Niokhor Bakhoum - Academia.edu (original) (raw)

Papers by Niokhor Bakhoum

Plant Journal, Nov 22, 2021

Soil is a living ecosystem, the health of which depends on fine interactions among its abiotic an... more Soil is a living ecosystem, the health of which depends on fine interactions among its abiotic and biotic components. These form a delicate equilibrium maintained through a multilayer network that absorbs certain perturbations and guarantees soil functioning. Deciphering the principles governing the interactions within soils is of critical importance for their management and conservation. Here, we focus on soil microbiota and discuss the complexity of interactions that impact the composition and function of soil microbiota and their interaction with plants. We discuss how physical aspects of soils influence microbiota composition and how microbiota-plant interactions support plant growth and responses to nutrient deficiencies. We predict that understanding the principles determining the configuration and functioning of soil microbiota will contribute to the design of microbiota-based strategies to preserve natural resources and develop more environmentally friendly agricultural practices.

Acacia senegal (L) Willd. and Acacia seyalDel. are highly nitrogen-fixing and moderately salt tol... more Acacia senegal (L) Willd. and Acacia seyalDel. are highly nitrogen-fixing and moderately salt tolerant species. In this study we focused on the genetic and genomic diversity of Acacia mesorhizobia symbionts from diverse origins in Senegal and investigated possible correla-tions between the genetic diversity of the strains, their soil of origin, and their tolerance to sa-linity. We first performed a multi-locus sequence analysis on five markers gene fragments on a collection of 47 mesorhizobia strains of A. senegal and A. seyal from 8 localities. Most of the strains (60%) clustered with theM. plurifarium type strain ORS 1032T, while the others form four new clades (MSP1 to MSP4). We sequenced and assembled seven draft genomes: four in theM. plurifarium clade (ORS3356, ORS3365, STM8773 and ORS1032T), one in MSP1 (STM8789), MSP2 (ORS3359) and MSP3 (ORS3324). The average nucleotide identities be-tween these genomes together with the MLSA analysis reveal three new species ofMesorhi-zobiu...

Journal of Agricultural Biotechnology and Sustainable Development, 2017

This study aimed at selecting an effective microbial inoculum to enhance the performance of Seneg... more This study aimed at selecting an effective microbial inoculum to enhance the performance of Senegalia senegal, Vachellia seyal and Prosopis juliflora and assessing the combination effect of microbial inoculation and peanut shells amendment on their growth under salinity in greenhouse conditions. In the first experiment, seedlings were individually cultivated in plastic bags containing non-sterile sandy soil. Seedlings were inoculated at transplantation with rhizobial and arbuscular mycorrhizal fungi (AMF) strains. Four inoculation treatments were performed: control, inoculation with rhizobia, inoculation with AMF and dual-inoculation with rhizobia and AMF. After one month, seedlings were gradually watered with four saline solutions (0, 86, 171 and 257 mM NaCl) for 4 months. ANOVA showed that inoculation treatments significantly increased seedlings growth particularly in saline conditions and the best performance was obtained with dual inoculation. In the second experiment, seedlings were grown under the same experimental conditions on a mixture of non-sterile sandy soil and 6 tha-1 (169.56 g per bag) of peanut shells var 73-33. Results showed that inoculation, peanut shells and their combination significantly improved seedlings growth. The higher performance was obtained with the combination of microbial inoculation and peanut shells.

African Journal of Microbiology Research, 2018

The overuse of chemical fertilizers in agriculture remains an environmental concern, especially i... more The overuse of chemical fertilizers in agriculture remains an environmental concern, especially in sub-Saharan areas of Africa where soil degradation lead to low crop yield. Crop inoculation with beneficial microorganisms appears a good alternative to reduce chemical substances and improve yield. In this regard, studies on soil biological activities and inoculation experiments on maize (Zea mays L.) and peanut (Arachis hypogaea L.) crops were conducted. The aim of this work was to evaluate the effect of these crops on soil microbial activities and to assess their response to inoculation with two fungi (Glomus aggregatum and Glomus etunicatum) alone or in combination. Rhizospheric and non rhizospheric soils were collected in peanut and maize fields at Takali in northern Côte d'Ivoire. Soil enzymes activities, total microbial biomass, AMF spore and rhizobia densities were determined in these soils. Then, mycorrhizal inoculation experiment of these plant species was conducted in a greenhouse located at

International Journal of Biosciences (IJB), 2015

Microbial Ecology, 2021

The intensification of biological processes coping with salt stress became a major issue to mitig... more The intensification of biological processes coping with salt stress became a major issue to mitigate land degradation. The Sine-Saloum Delta in Senegal is characterized by salt-affected soils with vegetation dominated by salt-tolerant grass Sporobolus robustus and shrubs like Prosopis juliflora. Plant experiments in controlled conditions suggested that arbuscular mycorrhizal (AM) fungi might be the key actors of facilitation process observed between S. robustus and P. juliflora, but the AM fungal community determinants are largely unknown. The current field-based study aimed at (1) characterizing the environmental drivers (rhizosphere physico-chemical properties, plant type and season) of the AM fungal community along an environmental gradient and (2) identifying the AM fungal taxa that might explain the S. robustus-mediated benefits to P. juliflora. Glomeraceae predominated in the two plants, but a higher richness was observed for S. robustus. The pH and salinity were the main drivers of AM fungal community associated with the two plants, negatively impacting richness and diversity. However, while a negative impact was also observed on mycorrhizal colonization for S. robustus, P. juliflora showed opposite colonization patterns. Furthermore, no change was observed in terms of AM fungal community dissimilarity between the two plants along the environmental gradient as would be expected according to the stress-gradient and complementary hypotheses when a facilitation process occurs. However, changes in intraspecific diversity of shared AM fungal community between the two plants were observed, highlighting 23 AM fungal OTUs associated with both plants and the highest salinity levels. Consequently, the increase of their abundance and frequency along the environmental gradient might suggest their potential role in the facilitation process that can take place between the two plants. Their use in ecological engineering could also represent promising avenues for improving vegetation restoration in saline Senegalese's lands.

Arbuscular mycorrhizal fungi and rhizobia are two important plant symbionts. Rhizobia are known f... more Arbuscular mycorrhizal fungi and rhizobia are two important plant symbionts. Rhizobia are known for fixing nitrogen inside legume root nodules while Arbuscular mycorrhizal (AM) fungi provide plants with nutrients and other benefits. AM fungi are ubiquitous soil microorganisms and establish a symbiotic relationship with more than 80% of plant species of natural ecosystems while rhizobia association is more specific and involved almost leguminous plants. The symbiosis between legumes-Rhizobium and arbuscular mycorrhizal fungi (AMF) improves plant growth and tolerance against biotic and abiotic stress. This suggests that it is possible to use rhizobia and mycorrhizal to mitigate detrimental impacts of these stresses on terrestrial ecosystem health and agricultural productivity. This will lead to accelerate the natural process of re-vegetation in decertified semiarid ecosystem. AMF and rhizobia interactions in legumes host are complex and our understanding of their impact on plant growt...

Arid Land Research and Management, 2016

Seedlings of S. robustus were exposed to increasing NaCl concentrations (0, 50, 100, 150, 200, 25... more Seedlings of S. robustus were exposed to increasing NaCl concentrations (0, 50, 100, 150, 200, 250, and 300 mM) for 50, 100, and 150 days, in greenhouse conditions. Total dry weight and salt tolerance index decreased gradually with increasing NaCl concentrations. The optimum growth of S. robustus (4.12 to 5.25 g • plant À 1) was obtained between 0 and 150 mM at 150 days after salt stress. Foliar chlorophyll a and total chlorophyll contents increased with NaCl concentration at 50 days after treatment. There was no significant effect of salinity on chlorophyll a, b and total chlorophyll contents at 100 and 150 days after treatment. Higher Na contents were found in the shoots as compared to the roots. The Na content increased, while K decreased with increasing NaCl concentrations, suggesting competitive inhibition between absorptions of Na and K as a consequence, the K/Na ratios in shoots and roots decreased with increasing salinity. The proline contents in S. robustus were more pronounced at 300 mM (2.02 µmol/g), 250 mM (2.64 µmol/g), and 200 mM NaCl concentrations (2.98 µmol/g) for 50, 100, and 150 days, respectively, as compared to the treatment without added NaCl. Overall, S. robustus could be considered as salt tolerant on the basis of their performance in biomass production, accumulation of Na, similar foliar chlorophyll a, chlorophyll b and total chlorophyll contents, and accumulation of proline with increasing salinity. The potential ability of S. robustus to accumulate significant amounts of Na makes this halophyte promising as a desalinization tool of salted soils.

Frontiers in Plant Science, 2016

La salinisation des terres est un problème environnemental majeur et croissant, particulièrement ... more La salinisation des terres est un problème environnemental majeur et croissant, particulièrement dans les zones arides et semi-arides du monde. Les techniques d’inoculation microbienne contrôlée avec des espèces tolérantes au sel pourraient être exploitées pour la réhabilitation des sols affectés par la salinité. A l’effet de montrer l’importance des communautés microbiennes symbiotiques sur la tolérance au stress salin de plants d’A. seyal, nous avons testé l’efficience de différentes formes d’inoculum sur le fonctionnement de la symbiose A. seyal-rhizobium en conditions de stress salin. L’augmentation de la colonisation racinaire par les rhizobiums et les CMA, l’amélioration de la croissance des plants et de l’absorption de nutriments notées dans cette étude démontrent l’importance de l’inoculation microbienne pour la réduction des effets du stress salin sur les plants d’A. seyal cultivés en conditions de salinité. La double inoculation avec des rhizobiums et un cocktail de CMA a ...

Acacia senegal is a multipurpose legume that is economically and ecologically important in Saheli... more Acacia senegal is a multipurpose legume that is economically and ecologically important in Sahelian areas. The effects of arbuscular mycorrhizal fungal (AMF) inoculum (M) individually and in combination with rhizobia (R) and Pseudomonas fluorescens (P f) were investigated on the growth and nutrition of A. senegal seedlings. In glasshouse conditions, all the inocula except P f significantly enhanced A. senegal plant growth after 6 months in a non-sterile soil from Dahra (Senegal). However, no significant increase in shoot N content was recorded, whereas the application of MR, MP f and MRP f significantly improved shoot P content, and that of MR and MP f , shoot K content. The nodule number was significantly augmented by rhizobial inoculation and the root mycorrhizal colonization rate by MR, MP f and MRP f treatments. Soil spore density was increased by all inoculants except MP f , and soil AMF hyphal length by M, R and MRP f treatments. The inoculation with Pseudomonas and MP f signi...

Open Journal of Forestry, 2014

Distribution and diversity of rhizobial strains associated with Acacia senegal (L.) Willd. in rel... more Distribution and diversity of rhizobial strains associated with Acacia senegal (L.) Willd. in relation to seed provenances in soils from arid (Dahra) and semiarid (Goudiry) zones of Senegal were investigated. PCR-RFLP performed on 16S-23S rDNA intergenic spacer (IGS) of nodule crude extracts revealed a high genetic diversity of rhizobial strains, which was higher in the semiarid region than in the arid region. The distribution of rhizobial populations was influenced by soil physical and chemical characteristics, and by A. senegal provenances as shown by the analysis of correspondence. In contrast, the phenotypic diversity of rhizobial strains was not correlated with the soil origin. The phylogenetic tree (performed by the maximum likelihood algorithm) of IGS 16S-23S sequences showed that most of the rhizobial strains nodulating A. senegal were closely related to Mesorhizobium plurifarium. Our results showed that rhizobial taxa associated with A. senegal were mainly distributed according to soil physical and chemical characteristics, and A. senegal provenances. A large subset of A. senegal root-nodulating bacteria had high diversity that correlated with the most favourable environmental conditions. Understanding the diversity and distribution of rhizobial strains may be exploited in the formulation of A. senegal inoculants for different seed provenances for resilience to soil stresses in various environmental conditions.

Microbial Ecology, 2014

Acacia senegal and Acacia seyal are small, deciduous legume trees, most highly valued for nitroge... more Acacia senegal and Acacia seyal are small, deciduous legume trees, most highly valued for nitrogen fixation and for the production of gum arabic, a commodity of international trade since ancient times. Symbiotic nitrogen fixation by legumes represents the main natural input of atmospheric N 2 into ecosystems which may ultimately benefit all organisms. We analyzed the nod and nif symbiotic genes and symbiotic properties of root-nodulating bacteria isolated from A. senegal and A. seyal in Senegal. The symbiotic genes of rhizobial strains from the two Acacia species were closed to those of Mesorhizobium plurifarium and grouped separately in the phylogenetic trees. Phylogeny of rhizobial nitrogen fixation gene nifH was similar to those of nodulation genes (nodA and nodC). All A. senegal rhizobial strains showed identical nodA, nodC, and nifH gene sequences. By contrast, A. seyal rhizobial strains exhibited different symbiotic gene sequences. Efficiency tests demonstrated that inoculation of both Acacia species significantly affected nodulation, total dry weight, acetylene reduction activity (ARA), and specific acetylene reduction activity (SARA) of plants. However, these cross-inoculation tests did not show any specificity of Mesorhizobium strains toward a given Acacia host species in terms of infectivity and efficiency as stated by principal component analysis (PCA). This study demonstrates that largescale inoculation of A. senegal and A. seyal in the framework of reafforestation programs requires a preliminary step of rhizobial strain selection for both Acacia species.

ISRN Ecology, 2012

The responses of the soil microbial community features associated to the legume tree Acacia seneg... more The responses of the soil microbial community features associated to the legume tree Acacia senegal (L.) Willd. including both arbuscular mycorrhizal fungal (AMF) diversity and soil bacterial functions, were investigated under contrasting environmental conditions. Soil samples were collected during dry and rainy seasons in two contrasting rainfall sites of Senegal (Dahra and Goudiry, in arid and semiarid zone, resp.). Soils were taken from the rhizosphere of A. senegal both in plantation and natural stands in comparison to bulk soil. A multiple analysis revealed positive correlations between soil physicochemical properties, mycorrhizal potential and enzyme activities variables. The positive effects of A. senegal trees on soil mycorrhizal potential and enzyme activities indicates that in sahelian regions, AMF spore density and diversity as well as soil microbial functions can be influenced by land-use systems (plantation versus natural population of A. senegal) and environmental cond...

Symbiosis, 2011

The combined effects of drought and salinity were investigated on the growth, efficiency and comp... more The combined effects of drought and salinity were investigated on the growth, efficiency and competitiveness of three Mesorhizobium sp. strains (ORS 3416, ORS 3428 and ORS 3437) isolated from Acacia senegal (L.) Willd. Sixteen combinations of polyethylene glycol (PEG) 6000 (0, 6, 12, 20%, w/v) and NaCl (0.005, 0.5, 1, 1.5%, w/v) were used to study rhizobial strains growth in screw-capped tubes containing yeast extract mannitol liquid medium. Whatever the combination, the strains grew. However, high concentrations of PEG 6000 and NaCl were depressed on rhizobial growth but strain ORS 3428 was the most tolerant. The effect of rhizobial inoculation on growth of A. senegal plants was also examined under non-limited (100% of water holding capacity, WHC) and water-limited conditions (50% WHC) in the greenhouse for 4 months on non-sterile sandy soil. A significant decrease in the nodulation rate, nodule dry weight, plant height and shoot dry weight was observed under water-limited conditions. Nevertheless, inoculation with the three selected Mesorhizobium strains significantly improved nodulation and A. senegal plant growth under water-limited conditions. Whatever the irrigation condition, strains ORS 3428 and ORS 3437 were more competitive than ORS 3416. These rhizobial strains may prove valuable for inoculation of Acacia senegal plants grown for transplantation to dry saline habitats.