ABSTRACT The use of rock dust in Brazil has been studied and encouraged to reduce the Brazilian dependence on the foreign market for chemical fertilizers and as an alternative to organic agriculture. The objective of this research was to evaluate the effects of using phonolite rock powder and organic compound, associated with inoculation with the potassium solubilizing bacteria (KSB) of the genus Burkholderia on the chemical characteristics of the soil, macro and micronutrients in the aerial part, and tomato productivity. The experiment was installed in pots in a greenhouse, using a randomized block design in a 5 × 2 factorial arrangement, representing five doses of phonolite added in an organic compound, with the presence or absence of inoculation with the strain 100-13. The nutrient contents in the soil and the aerial part and the production of tomato were evaluated. Differences were observed between the doses of the organic compound and the phonolite associated with the inoculation. The treatments containing the highest doses of an organic compound provided better levels of nutrients in the soil and the aerial part, and in the tomato productivity. The inoculation with the bacterial strain improved the release of potassium from the powder of the phonolite rock.

ABSTRACT The objective of this study was to evaluate the influence of a commercial product, a soil bioactivator, on the establishment and efficiency of symbiosis between rhizobia and Arachis pintoi (forage peanut). The experiment was conducted in a greenhouse in 8 dm3 pots and 12 treatments were used, ten inoculated with different strains of rhizobia and two without inoculation (presence or absence of mineral nitrogen), associated or not with the application of soil bioactivator. The experimental design used was a randomized block design with four repetitions. The experiment was conducted until the time of flowering, when the agronomic characteristics referring to the shoot dry matter (SDM) and root (RDM), relative symbiotic efficiency (RS), number (NN) and nodule dry matter (NMS) and the bromatological characteristics, given by the content of crude protein (CP), neutral detergent fiber (NDF) and acid (ADF) were evaluated. The use of soil bioactivator did not influence the bromatological characteristics, but potentiated the inoculation with rhizobia strains, UNIFENAS 03-16, UNIFENAS 03-31 and UNIFENAS 03-36, effectively contributing to increases in the values of SDM, RS and NN, thus constituting a sustainable alternative for the production of A. pintoi.

ABSTRACT Studies have shown the synergism of co-inoculation with symbiotic and non-symbiotic N2-fixing bacteria, efficiently contribute to plant development. However, for crops such as forage legumes, data on the use of co-inoculation are still incipient, requiring studies to identify the contribution of this technique for application in pasture areas, thus ensuring greater sustainability. The objective of this study was to evaluate the effects of co-inoculation of Azospirillum brasilense (Ab-V5) and native rhizobia isolated from two forage legumes, Crotalaria spectabilis and Lupinus albus. Two experiments were installed in pots with 8dm3. Both were conducted in a randomized block design (DBC) with four replications and an 8 x 2 factorial scheme with six bacterial strains and two control treatments without inoculation (with presence or absence of mineral nitrogen), co-inoculated or not with the Ab-V5 strain. Plants were cultivated until the time of flowering when shoot (SDM) and root dry matter (RDM), number (NN) and nodule dry matter (NDM), and relative symbiotic efficiency (RSE) were evaluated. Isolates 05-21 and 06-03, for C. spectabilis and L. albus, respectively, indicated higher potential to promote plant growth when co-inoculated with Ab-V5, showing potential to act as substitutes for nitrogenous chemical fertilizers, reducing costs and increasing the sustainability of production.

ABSTRACT Currently, one of the most used practices in national coffee production is skeletal pruning, to preserve productive capacity, correct plant architecture, minimize the occurrence of diseases, among others. Also, it reduces the plants diameter, exposing the soil to climatic conditions, erosion, loss of moisture and nutrients, negatively affecting the development of coffee. The use of cover plants intercropped with coffee is presented as a technique to avoid and minimize these problems. Therefore, the objective of this research was to evaluate the effect of cover crops on the chemical and physical characteristics of the soil and the skeleton coffee tree. The experiment took place at Fazenda Boa Esperança, city of Serrania, South of Minas Gerais, from October/2017 to December/2018, in randomized blocks, composed of 8 treatments with and without cover crops. Three replicates per treatment were used, totaling 24 experimental plots, each with 14 plants, being the 10 central considered useful for evaluation. The cover crops contributed to the improvement of nutrient contents in the soil, maintained a better level of humidity and milder temperatures providing a greater development to the skeletonized coffee. They also positively influence weed control, but none could suppress all plants present in the research.

RESUMO O Brasil importa a maioria de fertilizantes fosfatados utilizados na agricultura, no entanto, possui em seu território jazidas nacionais que podem suprir parte da demanda do mercado interno. Para que estas possam ser utilizadas de forma efetiva, é necessário identificar técnicas para acelerar a liberação de fósforo (P) destas rochas. Com isso, objetivou-se avaliar a influência da inoculação com estirpes bacterianas solubilizadoras de fosfato (BSF) e decomposição de diferentes resíduos vegetais na solubilização de fosfato natural de Araxá (FNA). Foram realizados dois experimentos em delineamento inteiramente casualizado em esquema fatorial 5 x 4, com quatro repetições. No primeiro foi avaliado a solubilização de FNA por BSF em meio de cultura contendo quatro diferentes fontes de carbono, glicose, sacarose, celulose e pectina. Os tratamentos foram incubados por sete dias e analisou-se a concentração de P e o valor de pH. No segundo, o FNA foi aplicado em 300 cm3 no solo, disposto em câmaras de incubação e adicionados seis gramas de material vegetal seco e triturado de aveia branca, brachiaria, crotalária e tremoço e inoculação das BSF. A decomposição foi avaliada semanalmente pela quantificação do carbono do CO2 (CO2-C) liberado e, aos 42 dias, foi analisado a concentração de P no solo. A fonte de carbono influencia diretamente na solubilização do FNA pelas BSF, destacando-se o gênero Burkholderia. Os tratamentos contendo resíduos de crotalária e tremoço apresentaram maiores valores de CO2-C liberado. Os maiores teores de P no solo foram verificados nos tratamentos contendo resíduos vegetais associado à inoculação BSF.

ABSTRACT Brazil imports most of the phosphate fertilizers used in agriculture, however, it has national deposits in its territory that can supply part of the domestic market demand. In order of these to be used effectively, it is necessary to identify techniques to accelerate the release of phosphorus (P) from these rocks. The objective was to evaluate the influence of inoculation with phosphate solubilizing bacterial isolates (PSB) and decomposition of different plant residues in the solubilization of Araxá natural phosphate (ANP). Two experiments were carried out in a completely randomized design in a 5 x 4 factorial scheme, with four replicates. The first experiment evaluated the solubilization of ANP by PSB in culture medium with four different sources of carbon: glucose, saccharose, cellulose, and pectin. The treatments were incubated for seven days and then were analyzed the P concentration and pH values. In the second experiment, the ANP was applied in 300 cm3 of soil, placed in incubation chambers, with six grams of dry and crushed plant material of white oat, brachiaria, crotalaria, lupine, and the inoculation of PSB. Decomposition was evaluated weekly by quantifying the carbon of the CO2-C released and, after 42 days was analyzed the concentration of P in the soil. It was observed that the carbon source directly influences the solubilization of ANP by PSB, especially the genus Burkholderia. Treatments containing crotalaria and lupine residues showed higher CO2-C values, and the ones containing plant residues associated with BSF inoculation obtained the highest levels of P in the soil.

RESUMO O objetivo do estudo foi analisar a capacidade das bactérias diazotróficas, isoladas da rizosfera de Brachiaria brizantha, crescer em meios com diferentes valores de pH e concentrações salinas, de produzir ácido 3-indol acético (AIA) e solubilizar fosfato. Os testes de acidez e salinidade foram realizados em meio FAM sólido. Para acidez foram usados os valores de 4.0, 5.0, 6.0 e 7.0. Para salinidade foram utilizadas as seguintes concentrações: 0.01; 5.02; 9.99; 14.96; 19.98; 24.95; 29.98; 34.94; 39.97; 44.94 and 49.96 gꞏL-1. No teste de produção de AIA, as estirpes foram cultivadas em meio DYGS líquido, na ausência e presença de triptofano (Trp). A solubilização de fósforo, foi realizada em meio GL líquido. Todas as estirpes foram capazes de crescer em todos os valores de pH analisados. Já em relação aos testes de diferentes concentrações salinas, produção de AIA e solubilização de fosfato, foi verificada alta diversidade, havendo estirpes que se destacaram. As estirpes UNIFENAS 100-51; UNIFENAS 100-52; UNIFENAS 100-60; UNIFENAS 100-63 e UNIFENAS 100-65, foram as que apresentaram maior crescimento nas três maiores concentrações salinas. Na presença de triptofano, as estirpes UNIFENAS 100-63 e UNIFENAS 100-69 foram as que apresentaram maior produção de AIA. Já em solubilização de Fosfato in vitro, a estirpe UNIFENAS 100-52 foi a que obteve melhor resposta. Baseado nesses resultados, observa-se a importância de estudos relacionados às características fisiológicas e metabólicas de bactérias diazotróficas, de modo a garantir maior sucesso no campo.

ABSTRACT The objective of this study was to evaluate the ability of diazotrophic bacteria isolated from Brachiaria brizantha rhizosphere to grow at different pH values and salt concentrations, to produce indoleacetic acid (IAA), and to solubilize phosphate. Both acidity and salinity tolerance tests were performed on modified solid FAM medium. Acidity resistance tests were performed at pH values of 4.0, 5.0, 6.0, and 7.0, while, salt resistance was evaluated at concentrations of 0.01, 5.02, 9.99, 14.96, 19.98, 24.95, 29.98, 34.94, 39.97, 44.94, and 49.96 gL-1 NaCl. For the IAA production assay, bacterial strains were cultivated in liquid DYGS medium both in the absence and presence of tryptophan (Trp). In addition, phosphorus solubilization assay was performed in GL liquid medium. All strains grew at every pH value tested, and a high diversity was observed after salt resistance, IAA production, and phosphate solubilization testing. Strains UNIFENAS 100-51, UNIFENAS 100-52, UNIFENAS 100-60, UNIFENAS 100-63, and UNIFENAS 100-65 were those with the best growth at the highest salt concentrations. Furthermore, in the presence of Trp, strains UNIFENAS 100-63 and UNIFENAS 100-69 were the ones with the highest IAA production. Strain UNIFENAS 100-52 showed the best response to the in vitro phosphate solubilization assay. Based on these results, it can be seen that studies related to the physiological and metabolic characteristics of diazotrophic bacterial strains are important to ensure greater success in the field.

RESUMEN La piña ornamental es una planta rústica y de alto valor paisajístico. El cultivo de tejidos de la especie se muestra viable, produciendo plantas con alta calidad fitosanitaria. Una de las dificultades de ese cultivo es el proceso de aclimatación, que ocurre lentamente y puede causar pérdidas. El presente estudio tuvo como objetivo verificar el potencial de inoculación de las bacterias diazotróficas en el crecimiento in vitro y ex vitro de la planta de la piña ornamental. Un grupo de cepas de bacterias diazotróficas seleccionadas en la Universidade José do Rosário Vellano (UNIFENAS) fueron usadas en el estudio y las cepas bacterianas UNIFENAS 100-13, 100-60, 100-68, 100-153, 100 167 y 100-198, constituyeron los tratamientos. Se evaluaron las cepas con relación a la capacidad de producir ácido indol-3-acético. Posteriormente, las plantas fueron cultivadas en medio MS (1/4) y 1 mL de la cepa bacteriana. En el tratamiento control se mantuvieron las plantas con 2 mL de medio MS. Después de 7 días de la inoculación, las plantas fueron trasplantadas a MS, donde permanecieron por un período de 30 días. Después del cultivo in vitro, las plantas fueron transferidas a materas con el substrato comercial Plantmax®, donde se mantuvieron por 60 días en estas condiciones. Las bacterias son capaces de sintetizar auxinas y su inoculación promueve mayor crecimiento de las plantas in vitro y ex vitro. En la fase de aclimatación, las plantas inoculadas con cepas UNIFENAS 100-60, 100 68 y 100-153, promovieron un mayor crecimiento de brotes, un mayor contenido de clorofila y una actividad de la enzima nitrato reductasa.

ABSTRACT Ornamental pineapple is a hardy plant with significant landscaping value. Tissue culture of plants is viable for producing plants with a high phytosanitary quality. However, one of the difficulties with this cultivar is the acclimatization process, which is slow and can cause losses. The objective of the present study was to verify the potential of inoculation with diazotrophic bacteria for in vitro and ex vivo growth of ornamental pineapple. A group of diazotrophic bacterial strains selected at the Universidade José do Rosário Vellano (UNIFENAS) was prioritized in this study, and the treatments included bacterial strains UNIFENAS (100 13, 100-60, 100-68, 100-153, 100-167 and 100-198). These strains were evaluated in terms of their capacity to produce indole 3-acetic acid. Subsequently, plants were cultivated in a medium composed of MS medium salts (1/4), adding 1 mL of the bacterial strain. In the control treatment, the plants were maintained in 2 mL of MS medium. 7 days after inoculation, the plants were transplanted into the MS, where they were maintained for 30 days. After in vitro cultivation, the plants were transferred to pots containing commercial Plantmax® substrate and maintained under these conditions for 60 days. The diazotrophic bacteria were able to synthesize auxins, and their inoculation promoted greater growth in vitro and ex vitro in the plants. In the acclimatization phase, the plants inoculated with UNIFENAS strains (100-60, 100-68 and 100-153) promoted a higher shoot growth, chlorophyll content and nitrate reductase enzyme activity.

Resumo A adubação nitrogenada em cobertura é imprescindível para a produção de forragem, mas o elevado custo dos fertilizantes estimula a busca por novas tecnologias, como o uso de bactérias diazotróficas, que podem fixar o nitrogênio atmosférico. Para avaliar o potencial dessa tecnologia em suprir a quantidade de nitrogênio requerida pelo capim-xaraés em cobertura, as plantas foram adubadas em plantio com dose equivalente a 100 kg ha-1 de N e inoculadas com estirpes de bactérias diazotróficas e Azospirillum brasilense, e comparadas com plantas que receberam 100 kg ha-1 de N em plantio e em cobertura, durante dois períodos de crescimento da parte aérea (58 dias no primeiro período e 26 dias no segundo período), em vasos de 20 dm3. Os dados foram submetidos à análise de variância e as médias comparadas pelo teste Scott-Knott a 5% de significância. A área foliar do capim-xaraés inoculado com a estirpe UN42 foi semelhante a das plantas que receberam adubação nitrogenada em cobertura. Todavia, a produção de massa do capim foi maior quando houve adubação nitrogenada em cobertura. A inoculação das plantas com Azospirillum brasilense e as estirpes UN16, UN17, UN21, UN33, UN49 e UN78 aumentou os teores de proteína bruta do capim-xaraés em relação à adubação nitrogenada em plantio sem inoculação. Porém, a inoculação do capim com as bactérias diazotróficas não substitui totalmente a adubação nitrogenada em cobertura.

Abstract: Nitrogen topdressing is essential for forage production, but the high cost of fertilizers stimulates the search for new technologies, such as the use of diazotrophic bacteria, which can fix the atmospheric nitrogen. To evaluate the potential of this technology in providing the amount of nitrogen requested by xaraés grass as topdressing, plants were fertilized at planting with an N rate of 100 kg ha-1, inoculated with strains of diazotrophic bacteria and Azospirillum brasilense, and compared with plants that received 100 kg ha-1 of N at planting and as topdressing during two periods of shoot growth (58 days in the first period and 26 days in the second period) in 20-dm3 pots. The data were subjected to analysis of variance and means compared by the Scott-Knott test at 5% significance. The leaf area of xaraés grass inoculated with strain UN42 was similar to that of plants that received nitrogen topdressing. However, grass biomass production was higher when nitrogen topdressing was applied. Plant inoculation with Azospirillum brasilense and strains UN16, UN17, UN21, UN33, UN49, and UN78 increased crude protein contents of xaraés grass when compared to nitrogen fertilization at planting without inoculation. However, grass inoculation with diazotrophic bacteria does not replace nitrogen topdressing completely.

RESUMO A espécie Panicum maximum cv. Mombaça é uma forrageira adaptada às diversas condições edafoclimáticas encontradas no Brasil; no entanto, necessita de altas doses de fertilizantes nitrogenados para garantir altas produtividades. Objetivou-se avaliar o efeito da inoculação com estirpes de bactérias diazotróficas associativas nas características produtivas e bromatológicas do capim Mombaça. Utilizou-se delineamento em blocos casualizados, constituído por 25 tratamentos, sendo 23 inoculados com bactérias diazotróficas e dois sem inoculação (um com e o outro sem nitrogênio mineral), com quatro repetições. As variáveis analisadas foram: diâmetro do colmo; largura e comprimento da folha; produtividade da matéria seca das folhas, colmos e raiz; proteína bruta; fibra em detergente ácido e neutro. Para as variáveis matéria seca da raiz, diâmetro do colmo e fibra em detergente ácido, não foram observadas diferenças entre os tratamentos. Para as demais, verificou-se contribuição positiva da inoculação com bactérias diazotróficas, destacando-se as seguintes estirpes Unifenas: 100-06, 100-13, 100-26, 100-30, 100-35, 100-54, 100-69, 100-71 e 100-94. Isto revela o potencial destas estirpes bacterianas para uso em produção sustentável do capim Mombaça com redução de insumos nitrogenados.

ABSTRACT The Panicum maximum species (cv. Mombaça) is a forage plant well adapted to the different edaphoclimatic conditions found in Brazil; however, it requires high nitrogen fertilizer doses to ensure high yields. The present study aimed to assess the inoculation effect with associative diazotrophic bacteria strains on the yield and bromatological characteristics of the Guinea grass. A randomized block design was used, consisting of 25 treatments, being 23 of them inoculated with diazotrophic bacteria and two without inoculation (one with and the other without mineral nitrogen), with four repetitions. The analyzed variables were stem diameter; leaf width and length; leaf, stem and root dry mass yield; crude protein; acid and neutral detergent fibers. There were no differences among the treatments for root dry mass, stem diameter and acid detergent fiber. For the remaining variables, a positive effect of the inoculation with diazotrophic bacteria was observed, particularly for the following Unifenas strains: 100-06, 100-13, 100-26, 100-30, 10-35, 100-54, 100-69, 100-71 and 100-94. This reveals the potential of these bacterial strains for use at the sustainable production of the Guinea grass with a reduction in the use of nitrogen inputs.

Resumo Objetivou-se avaliar as características bromatológicas, microbiológicas e perdas fermentativas da silagem de grão de milho reidratado com água ou soro de leite associado a diferentes níveis de inclusão do resíduo de tilápia. Utilizou-se um delineamento inteiramente casualizado em esquema fatorial 5x2 (cinco níveis de inclusão do resíduo de tilápia: 0; 12,5; 25; 37,5 e 50% em substituição ao milho reidratado e duas fontes de reidratação do grão de milho: água ou soro de leite) para produção de silagem). A produção de gases da silagem com até 25% de inclusão do resíduo de tilápia foi 62,7% maior para o milho reidrato com soro de leite (P <0,01). A quantidade de bactérias ácido láticas foi menor em todos os níveis de inclusão de resíduo de tilápia quando a fonte de reidratação foi a água (P<0,01). Os teores de matéria mineral, matéria orgânica, proteína bruta, extrato etéreo, cálcio e fósforo foram maiores nas silagens reidratadas com soro de leite com o aumento do nível de inclusão de resíduo de tilápia (P<0,01). A silagem de resíduo de tilápia com milho reidratado é uma alternativa que pode ser utilizada na dieta de aves e suínos, entretanto, o seu uso está condicionado às avaliações do melhor nível de inclusão dentro de uma categoria animal.

Abstract The objective of this study was to evaluate the microbiological, chemical characteristcs and fermentative losses of corn silage rehydrated with water or whey associated to different levels of tilapia residue inclusion. A completely randomized design was used in a 5x2 factorial arrangement (five inclusion levels of tilapia residue: 0; 12.5; 25; 37.5 and 50% in substitution of dehydrated corn; and two sources of rehydration of corn: water or whey) for silage production. The production of gases of the silage with up to 25% inclusion of the tilapia residue was 62.7% greater for the corn rehydrate with whey (P <0.01). The amount of lactic acid bacteria was lesser for all levels of inclusion of tilapia residue when the source of rehydration was water (P <0.01). The levels of mineral matter, organic matter, crude protein, ethereal extract, calcium and phosphorus were greater in silages rehydrated with whey with the increase of the inclusion level of tilapia residue (P <0.01). Tilapia residue silage with rehydrated corn is an alternative that can be used in the poultry and swine diet, however, its use is conditioned to the evaluation of the best level of inclusion within an animal category.

RESUMO O objetivo com este estudo foi investigar as características de silagens preparadas com um resíduo seco de padaria hidratado com soro ácido de leite ou água associado ou não à ureia. O experimento foi conduzido em um arranjo fatorial 3 (três níveis de hidratação: 250, 300 e 350 mL kg−1 de subproduto) × 3 (três níveis de aplicação de ureia: 0, 5 e 10 g kg−1 de subproduto) × 2 (dois líquidos usados na hidratação: soro ácido de leite ou água). Mini silos foram utilizados como silos experimentais e permaneceram fechados por 30 dias. Em geral, silagens hidratadas com soro ácido de leite apresentaram maior (P<0,01) produção de ácido lático (19,6 vs. 18,5 g kg−1 de matéria seca [MS]), ácido acético (2,5 vs. 1,8 g kg−1 de MS) e ácido propiônico (8,0 vs. 5,4 g kg−1 de MS), e menores (P<0,05) contagens de fungos (5,35 e 5,01 ufg g−1 de silagem fresca) comparadas às silagens hidratadas com água. A maior hidratação das silagens aumentou a produção total de ácidos (P<0,01) reduzindo os valores de pH; mas o aumento na hidratação reduziu (P<0,01) a recuperação de MS das silagens. Silagens hidratadas com água e soro ácido de leite a 250 mL kg−1 e combinado com 5 e 10 g kg−1 de ureia exibiram maior (P<0,05) recuperação de MS. Silagens de resíduo seco de padaria hidratadas com soro ácido de leite apresentaram melhor padrão fermentativo, podendo representar uma estratégia prática para evitar o descarte de ambos os subprodutos no ambiente.

SUMMARY The objective of this study was to investigate the characteristics of silages prepared with a dry bakery by-product hydrated with acid whey or water associated or not at urea. The trial was a 3 (hydration at three moisture levels: 250, 300, and 350 mL kg−1 of by-product) × 3 (three application rates of urea: 0, 5, and 10 g kg−1 of by-product) × 2 (liquid used at hydration: acid whey or water) factorial arrangement. Mini-silos were used as experimental silos and remained closed for 30 days. Overall, silages hydrated with acid whey had higher (P<0.01) production of lactic (19.6 vs. 18.5 g kg−1 of dry matter [DM]), acetic (2.5 vs. 1.8 g kg−1 of DM) and propionic acid (8.0 vs. 5.4 g kg−1 of DM), and lower (P<0.05) fungi counts (5.35 and 5.01 cfu g−1 of fresh silage) compared to silages hydrated with water. Increased hydration led to the higher production of total acids (P<0.01), decreasing silage pH; but increased hydration reduced DM recovery (P<0.01). Silages hydrated with water and acid whey at 250 mL kg−1 and combined at 5 and 10 g kg−1 of urea exhibited higher DM recovery (P<0.05). Silages of a dry bakery by-product hydrated with acid whey had a better fermentation pattern and could represent a practical strategy to avoid discarding both by-products into environment.

Our objective was to investigate the effect of the replacement of aruana grass by gliricidia on the fermentative losses, chemical composition, and aerobic stability of silages. For ensiling, whole-crop aruana grass (75 d of growth) was chopped (275 g kg-1 dry matter - DM) and ensiled alone or associated with gliricidia (270 g kg-1 DM; 150 d of growth). For gliricidia, we used only the leaves and stalks to ensile. The evaluated treatments were different ratios of aruana grass to gliricidia (100:0, 75:25, 50:50, 25:75, and 0:100), with four replicates (mini-silos). The silage composed only of gliricidia exhibited a lower pH than the other silages. Dry matter recovery was not affected by the treatments, although effluent losses were affected. The replacement of aruana grass by gliricidia 50% at ensiling resulted in a higher lactic acid bacteria count. The aruana grass silages displayed lower protein contents and a higher neutral detergent fiber content than the gliricidia silages after 40 d of fermentation. Consequently, the silage consisting of 100% gliricidia showed higher in vitro DM digestibility, presenting an increase of 8.13% after 40 d of fermentation compared with 100% of aruana grass silage. After silo opening, the gliricidia silage was very stable (>72 h). The low quality of aruana grass silage is improved by replacing this grass with significant amounts of gliricidia (approximately 75%).

Cowpea (Vigna unguiculata) is an important grain-producing legume that can forego nitrogen fertilization by establishing an efficient symbiosis with nitrogen-fixing bacteria. Although inoculating strains have already been selected for this species, little is known about the genotypic and symbiotic diversity of native rhizobia. Recently, Bradyrhizobium has been shown to be the genus most frequently trapped by cowpea in agricultural soils of the Amazon region. We investigated the genetic and symbiotic diversity of 148 bacterial strains with different phenotypic and cultural properties isolated from the nodules of the trap species cowpea, which was inoculated with samples from soils under agroforestry systems from the western Amazon. Sixty non-nodulating strains indicated a high frequency of endophytic strains in the nodules. The 88 authenticated strains had varying symbiotic efficiency. The SPAD (Soil Plant Analysis Development) index (indirect measurement of chlorophyll content) was more efficient at evaluating the contribution of symbiotic N2-fixation than shoot dry matter under axenic conditions. Cowpea-nodulating bacteria exhibited a high level of genetic diversity, with 68 genotypes identified by BOX-PCR. Sequencing of the 16S rRNA gene showed a predominance of the genus Bradyrhizobium, which accounted for 70 % of all strains sequenced. Other genera identified were Rhizobium, Ochrobactrum, Paenibacillus, Bosea, Bacillus, Enterobacter, and Stenotrophomonas. These results support the promiscuity of cowpea and demonstrate the high genetic and symbiotic diversity of rhizobia in soils under agroforestry systems, with some strains exhibiting potential for use as inoculants. The predominance of Bradyrhizobium in land uses with different plant communities and soil characteristics reflects the adaptation of this genus to the Amazon region.

Diversos relatos evidenciam os benefícios de procariotos fixadores de nitrogênio atmosférico no crescimento e na nutrição de muitas espécies vegetais; entretanto, não há, até o momento, nenhum trabalho visando à prospecção desses microrganismos na rizosfera da seringueira (Hevea brasiliensis). Assim, os objetivos deste trabalho foram verificar a ocorrência de bactérias diazotróficas em solos sob plantio de seringueira, assim como em suas raízes, e isolar e caracterizar essas bactérias. Para essa finalidade, coletaram-se amostras de solo e de raízes finas de seringueiras cultivadas no Campus Experimental da Universidade Federal de Lavras (Lavras, MG) para inoculação em meios de cultura semissólidos sem N na forma combinada, de modo a favorecer o crescimento de algumas espécies de bactérias diazotróficas. Foram obtidos 19 isolados nas amostras de solo, e não houve crescimento de bactérias fixadoras de nitrogênio nas culturas com amostras de raízes. A caracterização celular e das colônias desses isolados indicou que 17 deles produzem grande quantidade de exopolissacarídeo elástico, algumas vezes cartilaginoso. Eles são todos Gram-negativos, com formato celular de bastonete, imóveis e com dois glóbulos de poli-β-hidroxibutirato (PBH), um em cada extremidade do bastonete. O sequenciamento do 16S rDNA e sua análise filogenética confirmaram que isolados representativos desse grupo pertencem ao gênero Beijerinckia (B. indica e B. derxii) e que os outros dois isolados Gram-positivos pertencem ao gênero Bacillus. A presença da nitrogenase - a enzima responsável pela fixação biológica do nitrogênio atmosférico (FBN) - foi confirmada por meio da técnica de redução do acetileno. Conclui-se que, no solo sob plantio de seringueira, houve predominância de diazotróficas de vida livre pertencentes ao gênero Beijerinckia (B. indica e B. derxii), não havendo indícios de bactérias endofiticas ou rizosféricas.

Several reports have shown the benefits of atmospheric nitrogen-fixing prokaryotes in growth and nutrition of many plant species; however, these microorganisms in the rhizosphere of rubber trees (Hevea brasiliensis) have not been investigated so far. Thus, the objective of this study was to verify the occurrence of diazotrophic bacteria in soils and roots of a plantation of rubber trees, and to isolate and characterize these bacteria. For this purpose, soil and fine roots of rubber trees were sampled on the Experimental Campus of the Federal University of Lavras, Minas Gerais, for inoculation in semi-solid culture medium without N, to favor the growth of some diazotrophic bacteria species. Nineteen isolates were obtained from soil samples, and no growth of N-fixing bacteria was verified in the cultures with root samples. The characterization of the cells and colonies of these isolates indicated that 17 of them produce large amounts of elastic and sometimes cartilagenous exopolysaccharide. They are all Gram-negative, have rod-shaped, motionless cells and a globule of poly-β-hydorxybutyrate (PBH) at either cell end. The sequencing of the 16S rDNA and its phylogenetic analysis confirmed that representative isolates of this group belong to the genus Beijerinckia (B.indica and B. derxii), and that the other two Gram-positive isolates belong to the genus Bacillus. The presence of the enzyme nitrogenase, responsible for biological nitrogen fixation (BNF), was confirmed by the acetylene reduction technique. It was concluded that the soil under rubber tree contained predominantly free-living diazotrophs of the genus Beijerinckia (B.indica and B.derxii), with no evidence of endophytic or rhizospheric bacteria.

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.