Nadja Maria Horta de Sá

Random amplified polymorphic DNA analysis of effective Rhizobium sp. associated with beans cultivated in brazilian cerrado soils

Efficient bean nodulating Rhizobium strains, isolated from different Brazilian cerrado soils, were characterized by RAPD. This study showed great genetic heterogeneity among R. tropici and R. leguminosarum bv. phaseoli strains and allowed the constitution of genetic clusters, besides indicating the most suitable primers for this characterization. The groups of genetically distinct strains can be used in competitiveness studies to select appropriate Rhizobium strains for bean inoculation in cerrado soils.

Decomposition of Arachis pintoi and Hyparrhenia rufa litters in monoculture and intercropped systems under lowland soil

Tropical grasslands under lowland soils are generally underutilized and the litter of forage legumes may be used to recover these degraded pastures. The objective of this work was to study the dynamics of litter decomposition of Arachis pintoi (pinto peanut), Hyparrhenia rufa (thatching grass) and a mixture of both species in a lowland soil. These treatments were analyzed in three areas: grass monoculture, legume monoculture and legume intercropped with the grass during the dry and wet seasons. Litter bags containing the legume, grass or a mixture of both species were incubated to estimate the decomposition rate and microorganism colonization. Decomposition constants (K) and litter half-lives (T1/2) were estimated by an exponential model whereas number of microorganisms in specific media were determined by plate dilution. The decomposition rate, release of nutrients and microorganisms number, especially bacteria, increased when pinto peanut was added to thatching grass, influenced by favorable lignin/N and C/N ratios in legume litter. When pinto peanut litter was incubated in the grass plots, 50% N and P was released within about 135 days in the dry season and in the wet season, the equivalent release occurred within 20 days. These results indicate that A. pintoi has a great potential for nutrient recycling via litter and can be used to recover degraded areas.

Characterization of rhizobia that nodulate Arachis pintoi by RAPD analysis

The genetic relationships of 85 Arachis pintoi nodulating Rhizobium strains were determined using the random amplified polymorphic DNA (RAPD) methods. The analysis included 75 strains isolated from Cerrado soils and 10 other ones of different origins. The results indicated that there is a high level of similarity between these strains and that geographic distribution may affect their phylogenetic relationship. In addition, the results allowed the selection of the most suitable primers for characterisation of these Rhizobium strains which will be useful for implementation of competitiveness studies in Cerrado soils.

Variability of isolated colonies in bean nodulating Rhizobium strains before and after exposure to high temperature

Irregular response to bean plants to Rhizobium inoculation has been attributed to among other factors, low competitive ability, low N2 fixation efficiency and genetic instability of the symbiont. This genetic instability caused by high rates of genomic rearrangements and/or plasmid deletions can be accentuated by high temperatures. This fact may limit the utilization of these strains as inoculants, especially in tropical soils. In this study, the variability of isolated colonies derived from effective R. leguminosarum bv. phaseoli (SLP1.3 and BR 10.026) and R tropici (SLA2.2 and BR322) strains was evaluated before and after exposure to high temperatures (four consecutive thermal shocks at 45oC). This evaluation involved plant dry matter analysis of inoculated plants and genotypic (plasmid profile and genomic patterns via RAPD) analysis of the Rhizobium strains. The results evidenced that high temperature improve the natural performance variability especially between isolated colonies from R. leguminosarum bv. phaseoli strains. The plasmid profile of isolated colonies from R. tropici strains were identical regardless of temperature treatment whereas isolated colonies from R. leguminosarum bv. phaseoli alterations were detected especially after the thermal treatment. The genomic patterns generated by AP-PCR showed more alterations and genetic variation in isolated colonies from R. leguminosarum bv. phaseoli strains indicating that R. tropici strains are more stable and lower affected by high temperature.

DECOMPOSITION, DYNAMIC OF INORGANIC ELEMENTS AND MICROBIAL COLONIZATION OF ARARIBÁ (Centrolobium tomentosum Guill. ex Benth) LEAVES ON LATOSOLS OF BRAZILIAN ATLANTIC FOREST

Se estan cultivando arboles de leguminosas para establecer unidades de restauracion en el ecosistema del bosque tropical atlantico de Brasil. El exito del establecimiento depende del crecimiento, productividad de las plantas, y de la tasa de descomposicion de las hojas. El objetivo de este estudio fue investigar la descomposicion de las hojas de arariba (Centrolobium tomentosum Guill. ex. Benth), en dos sitios. El Sitio 1 era una plantacion experimental de la especie nativa C. tomentosum, inoculado con rhizobios y hongos de la micorriza, y el Sitio 2 era una area con una plantacion de eucalipto (Eucalyptus grandis W. Hill ex Maiden). Las hojas caidas de C. tomentosum fueron incubadas durante 120, 240 y 360 dias en ambos sitios. La velocidad de descomposicion y la dinamica de mineralization de la materia organica y de los nutrientes K, Mg y Ca fue modificada por el efecto del sitio. La masa restante y la concentracion de nutrientes fueron mas bajas en el Sitio 2 que en el Sitio 1. La inmovilizacion del N y P ocurrio ocho meses despues de la incubacion en el Sitio 2 y cuatro meses en el Sitio 1. La colonizacion microbiana fue hecha por hongos en el Sitio 2, mientras que en el Sitio 1 fue por baterias. La alta concentracion de Cu, Mn y Zn en el Sitio 2 no tuvo en correlacion con los niveles de metales en los residuos. La concentracion de Cu y Mn en los residuos aumentaron en los dos sitios. El cambio de plantas de eucalipto a arboles de C. tomentosum modifico la biota del suelo y favorecio a las bacterias en comparacion a la poblacion de hongos.

Genomic heterogeneity within bean nodulating Rhizobium strains isolated from cerrado soils

Abstract Isolates of Rhizobium nodulating Phaseolus vulgaris L. sampled from cerrado soils of different regions, were characterized by PCR amplification of genomic DNA using different primers. These data were used to determine the pairwise genetic distances among R. tropici and R. leguminosarum bv. phaseoli strains. The amounts of genetic variation within R. tropici were from 0 to 48% and within R. leguminosarum bv. phaseoli from 5 to 39% indicating a high degree of genetic diversity in this indigenous population.

Effect of plant species and mycorrhizal inoculation on soil phosphate-solubilizing microorganisms in semi-arid Brazil: Growth promotion effect of rhizospheric phosphate-solubilizing microorganisms on Eucalyptus camaldulensis

The Jaiba Project is an irrigation enterprise in the north of the state of Minas Gerais and its native vegetation is a dry deciduous forest called woody Caatinga. Two experimental areas (1.5 ha/site) were established in a degraded area using native species intercropped with Eucalyptus camaldulensis in three blocks at random. In each experimental area six plots, randomly distributed in each of the three blocks were cultivated as follows: In area A: (1) Platymenia reticulata Benth (2) P. reticulata inoculated with Rhizobia and spores of Arbuscular Mycorrhizal Fungi (AMF) (3) Eucalyptus camaldulensis Dehnh, (4) Eucalyptus camaldulensis + AMF (5) P. reticulata + Eucalyptus camaldulensis + Tabebuia sp. (6) P. reticulata. (Rhizobia + AMF) + Eucalyptus camaldulensis (AMF) + Tabebuia sp. In the other area plots were cultivated as follows: (1) Schinopsis brasiliensis Engl (2) Schinopis brasiliensis + AMF (3) Eucalyptus camaldulensis (4) Eucalyptus camaldulensis + AMF (5) Schinopis brasiliensis + Myracrodruon urundeuva Fr. Allen + Eucalyptus camaldulensis (6) Schinopis brasiliensis (AMF) + Eucalyptus camaldulensis (AMF) + Myracroduon urundeuva. Soil samples were taken in the root zone of each cultivated plant and analyzed in relation to the number of phosphate solubilizing microorganisms (PSM) and AMF spores. The results showed that the number of PSM and MF spores was significantly higher in the inoculated Eucalyptus rhizosphere, when compared to the native species and also to the non-inoculated Eucalyptus plants. The treatment where PSM and AMF populations were increased the plants also showed greatest height and diameter growth and it was not related to soil phosphatase activity. The growth promotion effect of PSM and AMF was confirmed under greenhouse conditions where the double inoculation improved the dry matter production and phosphorus content. Double inoculation of PSM and MF was recommended to Eucalyptus plants cultivated in semiarid land.