Cowpea Nodules Research Articles

Impact of Soil Salinity on the Cowpea Nodule-Microbiome and the Isolation of Halotolerant PGPR Strains to Promote Plant Growth under Salinity Stress

Cowpea is one of the major legumes cultivated in arid and semiarid regions of the world. Four soil-microbial samples (SS-1 through SS-4) collected from semiarid soils in Punjab, Pakistan were planted with cowpea (Vigna unguiculata) crops, which were grown under salinity stress to analyze bacterial composition in the rhizosphere and within nodules using cultivation-dependent and -independent methods. Two varieties, 603 and the salt-tolerant CB 46, were each inoculated with or without the four different native soil samples or grown in medium either N-deficient (−N) or supplemented with N (+N). Plants inoculated with soil samples SS-2 and SS-4 grew better than plants inoculated with SS-1- and SS-3 and grew comparably with the +N controls. Environmental DNA (eDNA) was isolated from SS-1 and SS-4, and, by 16S ribosomal RNA sequencing, the soil microbiomes consisted mainly of Actinobacteria, Firmicutes, Proteobacteria, and other nonproteobacterial genera. However, analysis of eDNA isolated from cowpea nodules established by the trap plants showed that the nodule microbiome consisted almost exclusively of proteobacterial sequences, particularly species of Bradyrhizobium. Bacteria were isolated from both soils and nodules, and 34 of the 51 isolates tested positive for plant-growth-promoting rhizobacteria traits in plate assays. Many could serve as future inocula for crops in arid soils. The discrepancy between the types of bacteria isolated by culturing bacteria isolated from surface-sterilized cowpea nodules (proteobacteria and nonproteobacteria) versus those detected by sequencing DNA isolated from the nodules (proteobacteria) from cowpea nodules (proteobacteria and nonproteobacteria) versus those detected in the nodule microbiome (proteobacteria) needs further study.

Effect of some environmental conditions on the growth of rhizobium species

Rhizobium species are involved in symbiotic relationship which can be exploited in agriculture to enhance crop and pasture growth without the addition of nitrogen fertilizers. However, a number of environmental factors are known to affect the symbiotic efficiency of Rhizobium. This current study evaluated tolerance of Rhizobium species isolated from root nodules of cowpea obtained from Akure, Nigeria to variation in temperature, pH levels, salt concentrations, heavy metals as well as antibiotics. Three Rhizobium species were isolated from root nodules of Vignaunguiculata and Phaseolus vulgaris after 34 days of planting yeast extract mannitol agar (YEMA). Their tolerance to environmental factors such as temperature, pH, sodium chloride, heavy metals as well as antibiotics was determined. All the isolates grew very well at 28oC, moderately at 37oC but their growth was hampered at 50o C. Maximal growth was observed at neutral pH. However, Sinorhizobium sp showed high tolerance to pH 7.0. Also, the isolates showed high tolerance to low concentration of sodium chloride (0.1%) and heavy metals with reduction in their optical density at higher concentrations. Rhizobium sp showed high level of tolerance at 4% compared to Mesorhizobium sp. and Sinorhizobium sp. Rhizobium spp. showed resistance to all the antibiotics investigated while Mesorhizobium sp. was sensitive to only to pefloxacin and sparfloxacin, while Sinorhizobium sp. was only sensitive to pefloxacin. The isolates in this study can be assessed for their suitability as inoculants forcowpea in soils below temperature 50oC and at neutral pH.
 J. bio-sci. 26: 15-24, 2018

Abiotic and Biotic Limitations to Nodulation by Leguminous Cover Crops in South Texas

Many farms use leguminous cover crops as a nutrient management strategy to reduce their need for nitrogen fertilizer. When they are effective, leguminous cover crops are a valuable tool for sustainable nutrient management. However, the symbiotic partnership between legumes and nitrogen fixing rhizobia is vulnerable to several abiotic and biotic stressors that reduce nitrogen fixation efficiency in real world contexts. Sometimes, despite inoculation with rhizobial strains, this symbiosis fails to form. Such failure was observed in a 14-acre winter cover crop trial in the Rio Grande Valley (RGV) of Texas when three legume species produced no signs of nodulation or nitrogen fixation. This study examined the role of nitrogen, phosphorus, moisture, micronutrients, and native microbial communities in the nodulation of cowpea (Vigna unguiculata L. Walp) and assessed arbuscular mycorrhizal fungi as an intervention to improve nodulation. Results from two controlled studies confirm moisture and native microbial communities as major factors in nodulation success. Micronutrients showed mixed impacts on nodulation depending on plant stress conditions. Nitrogen and phosphorus deficiencies, however, were not likely causes, nor was mycorrhizal inoculation an effective intervention to improve nodulation. Inoculation method also had a major impact on nodulation rates. Continued research on improved inoculation practices and other ways to maximize nitrogen fixation efficiency will be required to increase successful on-farm implementation.

Effect of Seed Invigouration Treatments on Physiological Parameters and Nodulation of Grain Cowpea [Vigna unguiculata (L.) Walp

The experiment was conducted at Coconut Research Station, Balaramapuram with an objective to assess the effect of seed invigouration with ZnSO4 and borax alone and along with Trichoderma viride on physiological parameters and nodulation of grain cowpea. Seed invigouration treatments had significant effect on physiological parameters as well as nodulation parameters in grain cowpea. Leaf area index and total chlorophyll content were found to be higher in seeds primed in ZnSO4 0.025 and 0.05 per cent for 4h at both 30 and 60 days after sowing (DAS). From 30 to 60 DAS, crop growth rate (CGR) and relative growth rate (RGR) were the highest in seeds pelleted with borax 50 mg kg-1 seed and from 60 DAS to harvest, seeds primed in ZnSO4 0.05 per cent for 4h registered the highest CGR and RGR. Total number of nodules and effective nodules per plant were found to be higher in seeds pelleted with borax 50 and 100 mg kg-1 seed. However, the nodule fresh and dry weight were the highest in seeds primed in ZnSO4 0.05 per cent for 4h. Hence it can be concluded that compared to seed pelleting with borax, seed priming with ZnSO4 was found better for nodulation as well as better expression of physiological parameters in grain cowpea.

EFFECT OF DIFFERENT FERTILIZERS IN YIELD AND NODULATION OF COWPEA (VIGNA UNGUICULATA) UNDER MULCHED AND UN-MULCHED FIELD CONDITION IN CHITWAN DISTRICT, NEPAL

To study the effects on nodulation and yield of Cowpea (Vigna Unguiculata), a research had been conducted in the sandy loam soil of the horticulture farm of Agriculture and Forestry University in 2018. The experiment was laid out in factorial 2×5 Randomized complete block design with ten treatments and 3 replications which consists; 1st factor – mulched and un-mulched condition, 2nd factor – Rhizobium inoculation (R) at 1gm/ 16.66 gm seed, Phosphorus (P) at recommended dose of 120kg/ha ,use of R plus P(RP),RP plus Molybdenum (RPMo) at 2 gm Molybdenum per kg seed and control with no such application. The analysis of the findings showed that mulched and RPMo treatment were found significantly superior than other treatments in case of main effects of yield attributes like plant height, canopy diameter and stem number. The highest fresh weight of pods per plant i.e. 312.61 gm and 312.53 gm and no of nodules per plant i.e. 121.63 and 129.33 were found in mulched and RPMo treatment, significant at p

Coordinated Regulation of the Size and Number of Polyhydroxybutyrate Granules by Core and Accessory Phasins in the Facultative Microsymbiont Sinorhizobium fredii NGR234.

The exact roles of various granule-associated proteins (GAPs) of polyhydroxybutyrate (PHB) are poorly investigated, particularly for bacteria associated with plants. In this study, four structural GAPs, named phasins PhaP1 to PhaP4, were identified and demonstrated as true phasins colocalized with PHB granules in Sinorhizobium fredii NGR234, a facultative microsymbiont of Vigna unguiculata and many other legumes. The conserved PhaP2 dominated in regulation of granule size under both free-living and symbiotic conditions. PhaP1, another conserved phasin, made a higher contribution than accessory phasins PhaP4 and PhaP3 to PHB biosynthesis at stationary phase. PhaP3, with limited phyletic distribution on the symbiosis plasmid of Sinorhizobium, was more important than PhaP1 in regulating PHB biosynthesis in V. unguiculata nodules. Under the test conditions, no significant symbiotic defects were observed for mutants lacking individual or multiple phaP genes. The mutant lacking two PHB synthases showed impaired symbiotic performance, while mutations in individual PHB synthases or a PHB depolymerase yielded no symbiotic defects. This phenomenon is not related to either the number or size of PHB granules in test mutants within nodules. Distinct metabolic profiles and cocktail pools of GAPs of different phaP mutants imply that core and accessory phasins can be differentially involved in regulating other cellular processes in the facultative microsymbiont S. fredii NGR234.IMPORTANCE Polyhydroxybutyrate (PHB) granules are a store of carbon and energy in bacteria and archaea and play an important role in stress adaptation. Recent studies have highlighted distinct roles of several granule-associated proteins (GAPs) in regulating the size, number, and localization of PHB granules in free-living bacteria, though our knowledge of the role of GAPs in bacteria associated with plants is still limited. Here we report distinct roles of core and accessory phasins associated with PHB granules of Sinorhizobium fredii NGR234, a broad-host-range microsymbiont of diverse legumes. Core phasins PhaP2 and PhaP1 are conserved major phasins in free-living cells. PhaP2 and accessory phasin PhaP3, encoded by an auxiliary gene on the symbiosis plasmid, are major phasins in nitrogen-fixing bacteroids in cowpea nodules. GAPs and metabolic profiles can vary in different phaP mutants. Contrasting symbiotic performances between mutants lacking PHB synthases, depolymerase, or phasins were revealed.

Growth, Nodulation and Nutrients Uptakes of Cowpea (Vigna unguiculata L. Walp) following Zinc Fertilizer Applications in the Semi-deciduous Forest Zone of Ghana

Cowpea can fix atmospheric nitrogen through symbiotic association with indigenous rhizobia but unfortunately, the amount of N2-fixed is usually not enough due to the presence of ineffective or low numbers of indigenous rhizobia in the soil. The effect of Zinc applications on growth, nodulation and nutrient uptakes of cowpea was investigated during the major and minor cropping seasons (2016). Cowpea seed varieties were treated to foliar spray with three different rates of Zinc sulfate (0, 5 and 10 kg Zn ha-1) at 3 and 5 weeks after sowing. The split plot design was used for both cropping seasons. This study shows that the supply of Zn fertilizer applications did not affect growth and nodulation in 2016 major and minor cropping seasons. The application of the 5 kg Zn ha-1 led to better cowpea production and greatly improve the quantity (haulm and grain yield) and quality (NPK content and crude protein) of cowpea in both haulm and grain. The Zinc fertilizer significantly enhanced N2-Fixed in both cropping season’s trial investigating. These findings suggest that cowpea responds differently to Zinc Sulphate application depending on its rates and the application of the 5 kg Zn ha-1 is the optimum rate that will enhance the yield and nutrient quality of cowpea in the Semi-Deciduous Forest Zone of Ghana.

The Amount of Phosphate Solubilization Depends on the Strain, C-Source, Organic Acids and Type of Phosphate

Although production of organic acids (OAs) is usually mentioned as the main mechanism of phosphate solubilization, the relationship between carbon sources (C-sources) and OAs produced during phosphate-solubilization by microorganisms is still poorly understood. We evaluated the influence of different C-sources on FePO4·2H2O and Ca3(PO4)2 solubilization by bacteria and on the identity/quantity of the OAs produced. Our results showed that the amount of phosphate solubilization depends on the strain, C-source, OAs, and type of phosphate. Among the five strains under study isolated from cowpea nodules (Rhizobium tropici strain UFLA 03-08, Acinetobacter sp. strain UFLA 03-09, Paenibacillus kribbensis strain UFLA 03-10, P. kribbensis strain UFLA 03-106, and Paenibacillus sp. strain UFLA 03-116), three of them solubilized Ca3(PO4)2 in all C-sources. The influence of C-sources on Ca3(PO4)2-solubilization increased in the following order: cellulose < lactose < mannitol < glucose. A significant positive correlation between the amount of phosphorus solubilized from Ca3(PO4)2 and the concentration of total OAs in the presence of glucose and mannitol was observed for these three strains. In the presence of glucose, the highest solubilization rates are associated with high concentrations of tartaric acid, and in the presence of mannitol, are associated with maleic acid. Only one strain produced OAs in the medium with lactose and Ca3(PO4)2, but there was no OAs in the medium containing cellulose. Despite the production of OAs, albeit in small concentrations, in all the C-sources investigated, FePO4·2H2O-solubilization was not observed. Thus, a relationship among C-sources, OAs, and phosphate solubilization was not always verified.

Effect of Rhizobium Inoculation, Phosphorus and Molybdenum in Yield, Yield Attributes and Nodulation of Cowpea under Mulched and Un-Mulched Field Condition

Cowpea is an important source of nutrition being popular in Nepal. In order to study its effect on nodulation, yield and yield attributes, a research was conducted in the sandy loam soil of the horticulture farm of Agriculture and Forestry University in 2018. The experiment was laid out in factorial 2×5 RCBD which consists of mulched and un-mulched condition as 1st factor and rhizobium inoculation (R) at 1gm/ 16.66 gm seed, phosphorus (P) at recommended dose of 120kg/ha, use of R plus P (RP), RP plus Molybdenum (RPMo) at 2 gm per kg seed and control with no such application as 2nd factor. So altogether there are ten treatments with three replications. Regarding 1st factor, mulched treatment was found significantly superior than un-mulched treatment in case of all yield attributes like canopy, stem diameter and plant height. Yield and no of nodules per plant was found 312.61 gm and 121.63 respectively in mulched treatment which was highly significant (P < 0.001) than un-mulched. In case of 2nd factor, plant height at 60 days after sowing was found significantly superior in all applications than control. Yield and no of nodules per plant was found 312.53gm (P < 0.01) and 129.33 (P < 0.05) respectively in RPMo treatment which was statistically significant and at par with P, RP and R treatment respectively and lowest in control. The rise in number of nodules due to the different treatment applications had the high positive correlation (P < 0.01) with yield and yield attributes. There was no any significant interaction between the two factors. Use of mulching and RPMo treatment was found to be the most suitable combination for cowpea in sandy loam soil.

Distribution and correlation between phylogeny and functional traits of cowpea (Vigna unguiculata L. Walp.)-nodulating microsymbionts from Ghana and South Africa

Cowpea (Vigna unguiculata L. Walp.) is indigenous to Africa, and highly valued for its N2-fixing trait and the nutritional attributes of its grain and leaves. The species’ ability to establish effective symbiosis with diverse rhizobial populations gives it survival and growth advantage in N-limited environments. To explore the functional diversity and phylogenetic positions of rhizobia nodulating cowpea in Africa, nodules were collected from various cowpea varieties grown in soils from the Guinea savanna and Sudano-sahelian agroecologies of Northern Ghana, and from the lowveld and middleveld areas of Mpumalanga Province in South Africa. Box-PCR profiling and multilocus sequence analysis revealed the presence of diverse microsymbionts responsible for cowpea nodulation across the study sites. BOX-PCR amplifications yielded variable band sizes, ranging from 618 bp to 5354 bp, which placed the isolates in six major clusters (Cluster A–F). Phylogenetic analysis based on 16S rRNA, atpD, glnII, gyrB, rpoB, nifH and nodC genes revealed the presence of diverse Bradyrhizobium sp. closely related to Bradyrhizobium daqingense, Bradyrhizobium subterraneum, Bradyrhizobium yuanmingense, Bradyrhizobium embrapense, Bradyrhizobium pachyrhizi, Bradyrhizobium elkanii and novel Bradyrhizobium species in the soils studied, a finding that could be attributed to the unique edapho-climatic conditions of the contrasting environments. The test isolates exhibited distinct symbiotic efficiencies, and also induced variable (p ≤ 0.001) photosynthetic rates, leaf transpiration, total chlorophyll and shoot biomass accumulation on cowpea (their homologous host). Canonical correspondence analysis showed that the distribution of these microsymbionts was influenced by the concentrations of macro- and micronutrients in soils. The pairwise genetic distances derived from phylogenies and nodule functioning showed significant (p < 0.05) correlation, which suggests that local environmental factors played a major role in the cowpea-Bradyrhizobium symbiosis.

Influence of P Fertiliser on Nodulation, Growth and Nutrient Content of Cowpea (Vigna unguiculata L.) in Acidic Soils of South Western Kenya

Influence of P Fertiliser on Nodulation, Growth and Nutrient Content of Cowpea (Vigna unguiculata L.) in Acidic Soils of South Western Kenya

Evaluating the effect of increased rates of rhizobial inoculation on grain legume productivity

Intrinsic promiscuity in cowpea and bean enables plants to nodulate with native rhizobia, though sometimes ineffective rhizobia may occupy nodules, resulting in poor response to inoculation. Field trials were conducted from 2014 to 2017 in Marondera, Natural Region II, Zimbabwe, to determine the effect of increasing inoculation rates on legume growth parameters, nitrogen uptake and grain productivity. Treatments included an un-inoculated control and inoculant rates of ×1 (standard), ×2, ×3, ×4, ×5, ×7 and ×10 for both cowpea (rhizobia - inoculant-strain-MAR 1510) and bean (rhizobia-inoculant-strain-CIAT 899). Biomass productivity ranged from 2.05 (×2) - 2.94 t ha−1 (×4) and 1.10 (×10) – 1.95 t ha−1 (×4) for cowpea and bean, respectively. Nitrogen uptake increased with increasing inoculation rates reaching up to 57.56 kg N ha−1 for bean (×4) and 100.20 kg N ha−1 for cowpea (×3). The uninoculated control was not significantly different from the standard, {(×1); 1 g inoculant 500 g seed−1} treatment, for cowpea nodule weight and grain productivity. The highest cowpea and bean nodule weights were recorded from the ×3 and ×4 treatments, respectively, in the first season. Cowpea grain yield significantly varied across treatments, ranging between 0.63 and 1.55 t ha−1 with the ×3 recording the highest yield. The “×4” treatment recorded the highest bean grain productivity reaching up to 0.88 t ha−1. It can be concluded that, increasing rhizobia cells concentration per unit seed up to ×3 (cowpea) and ×4 (bean) improves response to inoculation and grain productivity suggesting a need to change product formulation or increase inoculation rate.

Bacteria related to Bradyrhizobium yuanmingense from Ghana are effective groundnut micro-symbionts

The identification of locally-adapted rhizobia for effective inoculation of grain legumes in Africa’s semiarid regions is strategic for developing and optimizing cheap nitrogen fixation technologies for smallholder farmers. This study was aimed at selecting and characterising effective native rhizobia, from Ghanaian soils for groundnut (Arachis hypogaea L.) inoculation. From surface-disinfected root nodules of cowpea and groundnut plants grown on farmers’ fields, 150 bacterial isolates were obtained, 30 of which were eventually found to nodulate groundnut plants. After testing the symbiotic potential of these isolates on groundnut on sterilized substrate, seven of them, designated as KNUST 1001–1007, were evaluated in an open field pot experiment using 15N-labelled soil. Although 15N dilution analyses did not indicate differences among treatments in the proportion of nitrogen (N) derived from the atmosphere (%Ndfa), all seven strains increased total N derived from N2 fixation by inoculated groundnut plants as compared to the non-inoculated control. Inoculation with KNUST 1002 led to total N accumulation as high as that of the groundnut reference strain 32H1. Genetic characterisation of the isolates by sequence analysis of 16S rRNA gene, 16S – 23S rRNA intergenic transcribed spacer (ITS) region and nodC gene revealed that isolates KNUST 1003 and 1007 were related to Rhizobium tropici, a common bean symbiont. The other five isolates, including KNUST 1002 belonged to the Bradyrhizobium genus, being closely related to Bradyrhizobium yuanmingense. Therefore, this study revealed novel native Ghanaian rhizobia with potential for the development of groundnut inoculants.

English

A total of eighty one (81) rhizobial isolates were recovered from root nodules of cowpea (Vigna unguiculata L. Walp.) and groundnut (Arachis hypogaea L.) grown in soils collected from eight different sites (Hawassa, Wondogenet, Chofa, Badawacho, Bodity, Gofa, Ziway, and Alemtena) in Ethiopia with no known history of inoculation. The test isolates together with seven reference strains belonging to five genera including Rhizobium, Ensifer, Mesorhizobium, Bradyrhizobium and Azorhizobium were characterized using ninety phenotypic traits. Thirty one isolates (38%) were found to be fast growers while fifty isolates (62%) were slow growers. The majority of the isolates showed an intrinsic resistance to antibiotics (µg/ml), Chloramphenicol (5 and 15), Lincomycin (100), Novobiocin (0.5 and 1.5), and Erythromycin (10 and 20) and to heavy metals manganese sulphate (500) and copper chloride (100). Most isolates did not tolerate NaCl concentration >3% (w/v) and high temperature (45°C). Dendrogram was constructed by applying the unweighted pair group method with arithmetic means (UPGMA) using NTSYSpc Version 2.1. They were grouped into seven clusters and eight unclustered positions, when 82% relative similarity was used as a cut point. Fifty eight percent of the test isolates were grouped with Bradyrhizobium japonicum and Bradyrhizobium elkanii superclades, thus indicating that rhizobia nodulating cowpea and groundnut are delineated within a branch that defines Bradyrhizobium genus. To elucidate the precise taxonomic positions of the isolates, further genetic studies are required using modern molecular biological methods. Key words: Groundnut, cowpea, isolates, phenotypic traits, Bradyrhizobium, Rhizobium.

Antioxidant response of cowpea co-inoculated with plant growth-promoting bacteria under salt stress.

Soil salinity is an important abiotic stress worldwide, and salt-induced oxidative stress can have detrimental effects on the biological nitrogen fixation. We hypothesized that co-inoculation of cowpea plants with Bradyrhizobium and plant growth-promoting bacteria would minimize the deleterious effects of salt stress via the induction of enzymatic and non-enzymatic antioxidative protection. To test our hypothesis, cowpea seeds were inoculated with Bradyrhizobium or co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and then submitted to salt stress. Afterward, the cowpea nodules were collected, and the levels of hydrogen peroxide; lipid peroxidation; total, reduced and oxidized forms of ascorbate and glutathione; and superoxide dismutase, catalase and phenol peroxidase activities were evaluated. The sodium and potassium ion concentrations were measured in shoot samples. Cowpea plants did not present significant differences in sodium and potassium levels when grown under non-saline conditions, but sodium content was strongly increased under salt stress conditions. Under non-saline and salt stress conditions, plants co-inoculated with Bradyrhizobium and Actinomadura or co-inoculated with Bradyrhizobium and Paenibacillus graminis showed lower hydrogen peroxide content in their nodules, whereas lipid peroxidation was increased by 31% in plants that were subjected to salt stress. Furthermore, cowpea nodules co-inoculated with Bradyrhizobium and plant growth-promoting bacteria and exposed to salt stress displayed significant alterations in the total, reduced and oxidized forms of ascorbate and glutathione. Inoculation with Bradyrhizobium and plant growth-promoting bacteria induced increased superoxide dismutase, catalase and phenol peroxidase activities in the nodules of cowpea plants exposed to salt stress. The catalase activity in plants co-inoculated with Bradyrhizobium and Streptomyces was 55% greater than in plants inoculated with Bradyrhizobium alone, and this value was remarkably greater than that in the other treatments. These results reinforce the beneficial effects of plant growth-promoting bacteria on the antioxidant system that detoxifies reactive oxygen species. We concluded that the combination of Bradyrhizobium and plant growth-promoting bacteria induces positive responses for coping with salt-induced oxidative stress in cowpea nodules, mainly in plants co-inoculated with Bradyrhizobium and P. graminis or co-inoculated with Bradyrhizobium and Bacillus.

Distribution and Phylogeny of Microsymbionts Associated with Cowpea (Vigna unguiculata) Nodulation in Three Agroecological Regions of Mozambique.

ABSTRACTCowpea derives most of its N nutrition from biological nitrogen fixation (BNF) via symbiotic bacteroids in root nodules. In Sub-Saharan Africa, the diversity and biogeographic distribution of bacterial microsymbionts nodulating cowpea and other indigenous legumes are not well understood, though needed for increased legume production. The aim of this study was to describe the distribution and phylogenies of rhizobia at different agroecological regions of Mozambique using PCR of the BOX element (BOX-PCR), restriction fragment length polymorphism of the internal transcribed spacer (ITS-RFLP), and sequence analysis of ribosomal, symbiotic, and housekeeping genes. A total of 122 microsymbionts isolated from two cowpea varieties (IT-1263 and IT-18) grouped into 17 clades within the BOX-PCR dendrogram. The PCR-ITS analysis yielded 17 ITS types for the bacterial isolates, while ITS-RFLP analysis placed all test isolates in six distinct clusters (I to VI). BLASTn sequence analysis of 16S rRNA and four housekeeping genes (glnII, gyrB, recA, and rpoB) showed their alignment with Rhizobium and Bradyrhizobium species. The results revealed a group of highly diverse and adapted cowpea-nodulating microsymbionts which included Bradyrhizobium pachyrhizi, Bradyrhizobium arachidis, Bradyrhizobium yuanmingense, and a novel Bradyrhizobium sp., as well as Rhizobium tropici, Rhizobium pusense, and Neorhizobium galegae in Mozambican soils. Discordances observed in single-gene phylogenies could be attributed to horizontal gene transfer and/or subsequent recombinations of the genes. Natural deletion of 60 bp of the gyrB region was observed in isolate TUTVU7; however, this deletion effect on DNA gyrase function still needs to be confirmed. The inconsistency of nifH with core gene phylogenies suggested differences in the evolutionary history of both chromosomal and symbiotic genes.IMPORTANCE A diverse group of both Bradyrhizobium and Rhizobium species responsible for cowpea nodulation in Mozambique was found in this study. Future studies could prove useful in evaluating these bacterial isolates for symbiotic efficiency and strain competitiveness in Mozambican soils.

Capacidade de rizobactérias na solubilização de fosfato e síntese de ácido indol acético em feijão caupi

As espécies de rhizobia são conhecidas como microorganismos efetivos para melhorar a fertilidade do solo, como solos de Cerrado com deficiência de crescimento da planta e problemas de fixação de nitrogênio. O objetivo deste trabalho foi avaliar a capacidade de solubilização de fosfato e síntese de ácido indol acético de isolados de rizóbio obtidos de solos de Cerrado em Tocantins, avaliando a eficiência simbiótica dos mesmos em plantas de feijão caupi (Vigna unguiculata L. Walp.). Foram utilizados 32 isolados de rizóbio e uma espécie referência de Bradyrhizobium, onde foram avaliadas a capacidade de solubilização de fosfato e síntese de ácido indool acético (AIA), in vitro, e capacidade simbiótica dos isolados de rizóbio e o efeito na biomassa de feijão caupi em casa de vegetação. Dos 32 isolados e a estirpes referência, apenas oito obtiveram capacidade de solubilizar fosfato de cálcio, e todos os isolados produziram AIA. Houve aumento significativo para a biomassa e nodulação de feijão caupi com a inoculação de diferentes isolados de rizóbio, com os isolados UFT R122 e UFT R124 com os maiores valores para os parâmetros estudados, com aumentos acima de 33% para a eficiência relativa em relação ao tratamento com adubação nitrogenada. Associando-se os resultados de capacidade de solubilização de fosfato, síntese de AIA e eficiência simbiótica e nodulação, observou-se que os isolados que apresentaram bom desempenho são potenciais inoculantes para o feijão caupi em solos de Cerrado.

Performance of cowpea as influenced by native strain of rhizobia, lime and phosphorus in Samaru, Nigeria

The complimentary effects of a native rhizobia strain (SAMFIX 286), lime and single superphosphate (SSP) as components of ISFM were evaluated on the biomass, nodulation and N2 fixation of cowpea (Vigna unguiculata L.). Lime was applied at the rate of 250 kg (Ca(OH)2) ha−1, while SSP was applied at 30 kg P ha−1. The trial was carried out in a screen house with the treatments arranged in randomized complete block design. Results obtained show that the performance of SAMFIX 286 inoculated plants did not significantly (p < 0.05) differ from that of the un-inoculated treatment. Application of lime significantly increased root dry weight, shoot dry weight, nodule number and dry weight by 42.5%, 35.3%, 65.6% and 50%, respectively. Nodulation was significantly (p < 0.05) increased by SSP. The complimentary effect of lime with SSP significantly increased total shoot N concentration. Similarly, combined inoculation of SAMFIX 286 with lime and SSP increased N concentration by 31.9% and N derived from atmosphere (Ndfa) by 16.3% compared to the un-inoculated treatment. Inoculation of SAMFIX 286 with SSP was also effective on Ndfa by cowpea. It was concluded that lime and SSP were good combination with native rhizobia strain in improving cowpea nodulation and biological N2 fixation.

Influence of Bradyrhizobium Inoculation and Fungicide Seed Treatment on Development and Yield of Cowpea, Lablab, and Soybean

Core Ideas Cowpea did not require Bradyrhizobium inoculation for nodulation. Lablab required Bradyrhizobium inoculation for nodulation. Fungicide seed treatment did not compromise nodulation of cowpea or lablab. Cowpea [Vigna unguiculata (L.) Walp.] and lablab (Lablab purpureus L.) are grain legumes with limited testing for grain, forage, and cover crop use in the US Corn Belt. We conducted a 2‐year field study to determine the influence of Bradyrhizobium spp. inoculation and fungicide seed treatment on development, nodulation, and yield of selected grain legumes. Soybean [Glycine max (L.) Merr.] was included as a well‐understood control. The experimental design was a randomized complete block in a factorial of four grain legumes with and without Bradyrhizobium spp. inoculation and a fungicide seed treatment. The cultivars used in the experiment were soybean P92Y82, cowpeas CA46 and Top Crop, and lablab Rongai. The seed treatments were fungicide, mefenoxam + fludioxonil (ApronMaxx), and Bradyrhizobium spp. inoculant. The two experimental sites had four blocks each year, every block consisting of 16 plots with different crop–fungicide–Bradyrhizobium combinations. Each crop had four treatments: fungicide only, Bradyrhizobium spp. inoculant only, fungicide + inoculant, and a control (with no fungicide or inoculant). Cowpea plants had numerous functional nodules (pinkish or reddish on the inside) in the absence of Bradyrhizobium spp. inoculation, but lablab never produced any nodules without inoculation. We found no significant effects of Bradyrhizobium spp. inoculation and fungicide seed treatment on cowpea, lablab, or soybean grain yield.

Nodulation and Yield Response of Cowpea [Vigna unguiculata (L) Walp.] to Integrated Use of Planting0 Pattern and Herbicide Mixtures in Wollo, Northern Ethiopia

Nodulation and Yield Response of Cowpea [Vigna unguiculata (L) Walp.] to Integrated Use of Planting0 Pattern and Herbicide Mixtures in Wollo, Northern Ethiopia