Feasibility of lowering soybean planting density without compromising nitrogen fixation and yield

Adjusting soybean [Glycine max (L.) Merrill] density can be critical to reduce inter-plant competition for water, nutrients, and sunlight, and to increase intercepted radiation, photosynthesis, and biomass production. The objective of this study was to evaluate the effects of soybean-population density on soybean nodulation, plant nutrient status, yield, and grain quality. Three field experiments were performed in southern Brazil with soybean cultivar BRS 284, of indeterminate growth type and maturity group 6.6, at 80,000 and 320,000 plants ha–1. For N supply plants were dependent either largely on biological fixation of atmospheric N—with a naturalized population of Bradyrhizobium or inoculated with Bradyrhizobium japonicum strain CNPSo 2050—or largely on N fertilizer—200 kg N ha–1, split-applied at sowing and R1 growth stage. The lower plant density resulted in increased nodulation parameters (number and mass), but plant nutritional status—evaluated by the diagnosis and recommendation integrated system (DRIS) method—in general was not affected. Seed oil content increased by 3.4%, but protein decreased by 4.5% at the lower plant density. The N source affected nodulation, but not nutritional status or grain yield. Although plant density was reduced by 75%, yield decreased by 16% during only one of the three cropping seasons. These results indicate a high plasticity of soybean to adapt photosynthesis and N fixation to different plant densities. Furthermore, planting at the lower density has the advantages of lower input costs and less susceptibility to environmental and plant nutritional stresses.Instituto de Fisiología y Recursos Genéticos VegetalesFil: De Luca, Marcos Javier. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Fisiología y Recursos Genéticos Vegetales; Argentina. Universidade Estadual de Londrina. Departamento Microbiologia; Brasil. Embrapa Soja; BrasilFil: Nogueira, Marco Antonio. Embrapa Soja; Brasil. Universidade Estadual de Londrina. Departamento Microbiologia; BrasilFil: Hungria, Mariangela. Embrapa Soja; Brasil. Universidade Estadual de Londrina. Departamento Microbiologia; Brasi

Phytobeneficial traits of Rhizobacteria isolated from degraded soil and evaluate their effect in augmentation of Acacia (Acacia abyssinica Hochst. Ex Benth) seeds germination

Microbes are an integral component of the soil ecosystem but degraded soil has few native beneficial microbes. This necessitates the characterization of phytobeneficial bacteria having numerous features. The study was initiated to evaluate rhizobacteria enhancing Acacia (Acacia abyssinica) seed germination. Isolates were selected based primarily on phosphate solubilization activity and other traits hydrogen cyanide (hcn), phytohormone, hydrolytic enzyme, siderophore, ammonia. Among isolates, 45% each was categorized as high and medium phosphate solubilizers and the amount was found to range from 195 to 373 µg/mL. The highest solubilization index (SI) 7 was recorded for Acinetobacter BS-27 and 6 for Pantoea BS-38. The maximum P and iaa were produced by Pseudomonas FB-49 (373 and 659.07µg/mL), respectively. Isolates with multiple traits were chosen for seed germination. Accordingly, Agrobacterium RS-79 and Pseudomonas BS-26 showed 100% activity. A 100% seed germination and vigor index (343.33 and 306.67) were observed in Pseudomonas BS-26 and FB-49. Degraded soil is considered a source for phosphate solubilizing and other beneficial bacteria with many traits to be used for seed germination assay

Effects of photosynthate manipulation on biological nitrogen fixation in common bean plants

Em dois experimentos, conduzidos em casa de vegetação, procurou-se verificar o efeito da disponibilidade de carbono para os nódulos na fixação biológica de nitrogênio em feijoeiro (Phaseolus vulgaris L.). A retirada das flores aumentou, inicialmente, a atividade da nitrogenase, a eficiência relativa dos elétrons destinados à nitrogenase (ER) e a taxa de translocação dos compostos nitrogenados na seiva do xilema, mas dentro de dez dias houve uma queda drástica nesses parâmetros, em virtude da aceleração no processo de  senescência dos nódulos. A retirada de 50% das folhas no florescimento provocou um declínio na atividade da nitrogenase, na ER e no transporte de N na seiva do xilema, mas, após dez dias, iniciou-se uma recuperação, atribuída à produção de folhas novas, o que não ocorreu quando a retirada das folhas foi realizada no período médio de enchimento dos grãos. O  anelamento do caule do feijão, impedindo a translocação de  fotossintatos para os nódulos, provocou uma queda na atividade da nitrogenase, na ER e no transporte de N na seiva, mas o decréscimo na atividade da nitrogenase só ocorreu 24 horas após o anelamento, indicando que no sistema radicular de feijão há uma quantidade considerável de substratos de reserva para a fixação de nitrogênio.Two experiments were performed, under greenhouse conditions, to investigate the effect of availability of carbon to the nodules on biological nitrogen fixation in common bean plants. Removal of flowers initially increased nitrogenase activity, relative efficiency of electrons for nitrogenase (RE) and rate of nitrogen translocation in the xylem sap, but within ten days all these parameters decreased due to an acceleration of nodule senescence. The removal of 50% of the leaves at flowering decreased nitrogenase activity, RE and N translocation in the xylem sap, but after ten days the plants began recover in these parameters due to the production of new leaves, which did not happen when the leaves where removed at mid-pod filling stage. The stem ringing, hampering translocation of photosynthates to the nodules, decreased nitrogenase activity, RE, and N transport in xylem sap, but the decrease in nitrogenase activity occurred 24 hours after ringing, indicating that in bean roots there is a considerable quantity of stored substrates for N2 fixation

Evaluation of soybean cultivars for biological nitrogen fixation

Este trabalho objetivou detectar cultivares de soja (Glycine max L. Merril) com maior capacidade de nodulação e fixação biológica do N2 (FBN) e cultivares que restringem a nodulação com as estirpes de Bradyrhizobium estabelecidas nos solos brasileiros. A avaliação foi feita com 152 cultivares, infectadas sob condições ambientais controladas, axênicas e na ausência de N mineral, com uma das três estirpes de Bradyrhizobium elkanii: SEMIA 5019 (=29w), SEMIA 587 e SEMIA 566. Das cultivares analisadas, nenhuma restringiu a nodulação, embora houvesse uma diferença de até quatro vezes no número e massa de nódulos por planta. A média geral de nitrogênio acumulado na parte aérea das cultivares infectadas foi de 50,24 mg N/planta. As cultivares que apresentaram melhor desempenho simbiótico com todas as estirpes e acumularam 30% a mais de N do que a média geral foram: Bossier, BR-29, J-200 e Ivaí. As cinco cultivares que apresentaram menores taxas de FBN foram: BR-7, EMBRAPA 9, EMGOPA-313, FT-Canarana e Paranagoiana.This work aimed at selecting cultivars for higher nodulation and biological N2 fixation (BNF) as well as for nodulation restriction with Bradyrhizobium strains established in Brazilian soils. The evaluation was done with 152 soybean genotypes. The cultivars were inoculated under environmentally controled and axenic conditions and in the absence of mineral N, with each one of the following Bradyrhizobium elkanii strains: SEMIA 5019 (=29w), SEMIA 587 and SEMIA 566. None of the cultivars tested restricted completely the nodulation, although up to four fold differences in nodule number and mass were found. General mean of total N accumulated in shoots of all cultivars with all strains was of 50.24 mg N/plant. The cultivars that showed better symbiotic performance with all strains and accumulated 30% more N than the general mean were: Bossier, BR-29, J-200, and Ivaí. The five cultivars characterized by lower BNF rates were: BR-7, EMBRAPA 9, EMGOPA-313, FT-Canarana and Paranagoiana

Nodulação e rendimento de soja co-infectada com Bacillus subtilis e Bradyrhizobium japonicum / bradyrhizobium elkanii

Bacillus subtilis can improve rhizobial symbiotic performance by inhibiting plant pathogens or by the exudation of hormones. To verify the viability of co-inoculation of soybean seeds with Bradyrhizobium and Bacillus, three experiments were performed, in the State of Paraná, Brazil, in soils with established population of Bradyrhizobium. The Bradyrhizobium strains SEMIA 5019 and SEMIA 5080, and their natural variant strains tolerant to the metabolites of Bacillus were co-inoculated with two strains of Bacillus (AP-3 and PRBS-1), or their metabolites. In 1993/94, in Londrina, the co-inoculation of Bradyrhizobium with formulated metabolites increased significantly, in relation to non-inoculated control, nodule number (59%, stage V3), nodule occupancy by Bradyrhizobium strains carried on the inoculant (76%, R2) and soybean yield (24%); in Ponta Grossa, these increases were of 60%, 145% and 22%, respectively. Also in Londrina, the co-inoculation of the variant strains with crude metabolites of Bacillus has also increased yield (26%) and total N in grains (17%) and increases were verified by the co-inoculation of the Bradyrhizobium variant strains with Bacillus cells (78%). Consequently, the results have shown the viability of co-inoculating soybean seeds with crude or formulated metabolites, or with cells of Bacillus subtilis, to increase the contribution of the biological nitrogen fixation process.O Bacillus subtilis pode favorecer o desempenho simbiótico do rizóbio, pelos efeitos na inibição de fitopatógenos ou pela exsudação de fitormônios. Com o objetivo de verificar a viabilidade da co-infecção de sementes de soja com Bradyrhizobium e Bacillus foram conduzidos três experimentos, no Paraná, em solos com população estabelecida de Bradyrhizobium, em que as estirpes de Bradyrhizobium SEMIA 5019 e SEMIA 5080 e suas variantes tolerantes aos metabólitos de Bacillus foram co-infectadas com duas estirpes de Bacillus (AP-3 e PRBS-1), ou seus metabólitos. Na safra 1993/94, em Londrina, o tratamento de co-inoculação de Bradyrhizobium com os metabólitos formulados de Bacillus incrementou, significativamente, em relação ao não-inoculado, o número de nódulos (59%, estádio V3), a ocupação dos nódulos pelas estirpes de Bradyrhizobium (76%, R2) e o rendimento de grãos (24%); em Ponta Grossa, esses incrementos foram de 60%, 145% e 22%, respectivamente. Nessa safra, em Londrina, a co-inoculação das variantes tolerantes com os metabólitos de Bacillus também aumentou o rendimento (26%) e N total (17%) dos grãos de soja e incrementos significativos foram constatados, na ocupação dos nódulos, pela co-inoculação das variantes tolerantes com as células de Bacillus (78%). Os resultados obtidos indicam a viabilidade da co-inoculação, em sementes de soja, de metabólitos brutos ou formulados ou, ainda, de células de Bacillus subtilis, para incrementar a contribuição do processo de fixação biológica do nitrogênio

Biotechnological potential of rhizobial metabolites to enhance the performance of Bradyrhizobium spp. and Azospirillum brasilense inoculants with soybean and maize

Agricultural sustainability may represent the greatest encumbrance to increasing food production. On the other hand, as a component of sustainability, replacement of chemical fertilizers by bio-fertilizers has the potential to lower costs for farmers, to increase yields, and to mitigate greenhouse-gas emissions and pollution of water and soil. Rhizobia and plant-growth-promoting rhizobacteria (PGPR) have been broadly used in agriculture, and advances in our understanding of plant-bacteria interactions have been achieved; however, the use of signaling molecules to enhance crop performance is still modest. In this study, we evaluated the effects of concentrated metabolites (CM) from two strains of rhizobia—Bradyrhizobium diazoefficiens USDA 110T (BD1) and Rhizobium tropici CIAT 899T (RT1)—at two concentrations of active compounds (10–8 and 10–9 M)—on the performances of two major plant-microbe interactions, of Bradyrhizobium spp.-soybean (Glycine max (L.) Merr.) and Azospirillum brasilense-maize (Zea mays L.). For soybean, one greenhouse and two field experiments were performed and effects of addition of CM from the homologous and heterologous strains, and of the flavonoid genistein were investigated. For maize, three field experiments were performed to examine the effects of CM from RT1. For soybean, compared to the treatment inoculated exclusively with Bradyrhizobium, benefits were achieved with the addition of CM-BD1; at 10–9 M, grain yield was increased by an average of 4.8%. For maize, the best result was obtained with the addition of CM-RT1, also at 10–9 M, increasing grain yield by an average of 11.4%. These benefits might be related to a combination of effects attributed to secondary compounds produced by the rhizobial strains, including exopolysaccharides (EPSs), plant hormones and lipo-chitooligosaccharides (LCOs). The results emphasize the biotechnological potential of using secondary metabolites of rhizobia together with inoculants containing both rhizobia and PGPR to improve the growth and yield of grain crops

Interação entre cultivares de Phaseolus vulgaris e estirpes de Rhizobium na fixação e transporte do nitrogênio

One experiment was performed, under greenhouse conditions, using five cultivars of Phaseolus vulgaris L. and six strains of Rhizobium leguminosarum biovar phaseoli to evaluate the nitrogen fixation and transport in the plants. Both cultivars and strains affected significantly the dry weight and total P4 of leaves, stems and pods; nodule dry weight; nodule efficiency (mg N. g nod-1); nitrogenize activity; H2evolution by the nodules; relative efficiency (RE); N concentration and rate of N translocation in the xylem sap and percentage of the N of the xylem sap as ureides. The parameters (estimated at flowering time, 35 days after germination) that showed best correlations with total N of pods at 50 days were: RE (0.872**), rate of N translocation in the xylem sap (0.949**) and percentage of N as ureides in the xylem sap (0.907**). A positive correlation was found between RE and percentage of N as ureides (0.903**), and this can be best explained in terms of a relationship between H2 metabolism and ureide metabolism.Utilizaram-se cinco cultivares de Phaseolus vulgaris L. e seis estirpes de Rhizobium leguminosarum biovar phaseoli em um experimento conduzido sob condições de casa de vegetação. Foram observados efeitos da cultivar e da estirpe nos seguintes parâmetros: peso seco e N total acumulado nas folhas, caules e vagens; peso seco dos nódulos; eficiência dos nódulos (mg N.g nódulo-1); atividade da nitrogenase; evolução do H2 pelos nódulos; eficiência relativa dos elétrons destinados à nitrogenase (ER); concentração de N total na seiva do xilema; taxa de translocação do N na seiva do xilema e percentagem do N total da seiva sob a forma de ureídos. Os parâmetros (avaliados no florescimento, aos 35 dias após a germinação) que apresentaram as melhores correlações com o N total das vagens aos 50 dias foram: ER (0,872**), taxa de translocação do N na seiva do xilema (0,949**) e percentagem do N sob a forma de ureídos (0,907**). Encontrou-se uma correlação positiva entre a ER e a percentagem N-ureído (0,903**), o que pode ser atribuído a uma possível relação entre o metabolismo do H2 e o metabolismo dos ureídos

Effects of shading on biological nitrogen fixation in bean plants

Conduziram-se dois experimentos com o objetivo de verificar o efeito da redução da luminosidade e da temperatura, causado pelo sombreamento, na fixação biológica do N2 em feijoeiro (Phaseolus vulgaris L.). Quando se realizou um sombreamento de 25%, houve um aumento, em relação à luminosidade total, do peso de matéria seca, atividade da nitrogenase, nitrogênio total transportado na seiva do xilema, percentagem de N transportado sob a forma de ureídos, e do nitrogênio-total acumulado na parte aérea. Nesse nível de sombreamento, o aumento na eficiência nodular compensou a redução no peso dos nódulos. O efeito favorável do sombreamento de 25% foi atribuído à redução das temperaturas máximas diurnas nos vasos sombreados e a redução da energia solar foi compensada por um aumento na área foliar. No nível de sombreamento de 40%, embora ocorresse redução da temperatura na zona radicular e aumento na área foliar, isso não foi suficiente para compensar a menor atividade fotossintética. De modo geral, as temperaturas elevadas não prejudicaram a formação e crescimento dos nódulos, mas sim o seu funcionamento, refletido na menor atividade da nitrogenase e no menor acúmulo de nitrogênio na parte aérea.Two experiments were performed to investigate the effect of decreasing luminosity and temperature caused by shading on biological nitrogen fixation of common beans (Phaseolus vulgaris L.). When the shading was at 25% level, there was an increase, in relation to full light, of the dry weight, nitrogenase activity, total nitrogen in xylem sap, rate of N as ureides and total nitrogen in shoots. At this level of shading, an increase in nodular efficiency compensated for the decrease in nodule weight. The favourable effect of reducing 25% of the luminosity was caused by the decrease in maximal diurnal temperature in the shaded pots and the decrease of solar energy was compensated by and increase in leaf area. At 40% shading, there was a decrease in the rhizosphere temperature and an increase in leaf area but this was not enough to compensate for the lower photosynthetic activity. Generally the high temperature did not affect the infection process and the growth of the nodules, but altered nodule metabolism, decreasing nitrogenase activity and total nitrogen in shoots