ABSTRACT: Identification and selection of nitrogen-fixing bacterial strains for inoculation into native leguminous tree species can assist in the recovery of degraded areas. Additionally, native strains from these areas are genetic resources adapted to these conditions and are thus suitable for selection. The aim of this study was to symbiotically and genetically characterize 18 bacterial strains from the Rhizobium and Bradyrhizobium genera isolated from Machaerium nyctitans, Platypodium elegans, and Ormosia arborea grown in a nursery in an iron mining area. Three experiments were conducted under axenic conditions in a greenhouse. The nodulation capacity of the strains was evaluated by the number (NN) and dry matter (NDM) of nodules. Symbiotic efficiency was evaluated based on the following parameters: SPAD index (SPAD), shoot dry matter (SDM), root dry matter (RDM), and total dry matter (TDM) of the plants, relative efficiency (RE), shoot nitrogen content (SNC), and total nitrogen content in the plant (TNC). The atpD and gyrB housekeeping genes and the nifH gene were sequenced for phylogenetic analysis, and the nodC and nodD symbiotic genes of the strains were amplified. Out of the 18 strains, 16 were authenticated by nodulation capacity in the species of origin. The SPAD variable allowed for the detection of differences between treatments before the SDM. Additionally, the SPAD index showed correlation with TNC, and the strain Bradyrhizobium sp., UFLA01-839, which may represent a new species, was outstanding in Machaerium nyctitans. The nifH, nodD, and nodC genes were detected in UFLA01-839.

ABSTRACT: We evaluated the compatibility between two nitrogen–fixing Bradyrhizobium inoculant strains and phosphate–solubilizing fungal strains and the effect of co–inoculation of these bacterial and fungal strains on cowpea growth under different N and P conditions. First, the compatibility between Bradyrhizobium strains UFLA03–84 and INPA03–11B and fungi Haematonectria ipomoeae FSA381, Eleutherascus lectardii FSA257a, Pochonia chlamydosporia var. catenulata FSA109, and Acremonium polychromum FSA115 was tested in both solid and liquid media. Cowpea growth and nodulation promotion under two mineral N doses and two P conditions (a low dose of soluble P plus a high dose of Ca3(PO4)2 and another condition with a high dose of soluble P) were tested with two N2 fixing Bradyrhizobium strains co–inoculated with each of the P–solubilizing fungal strains FSA109, FSA115, and FSA381. There was compatibility between each fungal strain and the two Bradyrhizobium strains, except for FSA257a with either of the bacterial strains in liquid medium. When both mineral N and P were limiting, plants were able to grow and accumulate N and P based on biological N2 fixation and solubilization of calcium phosphate in the same amount as the mineral N and soluble phosphate. Even when both nutrients were fully available, the type of co–inoculation promoted plant growth and nutrient accumulation. The responses varied in accordance with the co–inoculated strains, the N source, and the P source, reflecting the enormous complexity of the biological interactions between plants and microorganisms, and the nutrient conditions provided by the environment.

ABSTRACT. The BRSMG Uai common bean cultivar (Phaseolus vulgaris L.) unites traits required by producers, such as high yield and upright stands, the latter of which is considerably improved in relation to previously released cultivars such as BRSMG Madrepérola and Pérola. However, the potential of the cultivar to form symbiotic relationships with rhizobia to fix N2 has not yet been assessed. Here, field experiments were conducted to assess the efficiency of biological nitrogen fixation (BNF) in the cultivar, and to compare this to the efficiencies of other genetic materials widely grown throughout Brazil (BRSMG Madrepérola and Pérola). Experiments were conducted on two Oxisols in Minas Gerais State, Brazil (one during the dry season in the south, and the other during the winter season in the Alto-Paranaíba region), under a no-tillage system over maize stover. A randomized block experimental design was implemented in a 3 × 3 factorial arrangement with four replicates. Individual and combined Analysis of Variance were performed and the data were normalized. Homogeneity of the residual mean squares was observed. Significant effects of factors were identified by Scott-Knott tests and F tests. The BRSMG Uai cultivar responded to inoculation with the rhizobial strain CIAT 899, with yields similar to those achieved upon fertilization with 80 kg ha-1 of N-urea and to the yields of the BRSMG Madrepérola and Pérola cultivars inoculated with the same rhizobial strain. In terms of commercial use, this cultivar may be successful under either of the management practices adopted for N supply, and from the perspective of plant breeding, it has potential for inclusion in breeding programs directed toward improving BNF.

ABSTRACT In spite of the chemical, physical, and biological benefits that Crotalaria spectabilis can provide to the soil, it is little used as a green manure crop by farmers. Inoculation with strains of legume-nodulating nitrogen-fixing bacteria that are efficient and competitive may be a strategy to enhance accumulation of N in C. spectabilis and stimulate adoption of this green manure crop. The aims of this study were i) to evaluate the symbiotic and agronomic efficiency of new strains of Bradyrhizobium on C. spectabilis in an oxisol (red latosol) compared to that of noninoculated controls (without and with mineral N) and with the approved strain BR2811, seeking to corroborate possible recommendation as inoculants for this species; and ii) to determine, the contribution of these treatments to N accumulation in the plant of C. spectabilis in four periods of cutting for determining possible and ideal periods for its incorporation in the soil. Experiments were carried out in pots and field. Inoculation with the new strains UFLA05-03, UFLA05-09, and UFLA05-14 and with BR2811 on C. spectabilis is effective since it increases the production of N-enriched plant biomass when compared to the control without N mineral. However, UFLA05-03 stands out among these strains because it behaves similarly to the control with mineral N both in relation to shoot N accumulation and dry matter just after 150 days in the field.

ABSTRACT. Agar media with insoluble phosphates are used for semi-quantitative screening of phosphate-solubilizing bacteria based on the solubilization halo formed around the colonies. We show that the volume of the culture medium (15, 20, and 30 mL) and the inoculation method (toothpick vs microdrop) strongly influence the diameter of the solubilization halo, and this should be considered in advance selection of the isolates most efficient in this process.

RESUMO Mimosa foliolosa Mimosa foliolosa é uma espécie nativa de campos rupestres promissora para revegetação de áreas degradadas neste ecossistema. A simbiose entre leguminosas e bactérias fixadoras de N2 pode desempenhar um papel importante na recuperação dessas áreas, uma vez que estas plantas têm melhor desenvolvimento e são mais resistentes ao ataque de patógenos. Em adição à fixação biológica de N2 (-FBN), essas bactérias podem promover o crescimento vegetal por meio de outros processos, tais como solubilização de fosfatos e produção de sideróforos. Nós estudamos as características culturais e genéticas de 11 estirpes de bactérias isoladas de solo de campos rupestres utilizando Mimosa tenuiflora como planta isca. Nós avaliamos estas estirpes em relação as suas características simbióticas como nodulação e promoção de crescimento de Mimosa foliolosa, assim como sua habilidade de solubilizar fosfato e produzir sideróforos. Estirpes bacterianas fixadoras de N2 nativas pertencentes ao gênero Paraburkholderia (UFLA01-750, UFLA01-728, UFLA01-725 e UFLA01-757), apresentaram alta eficiência simbiótica com M. foliolosa, além de solubilizar fosfato de cálcio e produzir sideróforos, evidenciando uma alta diversidade funcional e potencial para uso em projetos de revegetação.

ABSTRACT Mimosa foliolosa is a promising native species of rupestrian fields for revegetation of degraded areas in this ecosystem. The symbiosis between leguminous plants and N2-fixing bacteria may play an important role in the recovery of these areas, since these plants have better development and are more resistant to the attack of pathogens. In addition to the biological nitrogen fixation (BNF), these bacteria can promote plant growth through other processes, such as phosphate solubilization and siderophore production. We studied the cultural and genetic characteristics of 11 bacterial strains, isolated from rupestrian field soils using Mimosa tenuiflora as “trap” plant. We evaluated these strains considering their symbiotic characteristics such as nodulation, and growth-promotion of Mimosa foliolosa, as well as their ability for siderophore production and phosphate solubilization. Native N2-fixing bacterial strains belonging to the Paraburkholderia genus (UFLA01-750, UFLA01-728, UFLA01-725, and UFLA01-757), showed high symbiotic efficiency with M. foliolosa. These strains also solubilized calcium phosphate and produced siderophores, exhibiting high functional diversity and potential for use in revegetation projects.

ABSTRACT Studies in the Amazon indicate a wide diversity of rhizobia with the ability for biological nitrogen fixation (BNF), which could expand the number of strains approved for cowpea. Thus, the aim of this field study was to evaluate the agronomic performance in cowpea of the several strains isolated from the soils of the Brazilian states Acre and Rondônia, and to compare them withstrains approved by the Ministry of Agriculture (MAPA) and withnon-inoculated controls (without and with mineral nitrogen fertilizer). The inoculants performed well. Though less effective than the other strains, the UFLA 03-36 strain also was prominent with respect to grain yield. Because of the positive response of the UFLA 03-129 strain, which led to yield increases greater than the obtained from the control without inoculation plus mineral-N, it can be recommended as an inoculum for cowpea. Further investigations should be carried out to obtain MAPA’s approval for their use. Other experiments involving this strain and several cultivars are being carried out on other types of soil and environmental conditions of the state of Minas Gerais.

RESUMO O uso de estimulantes para o estabelecimento de fungos micorrízicos arbusculares tem grande potencial em contribuir para a absorção de P pelas plantas. Objetivou-se avaliar a eficácia do isoflavonóide formononetina como estimulante da micorrização na cultura da soja, associada a adubação fosfatada, em dois Latossolos com teores de fósforo disponível médio (LPm) e baixo (LPb) no Cerrado piauiense. O delineamento experimental em cada solo foi em blocos casualizados no esquema fatorial 4×4, com quatro repetições. Os tratamentos foram constituídos por quatro doses de fósforo (0; 26,66; 40 e 80 kg ha-1 de P2O5) e quatro doses do isoflavonóide formononetina (0; 0,5; 0,9 e 1,8 g kg-1 de semente de soja). As variáveis avaliadas foram, o crescimento, a produção, a nodulação e taxa de colonização micorrízica da soja. Com exceção da taxa de colonização micorrízica no LPm, altura e número de vagens por planta de soja no LPb, as demais variáveis, não foram influenciados pela aplicação do isoflavonóide formononetina, em ambos os solos. A produtividade cresceu linearmente ao incremento das doses de fósforo no LPb, apresentando uma eficiência agronômica de ~15 kg ha-1 de grãos para cada kg ha-1 de P2O5 aplicado no solo.

ABSTRACT The use of stimulants in the establishment of arbuscular mycorrhizal fungi has great potential in contributing to P uptake by plants. This study aimed to evaluate the effect of isoflavonoid formononetin as mycorrhization stimulant on soybean associated with phosphate fertilizer in Oxisols with intermediate (OPi) and low (OPl) phosphorus availability, in the Cerrado region of Piauí. The experiment in each soil consisted of randomized blocks design in a 4×4 factorial scheme, with four replications. The treatments comprised of four phosphorus doses (0, 26.66, 40 and 80 kg ha-1 P2O5), and four isoflavonoid formononetin doses (0, 0.5, 0.9 and 1.8 g kg-1 soybean seeds). The variables evaluated were soybean growth, yield, nodulation and mycorrhizal colonization rate. With the exception of mycorrhizal colonization rate in OPi, plant height and number of pods per plant in OPl, the other variables were not affected by the application of isoflavonoid formononetin, in both soils. Yield linearly increased with increase in the phosphorus doses in OPl, and presented agronomic efficiency of ~15 kg ha-1 grain for each kg ha-1 P2O5 applied to the soil.

ABSTRACT: A significant number of bacterial species, particularly in the rhizosphere, may benefit plant growth and development. This group of bacteria is known as plant growth-promoting rhizobacteria (PGPR). This study identified genetically isolates of common bean nodules used to trap bacteria from Amazon pastureland and investigated their capacity of nodulating and promoting growth of common bean when inoculated or co-inoculated with CIAT899 strain (Rhizobium tropici). Two experiments were carried out in a greenhouse, in axenic conditions, using the common bean cultivar Talismã. In the first experiment, 56 PGPR strains were evaluated individually regarding growth promotion and nodulation. In the second experiment, inoculation of seven PGPR strains previously selected in the first experiment was evaluated in three forms of N supply: Co-inoculation with CIAT 899 in the presence of low N-mineral concentration; individual inoculation in the presence of high N-mineral concentration; and individual inoculation in the presence of low N-mineral concentration. The 16S rRNA gene sequencing showed predominance of Pseudomonas genus, identified in 35 % of the sequenced strains. Other genera were identified: Rhizobium, Burkholderia, Xanthomonas and Bacillus. Inoculation of the seven strains with CIAT 899 promoted distinct plant growth in different forms of N supply. In addition, N-mineral supply can be replaced by co-inoculation with strains of Pseudomonas sp. (UFLA 02-281 and UFLA 02-293) and Bacillus sp. (UFLA 02-298) identified in this study.

ABSTRACT: Among soil microorganisms, the genus Cupriavidus has garnered particular scientific, economic and ecological interest because of its ability to fix nitrogen and tolerate high concentrations of metals. The aim of this study was to analyze four strains of Cupriavidus necator for their ability to tolerate and bioaccumulate cadmium and zinc. The tolerance of these strains to these metals was assessed in liquid culture medium containing different concentrations of Zn + Cd and in soil solutions and soils contaminated with multiple elements including Zn, Cd, Cu and Pb. The four strains showed high tolerance to Zn and Cd, both in culture medium and when inoculated into contaminated soil solutions or multi-element contaminated soil. The UFLA02-71 strain displayed the highest ability to bioaccumulate these metals. It was able to accumulate 93.76 µmol g cell−1 of Zn and 16.03 µmol g cell−1 of Cd when cultured in liquid medium with a total heavy metal concentration of 9,140 µmol L−1 (9,000 Zn + 140 Cd) and was able to accumulate 16.98 µmol g cell−1 of Cd in the soil solution. An increase in the pH of the culture medium resulting from the growth of the C. necator strains reduced the Zn2+ and Cd2+ ions in the medium and increased the concentrations of the ZnHPO4 and CdHPO4 species in solution. Thus, we concluded that they show great potential for use in the bioremediation of HM-contaminated areas.

ABSTRACT Although the use of inoculants containing rhizobia is encouraged, there are no official recommendations for inoculation of snap bean. In this respect, the aim of this study was to evaluate the agronomic performance of Rhizobium strains in symbiosis with snap bean cultivars with different growth habits and crop cycles. The experiment was carried out in pots with soil in a greenhouse in the spring-summer season in Lavras, state of Minas Gerais, Brazil. A completely randomized experimental design was used, with 4 replications, in a 4 × 7 factorial arrangement involving four snap bean cultivars and seven treatments – five strains of Rhizobium (UFLA 02-100, UFLA 02-127, UFLA 04-173, CIAT 899, and PRF 81), plus two controls without inoculation (with and without 500 mg N-NH4NO3∙dm–3). We conclude that: i) while genetic differences were observed among cultivars with respect to nodulating capacity, in all cases significant benefits were observed from BNF inoculation and ii) inoculation with selected strains of Rhizobium, as well as fertilization with mineral N, favors plant growtht, snap bean yields, and accumulation of N in the pods and, therefore, can fully substitute nitrogen fertilization in snap bean grown under protected cultivation.

Resumo: O objetivo deste trabalho foi avaliar a viabilidade da inoculação líquida de Rhizobium etli no sulco de semeadura e certificar a eficiência da estirpe UFLA 02-100 como inoculante potencial para o feijoeiro-comum (Phaseolus vulgaris). Os tratamentos consistiram de três doses do inoculante líquido aplicadas aos sulcos e uma dose aplicada às sementes de feijão-comum, além de dois controles sem inoculação. O inoculante continha 109células de Rhizobium etli mL-1. Independentemente do método de aplicação, a produtividade obtida com a inoculação foi equivalente à da aplicação de N da ureia, mas a aplicação ao sulco, com 0,6 L ha-1, é mais vantajosa pela praticidade operacional e redução de custos.

Abstract: The objective of this work was to evaluate the viability of liquid medium inoculation of Rhizobium etli in the planting furrow and to certify the efficiency of its strain UFLA 02-100 as a potential inoculant for common bean (Phaseolus vulgaris). The treatments consisted of three application rates of liquid inoculant applied in the planting furrows or in common bean seed, besides two controls without inoculation. The inoculant contained 109 cells of Rhizobium etli mL-1. Regardless of the application method, the yield obtained with the inoculation was equivalent to that of N from urea; however, the application in the furrows, at 0.6 L ha-1, is more advantageous due to the operational practicality and reduced costs.

ABSTRACT Preliminary results of in vitro experiments with multicontaminated soils and solid media indicated that nodulating diazotrophic bacteria of the genus Cupriavidus are promising for the remediation of contaminated environments due to their symbiosis with legumes and metal tolerance. Thus, strains of Cupriavidus spp. (LMG 19424T, UFLA 01-659, UFLA 01-663, and UFLA 02-71) were tested for their ability to tolerate and bioaccumulate cadmium (Cd), copper (Cu), and zinc (Zn) in Luria-Bertani broth. Changes in the growth pattern of Cupriavidus strains in the presence or absence of heavy metals were analyzed by scanning electron microscopy and metal allocation by transmission electron microscopy, to clarify the mechanisms of bioremediation. Highest tolerance was detected for strain UFLA 01-659 (minimum inhibitory concentration of 5, 4.95, and 14.66 mmol L−1 of Cd, Cu, and Zn, respectively). Among the removal rates of the metals tested (9.0, 4.6, and 3.2 mg L−1 of Cd, Cu, and Zn, respectively), the bacterial activity was clearly highest for Cd. The efficiency of strain UFLA 01-659 in removing the heavy metals is associated with its high biomass production and/or higher contents of heavy metals adsorbed and absorbed in the biomass. In response to the presence of heavy metals in the liquid culture medium, the bacteria produced exopolysaccharides and small and aggregated cells. However, these responses varied according to the strains and heavy metals. Regarding allocation, all heavy metals were adsorbed on the cell wall and membrane, whereas complexation was observed intracellularly and only for Cu and Zn. These results indicate the possibility of using C. necator UFLA 01-659 for remediation in areas with very high Cd, Cu, and Zn contents.

RESUMO. Gliricídia (Gliricidia sepium) e sombreiro (Clitoria fairchildiana) têm sido recomendadas para uso em sistemas agroflorestais e reflorestamento de áreas degradadas devido ao seu rápido crescimento e simbiose com rizóbios. No entanto, pouco é conhecido em relação às populações nativas que nodulam estas espécies. O objetivo deste estudo foi avaliar a diversidade genética e fenotípica das bactérias fixadoras de nitrogênio isoladas de nódulos de gliricídia e sombreiro em sistemas alley cropping localizados na região pré-Amazônica do Estado do Maranhão, e autenticar sua capacidade de nodulação. Foram realizados: coleta dos nódulos em campo, isolamento, caracterização cultural, sequenciamento parcial do gene 16S rRNA e autenticação da capacidade simbiótica das estirpes em siratro (Macroptilium atropurpureum). Apesar de estarem sob as mesmas condições edafoclimáticas, gliricídia e sombreiro são colonizados por distintos gêneros de rizóbios, com predominância de Rhizobium em gliricídia, e Bradyrhizobium em sombreiro. Estirpes endofíticas também foram encontradas colonizando os nódulos. Cerca de 60% das estirpes de Rhizobium não nodularam siratro e todas de Bradyrhizobium nodularam esta espécie. Todas as estirpes nativas isoladas de nódulos de gliricídia apresentaram baixa eficiência, e somente quatro de sombreiro foram eficientes em siratro. Estes resultados ressaltam a importância das relações simbióticas no manejo da fixação biológica de N2.

ABSTRACT. Gliricidia (Gliricidia sepium) and sombreiro (Clitoria fairchildiana) have been recommended for agroforestry systems and reforestation of degraded areas due to their fast growth and symbiosis with rhizobia. However, little is known about native populations that nodulate these species. The objective of this study was to evaluate the phenotypic and genetic diversity of nitrogen-fixing bacteria isolated from nodules of gliricidia and sombreiro in alley cropping systems located in the pre-Amazon region of Maranhão State and to confirm their nodulation ability. Nodules were field collected from 20 plants of each species. The isolated strains were characterized morphologically, their 16S rRNA gene was partially sequenced, and their symbiotic ability was authenticated in siratro (Macroptilium atropurpureum). Despite being in the same climate and soil conditions, gliricidia and sombreiro are nodulated by different rhizobia genera, with Rhizobium predominant in gliricidia and Bradyrhizobium in sombreiro. Endophytic strains also colonized nodules in the field. Approximately 60% of Rhizobium strains did not nodulate siratro, whereas all Bradyrhizobium strains did. Native strains isolated from gliricidia nodules had low efficiency, and only four strains isolated from sombreiro nodules were efficient in siratro. These results highlight the importance of symbiotic relationships in the regulation of biological nitrogen fixation.

RESUMO A determinação de atributos do solo auxilia no correto manejo da sua fertilidade. O equipamento portátil de fluorescência de raios-X (pXRF) foi recentemente adotado para determinar o teor total de elementos químicos em solos, permitindo inferências sobre atributos do solo. No entanto, esses estudos ainda são escassos no Brasil e em outros países. Os objetivos deste trabalho foram prever atributos do solo a partir de dados do pXRF, comparando-se os métodos de regressão linear múltipla stepwise (SMLR) e de random forest (RF), além de mapear e validar atributos do solo. 120 amostras de solo foram coletadas em três profundidades e submetidas a análises laboratoriais. Utilizou-se o pXRF para leitura das amostras e determinou-se o teor total de elementos. A partir dos dados do pXRF, foram utilizadas SMLR e RF para predizer resultados laboratoriais, que refletem atributos do solo, e os modelos foram validados. O melhor método foi utilizado para espacializar os atributos do solo. Utilizando SMLR, os modelos apresentaram valores elevados de R² (≥0,8), porém maior acurácia foi obtida na modelagem com RF. A capacidade de troca de cátions potencial e efetiva, matéria orgânica do solo, pH, saturação por bases e teores trocáveis de Ca, Al e Mg apresentaram ajustes adequados e predições acuradas com RF. Dos dez atributos do solo preditos por RF a partir de dados do pXRF, sete apresentavam CaO como a variável mais importante para auxiliar as predições, seguido por P2O5, Zn e Cr. Os mapas gerados a partir de dados do pXRF usando RF apresentaram adequados valores de R² para seis atributos do solo, atingindo R2 de até 0,83. O pXRF em associação com RF pode ser usado para prever atributos do solo com elevada acurácia, com rapidez e a baixo custo, além de proporcionar variáveis que auxiliam o mapeamento digital de solos.

ABSTRACT Determination of soil properties helps in the correct management of soil fertility. The portable X-ray fluorescence spectrometer (pXRF) has been recently adopted to determine total chemical element contents in soils, allowing soil property inferences. However, these studies are still scarce in Brazil and other countries. The objectives of this work were to predict soil properties using pXRF data, comparing stepwise multiple linear regression (SMLR) and random forest (RF) methods, as well as mapping and validating soil properties. 120 soil samples were collected at three depths and submitted to laboratory analyses. pXRF was used in the samples and total element contents were determined. From pXRF data, SMLR and RF were used to predict soil laboratory results, reflecting soil properties, and the models were validated. The best method was used to spatialize soil properties. Using SMLR, models had high values of R² (≥0.8), however the highest accuracy was obtained in RF modeling. Exchangeable Ca, Al, Mg, potential and effective cation exchange capacity, soil organic matter, pH, and base saturation had adequate adjustment and accurate predictions with RF. Eight out of the 10 soil properties predicted by RF using pXRF data had CaO as the most important variable helping predictions, followed by P2O5, Zn and Cr. Maps generated using RF from pXRF data had high accuracy for six soil properties, reaching R2 up to 0.83. pXRF in association with RF can be used to predict soil properties with high accuracy at low cost and time, besides providing variables aiding digital soil mapping.