Pseudomonads and symbiotic micro-organisms as biocontrol agents against fungal disease caused by

Experiments were undertaken to assess the antagonistic aptitude of Pseudomonas spp. alone or associated with mycorrhizal fungi on Pythium aphanidermaturm, the causal agent of seedlings dampingoffand stem rot of cowpea (Vigna unguiculata L. Walp). Evaluation was made using selected strains of pseudomonad (Pseudomonas fluorescens, P. putida and Pseudomonas sp.) isolated from V. unguiculata and Solanum tuberosum rhizospheric soils collected in three agroecological zones of Cameroon. Cultures were conducted on agar plates and in liquid media to evaluate the antagonistic capacity of those strains against Pythium aphanidermaturm and to evaluate their biocontrol activity in protecting cowpea plants. The results showed a direct inhibition of the pathogenic fungus by these bacteria. P. fluorescens used alone against Pythium aphanidermaturm, provided a reduction of the disease index from 3.44 to 1.06. When the arbuscular mycorrhizal fungi Glomus deserticola is associated to P. fluorescens, the disease index dropped to 0.13, confirming the synergistic effect of those beneficial micro-organisms

Occurrence and functioning of phosphate solubilizing microorganisms from oil palm tree (Elaeis guineensis) rhizosphere in Cameroon

Phosphorus replenishment, particularly in smallholder agriculture, remains a challenge as it is mainly fertilizer dependent. While the use of soluble mineral phosphate fertilizers is the obvious best means tocombat phosphate deficiency in Cameroon, their use is limited by their high cost and availability at farmer’s level. This study was aimed at maintaining the fertility of Cameroon soils by biological means,in order to improve agricultural production, using low inputs technology. Isolates were obtained from oil palm tree (Elaeis guineensis) root fragments and rhizospheric soils and their activity in mobilizingphosphate from insoluble sources was evaluated on agar plates and liquid culture media containing sparingly soluble phosphates. At the end of incubation time, it appeared that, phosphate solubilizationresulted from a combined effect of pH decrease of the media and organic acids production. Furthermore, each of the tested isolates was able to produce at least one of the most important organic acids such as citrate, malate and tartrate. Among the ten isolates tested, three were identified as Pseudomonas fluorescens and would be considered as potential biofertilizers

Niveau d'infestation des arbres fruitiers des groupements végétaux par Phragmanthera capitata (Sprengel) S. Balle (Loranthaceae) dans la région littorale du Cameroun

Au Cameroun, Phragmanthera capitata parasite de nombreuses essences ligneuses sauvages et cultivées, et est responsable de la réduction de leur rendement. L’optique de cette étude est de justifier le comportement de cette Loranthaceae ubiquiste dans les groupements végétaux homogènes et hétérogènes des sites retenus du littoral camerounais. Les groupements végétaux homogènes sont des plantations agricolesconstituées de Hevea brasiliensis et appartenant à la société Hévéa du Cameroun (Hévécam) située à Nyétté. Les groupements végétaux hétérogènes appartiennent à quatre sites de la région de Douala : un verger à Makondo et une plantation agricole paysanne à Cola acuminata à Penja, deux jardins de cases (Logbessou et axe routier aéroport-Bonanjo). Sur chaque arbre hôte ont été notés: le diamètre du tronc à 1,30 m du sol, les différentes espèces de Loranthaceae reconnues et le nombre de touffes comptées. Dans les groupements végétaux hétérogènes, 16 espèces hôtes réparties dans 12 genres et 10 familles sont parasitées par P. capitata. Cette dernière est la plus fréquente et la plus abondante de toutes les Loranthaceae et sa dissémination est facilitée par des facteurs d’origine anthropique. Il est indispensable et urgent de mettre en place un programme de recherche de lutte ciblée pour les plantes fruitières et ornementales

Modeling the role of fomites in a norovirus outbreak

Norovirus accounts for a large portion of the gastroenteritis disease burden, and outbreaks have occurred in a wide variety of environments. Understanding the role of fomites in norovirus transmission will inform behavioral interventions, such as hand washing and surface disinfection. The purpose of this study was to estimate the contribution of fomite-mediated exposures to infection and illness risks in outbreaks. A simulation model in discrete time that accounted for hand-to-porous surfaces, hand-to-nonporous surfaces, hand-to-mouth, -eyes, -nose, and hand washing events was used to predict 17 hr of simulated human behavior. Norovirus concentrations originated from monitoring contamination levels on surfaces during an outbreak on houseboats. To predict infection risk, two dose-response models (fractional Poisson and 2F1 hypergeometric) were used to capture a range of infection risks. A triangular distribution describing the conditional probability of illness given an infection was multiplied by modeled infection risks to estimate illness risks. Infection risks ranged from 70.22% to 72.20% and illness risks ranged from 21.29% to 70.36%. A sensitivity analysis revealed that the number of hand-to-mouth contacts and the number of hand washing events had strong relationships with model-predicted doses. Predicted illness risks overlapped with leisure setting and environmental attack rates reported in the literature. In the outbreak associated with the viral concentrations used in this study, attack rates ranged from 50% to 86%. This model suggests that fomites may have accounted for 25% to 82% of illnesses in this outbreak. Fomite-mediated exposures may contribute to a large portion of total attack rates in outbreaks involving multiple transmission modes. The findings of this study reinforce the importance of frequent fomite cleaning and hand washing, especially when ill persons are present.12 month embargo; published online: 04 Feb 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Variation in nodulation and growth of groundnut (Arachis hypogaea L.) on oxisols from land use systems of the humid forest zone in southern Cameroon

Improving biological nitrogen fixation through legume nodulating bacteria (LNB) inoculation requires knowledge on the abundance and effectiveness of indigenous population in the ferralsols. Nodulation of groundnut was examined under pots experiment in four location sites of the Humid-forest zone: Bertoua in the East; Ebolowa in the South; Bokito and Yaoundé in the Centre Regions of Cameroon and within each of the locations, in four land use systems (LUSs) of different levels of disturbance: mixed farming (1 to 3 years old); fallows (3 to 5 years old); cocoa plantation (> 20 years old); forest (> 30 years old). Results indicate that, soils under investigation are acidic with pH ranging from 3.68 in the Ebolowa forest to 6.92 in mixed farming at Bokito. Groundnut formed nodules in all the four LUSs. Soils from plantations and forests were poorly nodulated, whereas those from mixed farming and fallows were highly nodulated, with a positive and significant correlation (r 0.406; p < 0.0001) observed between nodulation and plant biomass in all the studied sites. These results suggest a high variation in groundnut nodulating bacteria density in soils from diverse LUSs of the humid forest zone of Cameroon; although, there was a site effect.Key words: Acid soil, Arachis hypogaea, biomass, land use systems, multilocal, nodulation

Optimization of Sensorless Sliding Mode Control of an Induction Motor Taking Into Account Magnetic Saturation Effects

This paper presents the optimization of sensorless sliding-mode control for induction motor, considering magnetic saturation effects. A five-order sliding-mode observers and estimators are elaborated to replace the sensors of an induction motor. The proposal is based on double optimization of sensorless sliding mode control of an induction motor in the point of view of dynamic and energetic performances. In order to obtain better performances of the proposed control method, Particle Swarm Optimization (PSO) algorithm is used notably to determine the optimal gains of the observers as well as the optimal parameters of the regulators. Regarding the energetic optimization, the reference of the rotor flux is generated using another developed algorithm that permits us to dynamically determine the optimal rotor flux for each given value of motor load and speed. As results, sensorless sliding mode control takes into account all operating ranges of the machine from very low speeds, low speeds, to high speed with or without load. Numerical simulations are carried out each time to confirm theoretical predictions

Les Loranthaceae : un atout pour l’essor de la pharmacopée traditionnelle au Cameroun

La famille des Loranthaceae est largement distribuée dans les zones tropicales en Afrique, Amérique, Asie, Australie et s’étend en zones tempérées. Les Loranthaceae appartiennent à l’ordre des Santalales. Danscette famille sont reconnus 950 espèces et 77 genres. Au Cameroun 26 espèces distribuées dans 7 genres sont citées. L’objectif de ce travail est d’évaluer, l’impact des Loranthaceae dans la pharmacopée traditionnelle des paysans. A travers un questionnaire sémi-structuré, 150 tradipraticiens en activité ont été interviewés en 2008 à Logbessou (quartier périphérique de la ville de Douala). Les réponses de l’enquête mise sur pied révèlent des informations selon lesquelles, les Loranthaceae sont des plantes parasites connues pour les dégâts considérables, occasionnés sur les essences ligneuses sauvages ou cultivées. Cependant, leur intérêt pour lapharmacopée traditionnelle est attesté. Les Loranthaceae fortifient le métabolisme et se présentent comme une panacée. Toutefois, l’ingestion des pseudobaies provoque des vomissements, de l’hypotension et des troubles nerveux. Les parties du végétal utilisées dans le traitement sont les feuilles, les rameaux et la tige sous forme d’extraits aqueux. Les allergies sévères sont rares. Le mode d’action des extraits aqueux des Loranthaceae européennes aux niveaux cellulaire et moléculaire est discuté. Keywords: Loranthaceae, plantes parasites, dégâts, pharmacopée traditionnelle