Editorial

A educação profissional e tecnológica tem sido reiteradamente discutida neste periódico desde a sua criação em 1996, tendo em vista sua proximidade com o tema trabalho-educação

Editorial

A educação profissional e tecnológica tem sido reiteradamente discutida neste periódico desde a sua criação em 1996, tendo em vista sua proximidade com o tema trabalho-educação

Diversity and efficiency of bradyrhizobium strains isolated from soil samples collected from around sesbania virgata roots using cowpea as trap species Diversidade e eficiência simbiótica de estirpes de bradyrhizobium capturadas próximo ao sistema radicular de sesbania virgata usando caupi como planta-isca

The genetic diversity of ten Bradyrhizobium strains was evaluated for tolerance to high temperatures, to different salinity levels and for the efficiency of symbiosis with cowpea plants (Vigna unguiculata (L.) Walp.). Eight of these strains were isolated from nodules that appeared on cowpea after inoculation with suspensions of soil sampled from around the root system of Sesbania virgata (wand riverhemp) in ecosystems of South Minas Gerais. The other two strains used in our analyses as references, were from the Amazon and are currently recommended as cowpea inoculants. Genetic diversity was analyzed by amplifying repetitive DNA elements with the BOX primer, revealing high genetic diversity with each strain presenting a unique band profile. Leonard jar assays showed that the strains UFLA 03-30 and UFLA 03-38 had the highest N2-fixing potentials in symbiosis with cowpea. These strains had more shoot and nodule dry matter, more shoot N accumulation, and a higher relative efficiency than the strains recommended as inoculants. All strains grew in media of pH levels ranging from 4.0 to 9.0. The strains with the highest N2-fixing efficiencies in symbiosis with cowpea were also tolerant to the greatest number of antibiotics. However, these strains also had the lowest tolerance to high salt concentrations. All strains, with the exceptions of UFLA 03-84 and UFLA 03-37, tolerated temperatures of up to 40 ºC. The genetic and phenotypic characteristics of the eight strains isolated from soils of the same region were highly variable, as well as their symbiotic efficiencies, despite their common origin. This variability highlights the importance of including these tests in the selection of cowpea inoculant strains.<br>Dez estirpes de rizóbios, sendo oito isoladas de amostras de solos coletadas próximo ao sistema radicular de Sesbania virgata, no Sul de Minas Gerais, e duas recomendadas como inoculante para o caupi (Vigna unguiculata (L.) Walp.) usadas como referências, foram avaliadas quanto a: diversidade genética, eficiência simbiótica em caupi, tolerância a altas temperaturas e concentrações salinas, valores extremos de pH e 15 tipos de antibióticos. A análise de diversidade genética utilizando a técnica do Rep-PCR, com o primer BOX, revelou alta diversidade, pois cada estirpe apresentou perfil único de DNA. O teste de eficiência simbiótica conduzido em vasos de Leonard indicou que as estirpes UFLA 03-30 e UFLA 03-38 demonstraram alto potencial em fixar N2 em simbiose com o caupi, proporcionando resultados de matéria seca da parte aérea e dos nódulos, eficiência relativa e acúmulo de N na parte aérea superiores aos das estirpes recomendadas como inoculantes. Todas as estirpes cresceram em meios com valores de pH variando de 4,0 a 9,0. Em relação à tolerância aos antibióticos, foi observado que as estirpes eficientes em fixar N2 em simbiose com o caupi foram as que apresentaram tolerância a um maior número desses compostos. No entanto, estas estirpes mostraram comportamentos semelhantes em relação a tolerância a salinidade, constituindo o grupo de maior sensibilidade. Com exceção das estirpes UFLA 03-84 e UFLA 03-37, as demais toleraram até 40 ºC. Embora as estirpes estudadas tenham sido isoladas de solos da mesma região, com exceção das recomendadas para inoculante oriundas da Amazônia, foi observado que elas apresentaram comportamentos distintos quando submetidas aos diferentes testes de diversidade genética, fenotípica e simbiótica, justificando a importância de incluir estes testes no processo de seleção de estirpes simbióticas em caupi

Bacterial strains from floodplain soils perform different plant-growth promoting processes and enhance cowpea growth

Certain nodulating nitrogen-fixing bacteria in legumes and other nodule endophytes perform different plant-growth promoting processes. The objective of this study was to evaluate 26 bacterial strains isolated from cowpea nodules grown in floodplain soils in the Brazilian savannas, regarding performance of plant-growth promoting processes and ability to enhance cowpea growth. We also identified these strains by 16S rRNA sequencing. The following processes were evaluated: free-living biological nitrogen fixation (BNF), solubilization of calcium, aluminum and iron phosphates and production of indole-3-acetic acid (IAA). The abilities to nodulate and promote cowpea growth were evaluated in Leonard jars. Partial sequencing of the 16S rRNA gene identified 60 % of the strains as belonging to genus Paenibacillus. The following four genera were also identified: Bacillus, Bradyrhizobium, Enterobacter and Pseudomonas. None of the strains fixed N2 free-living. Among the strains, 80 % solubilized Ca phosphate and one solubilized Al phosphate and none solubilized Fe phosphate. The highest IAA concentrations (52.37, 51.52 and 51.00 μg mL−1) were obtained in the 79 medium with tryptophan by Enterobacter strains UFPI B5-7A, UFPI B5-4 and UFPI B5-6, respectively. Only eight strains nodulated cowpea, however, all increased production of total dry matter. The fact that the strains evaluated perform different biological processes to promote plant growth indicates that these strains have potential use in agricultural crops to increase production and environmental sustainability

Physiological and symbiotic diversity of Cupriavidus necator strains isolated from nodules of Leguminosae species

Biological nitrogen fixation, performed by diazotrophic bacteria, plays an important role in the maintenance of agricultural systems, as it contributes with significant amounts of the nitrogen (N) needed for plant growth, totally or partially exempting the use of industrial N fertilisers. Twenty-five bacterial strains isolated from nodules of Leucaena leucocephala and Phaseolus vulgaris trap plants were studied. These nodules were formed after inoculation with suspensions of soil samples collected close to the root system of Sesbania virgata. In previous studies, these bacteria were identified as Cupriavidus necator. This study aimed to evaluate the ability of these strains to fix N2 in the free-living state and to use carbon (C) sources; their resistance to antibiotics; growth in media with different pH values and salt concentrations and symbiotic efficiency with L. leucocephala and P. vulgaris. In each test, these strains were compared to C. taiwanensis LMG 19424T. Although a high variability regarding antibiotic resistance, salt tolerance and use of C sources were observed among the 25 C. necator strains, a large group behaved similar regarding salt tolerance (20 strains) and antibiotic resistance (22 strains). C. necator strains behaved in a different way of LMG 19424T. Only one of the 25 strains studied, UFLA02-69, was not able to establish symbiosis with its trap species, P. vulgaris. Only the strains LMG19424T and UFLA01-672 were efficient in symbiosis with L. leucocephala. The ability to use C sources, grow in different pHs and salt concentrations and resistance to several antibiotics, may grant high saprophytic competence and greater competitivity to these strains in relation to the native Leguminosae-nodulating bacterial populations, suggesting potential use in inoculant strain selection studies for legumes cultivated in soils with a wide range of pH and salt concentrations