarcoglycan, failed in reproducing the dystrophic phenotype observed in human patients. Based on these results and the need to test therapies for these fatal diseases, we decided to generate a new knock-in mouse model carrying the missense mutation T151R in the β-sarcoglycan gene since this is the second sarcoglycan protein with the most frequently reported missense mutations. Muscle analysis, performed at the age of 4 and 9-months, showed the presence of the mutated β-sarcoglycan protein and of the other components of the dystrophin-associated glycoprotein complex at the muscle membrane. In addition, these mice did not develop a dystrophic phenotype, even at a late stage or in condition of stress-inducing exercise. We can speculate that the absence of phenotype in mouse may be due to a higher tolerance of the endoplasmic reticulum quality control for amino-acid changes in mice compared to human

Small scale palm oil producers and supply chains left out from existing certification schemes. [ID781]

Agricultural history explains most of current palm oil production models (organization of actors including oil palm growers and supply chains). An indigenous non-timber forest product in Central Africa which plant was domesticated and integrated into family farming, later joined by colonial industrial plantations. An imported cash crop in Southeast Asia, dominated by industrial producers while smallholders have still to learn artisanal milling to get their autonomy from industrial mills. Also an imported cash crop in Latin America, but whose production models evolved in the confrontation with social agrarian reforms, ending with original 'social models'. These production models have a great diversity of social, economic and environmental impacts. Taking into consideration national specificities (social organization, market, public policies, and environment) and local knowledge regarding palm oil, can we draw lessons learnt from one place to improve palm oil local and global benefits in another? Industrial models are targeted to promote sustainable and zero-deforestation in the palm oil sector, because industries are generally considered as the main culprits of deforestation and land grabbing resulting from oil palm plantations expansion in Southeast Asia. However the expansion patterns in the original producing countries of Africa or in Latin America might prove different. Hence, are certification schemes efficient to shape sustainable oil palm landscapes? In an attempt to answer these questions, we built on pantropical expertise in palm oil producing countries (Indonesia, Central African countries, Colombia) with strong field experience, on literature review and on recent field work in Mexico and Peru, to argue on the inadequacy of certification schemes to reach non-industrial palm oil production models. Furthermore, we highlight some social and economic risks reinforced by this strategy, such as exclusion of smallholders from supply chains, or the development of informal supply chains not regulated regarding working conditions and environment impacts

Molecular characterization of Salmonella Enteritidis : comparison of an optimized multi-locus variable-number of tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis

Salmonella Enteritidis (SE) is a genetically homogenous serovar, which makes optimal subtype discrimination crucial for epidemiological research. This study describes the development and evaluation of an optimized multiple-locus variable number tandem-repeat assay (MLVA) for characterization of SE. The typeability and discriminatory power of this MLVA was determined on a selected collection of 60 SE isolates and compared with pulsed-field gel electrophoresis (PFGE) using restriction enzymes XbaI, NotI, or SfiI. In addition, the estimated Wallace coefficient (W) was calculated to assess the congruence of the typing methods. Selection of epidemiologically unrelated isolates and more related isolates (originating from layer farms) was also based on the given phage type (PT). When targeting six loci, MLVA generated 16 profiles, while PFGE produced 10, 9, and 16 pulsotypes using XbaI, NotI, and SfiI, respectively, for the entire strain collection. For the epidemiologically unrelated isolates, MLVA had the highest discriminatory power and showed good discrimination between isolates from different layer farms and among isolates from the same layer farm. MLVA performed together with PT showed higher discriminatory power compared to PFGE using one restriction enzyme together with PT. Results showed that combining PT with the optimized MLVA presented here provides a rapid typing tool with good discriminatory power for characterizing SE isolates of various origins and isolates originating from the same layer farm

Étudiants adultes et études collégiales à la formation régulière

La présente recherche a été subventionnée par le ministère de l’Éducation et de l’Enseignement supérieur dans le cadre du Programme de recherche et d’expérimentation pédagogique (PREP) de l’Association des collèges privés du Québec (ACPQ)

Can electrical resistivity tomography describe soil structure evolution?

Variations of soil structure is significant for the understanding of water and gas transfer in soil profiles. In the context of arable land, soil structure can be compacted due to either agriculture operation (wheel tracks), or hardsetting and crusting processes. As a consequence, soil porosity is reduced which may lead to decrease water infiltration and to anoxic conditions. Porosity can be increased by cracks formation due to swelling and shrinking phenomenon. We present here a laboratory experiment based on soil electrical characteristics. Electrical resistivity allows a non destructive three dimensional and dynamical analysis of the soil structure. Our main objective is to detect cracks in the soil. Cracks form an electrical resistant object and the contrast of resistivity between air and soil is large enough to be detected. Our sample is an undisturbed soil block 240mm*170mm*160mm with an initial structure compacted by wheel traffic. Successive artificial cracks are generated. Electrodes built with 2 mm ceramic cups permit a good electrical contact at the soil surface whatever its water content. They are installed 15 mm apart and the electrical resistivity is monitored using a dipole-dipole and wenner multi-electrodes 2D imaging method which gives a picture of the subsurface resistivity. The interpreted resistivity sections show the major soil structure. The electrical response changes with the cracks formation. The structure information extracted from the electrical map is in good agreement with the artificially man-made cracks. These first results demonstrate the relevance of high resolution electrical imaging of the soil profile. Further experiments need to be carried out in order to monitor natural soil structure evolution during wetting-drying cycles

Fano Resonances in Mid-Infrared Spectra of Single-Walled Carbon Nanotubes

This work revisits the physics giving rise to the carbon nanotubes phonon bands in the mid- infrared. Our measurements of doped and undoped samples of single-walled carbon nanotubes in Fourier transform infrared spectroscopy show that the phonon bands exhibit an asymmetric lineshape and that their effective cross-section is enhanced upon doping. We relate these observations to electron-phonon coupling or, more specifically, to a Fano resonance phenomenon. We note that only the dopant-induced intraband continuum couples to the phonon modes and that defects induced in the sidewall increase the resonance probabilities.Comment: 5 pages, 4 figures and 1 Supplementary Information File (in pdf

Soil cracks detection by 3D electrical resistivity.

Soil cracks, whose formation are associated to natural climate phenomena such as swelling and shrinking, play an important role in water and gas transfers. Up to now, their 3D structure was characterised either by serial sections (Cousin, 1996) which is a destructive technique or X-ray tomography (Macedo et al., 1998) which is applicable on limited size sample. Three-dimensional electrical resistivity prospecting enables now to monitor crack development and to characterise their geometry without any destruction of the medium under study. Three-dimensional electrical resistivity surveys are commonly gathered by a network of in-line survey arrays, such as Wenner, Schlummberg, or dipole-dipole (Xu and Noel, 1993; Zhou et al., 2002). As emphasized by Meheni et al. (1996) the resulting apparent resistivity maps are often different depending on the array orientation related to an electrical discontinuity. Chambers et al. (2002) underline that in heterogeneous medium 3D electrical resistivity model resolution was sensitive to electrode configuration orientation. Indeed asymmetric bodies or anisotropic material exhibit different behaviours depending on whether the current passes through them in one direction or in another (Scollar et al., 1990). It would be all the more true for medium having very contrasted resistivities like cracking soil. In that case the electrical current does not encounter the same resistance when it passes perpendicular or parallel to the resistant bodies. Measurements of apparent resistivity depend then on the location and orientation of the current source relative to the body under study (Bibby, 1986). Studies conducted by Habberjam and Watkins (1967) emphasized that the square array provide a measurement of resistivity less orientationally dependent than that given by a in-line array investigation. Intending to lead a more 3D accurate inversion, we have chosen to focus our attention on a 3D electrical resistivity data acquisition. We present here a three-dimensional electrical survey carried out by a square array quadripole for characterising the soil cracks network developing during a desiccation period

Seismic oceanography imaging of thermal intrusions in strong frontal regions

The Naval Research Laboratory and collaborating partners carried out two dedicated seismic oceanography field experiments in two very different strong frontal regions. ADRIASEISMIC took seismic oceanography measurements at the confluence of North Adriatic Dense Water advected along the Western Adriatic Current and Modified Levantine Intermediate Water advected around the topographic rim of the Southern Adriatic basin. ARC12 took seismic oceanography measurements in and around the Agulhas Return Current as it curved northwards past the Agulhas Plateau and interacted with a large anticyclone that had collided with the current. Despite one study focused on coastal boundary currents and the other focused on a major Western Boundary Current extension, the complex horizontal structures seen through seismic imaging are tied to the processes of thermal intrusions and interleaving in both systems. Seismic Oceanography provides a unique capability of tracking the fine-scale horizontal extent of these intrusions