African Journals OnLine
African Journal of Science & Technology

Volume 3 Number 2 December 2002
ABSTRACTS/RÉSUMÉ

The Influence of Grinding Media on the Pulp Chemical Conditions and Flotation Performance of Nchanga Underground Copper Ore

E. Siame¹, D. Bradshaw¹, P. Gaylard¹ and S. Simukanga²

¹Mineral Processing Research Unit, UCT, Rondebosch 7700, South Africa.

²School of Mines, Department of Metallurgy and Mineral Processing, UNZA, P.O. Box 32379, Lusaka, Zambia.

Abstract:

Nchanga copper ore is a complex mixture of sulphide and oxide minerals and processing consists of sulphide flotation followed by sulphidisation and an oxide flotation step. The copper oxides have proved difficult to recover. The reason for poor recovery has been attributed to complex mineralogical characteristics of the ore. Previous laboratory test work carried out on the ore showed an improvement in the flotation recovery of oxide minerals after regrinding the sulphide rougher tails with mild steel media. However, further investigation showed that the increase in recovery was not due to increased liberation. This indicated that the increase was due to some other factors resulting from the regrind, such as change in the chemical environment. The influence of grinding media on the pulp chemical conditions and the resulting flotation performance of Nchanga underground copper ore has been studied to understand how grinding media affect the chemical conditions of the pulp. The media employed were stainless steel and mild steel, which created different chemical conditions in the pulp as measured by dissolved oxygen (DO), oxidation-reduction potential (ORP) and pH. Better overall flotation performance was obtained in pulp ground by stainless steel media than by mild steel media. There was an improvement in the recovery of both sulphide and oxide minerals in the oxide flotation stage after regrinding by mild steel media. Stainless steel regrind did not increase the recovery but improved the grade of the oxide minerals in the oxide flotation stage. However, the flotation recovery of copper obtained after regrind by mild steel media was almost the same as that obtained without regrind by stainless steel media again indicating that the increased recovery obtained was not due to increased liberation. Several interesting observations concerning pulp chemistry measurements are discussed.

Keywords: Pulp chemistry; grinding media; dissolved oxygen; pulp potential; copper flotation.

Antimicrobial Effects of Acacia nilotica and Vitex doniana on the Thermophilic Campylobacter Species

Raji, M.A¹, Adekeye, J.O¹, Kwaga, J.K.P², and Bale, J.O.O³

¹Department of Veterinary Pathology and Microbiology

²Department of Veterinary Public Health and Preventive Medicine

³Department of Animal Reproduction, National Animal Research Institute (N.A.P.R.I) Ahmadu Bello University Zaria-Kaduna State-Nigeria.

Abstract:

This study was carried out to investigate the in vitro activity of the extracts of Acacia nilotica and Vitex doniana against Campylobacter jejuni, C. coli, and C. laridis isolated from sheep in Zaria and Kaduna. Water and ethanol crude extracts of Acacia nilotica and Vitex doniana were tested on the thermophilic Campylobacter species. The results obtained show that ethanol extract of Acacia nilotica had minimal inhibition concentration (MIC) of 80 mg/ml, while water extract of the same plant gave an MIC of 250mg/ml. However, ethanol extracts of Vitex doniana had no inhibitory effects on the Campylobacter species tested. A. nilotica and Vitex doniana were used at concentrations ranging from 2 to 200mg/ml of the extracts. Ethanol extract of A. nilotica at concentration of 200mg/ ml and 20mg/ml had inhibitory diameters zone of 6mm and 4mm respectively. Water extract of the same plant at concentrations of 200mg and 20mg had diameters of only 2mm and 1 mm respectively. There was very little or no inhibitions with Vitex doniana water and ethanol extracts. The emergence

of Campylobacter strains resistant to most common antibiotics highlights the need to explore new methods for therapeutics against Campylobacter infections. This study has demonstrated that extracts of Acacia nilotica show antibacterial activities against Campylobacter species isolated from sheep in Zaria and Kaduna.

Indigenous Browses as Feed Resource for Grazing Herbivores in Botswana

A.A. Aganga

Department of Animal Science and Production, Botswana College of Agriculture, Private Bag 0027.Gaborone

Abstract:

Animal production in Botswana suffers from inadequate feed quantities and qualities, due mainly to semi-arid low rainfall which can barely support arable farming in most years. This problem is compounded by the competition between the livestock and human feed industries for the little available pulses and cereals. Consequently, tree fodders are available forage resources which grazing herbivores can utilize without competition from monogastric animals and man. Tree fodders can be utilized as supplements to low quality grasses and straws. Most tree leaves and twigs contain tannins, an antinutritional factor for which proper precautions need to be taken in selecting the species of trees and their level of feeding to grazing animals.

Effect of Post-Treatment Temperature on the Insecticidal Activity of Melia volkensii (Gurke) Fruit Extract Against the African Migratory Locust Locusta migratoria (Reiche & Fairmaire)

J. M. Kabaru and Mwangi R.W.

Department of Zoology, University of Nairobi, P.O. Box 30197, Nairobi, Kenya

Abstract:

The influence of post- treatment temperature on the insecticidal activity of Melia volkensii (Gurke) fruit extract against the African migratory locust, Locusta migratoria (Reiche & Fairmaire) is reported. In laboratory tests conducted on adult locusts, the toxicity of crude 80% methanol extracts of M. volkensii fruit increased by more than 20-fold when the post-treatment temperature was raised from 15ºC to 40ºC. This temperature-dependent toxicity was observed in insects treated either topically or via injection. This phenomenon could partly explain the wide variability in efficacy of M. volkensii fruit extracts reported by different investigators.

Geological Controls on Groundwater Geochemistry in Butula Area, Busia District, Kenya

John I.O. Ogege¹, E. O. Odada² and D.O. Olago²

¹Groundwater Survey (K) Ltd., PO Box 25069, Nairobi, Kenya

²Department of Geology, University of Nairobi, PO Box 30197, Nairobi, Kenya

Abstract:

The geology of Butula area comprises mainly of rocks of the Archaean Greenstone belt of Western Kenya, especially the metavolcanics of the Nyanzian Group and the metasediments of Kavirondo Group both of which are intruded by the Mumias granite. High groundwater potential area is found within the Kavirondian sediments and the Mumias granite. Water rest levels in the wells within this area ranges in depth from 3.5-18.98m. The groundwater is slightly acidic, sodiumbicarbonate type. Iron and manganese were found to be in excess of the WHO recommended limits for potable water quality while fluoride was in relatively low amounts. PCA and factor analysis revealed that Ca, Cl, Conductivity, F and Fe are the major principal components that determine the groundwater chemistry in this area. It is established that the area is underlain by a single (1) groundwater field, and a significant component of the groundwater recharge is derived from outside the sutdy area. The waters are, in general, suitable for most purposes be it domestic, agricultural or industrial.

Voluminous Occurrence of High-K Dacites and Related Granites of Archean Age in Kenya

D.W. Ichang’i ¹ and W.H. MacLean²

¹Department of Geology, University of Nairobi, P.O. Box 30197, Nairobi, Kenya

²Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, Quebec, Canada H3A 2A7

Abstract:

The Oyani Formation of the Migori Group of the Archean Nyanza (2.8-2.6 Ga) greenstone belt in western Kenya consists of a voluminous occurrence of high-K dacite. The formation underlies an area of >400km2, and is estimated to have a volume of at least 1000 km3. Such a large occurrence of high-K volcanic rocks is rare in Archean greenstone belts. The major granitic plutons intruding into the greenstone belt are also high-K, and form a continuous compositional series with the dacites. The dacites are homogeneous subaerial porphyritic lava flows, with minor tuff and agglomerate. The principal phenocrysts are plagioclase (An31-36), clinopyroxene (Wo₄₂En₄₂Fs16), oxyhornblende, microperthitic K-feldspar (Or52-97) and titaniferous magnetite. Lavas average 3.6 wt% K2O, 64 wt% SiO2, 995 ppm Ba, 702 ppm Sr, and 113 ppm Rb; REE patterns are steep and uniform - LaN/YbN = 21-24. LIL and HFS normalized profiles are identical to other Archean and to modern orogenic high-K suites. Geochemical patterns suggest the high-K suite was formed in a continental margin magmatic arc. Our data do not support a gradual global secular decrease in Na/K from Archean to Phanerozoic high-K suites, as previously suggested.

Antibacterial & Catalytic Activities of 2,2’-Dithio (2-Hydroxyphenyl) Benzamide (Dnbh) and its Ruthenium Metal Complexes.

Sabina Jhaumeer-Laulloo*, Minu G. Bhowon & Amit Hosany

Department of Chemistry Faculty of Science University of Mauritius, Reduit, Mauritius

Abstract:

This paper describes the in vitro evaluation of antibacterial activity of DNBH and its ruthenium complexes. All the synthesized compounds exhibited antibacterial activity against the Gram-positive bacteria namely Staphylococcus aureus at a conc of 100-25 mg/ml and Gram-negative bacteria such as Escherichia coli, Salmonella typhi and Pseudomonas aeruginosa at a conc of 1µg/ml. All the metal complexes display catalytic activities towards oxidation of primary alcohols in the presence of N-methylmorpholine-N-Oxide (NMO) as co-oxidant.

Stability of Anthocyanin Sensitized TiO₂ Photoelectrochemical (PEC) Solar Cells Prepared by Sol Gel Process

J., Simiyu+, B. O. Aduda, J. M. Mwabora

Department of Physics, University of Nairobi, P. O. Box 30197, Nairobi-KENYA

Abstract:

Highly porous dye sensitized TiO2 thin film solar cells have been prepared by the sol gel process. Sensitization was achieved by use of anthocyanin pigment extracted from delphinidin purple and cyanidin 3-5 diglucose (C35D). Sensitization was also studied on ruthenium complex RuL* sensitization dye. Dye sensitized photoelectrodes have exhibited broad transmission minimum in the visible range. Solar cells fabricated from these electrodes gave overall conversion efficiencies of 3.16% for delphinidin purple and 2.97% for C35D. RuL dye sensitized solar cell gave 4.84%. The cells’ stability performance in terms of photovoltage was found to drop with time of exposure. However the cells still exhibited I-V characteristics over a long period (six months) of study.

*L = bis (isothiocyanato) ruthenium (II)-bis-2,2-bipyridine-4,4’-dicarboxylic ligand

The Impact of Vehicular Emissions on the Environmental Aerosol Concentration in Gaborone, Botswana

E.R. Jayaratne+, T.S. Verma* and T.A. Thomas

Department of Physics, University of Botswana, Private Bag 0022, Gaborone, Botswana

*School of Physical Sciences, Queensland University of Technology, Brisbane 4001, Australia

Abstract:

Motor vehicle emissions have a profound effect on the aerosol number concentrations in urban environments where it has been linked to several adverse health effects. Measurements were carried out in Gaborone, Botswana, using two automatic laser scattering particle counters. Particles were monitored in eight size ranges from 0.1 µm to 5.0 µm. The number-size distributions of the aerosols were investigated during periods of low and high traffic. Total particle concentrations were found to increase by over a factor of six, from approximately 1000 to 6000 cm-3. A hand held particle counter was used for measurements around the city. In a set of measurements carried out across the city on a calm day, the concentration within the city was found to be greater than that outside by over a factor of two.

New Theoretical Expressions for the Five Adsorption Type Isotherms Classified by Bet Basing on Statistical Physics Treatment

¹M. Khalfaoui and A. Ben Lamine

Laboratoire de Physique Quantique, Département de Physique, Faculté des Sciences de Monastir 5019, Tunisia.

Abstract:

New theoretical expressions to model the five adsorption Type isotherms have been established. Using the grand canonical ensemble in statistical physics, we could give an analytical expression to each five physical adsorption Type isotherms classified by Brunauer-Emetter-Teller, called often BET isotherms [1]. The establishment of these expressions is based on statistical physics treatment and theoretical considerations. This method allowed an estimation of all the mathematical parameters in the models. The physico-chemical parameters intervening in the adsorption process that present the models could deduced directly from the adsorption isotherms with numerical simulation. We determine the adequate model for each Type isotherm, which fixes with direct numerical simulation the monlayer, multilayer or condensation character. The new theoretical expressions that we have proposed, basing on statistical physics treatment, are rather powerful to better understand and interpret the various five physical adsorption Type isotherms at a microscopic level.

Etude de la Migration Globale et de l’Etancheite de Quelques Emballages Plastiques Fabriques en Côte d’Ivoire

Ado Gossan*, Koffi Mouroufie Gabriel*, Yao Benjamin*, Deshayes Henri**

* Laboratoire de Procédés Industriels de Synthèse et de l’Environnement du Département de Génie Chimique et Agroalimentaire de l’Institut National Polytechnique

Félix Houphouët-Boigny de Yamoussoukro BP 1093 Yamoussoukro.

** LASSI / DTIEP CNRS no 120 Faculté des Sciences de Reims.

Résumé:

Dans cette étude nous avons mis en évidence l’importance des films plastiques utilisés en Côte d’Ivoire comme emballage dans la conservation des aliments. Les phénomènes de migration entre les films plastiques et les aliments d’une part et la diffusion de l’air atmosphérique à travers les micro pores au sein des films d’autre part ont été étudiés. Il ressort de ces investigations que ces phénomènes sont responsables de la détérioration de la valeur nutritionnelle et organoleptique des aliments. Pour limiter ces altérations, nous avons montré qu’il est nécessaire d’utiliser des emballages plus épais et une conservation à l’obscurité.

Mots clés : Migration globale, perméabilité des films plastiques, simulation, emballage plastique

Abstract:

In this study we have placed in a prominent position of the important part of plastic films used as packing for aliment quality conservation. The migrations phenomena between plastic films and aliment on the one hand and air diffusion through film on the other hand have been studied. We have shown that these phenomena are responsible of nutritional and organoleptic deterioration of aliment. To limit these phenomena we have found that it is necessary to use thick plastic film and conduct the conservation at obscurity.

Keywords: Global migration, plastic films permeability, simulation, plastic packing.

Etude en Laboratoire des Caracteristques Geotechniques de Compressibilite et de Cisaillement de l’Argile-Sableuse Jaunatre de Ndogbong dans la Region de Douala au Cameroun

¹HIENG Isaac Olivier, ¹LEMBE Dezalabert Daniel et ²DANWE Raidandi

¹Département de Génie Civile de l’Ecole Normale Supérieure d’enseignement technique de l’Université de Douala Cameroun BP 2506

²Département de Génie Mécanique de l’Institut Universitaire de Technologie de l’Université de Douala Cameroun S/C BP 2506.

Résumé:

La connaissance du comportement des sols est l’un des aspects du programme de recherche du département de génie civil de l’Ecole Normale Supérieure de l’Enseignement Technique de l’Université de Douala. Dans cette optique des études de sols ont été conduites dans le but de déterminer les différents paramètres du sol du campus II, qui est le domaine pressenti pour recevoir les infrastructures futures de cette Université. Aussi, des prélèvements d’échantillons intacts ont-ils été exécutés sur le site. Ces prélèvements ont permis l’exécution en laboratoire des différents types d’essais. Le but de ces essais était d’obtenir les caractéristiques d’état, de compressibilité et de cisaillement. Les résultats obtenus ont permis de comprendre la nature du sol, son comportement sous l’effet des chargements à l’œdomètre d’une part et, sous l’action de cisaillement au triaxial de l’autre. Les résultats de la présente étude constituent une base de données géotechniques utilisables dans le dimensionnement des ouvrages enterrés. Un bref aperçu de la pédologie de la région faisant état d’un vaste bassin sédimentaire constitué des sols en formation a permis de mieux comprendre les résultats obtenus dans cette étude. En outre, une revue bibliographique relative aux parameters géotechniques des sols argileux sableux dans la région a permis de cadrer les résultats obtenus. Cette étude a été menée avec la collaboration du laboratoire d’essais « LABOGENIE-AGENCE DE

DOUALA ».

MOTS CLES : Pédologie, échantillons, cisaillement, compressibilité, identification, argile sableuse, contrainte de préconsolidation, indice des vides, poids spécifique, teneur en eau, angle de frottement.

Abstract:

The knowledge on the behaviour of soil is one of aspects in the research programme of the department of civil engineering of ENSET of University of Douala. In this aspect, studies have been carried out on soils with the aim of determining the different parameters of the soil on campus II, which is the proposed site on which future infrastructure of the university of Douala have to be built. Also the collection of samples intact had been effected on the site.These samples collected have permitted the execution of the different types of tests in the laboratory.The aim of this tests was to obtain the characteristics of the state, compressibility and shearing of the soil. The obtained results have permitted us to understand the nature of soil, its behaviour under the effect of loading by an odometer and its short term behaviour when subjected to shearing by a triaxial test in non-drained conditions. The results of the present study forms a geotecnical bank of data base usable in dimensioning the underground or buried buildings. A brief recall of the pedology of the region and a bibliographical review relative to the geotechnical parameters of the sandy-clays in the region permitted us to frame the results obtained in this study. This study was carried out with the collaboration of the tests laboratory “LABOGENIE” of Douala.

KEY-WORDS: Pedology, samples, shearing, compressibility, identification, sandy-clays, stress of preconsolidation stress, void indices, specific weight, water content, frictional angle.

La Sedimentation Argileuse dans le Bassin Côtier du Togo, Reflet de la Tectonique du Cretacetertiare et Reponse des Milieux Recepteurs

Par Ampah K. C. JOHNSON

Université de Lomé, Département des Sciences de la Terre BP : 1515 Lomé – TOGO

Résumé:

Tout au long de la sédimentation marine dans le bassin côtier du Togo, l’impact des apports d’origine continentale a toujours été important, malgré leur nature variable et les modifications sédimentaires et diagénétiques imposées par le milieu récepteur actif ou passif. Les argiles sédimentaires du bassin reflètent l’évolution climatique, tectonique et morphologique du Crétacé-Tertiare: érosion, altération, stabilisation des marges, développement des pédogenèses et subsidence du bassin.

Mots clés: Argile minérale, sédimentation, bassin côtier, Togo Maastrichtien, Paléocène, Eocène, marge, subsidence, climat, transgression.

Abstract:

During the marine sedimentation within the Togo coastal basin, the impact of input continental origin was very important despite their various nature and the sedimentary or diagenetic modifications demanded by active or passive receptive depositional environment. Sedimentary clays in the basin reflect climatic, tectonic and morphological evolution from the late Cretaceous through Tertiary: erosion, weathering, margins stabilisation, pedogenesis and basin subsidence.

Key words: Clay mineral, sedimentation, coastal basin, Togo Maastrichtian, Palaeocene, Eocene, margin, subsidence, climate, trangression.

Using Information Technology as a Strategic Tool for Competitive Advantage

E.A.M. MJEMA

¹Department of Mechanical Engineering, University of Dar es Salaam P.O. Box 35131, Dar es Salaam, Tanzania

Abstract:

Application of IT in modern industry is gaining momentum and IT has now been recategorized as the fourth production factor after material, machine and labour [1][2]. However, there are very few researches, which show the strategic role of IT in a company [3]. The introduction of IT has rarely helped the companies to acquire the expected competitive advantage. The main hurdle is the historical growth of the IT and the deficiency in taking into consideration the interactions between IT and the corporate strategic planning [4]. Corporate strategies can be effectively implemented, only when concrete measures have been taken to make sure that the individual business processes, the functional departments and the overall corporate strategy are in harmony (i.e. all of them are running in the same tune). However, it is disconcerting to mention that, the correspondence between overall corporate strategy and IT-strategy are rarely harmonized. The requirement for a strategic adaptation of IT is very important for modern companies since for them such communication techniques are very important for the success of the company. The endeavour in this article is to display how one could use IT strategically for gaining competitive advantage.

Unification of Gravitation and Electromagnetism in a Relativistic Version of Finslerian Geometry

P. Baki

Department of Physics, University of Nairobi, Box 30197, Nairobi, Keny

Abstract:

A theory of gravitation is considered in a relativistic version of Finslerian geometry. It is found that both the geodesic equations and the Finslerian analogue of the Einstein’s field equations have terms that involve the electromagnetic field tensor, thereby pointing out to the geometrization of electrodynamics and hence to a unification of gravitation and electromagnetism. A possibility of a non-gravitational electromagnetic redshift is explored. Mical antiozonant were incorporated.

Optical Co-Incidence Gate

Avireni Srinivasulu, Kumelachew Baynesagn Kebede, Sivadasan Kottayi

¹Department of Communication Technology College of Engineering, Defence University Debre Zeit, Ethiopia

²Faculty of Electrical Engineering,College of Engineering,

³Department of Instrumentation Technology, Faculty of Electrical Engineering,

Abstract:

The paper explains Optical co-incidence gate, realized using Unijunction transistors (UJT), Light emitting diodes (LED) and Photo-resistors (LDR), which works on 1.8Vdc instead of 3Vdc. The power dissipation of the designed gate is only 3 mW. This optical gate finds application in the field of Mechatronics, Instrumentation and Fiber optics systems where intrinsic safety is of prime importance rather than speed of operation.

Key words: Bistability, Intrinsic safety, and Low speed.

Production of Solid Fuel Briquettes from Agricultural and Wood Waste (Saw Dust and Rice Husk)

A.O. Inegbenebor

Department of Mechanical Engineering, University of Maiduguri Maiduguri, Borno State, Nigeria

Abstract:

Fibrous agricultural and wood waste materials have been compressed with suitable adhesive into solid fuel briquettes in a compressing machine, which was designed and constructed for this purpose. Nine samples of fibrous waste materials were prepared into different categories:- Category A (100% saw-dust, 100% rice-husk, 50-50% rice-husk/sawdust using starch as adhesive). Category B (100% saw-dust, 100% rice-husk, 50-50% rice-husk/ saw dust using gum arabic as adhesive) and category C (100% saw-dust, 100% rice husk, 50-50% rice-husk/saw dust using bentonite as adhesive). The solid fuel briquettes in category C had the lowest average moisture content of 9.1%, categories A and B solid fuel briquettes had 10.5% and 13.0%, respectively. The results from a water boiling test (WBT), involving comparsion of the burning abilities of the solid fuel briquettes and fire wood of the same quantity (200 grammes) in boiling 1.5 litres of water showed that the solid fuel briquettes bound with each of the three adhesives; bentonite, gum arabic and starch; boiled water within a period of 14 to 22 minutes, while firewood did so within a period of 22 to 27 minutes. The open flame test showed that the solid fuel briquettes bound with starch burnt with bluish yellow flame with little black smoke indicating that the stoichiometric (air-fuel) ratio was almost correct. The solid fuel briquettes bound with gum arabic and bentonite burnt with yellow flame with moderate black smoke., indicating incomplete combustion due to poor air-fuel ratio. The reason for this cannot be ascertained.

Investigating the Use of a Protective Coating Material as an Antiozonant for Natural Rubber Under Dynamic Deformation

M. J. Bhala

Department of Applied Chemistry, National University of Science and Technology, P.O. Box, AC939 Ascot, Bulawayo, Zimbabwe

Abstract:

Petroleum wax is known to provide ozone protection to natural rubber under static deformation while a combination of chemical antiozonant and wax is normally used for ozone protection under dynamic conditions. The work described in this paper, aims at investigating the effectiveness of a coating material in protecting a natural rubber substrate from ozone cracking under dynamic deformation. Two compounds (without an antiozonant system) and NR_Ao (with an antiozonant system) were used as substrates while a grade of liquid nitrile-butadiene rubber was applied as a coating on the substrate surface. Dynamic ozone tests were carried out under standard ASTM D430-88 methods with samples strained to 25%. Comparison of cracking under continuous dynamic conditions and intermittent dynamic conditions were made. Initial results showed that the protective coating was more effective as an antiozonant under intermittent conditions where a combination of wax and a chemical antiozonant were incorporated.

Variabilité des Composés Phénoliques chez Vigna unguiculata (L.) Walp. (Légumineuses) et Influence de l’Inoculation par les Rhizobia et les Champignons Mycorhiziens sur Leur Biosynthèse.

Nana Wakam L.¹ Nwaga D. ², Fokom R¹.,;Oneya S¹. et Ngakou A³.

¹Département de Biochimie, Faculté des Sciences, Université de Yaoundé I.

²Département de Biologie et de Physiologie Végétales ; Faculté des Sciences, Centre de Biotechnologie, Laboratoire de Microbiologie. B.P. 812 Université de Yaoundé I.

³Département des Sciences Biologiques, Faculté des Sciences, Université de Ngaoundéré B.P. 456 Ngaoundéré, Cameroun.

Résumé:

Cette étude préliminaire se propose d’évaluer la variabilité des composés phénoliques du niébé (Vigna unguiculata (L.) Walp.) et la modification de leur métabolisme par les microorganismes symbiotiques (rhizobia et mycorhizes). Pour cela, trois expérimentations ont été menées. L’analyse des composés phénoliques de 13 variétés de niébé, l’influence de l’inoculation de 10 souches de mycorhizes sur la synthèse des composés phénoliques du niébé en serre et l’effet de la double inoculation des biofertilisants rhizobien et mycorhizien sur la synthèse des composes phénoliques, en conditions de champ, sur deux sites (Nkolbisson et Mbalmayo). Les résultats obtenus montrent que: la variabilité de la teneur des graines de niébé en polyphénols est importante, car la variété la plus riche a une teneur en phénols 33 fois plus élevée que la variété la plus pauvre. Les champignons mycorhiziens sont capables de modifier significativement le métabolisme de la synthèse en polyphénols des feuilles de niébé; la double inoculation du niébé avec les biofertilisants entraînerait une baisse significative de la teneur en phénols totaux des graines, mais surtout une augmentation qualitative du nombre de composés phénoliques en champ. Ces modifications dépendent, aussi fortement de facteurs écologiques liés au site comme la présence d’insectes ravageurs. A partir de ces résultats, nous suggérons un approfondissement des connaissances sur le rôle de ces composés pour la défense des plantes.

Mots clés: chromatographie sur couche mince, composés phénoliques, mycorhizes, rhizobia, spectrophotométrie, Vigna unguiculata.

Abstract:

The major objective of this preliminary work is to assess the variability of phenolic compounds and the modification of their metabolism by symbiotic microorganisms (rhizobia and mycorrhiza). Three experiments have been carried out: the variability of phenolic compounds of 13 varieties of cowpea; the influence of the inoculation of 10 mycorrhizal strains on the biosynthesis of phenolic compounds, under green house and the effect of the double inoculation by rhizobia and mycorrhiza in two sites (Nkolbisson and Mbalmayo) on phenolics biosynthesis. The results show that: there is an important variability in cowpea seed polyphenol concentration, because the most rich variety has 33 times phenol compared to the less rich one; mycorrhiza fungi are able to significantly modify the metabolism of polyphenols biosynthesis in cowpea; the double inoculation of rhizobia and

mycorrhiza may reduce the amount of phenolic compounds in cowpea, but a qualitative increase of the number of phenolic compounds was noticed. These observations are also related to ecological factors such as insects pests. From these results it is suggest that more basic studies are needed to improve our knowledge on the role of these compounds for plants defense.

Key words: phenolic compounds, mycorrhiza, rhizobia, spectrophotometry, thin layer chromatography, Vigna unguiculata.