Isolement et identification de microorganismes indigènes de cacaoyères en côte d’ivoire et mise en évidence de leurs effets antagonistes vis-àvis de Phytophthora palmivora, agent de la pourriture brune des cabosses.

En Côte d’Ivoire, avec des pertes de production qui avoisinent 60 % dans certaines régions, la lutte contre la pourriture brune des cabosses du cacaoyer est devenue une priorité. La stratégie préconisée par la recherche est le développement d’une méthode de lutte intégrée, peu onéreuse et compatible avec les préoccupations environnementales. L’une des approches privilégiées de cette stratégie est l’utilisation des antagonistes naturels de Phytophthora sp. Dans cette optique, la biodiversité a été explorée dans l’écosystème de la cacaoyère. Des champignons et des bactéries ont été isolés à partir des sols sous cacaoyères et des cabosses. L’action antagoniste des champignons sur P. palmivora a été évaluée in vitro ainsi que la sensibilité foliaire à P. palmivora sur des disques de feuilles de cacaoyers en présence des bactéries. Les résultats montrent qu’en culture mixte avec P. palmivora, des isolats de Trichoderma sp ont montré un effet fongistatique et fongicide. Une réduction significative des notes de sensibilité selon l’échelle de Blaha a été obtenue avec deux bactéries, appartenant au genre Bacillus. L’étude se poursuit avec l’évaluation de l’efficacité des antagonistes naturels de Phytophthora sp en milieu réel sur le cacaoyer.In Côte d’Ivoire, yield losses due to Phytophthora sp. reach of about 60% in some cocoa growing areas; therefore, the control of cocoa black pod disease has become a priority. The management strategy is based on thedevelopment of an integrated control method which is cost effective and environmentally sound. The emphasis has been put on the use of natural antagonists of Phytophthora sp. Thus, the microbial biodiversity in the cocoa ecosystem has been explored. Fungi and bacteria have been isolated from pods and soil in cocoa farms. The antagonistic effects of these micro-organisms on Phytophthora sp. have been assessed in vitro. In addition, the leaf susceptibility to P. palmivora was assessed on cocoa leaf disks in the presence of the bacteria. The results showed that in a mix culture with P. palmivora, some isolates of Trichoderma sp. showed fungicidal effects. Two bacteria belonging to the genus Bacillus significantly reduced cocoa leaf susceptibility to P. palmivora. The study will continue to assess the efficacy of the potentially effective micro-organisms in the field for the control of the black pod disease.Mots clés : Cacaoyer ; pourriture brune ; Phytophthora ; Trichoderma ; antagoniste

Effects of EGR rate on performance and emissions of a diesel power generator fueled by B7

This paper analyses the impacts of the application of an exhaust gas recirculation (EGR) system on the performance and emissions of a stationary, direct-injection diesel engine operating with diesel oil containing 7% biodiesel (B7). Experiments were carried out in a 49-kW diesel power generator with the adapted EGR system, and engine performance and emissions were evaluated for different load and EGR settings. The results were compared with the engine operating with its original configuration without the EGR system, and revealed a reduction of peak cylinder pressure and fuel conversion efficiency, mainly at high engine loads. The use of EGR caused opposite effects on carbon dioxide (CO2), carbon monoxide (CO) and total hydrocarbons (THC) emissions, depending on load and EGR rate, showing an increase in most situations. The application of EGR consistently reduced oxides of nitrogen (NOX) emissions, reaching a maximum reduction close to 30%. In general, the use of EGR increased CO2, CO and THC emissions at high loads. The use of 7.5% EGR was found to be at an adequate rate to simultaneously reduce CO, THC and NOX emissions at low and moderate loads, without major penalties on CO2 emissions and engine performance

Toxoplasma gondii Clonal Strains All Inhibit STAT1 Transcriptional Activity but Polymorphic Effectors Differentially Modulate IFN gamma Induced Gene Expression and STAT1 Phosphorylation

Host defense against the parasite Toxoplasma gondii requires the cytokine interferon-gamma (IFNγ). However, Toxoplasma inhibits the host cell transcriptional response to IFNγ, which is thought to allow the parasite to establish a chronic infection. It is not known whether all strains of Toxoplasma block IFNγ-responsive transcription equally and whether this inhibition occurs solely through the modulation of STAT1 activity or whether other transcription factors are involved. We find that strains from three North American/European clonal lineages of Toxoplasma, types I, II, and III, can differentially modulate specific aspects of IFNγ signaling through the polymorphic effector proteins ROP16 and GRA15. STAT1 tyrosine phosphorylation is activated in the absence of IFNγ by the Toxoplasma kinase ROP16, but this ROP16-activated STAT1 is not transcriptionally active. Many genes induced by STAT1 can also be controlled by other transcription factors and therefore using these genes as specific readouts to determine Toxoplasma inhibition of STAT1 activity might be inappropriate. Indeed, GRA15 and ROP16 modulate the expression of subsets of IFNγ responsive genes through activation of the NF-κB/IRF1 and STAT3/6 transcription factors, respectively. However, using a stable STAT1-specific reporter cell line we show that strains from the type I, II, and III clonal lineages equally inhibit STAT1 transcriptional activity. Furthermore, all three of the clonal lineages significantly inhibit global IFNγ induced gene expression