Presence Of Rhizobia Research Articles

A Comprehensive Process Of Nitrogen Fixation In Plants

Nitrogen is a component of several biomolecules that are essential for all organisms' growth and development. Nitrogen fixation is the biological process that converts molecular nitrogen to ammonia. Biological nitrogen fixation is mediated by diazotroph microorganisms that use nitrogenase enzymes to enhance atmospheric nitrogen. Much of this is accomplished through a symbiotic interaction between plants and diazotrophic bacteria. Microbiology and plant biology are discussed in symbiotic nitrogen fixation discussions. Some of the nitrogen fixation mechanisms mentioned in this paper begin with the formation of nodules, the action of the nitrogenase enzyme in reducing nitrogen to ammonia, and the presence of rhizobia in nodules. This study provides a comprehensive overview of the nodule formation process, the role of the nitrogenase enzyme in reducing nitrogen to ammonia, and the presence of rhizobia in nodules. A more complete literature review on biological nitrogen fixing in plants is required to obtain more specific information.

Sucrose-induced auxin conjugate hydrolase restores symbiosis in a Medicago cytokinin perception mutant.

Rhizobia-legume interactions recruit cytokinin for the induction of nodule primordia in the cortex. Cytokinin signaling regulates auxin transport and biosynthesis, causing local auxin accumulation, which triggers cortical cell division. Since sugar signaling can trigger auxin responses, we explored whether sugar treatments could rescue symbiosis in the Medicago truncatula cytokinin response 1 (cre1) mutant. Herein, we demonstrate that sucrose and its nonmetabolizable isomer turanose can trigger auxin response and recover functional symbiosis in cre1, indicating sucrose signaling to be necessary for the restoration of symbiosis. In both M. truncatula A17 (wild type) and cre1, sucrose signaling significantly upregulated IAA-Ala Resistant 3 (IAR33), encoding an auxin conjugate hydrolase, in rhizobia-infected as well as in uninfected roots. Knockdown of IAR33 (IAR33-KD) significantly reduced nodulation in A17, highlighting the importance of deconjugation-mediated auxin accumulation during nodule inception. In cre1, IAR33-KD restricted the sucrose-mediated restoration of functional symbiosis, suggesting that deconjugation-mediated auxin accumulation plays a key role in the absence of CRE1-mediated auxin biosynthesis and transport control. Overexpression of IAR33 also restored functional symbiosis in cre1, further suggesting that IAR33 mediates auxin accumulation in response to sucrose signaling. Since all the observed sucrose-mediated responses were common to A17 and cre1, deconjugation-mediated auxin response appeared to be independent of CRE1, which normally governs local auxin accumulation in the presence of rhizobia. We propose that sucrose-dependent restoration of symbiosis in cre1 occurs by the activation of IAR33-mediated auxin deconjugation.

Presence of rhizobia nodulating common birdsfoot trefoil (Lotus corniculatus L.) in soils of Serbia

Common birdsfoot trefoil (Lotus corniculatus L.) is a perennial forage legume tolerant to adverse environmental conditions such as low soil pH, poor drainage, various insects and plant diseases. Owing to its ability to establish a symbiosis with nitrogen-fixing bacteria, rhizobia, thrives on soils of low fertility and is used in grass mixtures to enrich the soil with nitrogen. The aim of the work was to investigate the presence of rhizobia that nodulate birdsfoot trefoil in the soils of Serbia and to perform the isolation and evaluation of their nitrogen fixation potential. The presence and abundance of birdsfoot trefoil rhizobia in 28 soil samples from different localities and types of soil in Serbia, as well as different ways of use, was tested. From positive samples the rhizobial strains were isolated and their efficiency of nitrogen fixation was tested under controlled conditions. The presence of rhizobia that nodulate birdsfoot trefoil was recorded in 23 samples, while all 5 samples where the presence of rhizobia was not recorded are characterized by the absence of the host plant. The number of rhizobia in samples where there was no host plant was significantly less than in its presence. A total of 49 rhizobial strains were isolated, and in some samples of low abundance it was not possible to isolate strains. In controlled conditions during reinoculation, 80% of the strains were active, achieving 2.5 times greater dry above-ground mass than non-inoculated plants. The percentage of nitrogen in plants ranged from 1.6% in the case of inactive strains to 4.6% in the case of highly active strains. The results of the study indicate the necessity of inoculation, that is, the application of rhizobia on the lands where the common birdsfoot trefoil is sown for the first time due to their reduced number and activity.

Prosopis laevigata and Acacia farnesiana in association with Rhizobium sp. remove copper from soil

• Cu affects the development of P. laevigata and A. farnesiana at a concentration greater than that at which it affects other plants. • Rhizobium sp provides better conditions for both P. laevigata and A. farnesiana to better tolerate the stress produced by the presence of Cu . • Rhizobium sp facilitates Cu to accumulate in the root of P. laevigata and A. farnesiana more than in the aerial part of the plants. • P. laevigata cultivated in the presence of Rhizobium has the potential to be used in phytoremediation of soil contaminated with Cu. Industrial and agricultural activities have increased the amounts of heavy metals on the Earth's crust, risking organisms and ecosystem stability. Phytoremediation is a technique to remove heavy metals from contaminated sites. Soil phytoremediation involves many processes in which, not only plants participate, but also microorganisms present in the rhizosphere. Legumes form symbiotic associations with rhizobacteria that promote plant development. Acacia farnesiana and Prosopis laevigata are two species of the legume family with suitable characteristics for phytoremediation. In this work, we found that both A. farnesiana and P. laevigata tolerate high concentrations of copper, and can remove this metal from the soil. P. laevigata gave better results than A. farnesiana. P. laevigata inoculated with Rhizobium sp showed greater copper bioaccumulation in the root, while the plants without these bacteria presented more copper accumulation in the aerial parts of the plants.

Host mediated microbiome selection to study the changes in the nutrient cycling, root exudation and microbial population in the rhizosphere of soybean genotypes

The study was conducted with an aim to understand the changes in soil enzyme activity in the plant rhizosphere during host mediated selection of rhizosphere microbiome. Soil samples were collected from three different locations on a farm in the Reading area, UK. Two popular genotypes of Soybean (Glycine max) were chosen for the study, Kenchen and Siverka. Initial microbiome inoculum was prepared by mixing field soil with sterilized water and this was added to the autoclaved coir: sand mix. After four weeks of plant growth, plants were uprooted from the soil, rhizosphere soil collected for soil enzyme estimation and NGS analysis. Root exudates were collected and stored in freezer for analysis. Growth of plants in legume soils was significantly higher. The plants in legume soil produced nodules which confirmed the presence of rhizobia in these soils. Independent analysis within each soil type showed that, the interaction between soil type and genotype is very significant with respect to enzyme activity. The presence of microbiome along with plants had a significant effect on enzymatic activity. GCMS analysis of root exudates from plants in each soil showed variations in individual chromatograms. The difference in enzyme activity with plant growth shows that there are changes taking place in the soil. Further in this study, NGS analysis of rhizosphere soil will shed more light into the changes happening in the soil microbiome and if the changes are related to the enzymatic changes and plant root exudation.

Differential Response of Rhizobium Leguminosarum Inoculation for Inducing Water Deficit Tolerance in Triticum Durum

Limited soil water availability is a major threat to agricultural productivity because it inhibits plant growth and yields. Soil microorganisms having the ability to alleviate abiotic stress and promoting plant development would be highly valuable tools in sustainable agriculture. To this purpose, two Rhizobium leguminosarum strains were tested for their potential to induce tolerance against water deficits in Triticum durum grown under two hydric conditions in greenhouse experiments. For this, physiological and biochemical parameters were measured as criteria to assess the effect of R. leguminosarum inoculation on T. durum under water deficiency. In the presence of rhizobia, wheat plants were able to withstand water stress more effectively than un-inoculated plant, as indicated by the recorded increases in relative water content of inoculated plants compared to un-inoculated plants, higher accumulation of osmoprotectant (soluble sugar), lower MDA and H2O2 accumulation, and increased in antioxidant responses (peroxidase). Under water-limited condition, co-inoculation of selected rhizobia was better than single application for one of studied genotype, which let us hypothesize that this variation in responsiveness indicates a possible genotype effect. As a result, rhizobia from various legumes have a huge potential for enhancing the water deficiency stress tolerance of cereals.

Selected autochthonous rhizobia, applied in combination with AM fungi, improve seed quality of common bean cultivated in reduced fertilization condition

Phaseolus vulgaris cv. Billò is an important crop, widely cultivated in Western Piedmont (Italy). It can form symbioses both with arbuscular mycorrhizal fungi (AMF) and bacteria belonging to the Rhizobium genus: AMF can improve plant nutrition and fruit/seed quality, whereas R. leguminosarum is a Gram-negative bacterium able to fix atmospheric nitrogen. In this study, 15 Rhizobium strains, isolated either from root nodules or soil, were characterized by molecular and biochemical point of view (P-solubilization, siderophore and IAA production, intrinsic antibiotic resistance) and one of the selected strains was used for field trial. The aims were: i) to select highly efficient symbiotic bacteria adapted to local conditions and ii) to assess bean seed yield and quality, in response to AMF/rhizobia inoculation at reduced fertilization level. At harvest, yield (pod and seed number and weight) and seed quality (starch, protein, fiber and mineral concentrations), root nodulation and mycorrhizal colonization were measured. Inoculation did not influence yield and fiber concentration. On the contrary, the total seed protein amount was higher in the seeds of rhizobium-inoculated plants in combination or without AMF than in uninoculated plants. The starch content in seeds was increased by rhizobia inoculation. Mg, K and Zn seed accumulation was positively affected by AMF, while the Mn concentration was higher in the presence of rhizobia. In conclusion, plant inoculation strongly affected seed characteristics, improving bean quality also in conditions of reduced fertilization.

Root colonization by heavy metal resistant Enterobacter and its influence on metal induced oxidative stress on Cajanus cajan.

Heavy metal resistant bacterium Enterobacter sp. C1D was evaluated for cadmium (Cd) mediated exopolysaccharide production, biofilm formation and legume root colonization ability under Cd stress to alleviate metal induced stress. The plant was sensitive to Cd (IC50 3-4μg mL-1 ), whereas the bacterium showed high Cd tolerance (MIC99 120 μg mL-1 ). Confocal laser scanning microscopy of the Cajanus cajan roots showed heavy loads of green fluorescence protein labelled Enterobacter sp. C1D on the surface of plant root, specifically at the point of root hair/lateral root formation along with cortex, even under metal stress. The root colonizing ability of Enterobacter sp. C1D was not affected by the presence of Rhizobium and the bacteria could be observed after 30 days of incubation in soil. Various plant growth parameters, antioxidant metabolites and oxidative stress indicator were significantly influenced by bacterial treatment, which, overall, reduced the adverse effect of Cd. Heavy metal tolerant bacteria may be a good choice for the development of biofertilizers and may work well with the native soil microbes such as Rhizobium under the metal polluted soil. © 2019 Society of Chemical Industry.

Plant Hormones Differentially Control the Sub-Cellular Localization of Plasma Membrane Microdomains during the Early Stage of Soybean Nodulation.

Phytohormones regulate the mutualistic symbiotic interaction between legumes and rhizobia, nitrogen-fixing soil bacteria, notably by controlling the formation of the infection thread in the root hair (RH). At the cellular level, the formation of the infection thread is promoted by the translocation of plasma membrane microdomains at the tip of the RH. We hypothesize that phytohormones regulate the translocation of plasma membrane microdomains to regulate infection thread formation. Accordingly, we treated with hormone and hormone inhibitors transgenic soybean roots expressing fusions between the Green Fluorescent Protein (GFP) and GmFWL1 or GmFLOT2/4, two microdomain-associated proteins translocated at the tip of the soybean RH in response to rhizobia. Auxin and cytokinin treatments are sufficient to trigger or inhibit the translocation of GmFWL1 and GmFLOT2/4 to the RH tip independently of the presence of rhizobia, respectively. Unexpectedly, the application of salicylic acid, a phytohormone regulating the plant defense system, also promotes the translocation of GmFWL1 and GmFLOT2/4 to the RH tip regardless of the presence of rhizobia. These results suggest that phytohormones are playing a central role in controlling the early stages of rhizobia infection by regulating the translocation of plasma membrane microdomains. They also support the concept of crosstalk of phytohormones to control nodulation.

ERN1 and CYCLOPS coordinately activate NIN signaling to promote infection thread formation in Lotus japonicus

Legumes engage in symbiosis with nitrogen-fixing soil bacteria, collectively called rhizobia, under nitrogen-limited conditions. In many legumes, the root invasion of rhizobia is mediated by infection threads (ITs), tubular invaginations of the host cell wall and plasma membrane, developed from infection foci of deformed root hairs. IT formation is regulated by a series of signal transduction in host root. Nodulation signals activate the host transcription factor (TF), CYCLOPS, which directly induces expression of two TF genes, ERF REQUIRED FOR NODULATION1 (ERN1) and NODULE INCEPTION (NIN), essential for IT development. Here, we explored the relationship among these three symbiotic TF genes in the model legume Lotus japonicus and examined how their interplay contributes to IT formation. qRT-PCR analysis showed that NIN expression induced by rhizobial infection was attenuated in ern1-1, and further declined in cyclops-3 ern1-1. ERN1 overexpression led to induction of NIN expression in cyclops-3 ern1-1 in the presence of rhizobia. Thus, in addition to CYCLOPS, ERN1 is able to increase the NIN expression level depending on infection. Furthermore, consistent with this transcriptional hierarchy, ectopic expression of ERN1 as well as NIN suppressed the IT-deficient cyclops-3 phenotype, but ERN1 failed to confer ITs in the nin-2 root. However, the ern1-1 symbiotic epidermal phenotype was not suppressed by the NIN ectopic expression. The cyclops-3 ern1-1 double mutant was less sensitive to rhizobial infection than the single mutants and defective in the symbiotic root hair response at earlier stages. This more severe phenotype of the double mutant suggests a role for ERN1 that independent of the CYCLOPS-mediated transcriptional regulation. We conclude that ERN1 is involved in regulating NIN expression in addition to CYCLOPS, and these TFs coordinately promote the symbiotic root hair response and IT development. Our data help to reveal the extensive role of ERN1 in root nodule symbiosis signaling.

Context-dependent interactions between pathogens and a mutualist affect pathogen fitness and mutualist benefits to hosts.

Plants and animals host many microbial symbionts, including both pathogens and mutualists. However, most experimental studies include only one symbiont, and few examine interactions of more than two microbes with their host. Here, we examined whether coinfection with two pathogens causes a synergistic reduction in the benefits that hosts receive from a microbial mutualist. We also measured the effects of a microbial mutualist on the within- and between-host competition between coinfecting pathogens. We manipulated the presence of Clover yellow vein virus (ClYVV), Bean common mosaic virus (BCMV), rhizobia bacteria, and nitrogen fertilizer in common beans (Phaseolus vulgaris). We found asymmetric, context-dependent interactions among the three microbial symbionts and their host. Coinfection with both viruses led to greater than additive negative effects on the amount of nitrogen that plants received from rhizobia. Rhizobia colonization decreased immune signaling in singly infected plants, but not in coinfected plants. Compared to single ClYVV infection, ClYVV reached higher concentrations within hosts coinfected with BCMV, but only in the presence of rhizobia. Coinfection increased BCMV vertical transmission rates for plants without supplemental nitrogen, but overall vertical transmission opportunities were not affected due to reduced seed production. Examining interactions between multiple microbes sharing a host can reveal important insights about nutrient cycling, disease severity, and pathogen epidemiology.

Epidermal LysM receptor ensures robust symbiotic signalling in Lotus japonicus.

Recognition of Nod factors by LysM receptors is crucial for nitrogen-fixing symbiosis in most legumes. The large families of LysM receptors in legumes suggest concerted functions, yet only NFR1 and NFR5 and their closest homologs are known to be required. Here we show that an epidermal LysM receptor (NFRe), ensures robust signalling in L. japonicus. Mutants of Nfre react to Nod factors with increased calcium spiking interval, reduced transcriptional response and fewer nodules in the presence of rhizobia. NFRe has an active kinase capable of phosphorylating NFR5, which in turn, controls NFRe downstream signalling. Our findings provide evidence for a more complex Nod factor signalling mechanism than previously anticipated. The spatio-temporal interplay between Nfre and Nfr1, and their divergent signalling through distinct kinases suggests the presence of an NFRe-mediated idling state keeping the epidermal cells of the expanding root system attuned to rhizobia.

Characterization of rhizobia from root nodule and rhizosphere of Vicia faba in Algeria

Nitrogen fixation resulting from mutual symbiosis of rhizobia and cultivated legume plants is therefore critical to food security as it directly affects agricultural production. Biological Nitrogen Fixation (BNF) can be an important factor in sustainable agriculture. A collection of 20 isolates from fresh Nodules of the legume plant Vicia faba was isolated from five soil of Algeria. The soil from each region has undergone physical-chemical analysis : (granulometry, total carbon, organic matter, pH, and electrical conductivity, determination of available phosphorus and determination of total nitrogen). A media viz., Glucose-Peptone Agar (GPA), Congo red, Yeast Mannitol Agar (YMA) containing 2% NaCl were employed to make presumptive decisions on the recognition and classification of the isolated bacterial strains. All the isolates were found with poor absorption of dye Congo red and little or no growth on the media of GPA and without altering the pH. Almost all of the isolates exhibit good growth on 2% NaCl, poor growth on GPA, thus confirming the rhizobia. After biochemical tests like catalase test and citrate utilization test isolates were confirmed. The presence of rhizobia on root nodules of leguminous plant.

Characterization of Rhizobia from Root Nodule and Rhizosphere of Lablab purpureus and Vigna sinensis in Bangladesh

Nitrogen fixation resulting from mutual symbiosis of rhizobia and cultivated legume plants is therefore critical to food security as it directly affects agricultural production. Biological Nitrogen Fixation (BNF) can be an important factor in sustainable agriculture.The isolation and identification of different slow growing and fast growing rhizobial strains from the nodules of two leguminous plant species. Symbiotic nitrogen fixing Rhizobium spp. was isolated from (Lablab purpureus and Vigna sinensis). Nodules samples were collected from plants growing in different Districts of Bangladesh and the Glucose-Peptone Agar (GPA), Congo red, Yeast Mannitol Agar (YMA) containing 2% NaCl were employed to make presumptive decisions on the recognition and classification of the isolated bacterial strains. All the isolates were found with poor absorption of dye Congo red and little or no growth on the media of GPA and without altering the pH. Almost all of the isolates exhibit growth on 2% NaCl, poor growth on GPA, thus confirming the rhizobia. After biochemical tests like catalase test and citrate utilization test isolates were confirmed as Rhizobia. The presence of rhizobia on root nodules of leguminous Plant. Not only the leguminous Plant but also the rhizosphere contains rhizobia which help in soil fertilization.

Environmental stress conditions affecting the N2 fixing Rhizobium-legume symbiosis and adaptation mechanisms

Rhizobia are bacteria which fix atmospheric nitrogen in association within the root or the stem nodules of legume plants and transform atmospheric nitrogen to ammonia. Biological nitrogen fixation is an important process for sustainable land management, because nitrogen is the principal crop production’s limiting factor. However, several environmental conditions such as salinity, temperature, acidity/alkalinity, drought, heavy metals, etc., are critical factors which can have detrimental effects on the steps involved in Rhizobium-legume symbiosis as infection process, nodule’s development and function, resulting in low nitrogen fixation and crop yield. The presence of Rhizobium- legume symbioses able to fix appreciable N2 amounts under unfavorable conditions is very interesting, because these symbioses represent the best source of nitrogen especially in arid and semi-arid regions, where they contribute to land stabilization and fertilization. Hence, the better understanding of rhizobial physiological responses to different intrinsic and extrinsic stresses factors is very important to improve crop production by harnessing biological nitrogen fixation process. Key words: Rhizobium, legume, symbiosis, environmental stress, heavy metals, soil fertility.

Intracellular catalytic domain of symbiosis receptor kinase hyperactivates spontaneous nodulation in absence of rhizobia.

Symbiosis Receptor Kinase (SYMRK), a member of the Nod factor signaling pathway, is indispensible for both nodule organogenesis and intracellular colonization of symbionts in rhizobia-legume symbiosis. Here, we show that the intracellular kinase domain of a SYMRK (SYMRK-kd) but not its inactive or full-length version leads to hyperactivation of the nodule organogenic program in Medicago truncatula TR25 (symrk knockout mutant) in the absence of rhizobia. Spontaneous nodulation in TR25/SYMRK-kd was 6-fold higher than rhizobia-induced nodulation in TR25/SYMRK roots. The merged clusters of spontaneous nodules indicated that TR25 roots in the presence of SYMRK-kd have overcome the control over both nodule numbers and their spatial position. In the presence of rhizobia, SYMRK-kd could rescue the epidermal infection processes in TR25, but colonization of symbionts in the nodule interior was significantly compromised. In summary, ligand-independent deregulated activation of SYMRK hyperactivates nodule organogenesis in the absence of rhizobia, but its ectodomain is required for proper symbiont colonization.

Role of Rhizobium, a plant growth promoting bacterium, in enhancing algal biomass through mutualistic interaction

Rhizobium plays the pivotal role in mutualistic interactions with plants and this study extends this mutualism to several species of green algae. Denaturing gradient gel electrophoresis (DGGE) and 16S rRNA gene clone library experiments of Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus sp., and Botryococcus braunii revealed that the dominant phycosphere bacteria hosted by these green algae were Rhizobium, Mesorhizobium, and Shinella within Rhizobiales, Flavobacterium within Flavobacteriales, and Pseudomonas within Pseudomonadales. When Rhizobium sp., most prevalent and dominant bacterium isolated from C. vulgaris, was co-cultured with green algae, it promoted algal cell count by ∼72%. The qPCR analysis of 16S rRNA, Rhizobium specific rirA and rhtA genes, performed to understand the effect of green algae on growth of Rhizobium sp., showed a significant increase in copy numbers indicating sustained growth of Rhizobium upon co-culture with green algae. Likewise, growth rates of algae and Rhizobium increased by an average of ∼11% and ∼110%, respectively, confirming mutualistic interaction. Considering the presence of Rhizobium sp. in a variety of green algae, this must be a major mutualistic relationship among green algae and this ubiquitous association might serve as a model for elucidating the mutualistic mechanism between green algae and rhizobacter. This interaction could be also utilized in enhancing microalgal biomass, especially slow growing organisms like B. braunii, to augment their bioenergy productivity.

Influence of arbusclar mycorrhiza in presence of Rhizobium , nitrogen and phosphorus on growth and yield of mungbea n

Influence of arbusclar mycorrhiza in presence of Rhizobium , nitrogen and phosphorus on growth and yield of mungbea n

Greenhouse evaluation of rhizobia as biocontrol agent of root-infecting fungi in okra

Nine rhizobial strains isolated from the root nodules of <em>Cicer arietinum, Vigna radiata, V. mungo, Samania saman, Sesbania sesban, Leucinia</em> sp., <em>Prosopis cineraria</em> and <em>Medicago sativa</em> were used to study their effects on root-infecting fungi viz., <em>Macrophomina phaseolina, Fusarium solani</em> and <em>Rhizoctonia solani</em>. In dual culture plate assay, strains of Bradyrhizobium sp., and R. meliloti were found to inhibit radial growth of <em>M. phaseolina, F. solani</em> and <em>R. solani</em> producing zones of inhibition. <em>Bradyrhizobium</em> sp., and <em>R. meliloti</em> either used as seed dressing or as soil drench significantly suppressed root-rot infection caused by <em>M. phaseolina, F. solani</em> and <em>R. solani</em> in okra, a non-1eguminous crop under greenhouse conditions. Biomass of plants was also higher in the presence of rhizobia.

Growth and development of jack-bean and pigeon-pea in cassiterirte mine spoil

Cassiterite mining has caused critical damages to the environment with respect to soil degradation and water pollution. In a greenhouse experiment two leguminous species, jack-bean (Canavalia ensiformis) and pigeon-pea (Cajanus cajan), were grown using cassiterite mine spoil as substrate, in the presence of rhizobia and with or without mycorrhizal fungi, and the substrate was amended or not with organic compost and thermo-phosphate, to evaluate the potential development of these plants to grow on this substrate. Shoot height and shoot dry weight, nitrogen and phosphorus shoot contents, root nodule numbers and their dry weight were determined. Amendment with organic compost was important for all observed parameters in both species, but jack-bean had greater shoot N contents and biomass and less mycorrhizal dependence, when comparing with pigeon-pea. However, it was verified that efficiently nodulated plants, as pigeon-pea, can be fundamental for soil reclamation, by reducing the need for fertilizers and by stimulating the biological activity in soil. In our study the utilization of organic compost was crucial for plant growth, while thermophosphate was not always essential, especially in the presence of mycorrhiza. However, the mycorrhizae were essential, at least for pigeon-pea. Key words: Cassiterite mine spoil, Canavalia ensiformis, Cajanus cajan, amazon region.