Resumo O estudo das populações nativas edáficas pode revelar um reservatório de recurso genético para a seleção de estirpes eficientes, além de constituir um indicador das intervenções antrópicas. O objetivo do trabalho foi caracterizar e avaliar a ocorrência de populações de bactérias que nodulam e fixam N2 utilizando o feijão caupi como planta isca. O estudo foi realizado em casa de vegetação do Instituto Federal do Pará, Campus Marabá Rural. As amostras de solo foram coletadas no Projeto de Assentamento 26 de Março em oito ambientes: três áreas individuais sob cultivo de banana e de mandioca, uma sob capoeira e uma sob floresta. O delineamento experimental foi inteiramente casualizado com três repetições e oito tratamentos sendo estes constituídos pelas áreas de estudos. Aos 35 dias após emergências, as plantas foram coletadas para determinação do número de nódulos (NN), massa seca da parte área (MSPA) e raiz (MSR). De cada tratamento realizou-se o isolamento de dez nódulos destinados a caracterização morfológica e fisiológica de suas colônias. A nodulação ocorreu em todos os tratamentos, apresentado uma grande variação de NN e produção de MSPA. Foram isoladas 53 estirpes demonstrando elevada diversidade cultural por meio das características morfológicas e fisiológicas.

Abstract The native edaphic population study can be a reservoir of genetic resources for the selection of efficient strains, besides being an indicator of anthropogenic activities. The aim of this work was to characterize and evaluate the occurrence of bacterial populations that nodulate and fix N2 using cowpea as a bait plant. This study was carried out in a greenhouse situated at the Federal Institute of Pará, Campus Marabá Rural, Brasil. Soil samples were collected in the Settlement Project 26 de Março into eight environments: being three individual areas under banana and cassava cultivation, one under capoeira and one under forest. The experimental design was completely randomized with three replications and eight treatments, which consisted of the study areas. At 35 days after emergencies of the plants, they were collected to determine the number of nodules (NN), dry matter of the shoots (DMA) and root (DMR). From each treatment in this process, ten nodules were isolated for the morphological and physiological characterization of their colonies. Nodulation occurred in all treatments, with a large variation in NN and DMA production. Fifty-three strains were isolated demonstrating high cultural diversity through morphological and physiological characteristics.

Resumo A mesorregião sudeste do Pará possui um número considerável de assentamentos rurais que cultivam Manihot Esculenta Crantz, sendo necessário investigar acerca dos sistemas de cultivos para sinalizar estratégias que possam potencializar a produção. Objetivou-se avaliar as características químicas e texturais de solo em cinco ambientes distintas no Projeto de Assentamento 26 de Março, Marabá-PA, Brasil. Foi realizada a coleta de amostra composta de solo na profundidade de 0-20 cm de três áreas de cultivo de mandioca, uma de floresta e outra degradada. O delineamento experimental utilizado foi blocos casualizado com quatro repetições e cinco tratamentos. Os dados obtidos foram submetidos à análise de variância e as médias foram comparadas pelo teste de Tukey ao nível de 5% de probabilidade e a análise de componentes principais utilizando o software R livre. A textura nas áreas estudadas é de predominância arenosa. São constatados teores de fósforo baixo para todos, inclusive teores de magnésio abaixo do ideal para as áreas do pequeno e médio agricultores. O teor de potássio é alto e não apresenta diferenças nas áreas estudadas entre os produtores. Os indicadores de acidez do solo demonstram serem os principais fatores limitantes nas áreas de estudo para melhor desempenho no rendimento da cultura.

Abstract The southeastern mesoregion of Pará has a considerable number of rural settlements which cultivate Manihot esculenta Crantz, being necessary to investigate about cropping systems to signal strategies that may potentialize the production. This study aimed at evaluating the chemical and textural soil characteristics in five different environments in the 26 de MarçoSettlement Project, Marabá-PA, Brazil. It was performed the collection of a sample composed of soil at a depth of 0-20 cm from three areas of cassava cultivation, one from forest area and other from degraded area. The experimental design used was randomized blocks with four replications and five treatments. Data obtained were subjected to analysis of variance and the means were compared by Tukey's test at the level of 5% probability, and the analysis of main components, by using the free R software. The texture in the studied areas is predominantly sandy. Low phosphorus levels were found for all, including less than ideal magnesium levels for small and medium-sized farmers areas. The potassium content is high and there are no differences in the studied areas for producers. The indicators of soil acidity prove to be the main limiting factors in the study areas for better performance in crop yield.

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 Cowpea is a very important crop to Brazilian Semi-Arid mainly small family-based farmers. Rhizobia inoculation is a practice, easy to use, and cheap technology that increases cowpea productivity. The aim of this study was to evaluate the efficiency of two new rhizobia isolates in greenhouse and field as well as classify them taxonomically. To bacterial identification the 16S rRNA gene of ESA 17 and ESA 18 isolates were sequenced. The greenhouse test was conducted with pots containing 3 L of soil and the bacterial isolates evaluated were ESA 17, ESA 18, BR 3267 or BR 3262 strains. A field experiment was implemented on a Vertisol in Juazeiro, Bahia State, to evaluate the cowpea growth and productivity. In this experiment, the peat-based inoculants with ESA 17, ESA 18, BR 3267 or UFLA 3-84 were used in 2 cowpea cultivars. Both bacteria were identified as Bradyrhizobium, but related to different species. ESA 17 was related to B. japonicum and ESA 18 was closer to B. pachyrhizi. At greenhouse, both isolates increased cowpea nitrogen content in the shoots due to the presence of very efficient nodules. In the field, the isolate ESA 18 inoculated at BRS Pujante cultivar induced higher production than observed for the absolute control, and for BR 17 Gurguéia cultivar, the ESA 17 and BR 3267 stood out both by inducing high production and grain protein content. The results indicate that both isolates can be evaluated in network experiments aiming at official recommendation for new bacteria to cowpea inoculant in Brazil.

O objetivo deste trabalho foi avaliar o potencial de promoção do crescimento vegetal e a diversidade genética de bactérias isoladas de nódulos de feijão-caupi cultivado em solos do Cerrado piauiense. Avaliaram-se 26 estirpes quanto à capacidade de fixar nitrogênio em vida livre, solubilizar fosfatos inorgânicos, produzir ácido-3-indolacético (AIA) na ausência e na presença do aminoácido triptofano (100 mg L-1), produzir nódulos e promover o crescimento de feijão-caupi em vasos Leonard. Nenhuma estirpe fixou nitrogênio em vida livre, e 69% foram capazes de solubilizar fosfato de cálcio in vitro. Na presença de triptofano, todas as estirpes foram capazes de sintetizar o AIA em meio 79, e 80% sintetizaram o AIA em meio DYGS. Apenas quatro estirpes nodularam o feijão-caupi. O sequenciamento do gene 16S rRNA identificou as estirpes nodulíferas como pertencentes aos gêneros Bradyrhizobium, Rhizobium, Bacillus e Paenibacillus. Entre as estirpes não nodulíferas promotoras do crescimento do feijão-caupi, estão os gêneros Bacillus e Paenibacillus.

The objective of this work was to evaluate the potential for plant growth promotion and the genetic diversity of bacteria isolated from nodules of cowpea grown in Cerrado soils in the state of Piauí, Brazil. Twenty-six strains were evaluated as to their ability to fixate free-living nitrogen, solubilize inorganic phosphates, produce indole-3-acetic acid (IAA) in the absence and presence of tryptophan (100 mg L-1), produce nodules, and promote cowpea growth in Leonard jars. No strain was able to fixate free-living nitrogen, and 69% were able to solubilize calcium phosphate in vitro. In the presence of tryptophan, all strains were able to synthesize IAA in the 79 medium, and 80% synthesized IAA in the DYGS medium. Only four strains nodulated cowpea. The sequencing of the 16S rRNA gene identified the nodulating strains as belonging to the genera Bradyrhizobium, Rhizobium, Bacillus, and Paenibacillus. Among the non-nodulating strains able to promote cowpea growth are the genera Bacillus and Paenibacillus.