Cowpea Nodules Research Articles

Short communication. Growth and nodulation of cowpea after 5 years of consecutive composted tannery sludge amendment

Tannery industry releases high amounts of tannery sludge which are currently composted and used in agricultural soils. The consecutive amendment of such composted tannery sludge (CTS) may affect soil microrganisms, such as rhizobia. In this study, we evaluated the effects of 5-year repeated CTS amendment on growth, nodulation, and yield of cowpea (Vigna unguiculata L.) CTS was applied in different amounts (0, 2.5, 5, 10 and 20 Mg/ha) to a sandy soil. Amendment of CTS increased soil pH, electrical conductivity (EC), sodium and chromium content. Plant growth, nodulation, N accumulation, and cowpea yield increased up to 10 Mg/ha; however, above this rate, these variables decreased. After 5 years of CTS amendment, the increase in soil chemical properties, particularly EC and Na content, exerted negative effects on the growth, nodulation, and yield of cowpea.

Soil allelochemical residue effects in a tomato cowpea rotation – nodulation and productivity of cowpea and nematode suppression

Soil allelochemical residue (SAR) effects from nemarioc-AL phytonematicide in a tomato–cowpea (Vigna unguiculata) succession system were investigated on nodulation of Bradyrhizobium japonicum, productivity of cowpea and suppressive capabilities of Meloidogyne species. Following a tomato (Solanum lycopersicum) crop which was subjected to five concentrations (CCs) and five application interval (AI) levels of nemarioc-AL, the cowpea var. Eureka was raised on spots previously occupied by tomato plants, without reapplying the treatments. SAR effects due to CC × AI consistently inhibited B. japonicum nodulation in 96% factorial pairwise combinations, while CC alone increased soil pH and seed yield, but reduced Meloidogyne incognita numbers. Similarly, AI alone increased dry shoot mass and reduced Meloidogyne species. Overall, at high CCs and repeated AIs, cowpea var. Eureka was not suitable for immediate use as successor crop in botinemagation systems where Meloidogyne species were managed using nemarioc-AL phytonematicide in tomato production.

Bradyrhizobium manausense sp. nov., isolated from effective nodules of Vigna unguiculata grown in Brazilian Amazonian rainforest soils.

Root nodule bacteria were trapped within cowpea (Vigna unguiculata) in soils with different cultivation histories collected from the Amazonian rainforest in northern Brazil. Analysis of the 16S rRNA gene sequences of six strains (BR 3351(T), BR 3307, BR 3310, BR 3315, BR 3323 BR and BR 3361) isolated from cowpea nodules showed that they formed a distinct group within the genus Bradyrhizobium, which was separate from previously identified type strains. Phylogenetic analyses of three housekeeping genes (glnII, recA and rpoB) revealed that Bradyrhizobium huanghuaihaiense CCBAU 23303(T) was the most closely related type strain (96% sequence similarity or lower). Chemotaxonomic data, including fatty acid profiles (predominant fatty acids being C16 : 0 and summed feature 8), the slow growth rate and carbon compound utilization patterns supported the assignment of the strains to the genus Bradyrhizobium. The results of DNA-DNA hybridizations, antibiotic resistance and physiological tests differentiated these novel strains from the most closely related species of the genus Bradyrhizobium with validly published names. Symbiosis-related genes for nodulation (nodC) and nitrogen fixation (nifH) grouped the novel strains of the genus Bradyrhizobium together with Bradyrhizobium iriomotense strain EK05(T), with 94% and 96% sequence similarity, respectively. Based on these data, these six strains represent a novel species for which the name Brabyrhizobium manausense sp. nov. (BR 3351(T) = HAMBI 3596(T)), is proposed.

Nodulation Productivity and Nutrient Uptake of Cowpea (Vigna unguiculata L. Walp) with Phosphorus and Potassium under Rainfed Conditions

Low availability of phosphorus (P) and potassium (K) in acidic soil is a major constraint for crop production. Therefore, a field study was conducted to determine the effects of K and P on nodulation, productivity, and nutrient uptake of cowpea (Vigna unguiculata L. Walp) under rainfed conditions. The K and P were subjected to main and subplots, respectively with 100, 75, and 50% of fertilizer application. The growth and yield attributes were better using 100% K with 100% P. However, 100% K resulted in 20.9 and 16.9% greater green pod and stover yield than 50% K. Similarly, 100% P recorded 20.2 and 15.6% greater green pod and stover yield than 50% P. Uptake of nutrients such as nitrogen (N), P, and K followed the trend of greater to lower, 100% > 75% > 50%, in order for K and P. Similarly, nutrient-use efficiencies and production efficiency followed the trend of nutrient uptake.

Nitrogen fixation and symbiosis-induced accumulation of mineral nutrients by cowpea (Vigna unguiculata L. Walp.)

Little information currently exists on the relationship between rhizobial symbiosis and mineral accumulation in nodulated legumes. The aim of this study was to measure fixed nitrogen (N) in whole plants and in young fully expanded trifoliate leaves of cowpea genotypes, and to relate this to mineral accumulation in the leaves. The data revealed marked differences between high and low N2-fixing genotypes, with the former consistently showing greater %N, plant or leaf total N, and amount of N fixed compared with the latter. There was a 2.0–3.8-fold difference in amount of N fixed at whole-plant level between high- and low-fixing cowpea genotypes at Taung, South Africa, and 2.4–4.0-fold at Manga, Ghana. Furthermore, the genotypes with high N2 fixation consistently exhibited greater concentration and content of minerals (e.g. P, K, Mg, S, Na, Fe, Cu, Zn, Mn and B) in their trifoliate leaves, whereas those that recorded low N2 fixation accumulated lesser amounts of mineral nutrients in leaves. In a nodulation assay, we found that rhizobial isolates TUT53b2vu and TUT33b4vu, which exhibited higher symbiotic efficiency (measured here as nodule number, nodule fresh weight, and plant dry matter yield), also elicited greater mineral accumulation in cowpea shoots, while strains with low N2-fixing ability induced limited mineral accumulation. These results, together with a correlation analysis, show that, at least in nodulated cowpea, there is a strong relationship between N2-fixing efficiency and mineral accumulation, two traits that could be exploited in breeding programs for improved human nutrition and health.

Eco-geographical diversity of cowpea bradyrhizobia in Senegal is marked by dominance of two genetic types

The genetic diversity of native cowpea rhizobia originating from 60 sites across four eco-geographic zones in Senegal was studied. More than 300 cowpea nodules were analyzed by PCR-RFLP of the 16S–23S rDNA InterGenic Spacer region (IGS). Alignments of IGS sequences indicated that all genotypes were grouping within the Bradyrhizobium genus. The geographical distribution showed that apart from five IGS types, the others were specifically found in only one region. The diversity was significantly higher in the Senegal River valley zone, which presents lower mean annual rainfalls and slightly alkaline soils. Interestingly, two IGS types dominated the Senegalese rhizobial collection, one IGS type (VI) was found on more than half of the nodules collected in the northern Senegal River valley while another IGS type (I) was recovered from the great majority of nodules in the three other regions sampled. Two representative strains from each of these two dominant types were isolated and further analyzed. Multi Locus Sequence Analyses using 6 housekeeping genes indicate that they belong to a new Bradyrhizobium species closely related to B. yuanmingense. Phylogenetic analyses of 2 symbiotic genes nodC and nifH show that they are clustered with B. arachidis. Physiological tests on these strains have shown that under laboratory conditions, the growth of the IGS type VI strains was slightly less affected by a higher osmotic strength in the medium and to alkaline pH, which corroborates the soil physico-chemical parameters.

Symbiotic nitrogen-fixing bacterial populations trapped from soils under agroforestry systems in the Western Amazon

Cowpea (Vigna unguiculata) is an important grain-producing legume that can forego nitrogen fertilization by establishing an efficient symbiosis with nitrogen-fixing bacteria. Although inoculating strains have already been selected for this species, little is known about the genotypic and symbiotic diversity of native rhizobia. Recently, Bradyrhizobium has been shown to be the genus most frequently trapped by cowpea in agricultural soils of the Amazon region. We investigated the genetic and symbiotic diversity of 148 bacterial strains with different phenotypic and cultural properties isolated from the nodules of the trap species cowpea, which was inoculated with samples from soils under agroforestry systems from the western Amazon. Sixty non-nodulating strains indicated a high frequency of endophytic strains in the nodules. The 88 authenticated strains had varying symbiotic efficiency. The SPAD (Soil Plant Analysis Development) index (indirect measurement of chlorophyll content) was more efficient at evaluating the contribution of symbiotic N2-fixation than shoot dry matter under axenic conditions. Cowpea-nodulating bacteria exhibited a high level of genetic diversity, with 68 genotypes identified by BOX-PCR. Sequencing of the 16S rRNA gene showed a predominance of the genus Bradyrhizobium, which accounted for 70 % of all strains sequenced. Other genera identified were Rhizobium, Ochrobactrum, Paenibacillus, Bosea, Bacillus, Enterobacter, and Stenotrophomonas. These results support the promiscuity of cowpea and demonstrate the high genetic and symbiotic diversity of rhizobia in soils under agroforestry systems, with some strains exhibiting potential for use as inoculants. The predominance of Bradyrhizobium in land uses with different plant communities and soil characteristics reflects the adaptation of this genus to the Amazon region.

Microvirga vignae sp. nov., a root nodule symbiotic bacterium isolated from cowpea grown in semi-arid Brazil

16S rRNA gene sequence analysis of eight strains (BR 3299(T), BR 3296, BR 10192, BR 10193, BR 10194, BR 10195, BR 10196 and BR 10197) isolated from nodules of cowpea collected from a semi-arid region of Brazil showed 97 % similarity to sequences of recently described rhizobial species of the genus Microvirga. Phylogenetic analyses of four housekeeping genes (gyrB, recA, dnaK and rpoB), DNA-DNA relatedness and AFLP further indicated that these strains belong to a novel species within the genus Microvirga. Our data support the hypothesis that genes related to nitrogen fixation were obtained via horizontal gene transfer, as sequences of nifH genes were very similar to those found in members of the genera Rhizobium and Mesorhizobium, which are not immediate relatives of the genus Microvirga, as shown by 16S rRNA gene sequence analysis. Phenotypic traits, such as host range and carbon utilization, differentiate the novel strains from the most closely related species, Microvirga lotononidis, Microvirga zambiensis and Microvirga lupini. Therefore, these symbiotic nitrogen-fixing bacteria are proposed to be representatives of a novel species, for which the name Microvirga vignae sp. nov. is suggested. The type strain is BR3299(T) ( = HAMBI 3457(T)).

Effects of biofertilizer with diazotrophic bacteria and mycorrhizal fungi in soil attribute, cowpea nodulation yield and nutrient uptake in field conditions

Biofertilizer made from rocks with Acidithiobacillus releases nutrients for plants and reduces the environmental impact of fertilizer on the soil. The aim of this study is to evaluate the effects of PK rock biofertilizers mixed with earthworm compound and inoculated with free living diazotrophic bacteria and arbuscular mycorrhizal fungi (AMF) on the nodulation, yield and nutrient uptake of cowpeas (Vigna unguiculata) and on the soil attributes in field conditions. In a greenhouse experiment, three rates (4.0tha−1, 6.0tha−1, and 8.0tha−1) of biofertilizer were compared with the addition of AMF (Glomus etunicatum and Gigaspora albida). A treatment with earthworm compound (20tha−1) without AMF was used as a control. In the field experiment, the treatments were as follows: three rates of biofertilizer (4.0, 6.0 and 8.0tha−1); mineral fertilizer at the recommended rate (RR) and two times RR; and earthworm compound (20tha−1). G. etunicatum was applied to all treatments. In both experiments, the seeds were inoculated with effective Bradyrhizobium strains. In the greenhouse experiment, the highest rate of biofertilizer showed the best results for all analyzed parameters. G. etunicatum produced the higher biomass yield of cowpeas but was not competitive with the indigenous AMF in the soil. In the field experiment, the highest rate of mixed biofertilizer effectively increased the grain and shoot biomass yield and increased the available P and K in soil. The mixed biofertilizer showed potential as an alternative for mineral NPK fertilization and seems to be an important factor for soil quality and long-term fertilization.

<b>Cowpea nodulation, biomass yield and nutrient uptake, as affected by biofertilizers and rhizobia, in a sodic soil amended with <i>Acidithiobacillus</i></b> - doi: 10.4025/actasciagron.v35i4.16994

Sodic soils require application of amendments as gypsum and organic matter. Many types of compost have been tested in sodic soils reclamation; however, these materials often do not provide satisfactory pH reduction. A recent study reported effective effects applying mixture of gypsum and sulfur inoculated with Acidithiobacillus in sodic soils with high pH and exchangeable sodium, though the effects on plant parameters were not evaluated. The present study was conducted to verify the effects of BPK rock biofertilizers on nodulation, biomass yield and nutrient uptake in cowpea compared with mineral fertilizer after sodic soil amendment. The BPK biofertilizers and PK mineral fertilizer were applied at different rates, and plants were inoculated with effective rhizobia strains. A control that did not receive PK fertilization was included. The results indicated that gypsum and sulfur with Acidithiobacillus reduced the soil’s pH and the amount of soil exchangeable sodium. BPK rock biofertilizer increased cowpea nodulation, biomass yield and nutrient uptake. The native rhizobia in the soil exhibited effectiveness in cowpea growth; displaying similar results compared with the rhizobia inoculated plants. BPK biofertilizers may be used as alternative to mineral PK fertilizers in sodic soils after the application of gypsum and sulfur inoculated with Acidithiobacillus.

Metabolism of nitrogen and carbon: Optimization of biological nitrogen fixation and cowpea development

Although the favorable role of plant growth-promoting bacteria (PGPB) in biological nitrogen fixation (BNF) is well established, their involvement in nodule metabolism is unknown. This study was performed to determine the relationship between C and N metabolism in cowpea nodules inoculated with only Bradyrhizobium sp. or with double and triple combinations of Bradyrhizobium sp., and two PGPB, Paenibacillus graminis and Paenibacillus durus during two critical phases of nodule development (flowering and beginning of senescence). The triple inoculation (Bradyrhizobium sp and two PGPB) induced higher N content in nodules, total-N accumulation per plant and shoot dry weight compared with other combinations at the beginning of senescence. This increased N performance was positively correlated with the nodule sucrose content but not with the content of total soluble carbohydrates, reduced sugars and starch. The higher BNF under triple inoculation conditions was not significantly associated with sucrose synthase activity but was slightly associated with soluble acid invertase activity in nodules at the beginning of senescence. These enzymes exhibited opposite responses between flowering and the beginning of senescence in all treatments. Glutamate synthase, glutamine synthetase and glutamate dehydrogenase were stimulated by double (Bradyrhizobium sp. + P. durus) and triple inoculation compared with other treatments. Our data revealed that inoculation with Bradyrhizobium sp. and PGPB is favorable for BNF activity in cowpeas. This positive interaction requires a complex balance involving enzymes and metabolites related to C and N metabolism.

Minimization of oxidative stress in cowpea nodules by the interrelationship between Bradyrhizobium sp. and plant growth-promoting bacteria

Oxidative damage can result in various degenerative processes, including membrane lipid peroxidation, a process promoted by chain reactions initiated by reactive oxygen species that can rapidly affect many lipid molecules, resulting in damage to cellular structures. This study aimed to evaluate the symbiotic performance of cowpea plants inoculated and co-inoculated with Bradyrhizobium sp. and different combinations of plant growth-promoting bacteria (PGPB), Paenibacillus graminis or P. durus, based on biochemical variables related to protection/oxidative stress and senescence during and after the establishment of symbiosis. The experiment was conducted under greenhouse conditions. Cowpea seeds were disinfected and inoculated as follows: Bradyrhizobium sp.; co-inoculated with Bradyrhizobium sp. and P. graminis or Bradyrhizobium sp. and P. durus; or co-inoculated with Bradyrhizobium sp. and the two PGPB (P. graminis and P. durus). The plants were grown in Leonard jars containing washed and autoclaved sand. Uninoculated plants were used as an absolute control. The cowpea nodules were harvested at flowering point and the beginning of senescence. The results showed significant differences in the variables related to antioxidant metabolism in response to the treatments and harvest times. Although there was reduced ascorbate peroxidase, catalase and phenol peroxidase activities were observed in the plants co-inoculated with Bradyrhizobium sp. and P. graminis and Bradyrhizobium sp. and P. durus at flowering point, no accumulation of hydrogen peroxide or increase in lipid peroxidation was observed, indicating that the enzymatic activity was effective in controlling the possible oxidative damage in these plants. The cowpeas co-inoculated with Bradyrhizobium sp. and the two PGPB (P. graminis and P. durus) showed a delay of the deleterious effects of senescence and, therefore, a better symbiotic performance.

Plant and soil characteristics affected by biofertilizers from rocks and organic matter inoculated with diazotrophic bacteria and fungi that produce chitosan

The aim of this study was to evaluate the effectiveness of a mixed biofertilizer with phosphate and potash rocks (PK biofertilizer) combined with an earthworm compound inoculated with free living diazotrophic bacteria and Cunninghamella elegans, fungi that produces chitosan, on cowpea nodulation, biomass yield and nutrient uptake. The effects of some chemical attributes from an acidic soil of the Brazilian Northeast were also studied. The treatments were as follows: a) biofertilizer enriched in N by free living diazotrophic bacteria(NPKB), applying crustaceous chitosan (ChCru) at a rate 2 mg mL -1 ; b) NPKB and ChCru at a rate 4 mg mL -1 ; c) NPKB and ChCru at a rate 6 mg mL -1 ; d) NPKB and fungi chitosan (ChFu, 2 mg mL -1 ); e) NPKB+C. elegans (NPKP); f) NPKB without chitosan; g) mineral fertilizers (NPKF); and h) control without NPK fertilizer and chitosan. Biofertilizer treatments increased cowpea nodules biomass, shoot biomass, and total N, P, and K in the shoots. The largest increase was obtained with ChCru, and the highest rate was obtained with NPKP. Furthermore, biofertilizers reduced soil pH and increased the total N and available P and K. These results reveal the potential of rock biofertilizer mixed with earthworm compound inoculated with free living diazotrophic bacteria and C. elegans (fungi chitosan) for plant production and nutrient uptake. The biofertilizer may be an alternative for NPK fertilization that slows the release of nutrients, favoring longterm soil fertility.

Interactive effects of Meloidogyne incognita race 2, Bradyrhizobium japonicum and crude extracts of Cucumis myriocarpus fruit on Vigna unguiculata

Crude extracts of wild cucumber (Cucumis myriocarpus) fruit, with scant information of their effects on nodulation and growth of cowpea (Vigna unguiculata), had been touted as having potential to serve as bio-nematicide and bio-fertilizer in low-input farming systems. Interactive effects of the southern root-knot nematode (Meloidogyne incognita), Bradyrhizobium japonicum and crude extracts of C. myriocarpus fruit on final nematode population density, nodulation and growth of cowpea variety Eureka were investigated in a 2 × 2 × 2 factorial experiment under greenhouse conditions. At 70 days after the treatments, significant (P ≤ 0.05), first order interactions in Nematode × Cucumis reduced final nematode population densities and nodule numbers by 79% and 20%, respectively. However, in the absence of nematodes, Cucumis increased nodule numbers by 9%. Similarly, Nematode × Bradyrhizobium reduced fresh shoot mass, dry shoot mass and nodule mass by 57%, 59% and 64%, respectively. However, in the absence of nematodes, Bradyrhizobium increased the variables by 50%, 42% and 35%, respectively. Compared to nematode alone, the two interactions had a relative ameliorative effect on the variables measured. Consequently, crude extracts of C. myriocarpus fruit are suitable for use in managing population densities of M. incognita on cowpea production.

Interactive effects of Meloidogyne incognita race 2, Bradyrhizobium japonicum and crude extracts of Cucumis myriocarpus fruit on Vigna unguiculata

Crude extracts of wild cucumber (Cucumis myriocarpus) fruit, without information on their effects on nodulation, had been touted as having potential as a nematicide and a fertiliser in low-input cowpea (Vigna unguiculata) production systems. Interactive effects of the southern root-knot nematode (Meloidogyne incognita), Bradyrhizobium japonicum and crude extracts of wild cucumber (C. myriocarpus) fruit on each other and growth of cowpea variety Eureka were investigated in a 23 factorial experiment. At harvest, 70 days after initiating the treatments, significant (P ≤ 0.05) first order interactions between any two of the three main factors on variables measured were observed, with interactive effects being either stimulatory or inhibitory. Crude extracts of C. myriocarpus fruit were basically suppressive on nematode numbers but stimulated nodulation and growth of cowpea. Consequently, the material is suitable for use in managing population densities of M. incognita on cowpea production in low-input cowpea production systems.

Soil Amendment on Growth, Nodulation, Yield, Soil Health, and Economics of Cowpea

Organic fertilizer might be able to be used without sacrificing cowpea [Vigna unguiculata (L.) Walp] productivity and contribute to maintaining soil health. A field experiment was conducted during the rainy season months of July to October of 2008 and 2009 to study effects of use of the organic amendments groundnut cake, Pongamia cake, neem cake, mustard cake, cow manure, vermicompost, and poultry manure used alone, and in combinations, on growth, nodulation, yield, soil health, and profitability of cowpea, cv. Utkal Manika, in a sandy loam soil. Use of organic amendments and beneficial bacteria could improve growth, nodulation, yield, and profitability of cowpea and improve soil health. Organic amendments were at least as good as the control (recommended rate of N–P–K fertilizer).

Expressão gênica induzida por estresses abióticos em nódulos de feijão-caupi

O objetivo deste trabalho foi avaliar o efeito isolado ou simultâneo dos estresses hídrico e térmico na expressão gênica em nódulos de feijão-caupi. A bactéria Bradyrhizobium japonicum (estirpe BR 3267) foi inoculada em sementes de feijão-caupi da cultivar IPA 206 e, 35 dias após a germinação, as plantas foram submetidas a diferentes regimes de disponibilidade hídrica e a estresse térmico, em casa de vegetação. Para a identificação dos genes diferencialmente expressos, foi utilizada a técnica de cDNA-AFLP, tendo-se isolado 67 fragmentos derivados de transcritos (FDTs) diferencialmente expressos. Após o sequenciamento dos FDTs e das análises de similaridade, com uso do programa Blastx, foram identificados 14 genes diferencialmente expressos envolvidos em diferentes processos metabólicos. O padrão de expressão de seis genes sob estresse abiótico foi confirmado por RT-qPCR, e observou-se indução de genes pertencentes a diferentes categorias funcionais, como biossíntese de ácido abscísico, sinalização celular, transportador de prolina e biossíntese de lipídeos de membranas. A expressão desses genes indica sua participação em processos relacionados à proteção dos nódulos ao estresse abiótico.

Biological nitrogen fixation and phosphate solubilization by bacteria isolated from tropical soils

In addition to fixing atmospheric nitrogen, some bacterial isolates can also solubilize insoluble phosphates, further contributing to plant growth. The objectives of this study were the following: isolate, select, and identify nodulating bacteria in the cowpea that are efficient not only in biological nitrogen fixation (BNF) but also in the solubilization of insoluble inorganic phosphates; identify and quantify the organic acids produced; and establish the relationship between those acids and the solubilizing capacity. The bacteria were captured from two soils containing high concentrations of insoluble phosphorus from the cities of Lavras and Patos de Minas, using the cowpea [Vigna unguiculata (L.) Walp.] as bait. We obtained 78 strains, which were characterized according to their cultural attributes in culture medium 79 with the strains UFLA 03-84, INPA 03-11B, and BR3267 (approved by the Ministry of Livestock and Supply Agriculture—MAPA, as inoculants for the cowpea) and Burkholderia cepacia (LMG1222T), which was used as a positive control for phosphate solubilization. Strains that were selected for their efficiency in both processes were identified by 16S rDNA sequence analysis. We evaluated the symbiotic efficiency (BNF) in a greenhouse and the solubilization efficiency of CaHPO4, Al(H2PO4)3, and FePO4.2H2O in solid and liquid GELP media. Strains that excelled at the solubilization of these phosphate sources were also evaluated for the production of the following organic acids: oxalic, citric, gluconic, lactic, succinic, and propionic. The presence of Acinetobacter, Bacillus, Firmicutes, Microbacterium, Paenibacillus, and Rhizobium was detected by 16S rDNA sequencing and analysis. Bacterial strains obtained from cowpea nodules varied greatly in the efficiency of their BNF and phosphate solubilization processes, especially in the strains UFLA 03-09, UFLA 03-10, UFLA 03-12, and UFLA 03-13, which were more efficient in both processes. More strains were able to solubilize insoluble inorganic calcium and iron phosphates in liquid medium than in solid medium. The production of organic acids was related to the solubilization of CaHPO4 and FePO4.2H2O for some strains, and the type and concentration of the acid influenced this process. These are the first results obtained with bacterial isolates from tropical soils in which the production of organic acids was detected and quantified to examine the solubilization of insoluble inorganic phosphates.

Genetic diversity of Rhizobia isolates from Amazon soils using cowpea (Vigna unguiculata) as trap plant

The aim of this work was to characterize rhizobia isolated from the root nodules of cowpea (Vigna unguiculata) plants cultivated in Amazon soils samples by means of ARDRA (Amplified rDNA Restriction Analysis) and sequencing analysis, to know their phylogenetic relationships. The 16S rRNA gene of rhizobia was amplified by PCR (polymerase chain reaction) using universal primers Y1 and Y3. The amplification products were analyzed by the restriction enzymes HinfI, MspI and DdeI and also sequenced with Y1, Y3 and six intermediate primers. The clustering analysis based on ARDRA profiles separated the Amazon isolates in three subgroups, which formed a group apart from the reference isolates of Bradyrhizobium japonicum and Bradyrhizobium elkanii. The clustering analysis of 16S rRNA gene sequences showed that the fast-growing isolates had similarity with Enterobacter, Rhizobium, Klebsiella and Bradyrhizobium and all the slow-growing clustered close to Bradyrhizobium.

Growth, nodulation and nitrogen fixation of cowpea in soils amended with composted tannery sludge

Tannery wastes generation is increasing every year and a suitable method for tannery sludge management is necessary in order to decrease this environmental problem. The composting is recognized as a suitable method for sludge recycling.. The effect of tannery sludge compost (TSC) rates on growth, nodulation and N fixation of cowpea was investigated. Sandy and clayey soils were amended with TSC at rates of 0, 7.5, 15, 30, and 60 t ha-1. The shoot dry weight of cowpea plants 45 days after emergence (DAE) was greater in the TSC-amended than in the unamended soil. In the sandy soil, nodule dry weight increased with TSC application 45 DAE. In the clayey soil, 45 DAE, nodule dry weight decreased with TSC amendment levels greater than 7.5 t ha-1 compared to the unamended control. The application of TSC increased N accumulation in the cowpea plants. The results suggest that cowpea responds differently to TSC depending on the amendment rate and initial soil type.