L’isolement et la caractérisation biologique des souches de bactéries du sol rhizosphérique de maïs solubilisant le phosphate au Mali

Forty-eight bacteria isolates from the rhizosphere of three cultivars of corn and three different soils were examined for their phosphate solubiling ability. The tests were realized on NBRIP (National Botanical Research Institute of Phosphate Growth medium) containing the Tilemsi phosphate rock (TPR) as the only source of insoluble phosphorus. All the isolates solubilized the TPR in solid and liquid media. Twenty isolates were selected for their high solubilizing capacity in liquid medium (105 to 311 mg P/ ml/g of TPR). These isolates were submitted to different stress conditions (acid medium with pH 7 to 5, five successive growths and the temperature range of 30°C to 45°C). Only six isolates (I 1 , I 2 , I 3 , I 4 I 5 ad I 6) were able to maintain their ability of solubilizing the TPR and also they were not antagonistics. These selected isolates were also tested for their solubilization efficiency (SE) of TPR and phytate on NBRIP solid medium containing the TPR and phytate as the only insoluble source of phosphorus and phytate respectively. The maximum solubilization (300%) for TPR was obtained with the isolate I 5 and 167% for phytate with the isolate I 1 . It has been observed that the bacteria isolates have an average solubilization capacity of 18.54 kg P 2 O 5 out off 30 kg contained in 100 kg of PNT. The same bacteria strains were tested for their plant growth promotion (PGPR) characteristics which indicated that all produced low molecular weight Organic Acids, Siderophores, Indole Acetic Acid (IAA or auxine), but none of them produced the Hydrocyanic Acid (HCN).Résumé Quarante huit (48) souches de bactéries isolées de la rhizosphère de trois (3) variétés différentes de maïs et de sol ont été testées pour leur habilité à dissoudre les phosphates naturels. Les tests ont été réalisés sur le milieu de culture NBRIP (National Botanical Research Institute of Phosphate Growth medium) contenant du Phosphate Naturel de Tilemsi (PNT) comme seule source de phosphore insoluble. Tous les isolats ont solubilisé le PNT en milieux solide et liquide. Vingt (20) isolats ont été sélectionnés pour leur grande capacité de solubilisation en milieu liquide qui varie de 105 à 311 mg de P/ml/g de PNT. Ces isolats ont été soumis à différentes conditions de stress (milieux acides de pH 7, 6, et 5) ; 5 repiquages successifs et à des températures de 30°, 35°, 40° et 45°C). Seulement 6 souches bactéries (I 1 , I 2 , I 3 , I 4 , I 5 , I 6) étaient capables de maintenir leur capacité de solubilisation du PNT et elles n'étaient pas Isolation and biological characterization of phosphate solubilizing bacteria strains from the rhizospheric soils of corn in Mali L'isolement et la caractérisation biologique des souches de bactéries du sol rhizosphérique de maïs solubilisant le phosphate au Mali Cahiers de l'Economie Rurale n°12 71 – Isolation and biological characterization of phosphate solubilizing bacteria strains from the rhizospheric soils of corn in Mali antagonistes. Ces isolats sélectionnés ont été testés aussi pour leur efficacité de solubilisation (ES) du PNT et du phytate en milieu solide contenant du PNT et du phytate comme seules sources insolubles de phosphore. L'efficacité maximale de solubilisation du PNT (300 %) a été obtenue avec l'isolat I 5 et 167 % du phytate avec l'isolat I 1 . Il a été observé également que les isolats des souches bactériennes ont une capacité moyenne de dissolution de 18 kg de P 2 O 5 sur les 30 kg contenus dans 100 kg de PNT. Les mêmes souches bactériennes ont été testées pour leurs caractéristiques de production de substances favorisant la croissance de la plante. Ces tests ont révélé que toutes les souches produisent des acides organiques de faible poids moléculaire comme les siderophores et de l'acide indole acétique (AIA ou l'auxine naturel) et qu'aucune ne produit de l'acide cyanhydriqu

Determination of the Content of Organochlorine Pesticides Residues in Chicken Eggs Sold in Bamako

Pesticides used in agriculture enter the food chain, because of their chemical stability persist and their accumulation in different media in regions where they are used regularly. Their high solubility in the fat means that they can be found in the chicken eggs through poultry feed. The present study, aimed to determine the levels of pesticide residues in eggs in 36 composite samples of chicken eggs at twelve sale points distributed between the six communes of the District of Bamako. The samples were extracted and analyzed in the laboratory by gas chromatography to determine the residues of four organochlorine pesticides. The results showed that 58% of eggs sold in Bamako are contaminated by organochlorine pesticides. The average concentrations of the pesticides detected and quantified was respectively 0.52 mg/Kg ± 0.05 for DDT, 0.15 mg/Kg ± 0.04 for endosulfan ?, 0.23 mg/Kg ± 0, 03 for ? endosulfan and 0.02 mg/Kg ± 0.01 for dieldrin. DDT was the most encountered pesticide in 53% of the samples, Endosulfan A and Endosulfan B were encountered in 36% and the lowest dosed dieldrin with less than 6% of the egg samples analysed. The feed for laying hens is largely made up of the following three ingredients: maize, fishmeal and cottonseed cake which are highly exposed to contamination by pesticides. These average levels of three residues identified in the egg samples are well above the maximum residue limit (MRL) and therefore unacceptable for consumption because they are already prohibited pesticides