Fábio Martins Mercante

Rhizobium tropici, a Novel Species Nodulating Phaseolus vulgaris L. Beans and Leucaena sp. Trees

A new Rhizobium species that nodulates Phaseolus vulgaris L. and Leucaena spp. is proposed on the basis of the results of multilocus enzyme electrophoresis, DNA-DNA hybridization, an analysis of ribosomal DNA organization, a sequence analysis of 16S rDNA, and an analysis of phenotypic characteristics. This taxon, Rhizobium tropici sp. nov., was previously named Rhizobium leguminosarum biovar phaseoli (type II strains) and was recognized by its host range (which includes Leucaena spp.) and nif gene organization. In contrast to R. leguminosarum biovar phaseoli, R. tropici strains tolerate high temperatures and high levels of acidity in culture and are symbiotically more stable. We identified two subgroups within R. tropici and describe them in this paper.

Sistemas de preparo do solo, plantas de cobertura e produtividade da cultura da mandioca

O objetivo deste trabalho foi avaliar os efeitos do uso de plantas de cobertura e de sistemas de preparo do solo, no desenvolvimento e na produtividade da cultura da mandioca (Manihot esculenta Crantz). O trabalho foi conduzido em Argissolo Vermelho, sob sistema convencional de preparo do solo, e em cultivo minimo sobre palhada de mucuna-cinza (Stizolobium cinereum Piper & Tracy), sorgo granifero [Sorghum bicolor (L.) Moench] e milheto [Pennisetum americanum (L.) K. Schum.]. Aos dezoito meses apos o plantio da mandioca, foram avaliados: altura de plantas, producao de massa de materia seca da parte aerea, numero de raizes tuberosas, produtividade, percentagem de materia seca e de amido nas raizes tuberosas e indice de colheita. Observou-se que o sistema convencional de preparo do solo pode ser substituido, na cultura da mandioca, pela pratica do cultivo minimo, associada ao uso de coberturas vegetais, por promover incrementos significativos na produtividade da cultura, especialmente, quando se utiliza o milheto como planta de cobertura. O uso de plantas de cobertura no pre-cultivo de mandioca, em sistema de preparo minimo do solo, representa uma alternativa eficiente para um melhor manejo dessa cultura.

Análise conjunta de atributos físicos e biológicos do solo sob sistema de integração lavoura-pecuária

The objective of this work was to evaluate the effects of the integrated crop-livestock system on the morphological, physical and biological properties of soil. The experiment was carried out in Dourados, Mato Grosso do Sul State, Brazil, in a typic Hapludox soil. The following systems were sampled: grain crop under conventional soil tillage system, integrated crop-livestock system under no-tillage, continuous Urochloa decumbens (Syn. Brachiaria decumbens) pasture and natural system. In each system, a trench was opened in order to detect morphological changes caused by different management, using the cultural profile method. Assessments of soil macroinvertebrates were done according to the method Tropical Soil Biology and Fertility. Undisturbed soil samples were also used to assess the physical attributes of soil (soil density, total porosity, macro and microporosity). Among the cultivated systems, better soil structure was observed in the integrated crop-livestock system, in the layers 0-0.1 and 0.1-0.2 m. The systems under crop-livestock and pasture continuously cultivated favored a more biologically active soil environment, among the other agricultural systems. The visualization of soil attributes showed that crop-livestock integration is a promising strategy to develop sustainable production systems and that the period of two years of management is considered suitable for crop-pasture rotation.

Complete Genome Sequence of Burkholderia phenoliruptrix BR3459a (CLA1), a Heat-Tolerant, Nitrogen-Fixing Symbiont of Mimosa flocculosa

The genus Burkholderia represents a challenge to the fields of taxonomy and phylogeny and, especially, to the understanding of the contrasting roles as either opportunistic pathogens or bacteria with biotechnological potential. Few genomes of nonpathogenic strains, especially of diazotrophic symbiotic bacteria, have been sequenced to improve understanding of the genus. Here, we contribute with the complete genome sequence of Burkholderia phenoliruptrix strain BR3459a (CLA1), an effective diazotrophic symbiont of the leguminous tree Mimosa flocculosa Burkart, which is endemic to South America.

INOCULAÇÃO DO FEIJOEIRO COM RHIZOBIUM TROPICI ASSOCIADA À EXSUDATO DE MIMOSA FLOCCULOSA COM DIFERENTES DOSES DE NITROGÊNIO

The aim of this work was to evaluate the effect of the Rhizobium inoculation, associated with seed exudates of Mimosa flocculosa, under different rates of nitrogen fertilization was evaluated in bean crops following soybean (Glycine max L. Merril) and corn (Zea mays L.). The experimental design was randomized blocks with four replications, with treatments arranged in sub-divided parcels. The parcels were constituted of two summer crops preceding the common bean crop: soybean and corn. In the sub-parcels three treatments involving inoculation of the common bean seeds were considered: control treatment without inoculation; bean seeds inoculated with Rhizobium tropici, strains CIAT 899 and PRF 81, and the association of Rhizobium with the exudates of the Mimosa flocculosa seeds. The sub-subparcels received of four doses of nitrogen fertilization applied on covering: 0, 40, 80 and 120 kg ha-1 N. The inoculation of Rhizobium associated with the addition of exudates of Mimosa flocculosa seeds resulted in higher shoot dry weight. Besides that, the nitrogen fertilization, on the tested doses, reduced, in a linear way, the nodulation of the bean plant. It was also verified that corn as a preceding crop for bean has contributed to the increase of the weight of 100 grains, while the addition of combined N did not contribute to the improvement on the number of beans per plant, neither of the grain yield of bean plants, independent of the dose that was used.

Fauna invertebrada e atributos físicos e químicos do solo em sistemas de integração lavoura-pecuária

The objective of this work was to evaluate the effect of integrated crop-livestock (ICL) systems on the main groups of soil invertebrate macrofauna and the relationship of these organisms with soil physical and chemical attributes. The conventional system, integrated crop-livestock system, no-tillage system, continuously cultivated pasture, and natural fragments of Cerrado and of semi-deciduous forest were compared. The experiment was carried out in Dourados, MS, Brazil, on a Typic Hapludox soil, divided into strips. The highest density, richness, and diversity of families were found in the ICL system, under no-tillage, and in the continuously cultivated pasture. The conventional system caused greater reduction of the soil invertebrate community. The ICL system favors the maintenance of the invertebrate fauna diversity, the formation of stable aggregates, and soil fertility. The Sthaphylinidae family is a potential soil quality bioindicator, especially in the semi-deciduous forest and in the ICL system.

Macrofauna invertebrada do solo em sistema integrado de produção agropecuária no Cerrado

The objective of this work was to evaluate the density and diversity of soil invertebrate macrofauna in a crop-livestock rotation production system under no-tillage. The field experiment was performed in Dourados, Mato Grosso do Sul State, Brazil, on a Typic Hapludox soil, in parcels under a conventional monoculture system, a crop-livestock rotation system under no-tillage and continuous pasture, and a native vegetation fragment. The evaluations were conducted in January 2002, June 2002, January 2003 and July 2003, according to the method recommended by the Tropical Soil Biology and Fertility (TSBF) program. Systems with less anthropic interference showed greater abundance and richness of soil invertebrate macrofauna.

Frações lábeis e recalcitrantes da matéria orgânica em solos sob integração lavoura‑pecuária

The objective of this work was to evaluate the soil total organic carbon (TOC) and total nitrogen (TN) stocks, C and N in labile and recalcitrant fractions of the soil organic matter (SOM), and the C management index, in soils under integrated crop-livestock (ICL) system after four (ICL4) and eight years (ICL8) of settlement. For comparison purposes, other management systems were used: pasture and crop under no tillage (NT), besides native vegetation. The experiment was carried out in a completely randomized block design, with five replicates. The crop-livestock established in a period of eight years can reach a new steady state equivalent to the no-tillage with 23 years of implementation. There was accumulation in total organic carbon of 101.0 (ICL8) and 104.2 Mg ha -1 (NT), and N total stock of 5.5 (ICL8) and 5.8 Mg ha -1 (NT) in the 0-30 cm layer, as well as increase in the stock of labile and recalcitrant C and N fractions of SOM. For crop-livestock with eight years, the C management index of 88 was higher than other management systems, and not different from native vegetation (0-10 cm), however, it was similar to NT in the analysis of the entire profile (0-30 cm).

Populações de oligoquetos (Annelida: Oligochaeta) em um Latossolo Vermelho submetido a sistemas de uso do solo

This paper objective was to evaluate earthworm population dynamics in agricultural and livestock systems using as reference an area under native vegetation. The work was carried out in Dourados, MS, in a Typic Hapludox soil under conventional soil tillage (CT), no-tillage (NT), cropping/livestock integration (CLI), a continuous pasture (CP), and a natural system (NS). Samples were taken during summer and winter cropping seasons between 2000 and 2003. SPD, SILP, and PC systems benefited the development and establishment of earthworm population. NS system showed the largest earthworm population, being the majority of organisms from Enchytraeidae family. Among the systems, SPD also benefited the occurrence of organisms from Enchytraeidae family.

Lectin from Canavalia brasiliensis Seeds (ConBr) Is a Valuable Biotechnological Tool to Stimulate the Growth of Rhizobium tropici in Vitro

To study the interactions between a Rhizobium tropici strain and lectins isolated from the seeds of Canavalia ensiformis (ConA) and Canavalia brasiliensis (ConBr), a lectin fluorescence assay was performed. In addition, an experiment was designed to evaluate the effect of the two lectins on bacterial growth. Both lectins were found to bind to R. tropici cells, but the interactions were inhibited by D-mannose. Interestingly, only ConBr stimulated bacterial growth in proportion to the concentrations used (15.6–500 µg/mL), and the bacterial growth stimulation was inhibited by D-mannose as well. Structure/Function analyses by bioinformatics were carried out to evaluate the volume and carbohydrate recognition domain (CRD) configuration of ConA and ConBr. The difference of spatial arrangement and volume of CRD may indicate the variation between biological activities of both lectins. The results suggest that ConBr could be a promising tool for studies focusing on the interactions between rhizobia and host plants.