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On a étudie le pH final des cultures pures de 49 souches de Rhizobium meliloti comme moyen rapide d’évaluation de leur efficacité symbiotique. Il existe une corrélation positive et très significative entre le pH final et l’efficacité des souches. Cette méthode peut être utilisée comme moyen simple et rapide de présélection d’un grand nombre d’isolats de R. meliloti.

Le rendement de la luzerne inoculée avec la souche très efficace A2 de Rhizobium meliloti a été étudié en présence des souches AL 123 de R. japonicum, FCVF2 de R. phaseoli, TL3 de R. trifolii et RL2 de R. leguminosarum. Aucune de ces quatre espèces de Rhizobium n’a significativement affecté le rendement de la luzerne après deux coupes. La présence de la souche FCVF2 en mélange avec la souche RL2 dans l’inoculant a baissé le rendement de la luzerne, alors que la présence de la souche AL123 avec la souche TL3 a donné le meilleur rendement et a aussi éliminé l’effet néfaste des deux premières souches.

Le but de ce travail était de déterminer l’effet de l’application du lisier de porc aux doses de 28, 56 et 112 tonnes/ha sur la croissance et la composition chimique du maïs. Dans un essai en serres, l’application du lisier n’a eu aucun effet significatif sur le rendement du maïs cultivé pendant 4 semaines sur le sable loameux St-Jude. Sur l’argile Kamouraska, le rendement du maïs n’a significativement augmenté qu’avec l’addition d’une dose de 112 tonnes/ha de lisier. Sur le loam sablo-argileux Janvier, le rendement du maïs a augmenté avec l’application de doses croissantes de lisier jusqu’à 56 tonnes/ha. A un taux de 112 tonnes/ha (325 kg N/ha), le lisier a augmenté le contenu en N du maïs et a eu un effet résiduel important tel qu’indiqué par le rendement élevé obtenu lors de la 2e récolte. Dans un essai de 2 ans au champ sur le sol Kamouraska, l’addition de 112 tonnes/ha (moy. 432 kg N/ha) de lisier a augmenté le rendement du maïs fourrager, ainsi que le contenu du sol en P, Ca et Mg après une année de culture, comparativement à un engrais chimique (150 kg N/ha, 65.5 kg P/ha et 125 kg K/ha). Le prélèvement des éléments nutritifs par le maïs a augmenté avec l’addition de doses croissantes de lisier. Cependant, la variation des doses de lisier n’a eu aucun effet sur la composition chimique du maïs. Aux taux utilisés dans cette étude le lisier de porc n’a pas réduit le rendement du maïs., The objective of this work was to determine the response of corn to liquid hog manure surface applied at rates of 28, 56 and 112 tonnes/ha. In greenhouse trials, yield of corn grown for 4 wk on St. Jude loamy sand was not affected by manure application. On Kamouraska silty clay, only manure applied at a rate of 112 tonnes/ ha increased corn yield, as compared to the non-treated control. Corn response on Janvier sandy clay loam improved with increasing rate of manure application up to 56 tonnes/ha. Application of 112 tonnes/ha (325 kg N/ha) manure increased N content of corn and had a significant residual effect as noted by the high yield obtained at the second harvest. In a 2-yr field experiment on Kamouraska soil, corn yield was significantly higher at 112 tonnes/ha (avg 432 kg N/ha) than chemical fertilizer application at 150 kg N/ha, and manure-treated soil contained more P, Ca and Mg after the first year. Nutrient uptake by corn increased with amount of manure applied. However, corn whole plant composition was not affected by rate of manure application. N recovery was higher from manure at 28 or 56 tonnes/ha than from a chemical fertilizer (150 kg N/ha, 65.5 kg P/ha and, 125 kg K/ha). At the rates applied, the liquid hog manure did not result in reduced corn yield.

Compost teas are fermented aqueous extracts of composted materials that are used for their ability to control plant pathogens. It had been previously reported that this inhibition by compost teas is at least partially attributed to the presence of live microorganisms. In this study, the inhibitory effects of bacteria from suppressive compost tea were examined against mycelial growth of Alternaria solani and Botrytis cinerea as well as disease development on tomato fruit. Isolation of antifungal extracts and identification of antifungal compounds from the most effective bacterial strains were also performed. Results showed that the bacteria had the ability to greatly inhibit the mycelial growth of B. cinerea and/or A. solani by up to 70%. The two most effective isolates, Brevibacterium linens (IC 10) and Bacillus subtilis, showed that co-application of bacterial antagonists (5 × 105 or 5 × 106 cells) with the pathogens on tomato fruit demonstrated inhibition of the development of B. cinerea lesions by up to 61%. A preventive application of the bacteria (5 × 105 or 5 × 106 cells) was more effective than co-application, allowing a significant reduction in lesions of A. solani and improving efficacy of low bacterial concentrations in reducing B. cinerea lesions. A combined B. linens/B. subtilis treatment was generally more inhibitory than either bacterium alone indicating possible synergistic effects. Antifungal compounds, including surfactins, were found in the bacterial extracts indicating that antibiosis is a main mechanism of action.

Les activités spécifiques des nitrates réductases assimilatoires et "régulatoires" ont été étudiées chez 41 souches de Rhizobium meliloti ayant des activités différentes de fixation symbiotique d’azote. Les deux nitrates réductases ont été retrouvées chez les souches très efficaces ainsi que chez les souches inefficaces et aucune corrélation significative n’a été trouvée entre les activités spécifiques et le rendement de la matière sèche de la luzerne obtenu avec les 41 souches à l’essai. La détermination des activités spécifiques de ces deux nitrates réductases chez les bactéries végétatives ne peut donc pas être utilisée comme un test physiologique rapide pour la sélection de souches très efficaces de R. meliloti., Specific activities of the assimilatory and "regulatory" types of nitrate reductase were studied in 41 strains of Rhizobium m,eliloti naving ditierent symbiotic nitrogen fixation activities. Both nitrate reductase enzymes were present in very effective ind ineffective strains and no significant correlation was iound between the specific activities of the two enzymes and the dry matter yields of alfalfa obtained with the 41 strains. Measurements of the specific activities of the two nitrate reductase enzymes in the vegetative bacteria cannot be used as a rapid physiological test for the seiection of very effective strains of R. meliloti.

La carence de phosphore (P) est l’un des principaux facteurs limitant la production agricole au Mali. Les cultures répondent bien à la fertilisation phosphatée, mais le coût élevé des engrais chimiques importés restreint leur utilisation par les agriculteurs. Cependant, dans la vallée de Tilemsi, le Mali dispose de gisements de phosphates estimés entre 20 à 25 millions de tonnes, avec une teneur en P2O5 de l’ordre de 23 % à 30 %. Dans le but d’améliorer biologiquement l’absorption de phosphore par le maïs fertilisé avec du phosphate naturel de Tilemsi (PNT), l’effet de l’inoculation de souches de Bacillus isolées des sols maliens a été étudié. La croissance et la teneur en P de trois variétés de maïs ont été mesurées en 2007 ; la croissance, la teneur en P et le rendement de la variété de maïs Sotubaka ont été mesurés en 2008 dans des conditions de champ au Mali. L’expérimentation a été menée au cours des saisons agricoles de 2007 et 2008 à la station de recherche agronomique de Samanko située à 15 km au Sud-Ouest du District de Bamako au Mali. Elle est à une latitude de 12°. 31.552’ Nord, à une longitude de 8°.04.906’ Ouest et à une altitude de 316,8 m. Le sol est de type ferrugineux tropical peu lessivé, de texture limono sableuse avec 76 % de sable, 15 % de limon et 9 % d’argile (Labosep, IER, 2008). Un dispositif expérimental de type split- plit- plot à trois répétitions a été utilisé avec, en parcelles principales, la fertilisation (le PNT 300 kg/ha (insoluble), l’engrais chimique, le complexe céréale 100 kg/ha (17-17-17) et le témoin sans phosphore. Toutes les parcelles ont reçu la même quantité d’azote N équivalente à 150 kg d’urée. Les compléments N et K de l’engrais chimique ont été corrigés pour toutes les autres parcelles. Les parcelles secondaires étaient composées de trois variétés de maïs (Dembanyuman, Sotubaka, Tiémantié) et les parcelles tertiaires étaient composées de témoin non inoculé et les six inoculations avec les lignées de Bacillus solubilisa, Phosphorus (P) deficiency is one of the major factors limiting crop production in Mali. Crops respond well to P fertilization, but the high cost of imported chemical fertilizers restrains their use by farmers. However, Mali has in the Tilemsi valley, phosphate rock (PR) deposits estimated between 20 to 25 million tonnes with P2 O5 content in the range of 23% to 30%. With the aim of improving biologically P uptake by maize fertilized with Tilemsi phosphate rock (TPR), the inoculation effect of TPR-solubilizing Bacillus strains isolated from Malian soils was investigated. The growth and P concentration of three cultivars of maize were measured in 2007 ; growth, P concentration and yield of the cultivar Sotubaka of maize were measured in 2008 under field conditions in Mali. Experimental plots were established at the Samanko agronomic research station (latitude 120 31’ N. 80 4’ W, altitude 316.8 m) in 2007 and 2008, located at 15 km from Bamako district. The soil is ferralitic tropical washed type, sand limon texture with 76% of sand, 15% of limon and 9% of clay (Labosep, IER, 2008). A split- split- plot experimental design with three replicates was used. The three main plot treatments included P addition at 300 kg/ha TRP, 100 kg/ha of Complex cereal, the chemical fertilizer (17-17-17) and a control which did not receive any P. All plots received the same amount of N equivalent to 150 kg/ ha urea. The additional N and K added with the chemical fertilizer were corrected for all other plots. The sub-plots were the three cultivars of maize (Dembanyuman, Sotubaka and Tiemantie) and the sub-sub plots included an uninoculated control and inoculation with six TRP-solubilizing Bacillus strains, all belonging to the Bacillus subtilis subsp. subtilis (T); DSM10. Our results have shown that P-fertilization of the cultivar of maize with TPR or the chemical fertilizer (17-17- 17) significantly improved grain and shoot dry matter yields. Inoculation with TPRsolubilizing bacteria did

Compost teas are fermented watery extracts of composted materials that are used for their beneficial effects on plants including antimicrobial activities. Non-aerated compost teas (NCT) prepared from seaweed compost, shrimp powder compost, and chicken, bovine and sheep manure composts were tested for their effect on the in vitro growth of tomato root pathogens and for their effect on the development of damping-off diseases caused by Pythium ultimum and Rhizoctonia solani. Results showed that NCT prepared from the five types of compost had the ability to greatly reduce mycelial growth of P. ultimum, R. solani, Fusarium oxysporum f. sp. radicis-lycopersici and Verticillium dahliae in vitro. Sterilization of the NCT caused complete or partial loss of their inhibitory effect on mycelial growth of the pathogens. Application of NCT decreased the percentage of necrotic seedlings in P. ultimum-inoculated tomato seeds from 42% to 100%, but did not reduce necrosis in R. solani-inoculated seeds. When applied on tomato seedlings inoculated with damping-off pathogens, various NCT also increased seedling fresh and/or dry weights., Les thés de compost sont des extraits aqueux fermentés de matériaux compostés. On reconnaît aux thés de compost des effets bénéfiques sur les plantes attribuables à leur activité antimicrobienne. Des thés de composts non-aérés (TCNA) à base de compost d'algues, de compost de poudre de crevette et de composts de fumier de poulet, de bovin et de mouton ont été testés afin d'évaluer leurs effets sur la croissance in vitro de différents agents pathogènes de la tomate. L'effet des TCNA sur le développement de la fonte des semis, causée par Pythium ultimum et Rhizoctonia solani, a également été évalué. Les résultats ont montré que les TCNA à base des cinq types de composts réduisent la croissance mycélienne de P. ultimum, R. solani, Fusarium oxysporum f. sp. radicis-lycopersici et Verticillium dahliae in vitro. La stérilisation des TCNA a par ailleurs conduit à une perte complète ou partielle de leur effet inhibiteur sur la croissance mycélienne des agents pathogènes. Appliqués sur les semences de tomate inoculées avec P. ultimum, les TCNA ont réduit de 42 à 100% le pourcentage de semences présentant des lésions nécrotiques. Les TCNA n'ont pas eu un tel effet chez les semences inoculées avec R. solani. L'application de certains TCNA sur les semences de tomate inoculées avec les agents pathogènes de la fonte des semis a résulté en une augmentation du poids sec et/ou humide des jeunes plants.

La fixation symbiotique d’azote chez 49 souches de Rhizobium meliloti a été étudiée sous un environnement contrôlé avec la variété de luzerne Saranac. Il a été mis en évidence que le rendement en poids sec de la plante peut être utilisé comme mesure indirecte de la fixation d’azote, et comme critère de sélection des souches efficaces de R. meliloti. L’étude statistique des rendements de trois coupes a établi que la deuxième coupe donne le plus d’information pour évaluer correctement l’efficacité symbiotique des souches. Six souches très efficaces ont été sélectionnées., Symbiotic nitrogen fixation with 49 isolates of Rhizobium meliloti was studied under controlled environment with alfalfa cv. Saranac. It was shown that plant yield in dry weight can be used as an indirect measurement of nitrogen fixation, and as a criterion for selecting efficient strains ofR. meliloti. Statistical study on yields of three cuttings has established that the second cutting gives the most necessary information to correctly evaluate the symbiotic efficiency of the isolates. Six very efficient strains were selected.

Plant growth promoting rhizobacteria (PGPR, B) have immense potential application in sustainable agriculture as ecofriendly biofertilizers and biopesticides. In this study, the effects of three nitrogen (N) sources (NO3-, NH4+ and NO3NH4) and PGPR on growth, crude fiber and nutrient uptake were investigated in squash plants. Some growth parameters [root dry weight (RDW), shoot dry weight (SDW), total plant dry weight (PDW), number of leaves (NL), shoot length (SL), stem diameter (SD) and number of ramifications (NR)], crude fiber (cellulose content) and nutrient uptake (N, P, K, Ca, Mg, Na, Fe, Cu, Mn and Zn) were determined. Application of NO3-, NH4+ or NO3NH4 singly or in combination with PGPR inoculation led to a significant increase in RDW, SDW, PDW, NL, SL, SD and NR. Na, Cu and Zn contents, on the contrary, decreased in inoculated treated plants while no significant differences were recorded in cellulose contents (CE) of leaves except in plants fed with NO3-. The leaf CE content ranged from 12.58 to 13.67%. The plants supplied with NO3+B, NH4+B and NO3NH4+B showed significantly higher plant biomass and accumulation of N, P, K and Mn concentrations in leaves compared to all other treatments. These results suggest that specific combinations of PGPR with NO3-, NH4+ or NO3NH4 fertilizers can be considered as efficient alternative biofertilizers to improve significantly the squash growth and nutrient uptake.

Biofilm formation on abiotic and biotic surfaces was studied with two hyphobacteria, strongly attached to the surface of the arbuscular mycorrhizal fungus (AMF) Rhizoglomus irregulare (Ri) DAOM 197198 and two mycorrhizobacteria, loosely attached to the roots of different mycorrhizal plants. When the sparingly soluble igneous phosphate rock (PR) from Quebec, or when the chemical hydroxyapatite were used as sole phosphorus (P) source, hyphobacteria Rhizobium miluonense Rm3 and Burkholderia anthina Ba8 produced significantly more biofilms than mycorrhizobacteria Rahnella sp. Rs11 and Burkholderiaphenazinium Bph12, as indicated by the crystal violet assay or by quantifying biofilm exopolysaccharides. As previously observed with planktonic bacteria, biofilms mobilized P by lowering the pH and releasing gluconic acid. The high efficiency of P mobilization by the hyphobacteria Ba8 was linked to the presence of more viable cells in its biofilm as revealed by the hydrolysis of fluorescein diacetate. Scanning electron microscopy micrographs showed a high adherence of the best P-solubilizer hyphobacteria Ba8 on the surface of Quebec PR. Hydroxyapatite porous structure did not allow a good adherence of Ba8. Ba8 formed an important biofilm on the hyphae of Ri DAOM 197198 with low reactive Quebec PR while no biofilm was observed with the high reactive hydroxyapatite. Results confirm the possible presence of specificity between the Ri DAOM 197198 and the hyphobacteria and suggest that the interaction would be regulated by the availability of P.

Plant growth promoting rhizobacteria (PGPR, B) have immense potential application in sustainable agriculture as ecofriendly biofertilizers and biopesticides. In this study, the effects of three nitrogen (N) sources (NO3-, NH4+ and NO3NH4) and PGPR on growth, crude fiber and nutrient uptake were investigated in squash plants. Some growth parameters [root dry weight (RDW), shoot dry weight (SDW), total plant dry weight (PDW), number of leaves (NL), shoot length (SL), stem diameter (SD) and number of ramifications (NR)], crude fiber (cellulose content) and nutrient uptake (N, P, K, Ca, Mg, Na, Fe, Cu, Mn and Zn) were determined. Application of NO3-, NH4+ or NO3NH4 singly or in combination with PGPR inoculation led to a significant increase in RDW, SDW, PDW, NL, SL, SD and NR. Na, Cu and Zn contents, on the contrary, decreased in inoculated treated plants while no significant differences were recorded in cellulose contents (CE) of leaves except in plants fed with NO3-. The leaf CE content ranged from 12.58 to 13.67%. The plants supplied with NO3+B, NH4+B and NO3NH4+B showed significantly higher plant biomass and accumulation of N, P, K and Mn concentrations in leaves compared to all other treatments. These results suggest that specific combinations of PGPR with NO3-, NH4+ or NO3NH4 fertilizers can be considered as efficient alternative biofertilizers to improve significantly the squash growth and nutrient uptake.

Le but de ce travail était de déterminer comment l’amendement d’un substrat de serre avec différents taux de biochars influence l’activité biologique, la biomasse microbienne, l’émission des gaz à effet de serre et le rendement de la tomate et du poivron de serre. L’effet du biochar sur l’utilisation de l’eau et des engrais lors de la production de ces deux cultures a aussi été étudié. Dans ce travail quatre biochars ont été fabriqués à partir de saule et d’écorce d’érable soumis à des températures de pyrolyse variant de 400°C à 700°C. Un biochar vendu commercialement au Colorado, préparé à partir de pin à 700°C, a aussi été utilisé. Ces biochars ont été utilisés dans des études d’incubations en laboratoire, mais aussi en serre dans deux essais de production avec la tomate et le poivron., Faculté des sciences de l’agriculture et de l’alimentation de l’Université Laval

Biofilm formation on abiotic and biotic surfaces was studied with two hyphobacteria, strongly attached to the surface of the arbuscular mycorrhizal fungus (AMF) Rhizoglomus irregulare (Ri) DAOM 197198 and two mycorrhizobacteria, loosely attached to the roots of different mycorrhizal plants. When the sparingly soluble igneous phosphate rock (PR) from Quebec, or when the chemical hydroxyapatite were used as sole phosphorus (P) source, hyphobacteria Rhizobium miluonense Rm3 and Burkholderia anthina Ba8 produced significantly more biofilms than mycorrhizobacteria Rahnella sp. Rs11 and Burkholderiaphenazinium Bph12, as indicated by the crystal violet assay or by quantifying biofilm exopolysaccharides. As previously observed with planktonic bacteria, biofilms mobilized P by lowering the pH and releasing gluconic acid. The high efficiency of P mobilization by the hyphobacteria Ba8 was linked to the presence of more viable cells in its biofilm as revealed by the hydrolysis of fluorescein diacetate. Scanning electron microscopy micrographs showed a high adherence of the best P-solubilizer hyphobacteria Ba8 on the surface of Quebec PR. Hydroxyapatite porous structure did not allow a good adherence of Ba8. Ba8 formed an important biofilm on the hyphae of Ri DAOM 197198 with low reactive Quebec PR while no biofilm was observed with the high reactive hydroxyapatite. Results confirm the possible presence of specificity between the Ri DAOM 197198 and the hyphobacteria and suggest that the interaction would be regulated by the availability of P.

Bradyrhizobia and rhizobia are symbiotic bacterial partners forming nitrogen fixing nodules on legumes. These bacteria share characteristics with plant growth promoting rhizobacteria (PGPR). Nodule inducing bacteria, like other PGPR, are capable of colonizing the roots of non-legumes and produce phytohormones, siderophores and HCN. They also exhibit antagonistic effects towards many plant pathogenic fungi. The potential of nodule inducing bacteria to function as PGPR, was examined by using radish as a model plant. Three percent of the 266 strains tested were found to be cyanogens, while a majority (83%) produced siderophores. Fifty eight percent of the strains produced indole 3-acetic acid (IAA) and 54% solubilized phosphorus. Some of the bacterial species examined were found to have a deleterious effect while others were neutral or displayed a stimulatory effect on radishes. Bradyrizobium japonicum strain Soy 213 was found to have the highest stimulatory effect (60%), and an arctic strain (N44) was the most deleterious, causing a 44% reduction in radish dry matter yield. A second plant inoculation test, performed in growth cabinets, revealed that only strain Tal 629 of B. japonicum significantly increased (15%) the dry matter yield of radish. This indicates that specific bradyrhizobia have the potential to be used as PGPR on non-legumes.

Background: Arctic Mesorhizobium strain N33 was isolated from nodules of the legume Oxytropis arctobia in Canada’s eastern Arctic. This symbiotic bacterium can grow at temperatures ranging from 0 to 30 °C, fix nitrogen at 10 °C, and is one of the best known cold-adapted rhizobia. Despite the economic potential of this bacterium for northern regions, the key molecular mechanisms of its cold adaptation remain poorly understood. Results: Using a microarray printed with 5760 Arctic Mesorhizobium genomic clones, we performed a partial transcriptome analysis of strain N33 grown under eight different temperature conditions, including both sustained and transient cold treatments, compared with cells grown at room temperature. Cells treated under constant (4 and 10 °C) low temperatures expressed a prominent number of induced genes distinct from cells treated to short-term cold-exposure (<60 min), but exhibited an intermediate expression profile when exposed to a prolonged cold exposure (240 min). The most prominent up-regulated genes encode proteins involved in metabolite transport, transcription regulation, protein turnover, oxidoreductase activity, cryoprotection (mannitol, polyamines), fatty acid metabolism, and membrane fluidity. The main categories of genes affected in N33 during cold treatment are sugar transport and protein translocation, lipid biosynthesis, and NADH oxidoreductase (quinone) activity. Some genes were significantly down-regulated and classified in secretion, energy production and conversion, amino acid transport, cell motility, cell envelope and outer membrane biogenesis functions. This might suggest growth cessation or reduction, which is an important strategy to adjust cellular function and save energy under cold stress conditions. Conclusion: Our analysis revealed a complex series of changes associated with cold exposure adaptation and constant growth at low temperatures. Moreover, it highlighted some of the strategies and different physiological st

A simple method is described for trapping phosphate solubilizing bacteria (PSB) strongly attached to the hyphae of the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis (Ri). Bacteria were isolated from the hyphosphere of mycorrhizal leek plants growing on Turface previously inoculated with soil suspensions, obtained from the mycorrhizosphere of mycorrhizal plants growing in agricultural settings or maple forests in Quebec, Canada. Among the best PSB strongly attached to the hyphae of Ri, 26 isolates belonged to Burkholderia spp. and one was identified as Rhizobium miluonense. Four hyphobacteria exhibiting high potential of inorganic and organic P mobilization were further compared with four equivalent mycorrhizobacteria directly isolated from mycorrhizospheric soils sampled. In general, hyphobacteria were superior in mobilizing P from hydroxyapatite and from a low reactivity igneous phosphate rock from Quebec. Release of gluconic acid or the product of its oxidation 2-ketogluconic acid, are the main mechanisms involved in P solubilization. In a two compartments Petri plate system, Ri extraradical hyphal exudates, supported PSB growth and activity. In the absence of PSB Ri showed a negligible P solubilization activity. In the presence of PSB a substantial increase in P mobilization was observed, and the superiority of hyphobacterial activity was also observed under this system. Our results suggest that in developing a bioinoculant based on selected PSB, their interaction with AMF hyphae should not be overlooked.

Compost teas are fermented aqueous extracts of composted materials that are used for their ability to control plant pathogens. It had been previously reported that this inhibition by compost teas is at least partially attributed to the presence of live microorganisms. In this study, the inhibitory effects of bacteria from suppressive compost tea were examined against mycelial growth of Alternaria solani and Botrytis cinerea as well as disease development on tomato fruit. Isolation of antifungal extracts and identification of antifungal compounds from the most effective bacterial strains were also performed. Results showed that the bacteria had the ability to greatly inhibit the mycelial growth of B. cinerea and/or A. solani by up to 70%. The two most effective isolates, Brevibacterium linens (IC 10) and Bacillus subtilis, showed that co-application of bacterial antagonists (5 105 or 5 106 cells) with the pathogens on tomato fruit demonstrated inhibition of the development of B. cinerea lesions by up to 61%. A preventive application of the bacteria (5 105 or 5 106 cells) was more effective than co-application, allowing a significant reduction in lesions of A. solani and improving efficacy of low bacterial concentrations in reducing B. cinerea lesions. A combined B. linens/B. subtilis treatment was generally more inhibitory than either bacterium alone indicating possible synergistic effects. Antifungal compounds, including surfactins, were found in the bacterial extracts indicating that antibiosis is a main mechanism of action.

La carence de phosphore (P) est l’un des principaux facteurs limitant la production agricole au Mali. Les cultures répondent bien à la fertilisation phosphatée, mais le coût élevé des engrais chimiques importés restreint leur utilisation par les agriculteurs. Cependant, dans la vallée de Tilemsi, le Mali dispose de gisements de phosphates estimés entre 20 à 25 millions de tonnes, avec une teneur en P2O5 de l’ordre de 23 % à 30 %. Dans le but d’améliorer biologiquement l’absorption de phosphore par le maïs fertilisé avec du phosphate naturel de Tilemsi (PNT), l’effet de l’inoculation de souches de Bacillus isolées des sols maliens a été étudié. La croissance et la teneur en P de trois variétés de maïs ont été mesurées en 2007 ; la croissance, la teneur en P et le rendement de la variété de maïs Sotubaka ont été mesurés en 2008 dans des conditions de champ au Mali. L’expérimentation a été menée au cours des saisons agricoles de 2007 et 2008 à la station de recherche agronomique de Samanko située à 15 km au Sud-Ouest du District de Bamako au Mali. Elle est à une latitude de 12°. 31.552’ Nord, à une longitude de 8°.04.906’ Ouest et à une altitude de 316,8 m. Le sol est de type ferrugineux tropical peu lessivé, de texture limono sableuse avec 76 % de sable, 15 % de limon et 9 % d’argile (Labosep, IER, 2008). Un dispositif expérimental de type split- plit- plot à trois répétitions a été utilisé avec, en parcelles principales, la fertilisation (le PNT 300 kg/ha (insoluble), l’engrais chimique, le complexe céréale 100 kg/ha (17-17-17) et le témoin sans phosphore. Toutes les parcelles ont reçu la même quantité d’azote N équivalente à 150 kg d’urée. Les compléments N et K de l’engrais chimique ont été corrigés pour toutes les autres parcelles. Les parcelles secondaires étaient composées de trois variétés de maïs (Dembanyuman, Sotubaka, Tiémantié) et les parcelles tertiaires étaient composées de témoin non inoculé et les six inoculations avec les lignées de Bacillus solubilisa, Phosphorus (P) deficiency is one of the major factors limiting crop production in Mali. Crops respond well to P fertilization, but the high cost of imported chemical fertilizers restrains their use by farmers. However, Mali has in the Tilemsi valley, phosphate rock (PR) deposits estimated between 20 to 25 million tonnes with P2 O5 content in the range of 23% to 30%. With the aim of improving biologically P uptake by maize fertilized with Tilemsi phosphate rock (TPR), the inoculation effect of TPR-solubilizing Bacillus strains isolated from Malian soils was investigated. The growth and P concentration of three cultivars of maize were measured in 2007 ; growth, P concentration and yield of the cultivar Sotubaka of maize were measured in 2008 under field conditions in Mali. Experimental plots were established at the Samanko agronomic research station (latitude 120 31’ N. 80 4’ W, altitude 316.8 m) in 2007 and 2008, located at 15 km from Bamako district. The soil is ferralitic tropical washed type, sand limon texture with 76% of sand, 15% of limon and 9% of clay (Labosep, IER, 2008). A split- split- plot experimental design with three replicates was used. The three main plot treatments included P addition at 300 kg/ha TRP, 100 kg/ha of Complex cereal, the chemical fertilizer (17-17-17) and a control which did not receive any P. All plots received the same amount of N equivalent to 150 kg/ ha urea. The additional N and K added with the chemical fertilizer were corrected for all other plots. The sub-plots were the three cultivars of maize (Dembanyuman, Sotubaka and Tiemantie) and the sub-sub plots included an uninoculated control and inoculation with six TRP-solubilizing Bacillus strains, all belonging to the Bacillus subtilis subsp. subtilis (T); DSM10. Our results have shown that P-fertilization of the cultivar of maize with TPR or the chemical fertilizer (17-17- 17) significantly improved grain and shoot dry matter yields. Inoculation with TPRsolubilizing bacteria did

About 2–5% of rhizobacteria, when present in large number, are able to promote plant growth. Production of plant hormones and improving mineral nutrition are examples of direct promotion, while protecting plants against many diseases caused by bacteria, fungi, viruses, nematodes, or insects is indirect mechanism of growth promotion.

Compost teas are fermented watery extracts of composted materials that are used for their beneficial effects on plants including antimicrobial activities. Non-aerated compost teas (NCT) prepared from seaweed compost, shrimp powder compost, and chicken, bovine and sheep manure composts were tested for their effect on the in vitro growth of tomato root pathogens and for their effect on the development of damping-off diseases caused by Pythium ultimum and Rhizoctonia solani. Results showed that NCT prepared from the five types of compost had the ability to greatly reduce mycelial growth of P. ultimum, R. solani, Fusarium oxysporum f. sp. radicis-lycopersici and Verticillium dahliae in vitro. Sterilization of the NCT caused complete or partial loss of their inhibitory effect on mycelial growth of the pathogens. Application of NCT decreased the percentage of necrotic seedlings in P. ultimum-inoculated tomato seeds from 42% to 100%, but did not reduce necrosis in R. solani-inoculated seeds. When applied on tomato seedlings inoculated with damping-off pathogens, various NCT also increased seedling fresh and/or dry weights., Les thés de compost sont des extraits aqueux fermentés de matériaux compostés. On reconnaît aux thés de compost des effets bénéfiques sur les plantes attribuables à leur activité antimicrobienne. Des thés de composts non-aérés (TCNA) à base de compost d'algues, de compost de poudre de crevette et de composts de fumier de poulet, de bovin et de mouton ont été testés afin d'évaluer leurs effets sur la croissance in vitro de différents agents pathogènes de la tomate. L'effet des TCNA sur le développement de la fonte des semis, causée par Pythium ultimum et Rhizoctonia solani, a également été évalué. Les résultats ont montré que les TCNA à base des cinq types de composts réduisent la croissance mycélienne de P. ultimum, R. solani, Fusarium oxysporum f. sp. radicis-lycopersici et Verticillium dahliae in vitro. La stérilisation des TCNA a par ailleurs conduit à une perte complète ou partielle de leur effet inhibiteur sur la croissance mycélienne des agents pathogènes. Appliqués sur les semences de tomate inoculées avec P. ultimum, les TCNA ont réduit de 42 à 100% le pourcentage de semences présentant des lésions nécrotiques. Les TCNA n'ont pas eu un tel effet chez les semences inoculées avec R. solani. L'application de certains TCNA sur les semences de tomate inoculées avec les agents pathogènes de la fonte des semis a résulté en une augmentation du poids sec et/ou humide des jeunes plants.

Phosphorus (P) is vital for plant growth. However, most added soluble P forms insoluble phosphates. Therefore, inorganic P (Pi) accumulates in soils. Soil organic P (Po) is another important reserve (20 to 80% of total soil P). To be available for plant Po must first be mineralized by soil microorganisms. The variability of the results of inoculation trials with P solubilizing microorganisms (PSMs) clearly reflects the complexity of the interactions occurring in the soil-plant-microbes-fauna ecosystem. Important points overlooked in previous studies will be presented and perspectives of the use of PSMs to allow the plant to benefit from soil reserves in Pi and Po will be discussed.

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 sub

Untreated greenhouse effluents or leak solution constitute a major environmental burden because their nitrate and phosphate concentrations may induce eutrophication. Artificial wetlands may offer a low cost alternative treatment of greenhouse effluents and consequently improve the sustainability of greenhouse growing systems. The objectives of this study were to 1) characterize the efficiency of different types of wetland to reduce ion content of greenhouse tomato effluent, and 2) improve the wetland efficiency by adding carbon of 0-800 mg L-1 sucrose. Experiments were conducted at Laval University where 30 pilot scale horizontal subsurface flow artificial wetlands (0.81 m3) were built. Two types of aquatic macrophytes, Pragmites australis and Typha latifolia, and a control group without plants were tested. The hydraulic retention time was 10 days. During the study, EC of the greenhouse effluent ranged between 1.5 to 5.5 mS cm-1, while 0 to 800 mg L-1 of sucrose was provided to improve the biological activity of the wetland. The macro- and micro-elements, the greenhouse gases (CH4, CO2, N2O) and the population of bacteria were measured for each unit. At commercial scale, two vertical subsurface wetlands (43.2 m3) were installed at Ste-Sophie Québec, on the production site of Les Serres Nouvelles Cultures (Sagami). According to our results, 50-90% of nitrate (NO3-) and 40-100% of phosphate (PO43-) were removed from the effluent. At Laval University, artificial wetlands with Typha latifolia were more efficient than wetlands with Phragmites australis or without plants. Addition of sucrose increased wetlands’ microbial population and consequently reduced the mineral content of the wastewater, but increased significantly the emission of greenhouse gases. Results will further be discussed in terms of the best wetland design to treat greenhouse effluents, but also in terms of the environmental impact.

We investigated the in vitro influence of humic substances (HS) extracted from de-inking paper sludge compost on the inhibition of Pythium ultimum by two compost bacteria, Rhizobium radiobacter (Agrobacterium radiobacter) and Pseudomonas aeruginosa. When low concentrations (5 or 50 mgzl−1) of HS were added to the culture medium, fungal inhibition by R. radiobacter significantly increased (P < 0.01) by 2–3%. In contrast, these low levels of HS had no effect on P. ultimum inhibition by P. aeruginosa. The Fe, chelated by HS, was in part responsible for the decrease of P. ultimum inhibition by the bacteria when increasing amounts of HS were added in the culture medium. The addition of 500 mgl−1 of humic acids isolated from de-inking paper sludge compost or from fossil origin completely eliminated the inhibition of P. ultimum by R. radiobacter. This Fe effect also stimulated growth of R. radiobacter and reduced its siderophore production in a minimal medium supplemented with HS as sole source of Fe. The results showed that HS influence microbial antagonism when added to a culture medium. However, this effect varies with different factors such as the type of bacteria, concentration of HS, molecular weight and Fe content.