Mantle sources and magma evolution beneath the Cameroon Volcanic Line: Geochemistry of mafic rocks from the Bamenda Mountains (NW Cameroon)

International audienceWe report the mineralogy, geochemistry and geochronology of the mafic rocks from the Bamenda Mountains, part of the Cameroon Volcanic Line (CVL), in order to discuss the origin and evolution of the magmas in this part of the CVL. Mafic rocks in the Bamenda Mountains are basanites, basalts, hawaiites and mugearites with an alkaline affinity. K-Ar ages have been obtained on 10 samples and range from 17.6 Myr to present. Trace element and isotopic compositions (Sr-Nd-Pb) show that some samples among the oldest are slightly contaminated by a crustal component with high La/Nb and 87Sr/86Sr ratios and low Pb isotopic ratios. The mafic rocks strongly resemble OIB in their trace element compositions. Some samples possess a positive Sr and Eu anomaly which cannot be explained by a process of plagioclase accumulation. These anomalies are also observed in some pyroxenites found as xenoliths in the Adamawa volcanic province further north. Furthermore, non-contaminated samples have high Pb isotopic ratios and point towards an HIMU component similar to the St. Helena mantle plume. We propose that the Bamenda mafic magmas with positive Sr and Eu anomalies were formed by hybridization of asthenospheric melts with melts formed by the partial melting of pyroxenites. Samples without these anomalies result from the hybridization of the same asthenopheric melts with melts coming from the metasomatized, amphibole-bearing, lithospheric mantle

Experimental cocoa cultivations systems in Cameroon: agronomical and economical performances assessment

On farm trial plots were set up in Cameroon, according to three intercropping designs: cocoa-fruit trees (970 cocoa trees and 160 fruit trees/ha), cocoa-oil palm trees (700 cocoa trees/ha and 120 oil palm trees / ha) and cocoa-coconut trees (810 cocoa trees / ha and 143 coconut trees/ha). Cocoa yield was recorded on 48 of these cocoa trial plots set up in five locations in Cameroon in 2006, 2007 and 2008, and showed a large range of variation (between 200 and 1,450 kg/ha/year) among plots, with an average value of 600 kg/ha/year, close to the yield usually observed on traditional cocoa plots in the central region of Cameroon. Despite their initial higher cocoa tree density, the plots where cocoa is intercropped with fruits trees show a slightly lower yield than the ones intercropped with oil palm or coconut trees. The yield of fruit trees was recorded on two sites (five plots per site) and was found to vary largely between these two sites. The gross revenue from fruits was estimated from information provided by four farmers in the site where fruit yield was higher, and was found to range between 300 and 800 US $/ha/year. In the case of two of the four plots, the cumulated annual gross revenue from cocoa and fruits was found higher than the one expected if the plot had been set up only with cocoa trees, at the cocoa density generally observed in the cocoa plots in this site (1,100 trees/ha). On the other hand, it appears that cocoa cultivation alone would have brought more revenues in the case of the two other plots. The gross annual revenue from oil palm trees, calculated from the information reported by four farmers, was found to range between 300 and 2,300 US$/ha. Two comparisons were made between annual cumulated gross revenues from cocoa and palm oil and 1) estimated revenue from cocoa if the plot was set up only with cocoa trees, at a 1,100 cocoa trees/ha 2) estimated revenue from palm oil if the plot was set up only with oil palm trees, at the recommended density of 169 trees/ha. 1)In the case of two of the four plots, intercropping failed to enhance the revenues from the plot. On the other hand, oil palm trees appeared to dramatically enhance the revenues from one of the other plot, while cocoa alone would have brought more revenue to the last plot. 2) In the case of three of the plots, intercropping cocoa with oil palm generated more revenue than oil palm only at the 169 oil palm trees/ha recommended density, the revenues being equivalent in the forth plot. The three farmers who sat up plots with intercropping cocoa with coconut trees in 2006 and 2007 whether failed to establish the coconut trees or, disappointed by the agronomical and economical of these trees, partially replaced them with oil palm trees. The consequences of these results for intercropping are discussed in the paper. (Résumé d'auteur

Évolution volcanologique du mont Manengouba (Ligne du Cameroun) ; nouvelles données pétrographiques, géochimiques et géochronologiques<br /> Volcanological evolution of the mount Manengouba (Cameroon line), new petrographical, geochemical, and geochronological data

Le mont Manengouba est un complexe volcanique polygénique de la Ligne du Cameroun édifié au Quaternaire, entre 1,55 et 0 Ma, en trois phases principales. La première phase, de 1,55 à 0,7 Ma, correspond à la construction du volcan Elengoum. La deuxième, entre 0,7 et 0,56 Ma, est marquée par l'effondrement de la partie sommitale de l'Elengoum. La troisième, de 0,56 à 0 Ma, voit l'édification du volcan Eboga, puis la formation de la caldeira, et comporte une activité fissurale adventive à partir de 0,48 Ma. Les produits émis définissent une série alcaline sodique, allant des basaltes à néphéline à des trachytes. Toutes ces laves ont évolué par cristallisation fractionnée dans une chambre magmatique périodiquement réalimentée. The mount Manengouba is a polygenic volcanic complex of the Cameroon line, which was built in the Quaternary, between 1.55 and 0 Ma, during three stages. The first stage, from 1.55 to 0.7 Ma, corresponds to the building of the Elengoum volcano. The second, between 0.7 and 0.56 Ma, points to the collapse of the Elengoum summit. The third, from 0.56 to 0 Ma, fits with the erection of the Eboga volcano and its caldera sinking, and, from 0.48 Ma, with the adventive fissural activity. The products define an alkaline sodic series, from nepheline-bearing basalts to trachytes. All the lavas evolved by fractional crystallization in a periodically replenished magmatic chamber

Cocoa variety assessment in on-farm progeny trials in Cameroon

In Cameroon, IRAD and CIRAD have collaboratively set up and implemented a participatory breeding program since 2006, consisting in the assessment of cocoa varieties under cocoa farm conditions. The present communication describes the results obtained so far on progenies compared in three progeny trials set up in 2006 and 2007. The first trial, set up in 2006, is composed of 12 trial plots, and allows the comparative assessment of nine progenies which are currently released to farmers. Data analyses performed on yield and establishment ability showed high performances for the progeny issued from the cross IMC 67 * SNK 109 and low performances for the one issued from the cross T 79/501 * SNK 64. Data analyses performed on mirid damage scores revealed a higher level of susceptibility for the progeny issued from the cross IMC 67 * SNK 109 and a lower one for the progenies issued from the crosses T 79/501 * SNK 64 and IMC 67 * SNK 64. The assessed progenies showed a mean weight of one bean of dried cocoa ranging between 1,17g (SCA 12 * SNK 16) and 1,52g (SNK 109 * IMC 67). The second progeny trial, set up in 2006, composed of four trial plots, allows the comparison between 16 cocoa progenies, issued from: commercially released progenies, progenies recently created at IRAD, progenies issued from on farm selection of promising trees. Data analyses show a higher level of yield for the commercially released progenies and a lower level for progenies issued from on farm selection. Data analyses of tolerance to Phytophthora megakarya, assessed using a leaf inoculation test showed a slightly higher level of tolerance for the progenies recently created at IRAD. The third trial set up in 2007, is composed of six trial plots and allows the comparison between eight progenies: one recently created at IRAD, three commercially released progenies, two issued from on farm selection of promising trees, two issued from trees chosen at random in cocoa farms set up with traditional (german cocoa) or commercial cocoa progenies. Data analyses show a high level of yield for the progeny recently created at IRAD (T 60/887 * POUND 7) and a low level for the progeny issued from traditional varieties (german cocoa). (Résumé d'auteur

Comparative assessment of agronomical performances of six commercial cocoa Varieties in on farm progeny trials in Cameroon

A long term participatory breeding program was launched in Cameroon in 2005, as a key component of a worldwide cocoa breeding project, funded by CFC (Common Fund for Commodities). One activity within this program has consisted in setting up on farm progeny trials in order to assess the performances of commercial cocoa varieties, when tested in on farm conditions. 4,500 cocoa trees, belonging to six commercial varieties (six full-sib progenies issued from bi-clonal seed-gardens) were assessed in 11 progeny trial plots, set up in 2006, in two geographical sites of Cameroon. Cocoa yield data recorded during the period from 2011 to 2015 were analyzed and showed significant differences among progenies, ranging between 830 and 1,480 kg cocoa/ha/year. In addition, 273 cocoa seedlings, sampled in nursery within a mixture of the commercial progenies issued from seed-gardens (CV), have been planted simultaneously with 170 seedlings issued from pods collected in farmers' plots, in three progeny trial plots set up in 2007. 85 of these farmers' seedlings were issued from pods collected on cocoa trees belonging to the traditional amelonado variety (named german cocoa) (GC), while 85 others were issued from pods collected on trees belonging to commercial varieties (half-sibs issued from commercial varieties) (FV). Under the conditions of our trial plots (no permanent shade during the first ten years, because of the simultaneous planting of cocoa and shade trees), GC trees yielded significantly less (450 kg/ha/year) than FV (880 kg/ha/year) and CV trees (910 kg/ha/year). The impact of these results on the future release of commercial cocoa varieties in Cameroon is discussed in this paper. (Résumé d'auteur

Biochemical Reactions Instigating Vision – Parameter Sensitivity Analysis

The purpose of this work is to investigate the sensitivity of parameters involved in a cascade of biochemical reactions occurring in photoreceptor cells in the retina of the eye. This cascade constitutes the first stage of the elaborate process of vision, by which light captured in a photoreceptor generates an electrical signal. It is this signal that travels to the brain enabling vision. Sensitivity on parameters was performed on an ODE model of the biochemical cascade using two methods. One method used SimLab, a statistical sensitivity analysis program. We found that there are at most five important parameters out of the sixteen that affect the production of activated phosphodiesterase (PDE* ) and the photoreceptor (electrical current) response (RR ). Another method performed was to vary each of the sixteen parameters separately over a range and observe the effect on PDE* ; this method also produced five most influential parameters essential to the production of PDE* . While the parameter rankings differed from one method to the other, the five parameters found using partial differential analysis of our ODE model agree with the parameters obtained via SimLab. The second aspect of our problem involved looking at the effect of the variations of parameters on the time at which PDE* and RR attain their maximum values. Only three of the parameters highly affecting variations of PDE* were also found to influence the time-of-peak values

The devices, experimental scaffolds, and biomaterials ontology (DEB): a tool for mapping, annotation, and analysis of biomaterials' data

The size and complexity of the biomaterials literature makes systematic data analysis an excruciating manual task. A practical solution is creating databases and information resources. Implant design and biomaterials research can greatly benefit from an open database for systematic data retrieval. Ontologies are pivotal to knowledge base creation, serving to represent and organize domain knowledge. To name but two examples, GO, the gene ontology, and CheBI, Chemical Entities of Biological Interest ontology and their associated databases are central resources to their respective research communities. The creation of the devices, experimental scaffolds, and biomaterials ontology (DEB), an open resource for organizing information about biomaterials, their design, manufacture, and biological testing, is described. It is developed using text analysis for identifying ontology terms from a biomaterials gold standard corpus, systematically curated to represent the domain's lexicon. Topics covered are validated by members of the biomaterials research community. The ontology may be used for searching terms, performing annotations for machine learning applications, standardized meta-data indexing, and other cross-disciplinary data exploitation. The input of the biomaterials community to this effort to create data-driven open-access research tools is encouraged and welcomed.Preprin

Parasitological prevalence of bovine trypanosomosis in the Faro and Deo division valley of the Adamaoua plateau, Cameroon

A cross sectional survey to determine the distribution and prevalence of trypanosomosis was conducted in the Faro and Deo division valley, on the Adamaoua Plateau in Cameroon. A total of 334 adult cattle from 5 sedentary herds were examined in 5 villages. Dark field buffy coat method, as well as stained thin blood film examination and packed cell volume (PCV) evaluation were the diagnostic techniques used. The overall prevalence of bovine trypanosomosis in the area was 23%. Among the positive animals, 44 (57.1%), 26 (33.8%), 5 (6.5%) and 2 (2.6%) were due to Trypanosoma congolense, Trypanosoma brucei, Trypanosoma vivax and mixed infection (T. congolense and T. brucei) respectively. The mean PCV of the positive and negative animals ranged between 21.1-27% and 28.2-30.1% respectively. The mean PCV of negative animals (29.1±0.7%) was significantly higher than the mean PCV of positive animals (24.2±2.5%) (P< 0.005). In view of the high risk of trypanosomosis, in the area, an integrated intervention approach to which combines the strategic application of appropriate tsetse fly control methods to reduce host fly contact and chemotherapy and chemoprophylaxis against trypanosomosis is recommended.© 2009 International Formulae Group. All rights reserved.Key words: Adamaoua, Cameroon, Cattle, Prevalence, Trypanosomosis, Tsetse

Composition, Structure And Diversity of The Vegetation of The Manda National Park (MNP) in The Moyen-Chari Province of Chad

The present work was initiated in order to evaluate the composition, structure and diversity of the flora of the Manda National Park (MNP) to contribute to its sustainable management. The survey area is a square plot of 1m x 1m and a semi plot of 10m x 10m respectively for grassy savannah and shrub savannah and a rectangular plot of 50m x 20m for woodland and tree savannah. The diameter at breast height and total height of all woody individuals were measured. The floristic inventory resulted in a total of 12885 individuals belonging to 102 species, 81 genera and 34 families. The tree savannah (78 species, 59 genera and 26 families) and woodland (65 species, 54 genera and 24 families) are richer in taxonomic groups than the shrub savannah (38 species, 32 genera and 16 families) and the grassy savannah (19 species, 18 genera and 8 families) The average density of the park and its Shannon index are respectively 1956 ind/ha and 2.82 bits. For these plant formations, their density and Shannon index are highest in the tree savannah (3507 ind/ha and 3.11 bits) and lowest in the shrub savannah (1133 ind/ha and 2.03 bits). The Piélou index for each of the plant formations is low (0.19 to 0.25), indicating a poor equi- distribution of individuals between the different species for the plant formations. In the woodland, the diametrical and vertical distributions are bell-shaped and skewed to the right, centered on young individuals. In contrast, in the Tree and Shrub Savannahs the distributions are in the shape of an inverted "J", characteristic of a formation dominated by juvenile individuals. These results lead to the conclusion that the Manda Park has a good species diversity and is under anthropic pressure due to the destruction of its vegetation cover