RESUMO

Fungal diseases lead to significant losses in soybean yields and a decline in seed quality; such is the case of the Asian soybean rust and anthracnose caused by Phakopsora pachyrhizi and Colletotrichum truncatum, respectively. Currently, the development of transgenic plants carrying antifungal defensins offers an alternative for plant protection against pathogens. This paper shows the production of transgenic soybean plants expressing the NmDef02 defensin gene using the biolistic delivery system, in an attempt to improve resistance against diseases and reduce the need for chemicals. Transgenic lines were assessed in field conditions under the natural infections of P. pachyrhizi and C. truncatum. The constitutive expression of the NmDef02 gene in transgenic soybean plants was shown to enhance resistance against these important plant pathogens. The quantification of the P. pachyrhizi biomass in infected soybean leaves revealed significant differences between transgenic lines and the non-transgenic control. In certain transgenic lines there was a strong reduction of fungal biomass, revealing a less severe disease. Integration and expression of the transgenes were confirmed by PCR, Southern blot, and qRT-PCR, where the Def1 line showed a higher relative expression of defensin. It was also found that the expression of the NmDef02 defensin gene in plants of the Def1 line did not have a negative effect on the nodulation induced by Bradyrhizobium japonicum. These results indicate that transgenic soybean plants expressing the NmDef02 defensin gene have a substantially enhanced resistance to economically important diseases, providing a sound environmental approach for decreasing yield losses and lowering the burden of chemicals in agriculture.

RESUMO

Black wattle (Acacia mearnsii De Wild.) is a tree legume native to southeast Australia, but present in all continents. Today it covers about 142,400 ha in Brazil, with plantations concentrated in the southern region of the country. Black wattle may form nodules and establish rhizobial symbiosis capable of fixing N2, but rhizobial inoculation is not done in commercial plantations. About 40 kg ha-1 of urea is applied during seedling transplantation. In this review, evidences by which rhizobial inoculation affects monoculture, mixed cultivation, and agroforestry black wattle production systems were searched in literature. Previous measurements in cultivated forests have indicated that biological nitrogen fixation in black wattle may provide up to 200 kg of N ha-1 year-1 to the soil. Therefore, rhizobia inoculation may bring several opportunities to improve black wattle production systems. Black wattle is not a very selective partner in the rhizobial symbiosis, but the genus Bradyrhizobium dominates the rhizobial diversity of black wattle nodules. Investigation on rhizobial diversity in soils where the crop is cultivated may represent an opportunity to find more effective rhizobia strains for inoculants. The successful history of biological nitrogen fixation in grain legumes must inspire the history of tree legumes. Microbiology applied to forestry must overcome challenges on the lack of trained professionals and the development of new application technologies.

Assuntos

RESUMO

Biological nitrogen fixation (BNF) with the soybean crop probably represents the major sustainable technology worldwide, saving billions of dollars in N fertilizers and decreasing water pollution and the emission of greenhouse gases. Accordingly, the identification of strains occupying nodules under field conditions represents a critical step in studies that are aimed at guaranteeing increased BNF contribution. Current methods of identification are mostly based on serology, or on DNA profiles. However, the production of antibodies is restricted to few laboratories, and to obtain DNA profiles of hundreds of isolates is costly and time-consuming. Conversely, the matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS technique might represent a golden opportunity for replacing serological and DNA-based methods. However, MALDI-TOF databases of environmental microorganisms are still limited, and, most importantly, there are concerns about the discrimination of protein profiles at the strain level. In this study, we investigated four soybean rhizobial strains carried in commercial inoculants used in over 35 million hectares in Brazil and also in other countries of South America and Africa. A supplementary MALDI-TOF database with the protein profiles of these rhizobial strains was built and allowed the identification of unique profiles statistically supported by multivariate analysis and neural networks. To test this new database, the nodule occupancy by Bradyrhizobium strains in symbiosis with soybean was characterized in a field experiment and the results were compared with serotyping of bacteria by immuno-agglutination. The results obtained by both techniques were highly correlated and confirmed the viability of using the MALDI-TOF MS technique to effectively distinguish bacteria at the strain level.

Assuntos

RESUMO

In this work we performed several in silico analyses to describe the relevant structural aspects of an enzyme N-Carbamoyl-d-amino acid amidohydrolase (d-NCAase) encoded on the genome of the Brazilian strain CPAC 15 (=SEMIA 5079) of Bradyrhizobium japonicum, a nonpathogenic species belonging to the order Rhizobiales. d-NCAase has wide applications particularly in the pharmaceutical industry, since it catalyzes the production of d-amino acids such as D-p-hydroxyphenylglycine (D-HPG), an intermediate in the synthesis of ß-lactam antibiotics. We applied a homology modelling approach and 50 ns of molecular dynamics simulations to predict the structure and the intersubunit interactions of this novel d-NCAase. Also, in order to evaluate the substrate binding site, the model was subjected to 50 ns of molecular dynamics simulations in the presence of N-Carbamoyl-d-p-hydroxyphenylglycine (Cp-HPG) (a d-NCAase canonical substrate) and water-protein/water-substrate interactions analyses were performed. Overall, the structural analysis and the molecular dynamics simulations suggest that d-NCAase of B. japonicum CPAC-15 has a homodimeric structure in solution. Here, we also examined the substrate specificity of the catalytic site of our model and the interactions with water molecules into the active binding site were comprehensively discussed. Also, these simulations showed that the amino acids Lys123, His125, Pro127, Cys172, Asp174 and Arg176 are responsible for recognition of ligand in the active binding site through several chemical associations, such as hydrogen bonds and hydrophobic interactions. Our results show a favourable environment for a reaction of hydrolysis that transforms N-Carbamoyl-d-p-hydroxyphenylglycine (Cp-HPG) into the active compound D-p-hydroxyphenylglycine (D-HPG). This work envisage the use of d-NCAase from the Brazilian Bradyrhizobium japonicum strain CPAC-15 (=SEMIA 5079) for the industrial production of D-HPG, an important intermediate for semi-synthesis of ß-lactam antibiotics such as penicillins, cephalosporins and amoxicillin.

Assuntos

RESUMO

Quorum-sensing (QS) mechanisms are important in intra- and inter-specific communication among bacteria. We investigated QS mechanisms in Bradyrhizobium japonicum strain CPAC 15 and Azospirillum brasilense strains Ab-V5 and Ab-V6, used in commercial co-inoculants for the soybean crop in Brazil. A transconjugant of CPAC 15-QS with partial inactivation of N-acyl-homoserine lactones (AHLs) was obtained and several parameters were evaluated; in vitro, CPAC 15 and the transconjugant differed in growth, but not in biofilm formation, and no differences were observed in the symbiotic performance in vivo. The genome of CPAC 15 carries functional luxI and luxR genes and low amounts of three AHL molecules were detected: 3-OH-C12-AHL, 3-OH-C14-AHL, and 3-oxo-C14-AHL. Multiple copies of luxR-like genes, but not of luxI are present in the genomes of Ab-V5 and Ab-V6, and differences in gene expression were observed when the strains were co-cultured with B. japonicum; we may infer that the luxR-genes of A. brasilense may perceive the AHL molecules of B. japonicum. Soybean symbiotic performance was improved especially by co-inoculation with Ab-V6, which, contrarily to Ab-V5, did not respond to the AHLs of CPAC 15. We concluded that A. brasilense Ab-V5, but not Ab-V6, responded to the QS signals of CPAC 15, and that the synergistic interaction may be credited, at least partially, to the QS interaction. In addition, we confirmed inter- and intra-species QS communication between B. japonicum and A. brasilense and, for Azospirillum, at the strain level, impacting several steps of the symbiosis, from cell growth to plant nodulation and growth.

Assuntos

RESUMO

Soybean is an economically very important crop throughout the word and particularly in Argentina. Soybean yield may be affected by many factors such as the lack of some essential nutrients or pathogens attack. In this work we demonstrated that the co-inoculation of the native biocontrol bacterium Bacillus sp. CHEP5 which induces resistance against Cercospora sojina in soybean and the nitrogen fixing strain Bradyrhizobium japonicum E109, was more effective in reducing frog leaf spot severity than the inoculation of the biocontrol agent alone. Probably, this is related with the increase in the ability to form biofilm when both bacteria are growing together. Furthermore, Bacillus sp. CHEP5 inoculation did not affect Bradyrhizobium japonicum E109 symbiotic behavior and flavonoids composition of root exudates in pathogen challenged plants. These results suggest that co-inoculation of plants with rhizobia and biocontrol agents could be a strategy to improve soybean production in a sustainable system.

Assuntos

RESUMO

A competitividade econômica da soja brasileira no mercado mundial se deve, em grande parte, aos benefícios da fixação biológica do nitrogênio na cultura. O trabalho foi conduzido a campo, sob sistema plantio direto, em condição de sequeiro, no Município de Maracaju-MS, com o objetivo de avaliar a nodulação, o crescimento, nutrição mineral e produtividade de grãos da soja submetida a diferentes doses de gesso agrícola e molibdênio. Foi utilizado o delineamento experimental de blocos ao acaso, com cinco repetições e esquema de parcelas subdivididas, sendo as parcelas representadas por quatro doses de gesso agrícola (0, 1.000, 2.000 e 3.000 kg ha-1) e as subparcelas, por quatro doses de molibdênio (0, 20, 40 e 60 g ha-1). Não houve efeito da interação gesso x Mo sobre a produtividade da soja. O gesso agrícola não influencia no teor foliar de N e na produtividade. O Mo proporciona incrementos na produtividade e no teor de proteínas dos grãos.

The economic competitiveness of Brazilian soybeans on the world market occurs, in large part, due to the benefits of biological nitrogen fixation in this crop. The field experiment was carried out in Maracaju, Mato Grosso do Sul State, Brazil, under no-tillage system, in rainfed condition. The aim was to evaluate nodulation, growth, mineral nutrition and grain yield of soybeans under different doses of gypsum and molybdenum. The experimental design used was a randomized block with five replicates and arranged in a split-plot squeme, with the plot represented by four doses of gypsum (0, 1.000, 2.000 and 3.000 kg ha-1) and the subplots by four doses of molybdenum (0, 20, 40 and 60 g ha-1). There were no interaction effects of Mo x gypsum for grain yield. Gypsum has no influence in the N leaf content and grain yield. Mo increases grain yield and protein levels in the grain.

RESUMO

In commercial plantations of soybean in both the Southern and the Cerrado regions, contributions from biological nitrogen fixation (BNF) are generally proportionately high. When using the 15N natural abundance technique to quantify BNF inputs, it is essential to determine, with accuracy, the 15N abundance of the N derived from BNF (the 'B' value). This study aimed to determine the effect of four recommended strains of Bradyrhizobium spp. (two B. japonicum and two B. elkanii) on the 'B' value of soybean grown in pots in an open field using an equation based on the determination of 15N natural abundance in a non-labelled soil, and estimate of the contribution of BNF derived from the use of 15N-isotope dilution in soils enriched with 15N. To evaluate N2 fixation by soybean, three non-N2-fixing reference crops were grown under the same conditions. Regardless of Bradyrhizobium strain, no differences were observed in dry matter, nodule weight and total N between labelled and non-labelled soil. The N2 fixation of the soybeans grown in the two soil conditions were similar. The mean 'B' values of the soybeans inoculated with the B. japonicum strains were -1.84 ‰ and -0.50 ‰, while those inoculated with B. elkanii were -3.67 ‰ and -1.0 ‰, for the shoot tissue and the whole plant, respectively. Finally, the 'B' value for the soybean crop varied considerably in function of the inoculated Bradyrhizobium strain, being most important when only the shoot tissue was utilised to estimate the proportion of N in the plant derived from N2 fixation.

Em plantações comerciais de soja na região Sul e do Cerrado, as contribuições da fixação biológica de Nitrogênio (FBN) são geralmente elevadas. Quando usamos a técnica da abundância natural de 15N para quantificar a FBN, é essencial determinar com exatidão a abundância de 15N do N derivado da FBN (valor 'B'). Este trabalho buscou determinar o efeito das quatro estirpes de Bradyrhizobium spp. (duas B. japonicum, duas B. elkanii) sobre o valor 'B' de soja crescida em vasos em ambiente aberto usando uma equação na determinação da abundância natural de 15N em um solo não enriquecido com 15N, e estimativas da contribuição da FBN derivado do uso da técnica de diluição isotópica de 15N em solo enriquecido com 15N. Para avaliar a fixação de N2 pela soja três plantas referenciam foram crescidas nas mesmas condições. Independente da estirpe de Bradyrhizobium, não foi observada diferença para matéria seca, massa de nódulos e N total entre solo marcado e não marcado. A fixação de N2 em soja crescida nas duas condições de marcação do solo foi semelhante. Os valores médios de 'B' para plantas de soja inoculadas com estirpes de B. japonicum foram, em média, de -1,84 ‰ e -0,50 ‰ enquanto as inoculadas com B. elkanii apresentaram médias de -3,67 ‰ e -1,00 ‰, para parte aérea e planta inteira, respectivamente. Finalmente, o valor 'B' para a cultura da soja variou consideravelmente em função da estirpe de Bradyrhizobium inoculada, sendo mais importante quando se utiliza somente a parte aérea da planta para estimar a proporção do N da planta derivado da fixação de N2.

RESUMO

In commercial plantations of soybean in both the Southern and the Cerrado regions, contributions from biological nitrogen fixation (BNF) are generally proportionately high. When using the 15N natural abundance technique to quantify BNF inputs, it is essential to determine, with accuracy, the 15N abundance of the N derived from BNF (the 'B' value). This study aimed to determine the effect of four recommended strains of Bradyrhizobium spp. (two B. japonicum and two B. elkanii) on the 'B' value of soybean grown in pots in an open field using an equation based on the determination of 15N natural abundance in a non-labelled soil, and estimate of the contribution of BNF derived from the use of 15N-isotope dilution in soils enriched with 15N. To evaluate N2 fixation by soybean, three non-N2-fixing reference crops were grown under the same conditions. Regardless of Bradyrhizobium strain, no differences were observed in dry matter, nodule weight and total N between labelled and non-labelled soil. The N2 fixation of the soybeans grown in the two soil conditions were similar. The mean 'B' values of the soybeans inoculated with the B. japonicum strains were -1.84 ‰ and -0.50 ‰, while those inoculated with B. elkanii were -3.67 ‰ and -1.0 ‰, for the shoot tissue and the whole plant, respectively. Finally, the 'B' value for the soybean crop varied considerably in function of the inoculated Bradyrhizobium strain, being most important when only the shoot tissue was utilised to estimate the proportion of N in the plant derived from N2 fixation.

Em plantações comerciais de soja na região Sul e do Cerrado, as contribuições da fixação biológica de Nitrogênio (FBN) são geralmente elevadas. Quando usamos a técnica da abundância natural de 15N para quantificar a FBN, é essencial determinar com exatidão a abundância de 15N do N derivado da FBN (valor 'B'). Este trabalho buscou determinar o efeito das quatro estirpes de Bradyrhizobium spp. (duas B. japonicum, duas B. elkanii) sobre o valor 'B' de soja crescida em vasos em ambiente aberto usando uma equação na determinação da abundância natural de 15N em um solo não enriquecido com 15N, e estimativas da contribuição da FBN derivado do uso da técnica de diluição isotópica de 15N em solo enriquecido com 15N. Para avaliar a fixação de N2 pela soja três plantas referenciam foram crescidas nas mesmas condições. Independente da estirpe de Bradyrhizobium, não foi observada diferença para matéria seca, massa de nódulos e N total entre solo marcado e não marcado. A fixação de N2 em soja crescida nas duas condições de marcação do solo foi semelhante. Os valores médios de 'B' para plantas de soja inoculadas com estirpes de B. japonicum foram, em média, de -1,84 ‰ e -0,50 ‰ enquanto as inoculadas com B. elkanii apresentaram médias de -3,67 ‰ e -1,00 ‰, para parte aérea e planta inteira, respectivamente. Finalmente, o valor 'B' para a cultura da soja variou consideravelmente em função da estirpe de Bradyrhizobium inoculada, sendo mais importante quando se utiliza somente a parte aérea da planta para estimar a proporção do N da planta derivado da fixação de N2.

RESUMO

This study was carried out to evaluate the effect of hexavalent chromium on dry matter production, nutrient uptake and nitrogen fixation in soybeans (Glycine max ) The seeds were inoculated with comercial strains of Bradyrhizobium japonicum (SEMIA 587 and 5019) and the plants were grown in "Leonard Jars" containing washed sand in the upper portion and nutrient solution (without N) in the lower. Five Cr6+ concentrations were used: 0, 5, 10, 20 e 40mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 in the nutrient solution. Concentrations of Cr6+ above 5mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 decreased plants and nodules dry matter production, number of nodules, nitrogen fixation and P, K, Ca e Mg uptake. Chromium concentrations in soybean tops above 3,4mg kg-1 were considered phytotoxic.

Foram avaliados os efeitos de doses crescentes de Cr6+ sobre a produção de matéria seca, absorção de nutrientes e fixação biológica de nitrogênio em plantas de soja. Antes da semeadura, as sementes foram tratadas com inóculo turfoso contendo Bradyrhizobium japonicum. As plantas foram cultivadas durante 40 dias em vasos "Leonard" que continha areia na parte superior e solução nutritiva sem nitrogênio na parte inferior. Os tratamentos constaram das seguintes doses de Cr6+ (K2Cr2O7) na solução nutritiva: 0, 5, 10, 20 e 40mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1. Foi constatado que concentrações de Cr6+ maiores que 5mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 diminuíram a produção de matéria seca da parte aérea e radicular da soja, o número e peso de nódulos secos de Bradyrhizobium, como também a fixação biológica de nitrogênio e a absorção de P, K, Ca e Mg. Teores de Cr na parte aérea de plantas de soja superiores a 3,4mg Kg-1 podem ser considerados fitotóxicos.

RESUMO

This study was carried out to evaluate the effect of hexavalent chromium on dry matter production, nutrient uptake and nitrogen fixation in soybeans (Glycine max ) The seeds were inoculated with comercial strains of Bradyrhizobium japonicum (SEMIA 587 and 5019) and the plants were grown in "Leonard Jars" containing washed sand in the upper portion and nutrient solution (without N) in the lower. Five Cr6+ concentrations were used: 0, 5, 10, 20 e 40mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 in the nutrient solution. Concentrations of Cr6+ above 5mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 decreased plants and nodules dry matter production, number of nodules, nitrogen fixation and P, K, Ca e Mg uptake. Chromium concentrations in soybean tops above 3,4mg kg-1 were considered phytotoxic.

Foram avaliados os efeitos de doses crescentes de Cr6+ sobre a produção de matéria seca, absorção de nutrientes e fixação biológica de nitrogênio em plantas de soja. Antes da semeadura, as sementes foram tratadas com inóculo turfoso contendo Bradyrhizobium japonicum. As plantas foram cultivadas durante 40 dias em vasos "Leonard" que continha areia na parte superior e solução nutritiva sem nitrogênio na parte inferior. Os tratamentos constaram das seguintes doses de Cr6+ (K2Cr2O7) na solução nutritiva: 0, 5, 10, 20 e 40mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1. Foi constatado que concentrações de Cr6+ maiores que 5mg img src="http:/img/fbpe/cr/v31n6/a08img01.gif"> -1 diminuíram a produção de matéria seca da parte aérea e radicular da soja, o número e peso de nódulos secos de Bradyrhizobium, como também a fixação biológica de nitrogênio e a absorção de P, K, Ca e Mg. Teores de Cr na parte aérea de plantas de soja superiores a 3,4mg Kg-1 podem ser considerados fitotóxicos.

RESUMO

Inoculation in the soybean crop is a practice widely adopted all over the world. Despite of this fact, so far researchers have not come to a agreement regarding the amount of peat inoculant to be used under the no-tillage cultivation system. While in Paraná State the recommended amount is of 500g of inoculant for 50kg of seeds, in Rio Grande do Sul and Santa Catarina States this recommendation is of 200g, what brings into evidence the need to intensify research in this particular area. This study was carried out in the 1994/95 cropping season, in an area cultivated under the no-tillage system for five years, in Cruz Alta, Rio Grande do Sul State, Brazil, aiming at evaluating the effect of the peat inoculant dose on soybean under no-tillage. The treatments used were: check without inoculation, inoculant dosis of 250, 500, 750 and 1000g for 50kg of seeds and a treatment with 200kg of N/ha, applied in parcels, without inoculation. There was no difference between the check plots without inoculation and inoculant dosis for number and weight of nodules, dry matter of the plant shoots, dry matter of the roots, plant height and N content in the leaf. The treatment with mineral nitrogen showed a smaller number and weight of nodules and higher production of dry matter of the plant shoots, but this last parameter did not differ from the treatments: check without inoculation, 250 and 500g of inoculant. With mineral N application, plant height was significantly higher than the check and the inoculant dosis treatments. There was no positive effect of the inoculant on grain yield. These results led us to conclude that there is no need to use inoculant in areas after five years under the no-tillage cultivation system.

Embora a inoculação na cultura da soja seja uma prática amplamente difundida, ainda não há um consenso sobre a quantidade de inoculante turfoso a utilizar-se em plantio direto. Enquanto no Paraná a quantidade recomendada é de 500g de inoculante para 50kg de sementes, no Rio Grande do Sul e Santa Catarina é de 200g, o que evidencia a necessidade de se intensificar as pesquisas nessa área. O trabalho foi realizado, na safra 1994/95, em área conduzida há cinco anos no sistema plantio direto, em Cruz Alta, RS, com o objetivo de avaliar o efeito da dose de inoculante turfoso na soja em plantio direto. Os tratamentos foram: testemunha sem inoculação, doses de 250, 500, 750 e 1000g de inoculante por 50kg de semente e um tratamento com 200kg de N/ha, parcelados, sem inoculação. Não houve diferenças entre a testemunha sem inoculação e as doses de inoculante para número e peso de nódulos, massa seca da parte aérea, massa seca de raízes, altura de planta e teor de N na folha. O tratamento com N mineral apresentou menor número e peso de nódulos e maior produção de matéria seca da parte aérea, porém, neste último parâmetro, não diferiu da testemunha sem inoculação, 250 e 500g de inoculante. Com a aplicação de N mineral, a altura de planta foi significativamente superior à testemunha e às doses de inoculante. Não houve efeito positivo da inoculação sobre o rendimento de grãos, já que este não diferiu significativamente entre as doses de inoculante e a testemunha sem inoculação. Estes resultados indicam não haver justificativa para o uso de inoculante em áreas a partir de cinco anos de plantio direto.

RESUMO

Inoculation in the soybean crop is a practice widely adopted all over the world. Despite of this fact, so far researchers have not come to a agreement regarding the amount of peat inoculant to be used under the no-tillage cultivation system. While in Paraná State the recommended amount is of 500g of inoculant for 50kg of seeds, in Rio Grande do Sul and Santa Catarina States this recommendation is of 200g, what brings into evidence the need to intensify research in this particular area. This study was carried out in the 1994/95 cropping season, in an area cultivated under the no-tillage system for five years, in Cruz Alta, Rio Grande do Sul State, Brazil, aiming at evaluating the effect of the peat inoculant dose on soybean under no-tillage. The treatments used were: check without inoculation, inoculant dosis of 250, 500, 750 and 1000g for 50kg of seeds and a treatment with 200kg of N/ha, applied in parcels, without inoculation. There was no difference between the check plots without inoculation and inoculant dosis for number and weight of nodules, dry matter of the plant shoots, dry matter of the roots, plant height and N content in the leaf. The treatment with mineral nitrogen showed a smaller number and weight of nodules and higher production of dry matter of the plant shoots, but this last parameter did not differ from the treatments: check without inoculation, 250 and 500g of inoculant. With mineral N application, plant height was significantly higher than the check and the inoculant dosis treatments. There was no positive effect of the inoculant on grain yield. These results led us to conclude that there is no need to use inoculant in areas after five years under the no-tillage cultivation system.

Embora a inoculação na cultura da soja seja uma prática amplamente difundida, ainda não há um consenso sobre a quantidade de inoculante turfoso a utilizar-se em plantio direto. Enquanto no Paraná a quantidade recomendada é de 500g de inoculante para 50kg de sementes, no Rio Grande do Sul e Santa Catarina é de 200g, o que evidencia a necessidade de se intensificar as pesquisas nessa área. O trabalho foi realizado, na safra 1994/95, em área conduzida há cinco anos no sistema plantio direto, em Cruz Alta, RS, com o objetivo de avaliar o efeito da dose de inoculante turfoso na soja em plantio direto. Os tratamentos foram: testemunha sem inoculação, doses de 250, 500, 750 e 1000g de inoculante por 50kg de semente e um tratamento com 200kg de N/ha, parcelados, sem inoculação. Não houve diferenças entre a testemunha sem inoculação e as doses de inoculante para número e peso de nódulos, massa seca da parte aérea, massa seca de raízes, altura de planta e teor de N na folha. O tratamento com N mineral apresentou menor número e peso de nódulos e maior produção de matéria seca da parte aérea, porém, neste último parâmetro, não diferiu da testemunha sem inoculação, 250 e 500g de inoculante. Com a aplicação de N mineral, a altura de planta foi significativamente superior à testemunha e às doses de inoculante. Não houve efeito positivo da inoculação sobre o rendimento de grãos, já que este não diferiu significativamente entre as doses de inoculante e a testemunha sem inoculação. Estes resultados indicam não haver justificativa para o uso de inoculante em áreas a partir de cinco anos de plantio direto.

RESUMO

A field study on the competion and on the dynamics of occupation of nodulation sites by naturalized and seed inoculated strains of Bradyrhizobium japonicum was conducted on a Dark Red Latosol. The experimental design consisted of randomized blocks, with eight replications of the following treatments: A) control without inoculation; B) control without inoculation, with nitrogen fertilizer; C) inoculation with about 107 rhizobia/g (8g/kg of seed); D) inoculation with about 1010 rhizobia/g (8g/kg of seed). The inoculant was prepared with the strains SMS-314 (= SEMIA-587) and SMS-463 (=SEMIA-5019 = 29W), officially recommended for inoculant production. The identification of the strains which formed nodules was made in samples collected at 10, 42 and 70 days after seed germination. The grains were harvested to evaluate production and nitrogen content. Sorological typification was made with antiserum prepared from antigens constituted by B. japonicum strains SEMIA-587, SEMIA-5019 and SEMIA-5052 (=USDA-6), using the immunodot method. The characterization of the strains in nodules revealed a small increase (6,2 to 8,7%) in the occurrence of nodules formed by the recommended strains for the three sampling dates. There was an expressive participation of the strain 5052 (serogroup USDA-6) in the formation of the nodules. It was also observed that the naturalized strains may contribute differently to the formation of the nodules during the cycle, depending on the time of sampling.

Fez-se um estudo de campo sobre a competição e a dinâmica de ocupação de sítios de nodulação de estirpes de Bradyrhizobium japonicum naturalizadas ou inoculadas em sementes. O ensaio foi instalado em Latossolo Vermelho Escuro utilizando blocos ao acaso, com 8 repetições dos seguintes tratamentos: A) controle sem inoculante; B) controle sem inoculante, com adubação nitrogenada; C) inoculante com cerca de 107 rizóbios/g (8g/kg de semente); D) inoculação com cerca de 1010 rizóbios/g (8g/kg de semente). Os inoculantes foram preparados com as estirpes recomendadas na ocasião, SMS - 314 (= SEMIA 587) e SMS - 463 (= SEMIA 5019 = 29W). A identificação das estirpes formadoras dos nódulos foi realizada em amostras coletadas aos 10, 42 e 70 dias após a germinação. Realizou-se também a colheita dos grãos para avaliação da produção e de N-total. A tipificação sorológica foi feita com antissoro preparado a partir de antígenos constituídos pelas seguintes estirpes de Bradyrhizobium japonicum: SEMIA 587, SEMIA 5019 e SEMIA 5052 (= USDA 6), utilizando-se da técnica "immunodot". A caracterização das estirpes dos nódulos revelou um pequeno aumento (6,2 a 8,7%), na ocorrência de nódulos formados pelas estirpes recomendadas, nas três épocas de amostragem. Houve expressiva participação da estirpe 5052 (= sorogrupo USDA 6) na formação dos nódulos. Verificou-se que as estirpes naturalizadas podem contribuir de forma diferente na formação dos nódulos durante o ciclo, dependendo da amostragem.

RESUMO

A field study on the competion and on the dynamics of occupation of nodulation sites by naturalized and seed inoculated strains of Bradyrhizobium japonicum was conducted on a Dark Red Latosol. The experimental design consisted of randomized blocks, with eight replications of the following treatments: A) control without inoculation; B) control without inoculation, with nitrogen fertilizer; C) inoculation with about 107 rhizobia/g (8g/kg of seed); D) inoculation with about 1010 rhizobia/g (8g/kg of seed). The inoculant was prepared with the strains SMS-314 (= SEMIA-587) and SMS-463 (=SEMIA-5019 = 29W), officially recommended for inoculant production. The identification of the strains which formed nodules was made in samples collected at 10, 42 and 70 days after seed germination. The grains were harvested to evaluate production and nitrogen content. Sorological typification was made with antiserum prepared from antigens constituted by B. japonicum strains SEMIA-587, SEMIA-5019 and SEMIA-5052 (=USDA-6), using the immunodot method. The characterization of the strains in nodules revealed a small increase (6,2 to 8,7%) in the occurrence of nodules formed by the recommended strains for the three sampling dates. There was an expressive participation of the strain 5052 (serogroup USDA-6) in the formation of the nodules. It was also observed that the naturalized strains may contribute differently to the formation of the nodules during the cycle, depending on the time of sampling.

Fez-se um estudo de campo sobre a competição e a dinâmica de ocupação de sítios de nodulação de estirpes de Bradyrhizobium japonicum naturalizadas ou inoculadas em sementes. O ensaio foi instalado em Latossolo Vermelho Escuro utilizando blocos ao acaso, com 8 repetições dos seguintes tratamentos: A) controle sem inoculante; B) controle sem inoculante, com adubação nitrogenada; C) inoculante com cerca de 107 rizóbios/g (8g/kg de semente); D) inoculação com cerca de 1010 rizóbios/g (8g/kg de semente). Os inoculantes foram preparados com as estirpes recomendadas na ocasião, SMS - 314 (= SEMIA 587) e SMS - 463 (= SEMIA 5019 = 29W). A identificação das estirpes formadoras dos nódulos foi realizada em amostras coletadas aos 10, 42 e 70 dias após a germinação. Realizou-se também a colheita dos grãos para avaliação da produção e de N-total. A tipificação sorológica foi feita com antissoro preparado a partir de antígenos constituídos pelas seguintes estirpes de Bradyrhizobium japonicum: SEMIA 587, SEMIA 5019 e SEMIA 5052 (= USDA 6), utilizando-se da técnica "immunodot". A caracterização das estirpes dos nódulos revelou um pequeno aumento (6,2 a 8,7%), na ocorrência de nódulos formados pelas estirpes recomendadas, nas três épocas de amostragem. Houve expressiva participação da estirpe 5052 (= sorogrupo USDA 6) na formação dos nódulos. Verificou-se que as estirpes naturalizadas podem contribuir de forma diferente na formação dos nódulos durante o ciclo, dependendo da amostragem.