Rhizobium Tropici Strain Research Articles

Impact of Fe + 2 ions on structural integrity of A0A6P1CI42_RHITR NifA protein from Rhizobium tropici strain CIAT 899

A0A6P1CI42_RHITR, a protein originating from Rhizobium tropici strain CIAT 899, has emerged as a key player in leguminous plant symbiosis and nitrogen fixation processes. Understanding the intricate details of its structure and function holds immense significance for unraveling the molecular mechanisms underlying its biological activities. In this study, we employed molecular modeling and molecular dynamics (MD) simulations to investigate the A0A6P1CI42_RHITR protein, with a specific emphasis on the influence of Fe-atoms, linker structural integrity, and conformational changes within the GAF domain. Our findings unveiled noteworthy conformational changes in the A0A6P1CI42_RHITR protein, particularly within the GAF domain, when Fe-atoms were present compared to its apo form. Significant conformational rearrangements after an initial 20 ns, accompanied by the opening of the ligand substrate accommodating loop in the GAF domain influenced by Fe-atoms was observed. At the residue level, the investigation revealed substantial activity variations in individual residues, particularly in those contributing to the GAF domain from positions 51 to 223. Intriguingly, the presence of Fe-atoms led to controlled movement of conserved cysteine residues at positions 467 and 472, indicating a correlation between interlinker domain motion and the activity of the GAF domain loop responsible for substrate accommodation. Moreover, in the presence of Fe-atoms, the distance between Cys467 and Cys472 residues was maintained, ensuring the overall structural integrity of the interdomain loop necessary for protein activation. Conversely, in the apo form, a sudden flip motion of cysteine residues’ thiol groups was observed, leading to a loss of structural integration. Overall, our study utilizing molecular modeling and MD simulations offers valuable insights into the structural dynamics and functional implications of the A0A6P1CI42_RHITR protein. Communicated by Ramaswamy H. Sarma

Rhizobia exopolysaccharides: promising biopolymers for use in the formulation of plant inoculants.

Inoculants with beneficial microorganisms comprise both selected strains and carriers that ensure a favorable microenvironment for cell survival and stability. Formulations of inoculants using synthetic polymers as carriers are common. However, only a few studies are available in the literature regarding the formulation of inoculants using natural biomolecules as carriers. Exopolysaccharides (EPS) are biomolecules produced by a vast array of microbial species, including symbiotic nitrogen-fixing bacteria, commonly known as rhizobia. EPS perform several functions, such as the protection against the deleterious effects of diverse environmental soil stresses. Two Rhizobium tropici strains and one Paraburkholderia strain were selected after semiquantitative analysis by scanning electron microscopy (SEM) of their EPS production in liquid YMA medium. Their EPS were characterized through a series of analytical techniques, aiming at their use in the formulation of plant inoculants. In addition, the effect of the carbon source on EPS yield was evaluated. Multi-stage fragmentation analysis showed the presence of xylose, glucose, galactose, galacturonic acid, and glucuronic acid in EPS chemical composition, which was confirmed by FT-IR spectra and 13C NMR spectroscopy. Thermal stability (thermogravimetric) was close to 270°C and viscosity ranged from 120 to 1053.3mPa.s. Surface morphology (SEM) was rough and irregular, with a cross-linked spongy matrix, which, together with the hydrophilic functional groups, confers water holding capacity. The present study showed that the three EPS have potential as microorganism carriers for formulation of microbial inoculants to be applied in plants.

Influence of common bean genotypes and rhizobia interaction for nodulation and nitrogen fixation

Bacteria from the rhizobia group are able to associate symbiotically with bean crop, forming nodules in the root, in which the biological nitrogen-fixing process occurs. However, the efficiency of this process has been low and it can be attributed to genetic and environmental factors. Thus, the objective of this study was to evaluate the capacity of nodulation of local varieties and commercial common bean cultivars inoculated with a Rhizobium tropici strain used in commercial inoculants and rhizobia isolates from common bean root nodules. The experiment was carried out in a factorial scheme (2x4), in a randomized block design with four replicates. It was tested two local varieties and two commercial cultivars, inoculated with the reference Rhizobium tropici strain CIAT899 and the RBZ14 strain isolated from common bean nodules grown in soils of Southern Brazil, in adapted Leonard-type pots. The CIAT899 strain promoted either higher mass of viable nodules and higher nitrogen accumulation in the aerial part. The black group local variety showed better response than the cultivar TAA Dama for nodule viability, suggesting more efficiency for nodulation. The interaction between genotypes (local varieties and commercial cultivars) and bacteria showed the specificity of the complex symbiotic relationship of biological nitrogen fixation in common bean, requiring further studies of these interactions.

Co-inoculation of Rhizobium and Bradyrhizobium promotes growth and yield of common beans

Some strains of Bradyrhizobium benefit the biological N2 fixation (BNF) and growth of common beans (Phaseolus vulgaris L.) when co-inoculated with Rhizobium tropici under greenhouse conditions. Here, we evaluated the benefit of Bradyrhizobium diazoefficiens strain CPAC 7 co-inoculated with Rhizobium tropici strain CIAT 899 on common bean in the field. Three Bradyrhizobium strains were co-inoculated with R. tropici CIAT 899 in one experiment in the greenhouse and two in the field. The greenhouse experiment combined each of three Bradyrhizobium strains (29w, USDA 110, and CPAC 7) in co-inoculation with CIAT 899 in Leonard jars. Then, two of these strains, 29w and CPAC 7, were co-inoculated with Rhizobium on-seeds (1.2 × 106 CFU seed−1) or both on-seed and in-furrow (1.08 × 108 CFU m−1) in a field experiment. Finally, a second field experiment evaluated strain CPAC 7 at doses ranging from 1.5 × 105 to 1.2 × 106 CFU seed−1. Co-inoculation with strain CPAC 7 improved shoot biomass accumulation in Leonard jars. In the field, co-inoculation of CPAC 7 with CIAT 899 on-seed enhanced grain yield by 20% compared with inoculation of CIAT 899 only (p < 0.10). The percentage of N derived from the air (%Ndfa) was between 50 and 60%, with only a tendency towards co-inoculation benefit. Given that the %Ndfa of the inoculated plants was not statistically different between treatments, the increased grain yield was not entirely due to BNF but also due to an increase of soil N uptake. In the second field trial, larger doses of inoculum increased nodulation and root biomass, but significant differences in grain yield were not observed. Our results show that the Rhizobium-Bradyrhizobium co-inoculation can enhance growth and grain yield of common beans and indicate that a plant growth-promoting mechanism besides BNF may be involved in the beneficial co-inoculation effect. However, further adjustments are needed to ensure a better response under field conditions.

Influence of two phosphate-potassium solubilizing bacterial species on biomass and nitrate concentration on mustard greens (Brassica juncea (L.) Czernjaew) cultivated on acid sulfate soils

Two field trials were conducted to determine the effect of P-K solubilizing bacteria and nitrogen chemical fertilizer on growth, yield and nitrate in leaf of mustard greens Brassica juncea L.) cultivated on acid sulfate soils. Eight P-K solubilizing bacterial strains composed of 3 strains of Acinetobacter calcoaceticus and 5 strains of Rhizobium sp., bacterial liquid were directly watered into plant at 3 stages [6, 12 and 21 days after planting] during vegetable cultivation, chemical fertilizer (60N – 40 P2O5 – 20 K2O) and control (no-inoculation). The study revealed that eight P-K solubilizing bacterial strains have good characteristics as nitrogen fixation, phosphate and potassium solubilisation. Application of nitrogen chemical concentration, increasing nitrate concentration of leaf of mustard greens. Application of bacterial liquid with Acinetobacter calcoaceticus strain NT4 and Acinetobacter calcoaceticus strain NT30 strain, Rhizobium tropici strain N18 and Rhizobium leguminosarum strain K35 on mustard greens cultivated on acid sulfate soils (basal fertilizer: 40 P2O5 – 20 K2O) was the best cultural practice because the this model not only supported the highest biomass, but also decreased nitrate concentration in leaf of mustard greens.

Fertilidade de um organossolo e produtividade do feijoeiro influenciados pela calagem e inoculação

O objetivo deste trabalho foi avaliar o efeito da calagem nos atributos químicos de um Organossolo Háplico e a influência da interação da calagem com a inoculação de bactérias fixadoras de N2 atmosférico (Rhizobium tropici), nos teores foliares de nitrogênio, fósforo e potássio e na produtividade de grãos de feijão, cultivar Carioca. O delineamento experimental foi o de blocos ao acaso, com três repetições e esquema de parcelas subdivididas. As parcelas foram constituídas pelas doses de calcário e as subparcelas pela presença e ausência de inoculação. As doses de calcário utilizadas foram 0,0; 4,9; 8,9; 15,0 e 27,2 Mg ha-1, visando elevar respectivamente os níveis de saturação por bases 20; 30; 45 e 75%. Aos 45 dias após a aplicação dos tratamentos, foi realizada uma amostragem do solo para verificar alterações nos atributos químicos do solo. Na fase de florescimento foi realizada a coleta de folhas para avaliação dos teores de nitrogênio, fósforo e potássio. Foi avaliada a produtividade de grãos. A superioridade dos teores de N foliar na interação calagem x inoculação em relação ao controle não inoculado evidência que a calagem favoreceu a simbiose entre o feijoeiro e as estirpes de Rhizobium tropici e, consequentemente, a fixação biológica de N. A calagem associada à inoculação promoveu aumentos nos teores foliares de nitrogênio e na produtividade de grãos.

Draft Genome Sequence of Biological N2-Fixing Bacterium Rhizobium tropici A12, Isolated from Root Nodule of Tropical Soybean (Glycine max), TGx-1148 Variety.

Here, we present the genome sequence and annotated features of Rhizobium tropici strain A12, which is able to nodulate tropical Glycine max (soybean). The draft genome of the strain consists of 107 contigs totaling 6.5 Mbp in size. The annotation revealed 6,204 protein-coding genes, 52 tRNAs, and 7 rRNAs.

Nitrogen in Shoots, Number of Tillers, Biomass Yield and Nutritive Value of Zuri Guinea Grass Inoculated with Plant-Growth Promoting Bacteria

The objective of this study was to evaluate the effects of plant growth-promoting bacteria (PGPB) strains of Azospirillum brasilense, Pseudomonas fluorescens and Rhizobium tropici on biomass yield, number of tillers, nitrogen accumulation and nutritive value of shoots of Megathyrsus (syn. Panicum) maximus cultivar BRS Zuri (Zuri Guinea grass). For that, one experiment was performed for 14 months to evaluate inoculation and re-inoculation with Azospirillum brasilense strains Ab-V5 and Ab-V6, Pseudomonas fluorescens strain CCTB 03 and of co-inoculation with Rhizobium tropici strain CIAT 899 + A. brasilense strain Ab-V6 combined with N-fertilizer (100 kg of N ha-1). Shoot dry weight yield (SDWY), number of tillers (NT), total N concentration (TNC), total N uptake (TNU) and nutritive value of Zuri Guinea grass was evaluated for eight cuts, and inoculation increased all parameters. In the NT, the treatments inoculated with PGPB were superior to the positive non-inoculated control receiving N-fertilizer, by up to 36%. For the accumulated of SDWY the treatment re-inoculated with P. fluorescens CCTB 03 after each cut was statistically superior tin 7% the positive control. The PGPB when combined N-fertilizer also increased SDWY, NT, the relative chlorophyll index, TNC, total N uptake, neutral detergent fiber, acid detergent fiber, crude protein and in vitro digestibility dry matter of Zuri Guinea grass. The results indicate that PGPB can represent a sustainable alternative for reducing the use of N-fertilizers. The lower effects of re-inoculation with PGPB on the nutrition or yield of Zuri Guinea grass, demonstrating that the determination of the method of application and periodicity of inoculation still require investigation.

Effects of growth‐promoting bacteria on soybean root activity, plant development, and yield

AbstractRhizobia and other plant growth‐promoting rhizobacteria (PGPR) have been broadly used as inoculants in agriculture, resulting in morphofunctional improvements in roots and grain yield. This study was carried out during two cropping seasons under field and greenhouse conditions in Brazil to verify the effects of inoculation of two soybean cultivars with PGPR and secondary microbial metabolites (SMMs) on root activity and nodulation, plant development, and grain yield. Inoculation and co‐inoculation treatments consisted of Bradyrhizobium japonicum strain SEMIA 5079 and B. diazoefficiens strain SEMIA 5080 inoculated together, in combination with Bacillus subtilis strain QST 713, Azospirillum brasilense strains Ab‐V5 and Ab‐V6, and SMMs extracted from B. diazoefficiens strain USDA 110 and Rhizobium tropici strain CIAT 889. Root systems were evaluated by direct (optical reading) and indirect (rubidium nitrate application, 85RbNO3) methods. Increases of up to 1.6% in root diameter (0.01‐ to 0.5‐mm class), 28.5% in length, 19.7% in root volume, 17.8% in root surface area, 29% in the number of nodules, 27.2% in nodule dry weight, 13.5% in root dry weight, and 3.8% in shoot dry weight. Greater exploration and activity within and between rows following inoculation at up to 40 and 10 cm in depth, respectively, were observed in plants co‐inoculated with the standard inoculation (only Bradyrhizobium spp.) + SMMs + A. brasilense, resulting in a yield increase of 485 kg ha−1. The results emphasize the biotechnological potential of using secondary metabolites of rhizobia with inoculants containing rhizobia and PGPR to improve the growth and soybean yield in tropical conditions.

Genomic insights into plant growth promoting rhizobia capable of enhancing soybean germination under drought stress

BackgroundThe role of soil microorganisms in plant growth, nutrient utilization, drought tolerance as well as biocontrol activity cannot be over-emphasized, especially in this era when food crisis is a global challenge. This research was therefore designed to gain genomic insights into plant growth promoting (PGP) Rhizobium species capable of enhancing soybean (Glycine max L.) seeds germination under drought condition.ResultsRhizobium sp. strain R1, Rhizobium tropici strain R2, Rhizobium cellulosilyticum strain R3, Rhizobium taibaishanense strain R4 and Ensifer meliloti strain R5 were found to possess the entire PGP traits tested. Specifically, these rhizobial strains were able to solubilize phosphate, produce exopolysaccharide (EPS), 1-aminocyclopropane-1-carboxylate (ACC), siderophore and indole-acetic-acid (IAA). These strains also survived and grew at a temperature of 45 °C and in an acidic condition with a pH 4. Consequently, all the Rhizobium strains enhanced the germination of soybean seeds (PAN 1532 R) under drought condition imposed by 4% poly-ethylene glycol (PEG); nevertheless, Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 inoculations were able to improve seeds germination more than R2, R4 and R5 strains. Thus, genomic insights into Rhizobium sp. strain R1 and R. cellulosilyticum strain R3 revealed the presence of some genes with their respective proteins involved in symbiotic establishment, nitrogen fixation, drought tolerance and plant growth promotion. In particular, exoX, htrA, Nif, nodA, eptA, IAA and siderophore-producing genes were found in the two rhizobial strains.ConclusionsTherefore, the availability of the whole genome sequences of R1 and R3 strains may further be exploited to comprehend the interaction of drought tolerant rhizobia with soybean and other legumes and the PGP ability of these rhizobial strains can also be harnessed for biotechnological application in the field especially in semiarid and arid regions of the globe.

Regulation of hsnT, nodF and nodE genes in Rhizobium tropici CIAT 899 and their roles in the synthesis of Nod factors and in the symbiosis

Rhizobium tropici strain CIAT 899 possesses outstanding agronomic properties as it displays tolerance to environmental stresses, a broad host range and high effectiveness in fixing nitrogen with the common bean (Phaseolus vulgaris L.); in addition, it carries intriguing features such as five copies of the regulatory nodD gene, and the capacity to synthesize a variety of nodulation factors (NFs), even in a flavonoid-independent manner, when submitted to abiotic stresses. However, the roles of several nod genes of the repertoire of CIAT 899 remain to be determined. In this study, we obtained mutants for the hsnT, nodF and nodE genes of CIAT 899 and investigated their expression, NF structures and symbiotic properties. Either in the presence of the flavonoid apigenin, or of salt the expression of hsnT, nodF and nodE in wild-type CIAT 899 was highly up-regulated in comparison to the mutants of all five copies of nodD, indicating the roles that regulatory nodD genes play in the activation of hsnT, nodF and nodE; however, NodD1 was recognized as the main inducer. In total, 29 different NF structures were synthesized by wild-type CIAT 899 induced by apigenin, and 36 when induced by salt, being drastically reduced by mutations in hsnT, nodF and nodE, especially under osmotic stress, with specific changes related to each gene, indicating that the three genes participate in the synthesis of NFs. Mutations in hsnT, nodF and nodE affected differently symbiotic performance (nodule number and shoot dry weight), according to the host plant. Our results indicate that the expression of hsnT, nodF and nodE genes of CIAT 899 is mediated by nodD genes, and although these three genes do not belong to the main set of genes controlling nodulation, they contribute to the synthesis of NFs that will impact symbiotic performance and host specificity.

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.

Response of common bean (Phaseolus vulgaris L.) to nitrogen, phosphorus and rhizobia inoculation across variable soils in Zimbabwe

Common bean is an important crop with potential to curb malnutrition in poor Sub-Saharan African populations. Yields of common bean (Phaseolus vulgaris L.) are, however poor, limited by low soil phosphorus (P), nitrogen (N) and poor biological N2-fixation. On-farm experiments were carried out to study the effect of N, P and rhizobia inoculation on common bean yield and yield components during the 2014/2015 and 2015/2016 cropping seasons in Eastern Zimbabwe. Experiments were conducted on five farmers’ fields located in two agroecologies; three fields were considered to be degraded with soil organic carbon (SOC) < 4 g kg−1 and available P < 6 mg kg−1, while the two non–degraded sites had SOC > 7 g kg−1 and available P > 15 mg kg−1. Two common bean varieties (Gloria and NUA45) were tested in a split-plot arranged in randomized complete block design. The main plot factor was the combination of N (0 and 40 kg ha−1) and P (0 and 20 kg ha−1), and the sub-plot factors were variety (Gloria and NUA 45) and inoculation with Rhizobium tropici strain CIAT899 (+/− inoculum). At planting, both N and P were applied at 20 kg ha−1, with an additional 20 kg ha−1 N top dressing applied at flowering. Analysis of variance indicated common bean did not respond to rhizobia inoculation (P > 0.05) whilst P significantly increased the number of nodules and active nodules per plant (P < 0.001), and grain yield. Application of 40 kg ha−1 N significantly increased the number of pods per plant, number of seeds per pod, and grain yields. A significant NP interaction was only observed on grain yield for non-degraded soils. Co-application of N and P in non-degraded sites increased grain yields from 0.27 to 1.48 Mg ha−1during the first season and from 0.37 to 2.09 Mg ha−1during the second season. On degraded sites, NP application resulted in uninspiring grain yield gains of 0.09 to 0.19 Mg ha−1 during the first season, and from 0.16 to 0.28 Mg ha−1 in the second season. In general, effects of N or P were not significantly different, suggesting that farmers could invest in either of these nutrients for increased common bean grain yields. Strategically, P investments would be more logical as residual P effects to rotational cereals improve overall cropping system performance. The response of common bean to inoculation in Zimbabwe still needs to be widely investigated for these and other varieties.

Co-inoculation of maize with Azospirillum brasilense and Rhizobium tropici as a strategy to mitigate salinity stress.

Plants are highly affected by salinity, but some plant growth-promoting bacteria (PGPB) may trigger induced systemic tolerance (IST), conferring protection against abiotic stresses. We investigated plant mechanisms under saline stress (170mM NaCl) when maize was singly or co-inoculated with Azospirillum brasilense strains Ab-V5 and Ab-V6 and Rhizobium tropici strain CIAT 899. Under greenhouse conditions, plants responded positively to inoculation and co-inoculation, but with differences between strains. Inoculation affected antioxidant enzymes that detoxify reactive oxygen species (ROS) - ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD) - mainly in leaves. Proline contents in leaves and roots and malondialdehyde (MDA) in leaves - plant-stress-marker molecules - were significantly reduced due to the inoculation, indicating reduced need for the synthesis of these molecules. Significant differences were attributed to inoculation in the expression of genes related to antioxidant activity, in general with upregulation of APX1, CAT1, SOD2 and SOD4 in leaves, and APX2 in roots. Pathogenesis-related genes PR1, prp2, prp4 and heat-shock protein hsp70 were downregulated in leaves and roots, indicating that inoculation with PGPB might reduce the need for this protection. Together the results indicate that inoculation with PGPB might provide protection from the negative effects of saline stress. However, differences were observed between strains, as A. brasilense Ab-V5 did not show salt tolerance, while the best inoculation treatments to mitigate saline stress were with Ab-V6 and co-inoculation with Ab-V6+CIAT 899. Inoculation with these strains may represent an effective strategy to mitigate salinity stress.

Characterization of new exopolysaccharide production by Rhizobium tropici during growth on hydrocarbon substrate

Exopolysaccharide (EPS) are produced by a diverse of rhizobia species and has been demonstrated to be a bioemulsifier with potential applications in the degradation of hydrocarbons. In the present study, attempts were made to obtain the new exopolysaccharide production by Rhizobium tropici (SEMIA 4080 and MUTZC3) strains during growth on hydrocarbon substrate. Under the different cultivation conditions, the high molecular weight exopolysaccharides from Rhizobium tropici strains cultivated for 96h mainly consisted of carbohydrates (79–85%) and a low percentage of protein. The EPSC3-D differed from the others, with only 60% of carbohydrate. However, all strains produced polymers with distinct rheology properties, such as viscosity of each EPS sample, suitable for different applications. In addition, RP-HPLC, FTIR and NMR studies revealed EPS produced by rhizobia strains were similar indicating minimal difference between EPS compositions.

The use of various strains of Rhizobium tropici for inoculation of snap bean cultivars with a determinate growth pattern

The snap bean (Phaseolus vulgaris L.) is an economically important vegetable in Brazil. Bean plants can establish symbiotic associations with bacteria that fix atmospheric nitrogen. These associations show specificity of host plants to certain bacteria. Nitrogen fertilization constitutes a crop production cost, and the use of Rhizobium inoculation to supply nitrogen to crops may decrease the production costs. The aim of this study was to evaluate the effects of inoculation of three different snap bean cultivars with three Rhizobium tropici strains on agronomical performance of the plant. A completely randomized experimental design was used, with a 3 ? 5 factorial scheme and four replicates per treatment. The factors tested were three snap bean cultivars (UEL 1, Alessa, and UEL 2), and five types of inoculation (uninoculated control, inoculation with SEMIA 4077, SEMIA 4080, SEMIA 4088, or with a mix of the three strains). The experiment was conducted in a greenhouse. Plant height, stem diameter, pod length, the number of pods per plant, and average weight and yield of commercial-grade pods, were determined. An analysis of variance was conducted using the F test, followed by Tukey’s test (p &lt; 0.05). Inoculation had a positive effect on all the parameters quantified. The beneficial effect was more pronounced in plants inoculated with the mix of Rhizobium strains.

GROWTH AND YIELD OF COMMON BEAN AS AFFECTED BY SEED INOCULATION WITH RHIZOBIUM AND NITROGEN FERTILIZATION

SUMMARYTwo field experiments were conducted during the rainy seasons of 2013 and 2014 to evaluate the effects of biological nitrogen fixation (BNF) and/or sowing N fertilization on the growth and yield of Phaseolus vulgaris L. In addition, leaf soluble protein content (LSPC) was measured at four growth stages in both seasons. Plants were subjected to the following treatments: only fertilized with 20 kg N ha−1 at sowing and with 40 kg N ha−1 at 25 days after emergence (DAE) (F); only inoculated with Rhizobium tropici strain SEMIA 4080 at sowing and fertilized with 40 kg N ha−1 at 25 DAE (I+N); and inoculated and fertilized with 20 kg N ha−1 at sowing and with 40 kg N ha−1 at 25 DAE (IF). An additional treatment was done only in the second season and plants were inoculated with no N fertilization at any phase (I−N). Crop growth rate and leaf area index were enhanced by IF and F treatments as compared to I+N treatment, however, net assimilation rate did not differ among the treatments. At the pollination and flowering stages for seasons, LSPC was significantly increased by IF treatment, which also caused the highest final yield compared with the remaining treatments in both seasons. Therefore, the fertilization with 20 kg N ha−1 at sowing together with inoculation and 40 kg N ha−1 at 25 DAE is recommended for obtaining high yield in bean cultivation with high technology. As the inoculation with Rhizobium at sowing and fertilization with 40 kg N ha−1 at 25 DAE (I+N) had the same crop yield as plants fertilized at sowing and at 25 DAE (F), it can be recommended for a low-cost technology cultivation employed by small farmers.

Seed Treatment with Fungicides Does Not Affect Symbiosis between Common Bean and Rhizobia

Results of the few studies on the symbiosis of rhizobia and common bean (Phaseolus vulgaris L.) that have evaluated the effects of new fungicides applied to seeds have been inconclusive, that is, some showed no effects and others showed harmful effects. This study tested the compatibility between commercial fungicides, currently recommended for treatment of seeds, and symbiosis of common bean with rhizobia. Two field experiments were performed in the 2012/2013 spring–summer crop season in two Brazilian municipalities. A randomized block experimental design with four replicates and a 5 × 2 factorial arrangement was used, consisting of five seed treatments {the fungicides: carboxin(carboxamide) + thiram (dimethyldithiocarbamate) = Vitavax‐Thiram (Macdermid Agricultural Solutions Ltda, Sumaré, Brazil); fludioxonil(phenylpyrrol) + metalaxyl‐M(acilalaninato) = MaximXL (Syngenta Ltda, São Paulo, Brazil); fluazinam (phenylpyridin‐amine) + thiophanate‐methyl[benzimidazole(precursor of)] = Certeza (Iharabras S.A., Sorocaba, Brazil), and carbendazim (benzimidazole) = Carbomax (Nufarm S.A., Maracanaú, Brazil) and one control without fungicide} with or without rhizobial inoculation. Seeds from the cultivar BRSMG Madrepérola were treated with the fungicides at manufacturer recommended application rates and then inoculated with Rhizobium tropici strain CIAT899T. The majority of parameters related to nodulation, plant growth, and N nutrition showed significant differences between sites. However, all parameters had values within or above the acceptable ranges. Depending on the site, the fungicide carboxin+thiram decreased the stand of plants, and carbendazim resulted in lower grain N concentration. However, regardless of the site, the fungicides did not influence nodulation, plant growth, shoot N concentration, or grain yield at the application rate recommended by the manufacturers.Core Ideas Environment influences effects of fungicide on rhizobia symbiosis. Native rhizobia resulted in grain yield similar to inoculation with CIAT 899T. The fungicides did not influence rhizobia symbiosis effects on plant.

Differences in Nodulation and Grain Yield on Common Bean Cultivars with Different Growth Cycles

ABSTRACTThe common bean can obtain nitrogen (N) from the decomposition of the soil organic matter, mineral fertilizers, and biological nitrogen fixation (BNF). This study aimed to evaluate the behavior of nodulation parameters related to BNF throughout the development of common bean cultivars with different growth cycles. The experiments were conducted for two consecutive years (2012 and 2013) with 22 common bean cultivars with different growth cycles. The common bean cultivars were inoculated with a mixture of Rhizobium tropici strains (SEMIA 4077, SEMIA 4080, and SEMIA 4088). In 2012, samplings were performed from the V4 to the R8 stage, and the parameters related to nodulation and crop growth were evaluated at each stage and in the R9 stage, the grain yield and its components were measured. For the 2013 experiment, the same evaluations were performed but the nodulation parameters were only measured in the R6 and the R7 stages. Differences in the number and activity of the nodules along the development of the cultivars were observed. For the early and semi-early cycle cultivars, the activity of the nodules was observed until the R7 stage, while for the regular and late cycle cultivars, this activity only occurred until the R6 stage, resulting in three more days of nodule activity for the early and semi-early cycle cultivars as compared to the regular and late ones. The number of nodules correlated significantly with the shoot dry weight and the shoot Total-N; while the nodules dry mass showed a significantly high correlation with both parameters. The overall mean grain yield was 2,766.75 kg ha−1. However significant difference related solely to the various cultivars cycles were not observed.

RNA-seq analysis of the Rhizobium tropici CIAT 899 transcriptome shows similarities in the activation patterns of symbiotic genes in the presence of apigenin and salt.

BackgroundRhizobium tropici strain CIAT 899 establishes effective symbioses with several legume species, including Phaseolus vulgaris and Leucaena leucocephala. This bacterium synthesizes a large variety of nodulation factors in response to nod-gene inducing flavonoids and, surprisingly, also under salt stress conditions. The aim of this study was to identify differentially expressed genes in the presence of both inducer molecules, and analyze the promoter regions located upstream of these genes.ResultsResults obtained by RNA-seq analyses of CIAT 899 induced with apigenin, a nod gene-inducing flavonoid for this strain, or salt allowed the identification of 19 and 790 differentially expressed genes, respectively. Fifteen of these genes were up-regulated in both conditions and were involved in the synthesis of both Nod factors and indole-3-acetic acid. Transcription of these genes was presumably activated through binding of at least one of the five NodD proteins present in this strain to specific nod box promoter sequences when the bacterium was induced by both apigenin and salt. Finally, under saline conditions, many other transcriptional responses were detected, including an increase in the transcription of genes involved in trehalose catabolism, chemotaxis and protein secretion, as well as ribosomal genes, and a decrease in the transcription of genes involved in transmembrane transport.ConclusionsTo our knowledge this is the first time that a transcriptomic study shows that salt stress induces the expression of nodulation genes in the absence of flavonoids. Thus, in the presence of both nodulation inducer molecules, apigenin and salt, R. tropici CIAT 899 up-regulated the same set of symbiotic genes. It could be possible that the increases in the transcription levels of several genes related to nodulation under saline conditions could represent a strategy to establish symbiosis under abiotic stressing conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2543-3) contains supplementary material, which is available to authorized users.