Response of common bean to Rhizobium reinoculation in topdressing

ABSTRACT The response capacity of the bean to fix atmospheric nitrogen is questionable, mainly due to its inability to supply all the nitrogen in the flowering and grain filling phases when the crop needs it most. Thus, a new application of inoculant can keep the population of rhizobia in the soil at adequate levels, meeting all the nitrogen demands of the plant. This study aimed to investigate the nodulation capacity and the production of beans submitted to doses and reinoculation of Rhizobium in topdressing under field conditions in two growth stages. For this, an experiment was conducted using a randomized block design with four replicates in a 4 × 2 + 2 factorial scheme. The treatments consisted of the application of four doses of liquid inoculant containing Rhizobium tropici (SEMIA 4088), in the concentration 2 × 109 CFU g-1, in topdressing (0, 100, 200 and 400 mL ha-1), in two development stages (V4 and R5) of plants, and two additional treatments (inoculation via seed at a dose of 100 g of the product per 50 kg of seeds and mineral nitrogen fertilization at a dose of 16 kg ha-1 applied at sowing and 60 kg ha-1 in topdressing, divided into two stages, with half being applied at the stage V3 and the other half in V4 stage).The inoculant application increased the nodulation rates of bean cultivar BRS Cometa and the dry biomass produced by plants, using doses of 232 and 221 mL ha-1, respectively. The dose of 257mL ha-1 of the liquid inoculant applied in topdressing at the V4 stage, and the inoculation via seed provide greater common bean yield without supplementing mineral nitrogen.

Weed coexistence in carioca bean inoculated

The supply of nitrogen (N) to the carioca bean plant via inoculation with Rhizobium tropici can prevent competition with the weed community by allowing the crop to absorb the nutrient available in the soil. On this basis, this study proposes to examine the period before weed interference (PBI) in the carioca bean plant following inoculation with R. tropici or N topdressing. The experiments were carried out under field conditions during the summer seasons of 2014 and 2015. A randomized-block experimental design with four replicates was adopted, in a 2 × 11 factorial arrangement (common bean plant inoculated or topdressed with N × 11 periods of coexistence with weeds, namely, 0, 7, 14, 21, 28, 35, 42, 49, 56, 63, or 90 days after emergence [DAE]). Nitrogen topdressing increased the crop's tolerance to coexist with weeds from 6 to 14 DAE, compared with inoculation with R. tropici The PBI for the inoculated common bean plant was 24 and 16 DAE in the years 2014 and 2015, respectively. For the N-topdressed plant, the PBI was 30 DAE in both years.

The nodD1 gene of Sinorhizobium fredii HH103 Restores Nodulation Capacity on Bean in a Rhizobium tropici CIAT 899 nodD1/nodD2 Mutant, but the Secondary Symbiotic Regulators nolR, nodD2 or syrM Prevent HH103 to Nodulate with This Legume

Rhizobial NodD proteins and appropriate flavonoids induce rhizobial nodulation gene expression. In this study, we show that the nodD1 gene of Sinorhizobium fredii HH103, but not the nodD2 gene, can restore the nodulation capacity of a double nodD1/nodD2 mutant of Rhizobium tropici CIAT 899 in bean plants (Phaseolus vulgaris). S. fredii HH103 only induces pseudonodules in beans. We have also studied whether the mutation of different symbiotic regulatory genes may affect the symbiotic interaction of HH103 with beans: ttsI (the positive regulator of the symbiotic type 3 protein secretion system), and nodD2, nolR and syrM (all of them controlling the level of Nod factor production). Inactivation of either nodD2, nolR or syrM, but not that of ttsI, affected positively the symbiotic behavior of HH103 with beans, leading to the formation of colonized nodules. Acetylene reduction assays showed certain levels of nitrogenase activity that were higher in the case of the nodD2 and nolR mutants. Similar results have been previously obtained by our group with the model legume Lotus japonicus. Hence, the results obtained in the present work confirm that repression of Nod factor production, provided by either NodD2, NolR or SyrM, prevents HH103 to effectively nodulate several putative host plants.

Produtividade do feijoeiro com inoculação e adubação nitrogenada em região central amazônica

A utilização de inoculante com rizóbios no feijoeiro tem a finalidade de fornecer nitrogênio para o desenvolvimento da planta. Atualmente, o rizóbio indicado para o feijão-comum é a espécie Rhizobium tropici. Poucos trabalhos são encontrados na literatura sobre a interação de outras espécies de rizóbio com Phaseolus vulgaris. O presente trabalho teve por objetivo avaliar a produtividade do feijoeiro cultivar Carioca em função de inoculação com Bradyrhizobium japonicum e adubação nitrogenada. Foi utilizado o delineamento experimental inteiramente casualizado, com quatro tratamentos e cinco repetições, sendo os tratamentos: testemunha (sem inoculação ou adubação nitrogenada); adubação nitrogenada (20 kg.ha-1 em plantio e 20 kg.ha-1 em cobertura); só inoculação; inoculação e adubação nitrogenada (20 kg.ha-1 em cobertura). O experimento foi conduzido entre linhas de um cafezal recém implantado. Foram avaliados altura da planta, altura da inserção da primeira vagem, número de vagem por planta, comprimento de vagem, quantidade de grãos por vagem, massa de 100 grãos, e produtividade dada em kg.ha-1. O tratamento inoculação com adubação nitrogenada alcançou os maiores valores de produtividade, destacando-se na maioria das características avaliadas. Concluiu-se que mesmo não sendo o rizóbio indicado para a cultura do feijão, Bradyrhizobium japonicum pode ser indicado para incremento na produtividade do feijoeiro cultivar Carioca.

Inoculação do feijoeiro associada à adubação foliar com Cobalto e Molibdênio

Acredita-se que o uso de adubação com cobalto e molibdênio associado à inoculação com Rhizobium spp. na cultura do feijão é capaz de favorecer a produtividade, neste sentido, o objetivo deste trabalho foi avaliar o efeito de doses de inoculante e suas interações com cobalto e molibdênio no cultivo do feijão comum. O experimento foi realizado no campo experimental da Universidade Estadual de Mato Grosso do Sul, em Aquidauana-MS. A cultivar utilizada foi Dama do grupo comercial Carioca. Sendo conduzido em delineamento em blocos casualizados, em esquema fatorial 2x5, com quatro repetições. Constituido da presença ou a ausência da aplicação foliar de cobalto e molibdênio e doses de inoculante (0 mL, 150 mL, 300 mL, 600 mL, 1200 mL a cada 50 kg de sementes). As avaliações realizadas foram matéria verde e seca de nódulos, matéria verde e seca da parte aérea e da raiz, densidade da raiz, número de nódulos por planta, atividade nodular, teor de nitrogênio e fósforo foliar, altura de inserção de primeira vagem, altura de plantas, número de ramificações, número de grãos por vagem, massa de cem grãos e produtividade de grãos. Conclui-se que a associação entre Rhizobium tropici e adubação foliar, com cobalto e molibdênio no feijão comum, embora não tenha promovido aumento de produtividade de grãos resultou em melhoras nos caracteres agronômicos na cultura.

Development of wheat plants coinoculated with rhizobium strains

ABSTRACT This study aimed to evaluate the efficiency of diaztrophic bacteria coinoculation in wheat cultivars grown in Cerrado Oxisol. A randomized block design was used, with a 13 x 3 factorial scheme and four replicates. The treatments consisted of inoculation with Azospirillum brasilense (strains AbV5 and AbV6 strains combined) and coinoculation with Bradyrhizobium japonicum (strains SEMIA 5079 and SEMIA 5080 combined, and strain BR3267), as well as Rhizobium tropici (strains MT08 and MT15) and R. leguminosarum (strain MT16) combined or in isolation, tested in wheat cultivars BRS 394, BRS 264 and BRS 254. The variables analyzed were grain nitrogen concentration and accumulation and crude protein content, 100-grain weight and total grain mass. The treatment containing the commercial cowpea inoculant showed a higher total grain mass (5.8766 g). Interaction was observed for grain nitrogen concentration, particularly for A. brasilense + MT 15 (R. tropici) and MT 15 in wheat cultivar BRS 264. Coinoculation with diazotrophic bacteria isolated from leguminous plants shows potential for use in wheat cultivars.

Complete genomic sequence and phylogenomics analysis of Agrobacterium strain AB2/73: a new Rhizobium species with a unique mega-Ti plasmid

Background The Agrobacterium strain AB2/73 has a unique host range for the induction of crown gall tumors, and contains an exceptionally large, over 500 kbp mega Ti plasmid. We used whole genome sequencing to fully characterize and comparatively analyze the complex genome of strain AB2/73, including its Ti plasmid and virulence factors. Results We obtained a high-quality, full genomic sequence of AB2/73 by a combination of short-read Illumina sequencing and long-read Nanopore sequencing. The AB2/73 genome has a total size of 7,266,754 bp with 59.5% GC for which 7012 genes (6948 protein coding sequences) are predicted. Phylogenetic and comparative genomics analysis revealed that strain AB2/73 does not belong to the genus Agrobacterium, but to a new species in the genus Rhizobium, which is most related to Rhizobium tropici. In addition to the chromosome, the genome consists of 6 plasmids of which the largest two, of more than 1 Mbp, have chromid-like properties. The mega Ti plasmid is 605 kbp in size and contains two, one of which is incomplete, repABC replication units and thus appears to be a cointegrate consisting of about 175 kbp derived from an unknown Ti plasmid linked to 430 kbp from another large plasmid. In pTiAB2/73 we identified a complete set of virulence genes and two T-DNAs. Besides the previously described T-DNA we found a larger, second T-DNA containing a 6b-like onc gene and the acs gene for agrocinopine synthase. Also we identified two clusters of genes responsible for opine catabolism, including an acc-operon for agrocinopine degradation, and genes putatively involved in ridéopine catabolism. The plasmid also harbours tzs, iaaM and iaaH genes for the biosynthesis of the plant growth regulators cytokinin and auxin. Conclusions The comparative genomics analysis of the high quality genome of strain AB2/73 provided insight into the unusual phylogeny and genetic composition of the limited host range Agrobacterium strain AB2/73. The description of its unique genomic composition and of all the virulence determinants in pTiAB2/73 will be an invaluable tool for further studies into the special host range properties of this bacterium.

Isolation and Characterization of High-Efficiency Rhizobia From Western Kenya Nodulating With Common Bean

Common bean is one of the primary protein sources in third-world countries. They form nodules with nitrogen-fixing rhizobia, which have to be adapted to the local soils. Commercial rhizobial strains such as Rhizobium tropici CIAT899 are often used in agriculture. However, this strain failed to significantly increase the common bean yield in many places, including Kenya, due to the local soils’ low pH. We isolated two indigenous rhizobial strains from the nodules of common bean from two fields in Western Kenya that have never been exposed to commercial inocula. We then determined their ability to fix nitrogen in common beans, solubilize phosphorus, and produce indole acetic acid. In greenhouse experiments, common bean plants inoculated with two isolates, B3 and S2 in sterile vermiculite, performed better than those inoculated with CIAT899 or plants grown with nitrogen fertilizer alone. In contrast to CIAT899, both isolates grew in the media with pH 4.8. Furthermore, isolate B3 had higher phosphate solubilization ability and produced more indole acetic acid than the other two rhizobia. Genome analyses revealed that B3 and S2 are different strains of Rhizobium phaseoli. We recommend fieldwork studies in Kenyan soils to test the efficacy of the two isolates in the natural environment in an effort to produce inoculants specific for these soils.