Screening of plant growth promotion ability among bacteria isolated from field-grown sorghum under different managements in Brazilian drylands.

Sorghum [Sorghum bicolor (L.) Moench] is a multipurpose grass cultivated in drylands due to its adaptation to drought. However the characteristics of sorghum-associated bacteria are not known in the Brazilian drylands. The aim of this study was to isolate and evaluate the plant growth promotion potential bacteria from field-grown sorghum under two irrigation and manure application levels in a Brazilian semi-arid reagion. Sorghum was irrigated with 3 or 1 mm day-1 and fertilized or not with liquid goat manure. Bacteria were obtained from surface-disinfected roots applying two nitrogen-free semi-solid media. The bacteria were evaluated for the presence of nifH gene, 16S rRNA sequences, calcium-phosphate solubilization, production of auxins and siderophores and for sorghum growth promotion. We obtained 20 out of 24 positive bacteria for nifH. The isolates were classified as in six different genera. All isolates produced auxins "in vitro", six bacteria produced siderophores and three Enterobacteriaceae solubilized calcium-phosphate. At least ten bacteria resulted in the increased total N content in the sorghum shoots, comparable to fertilization with 50 mg N plant-1 week-1 and to inoculation with Azospirillum brasilense Ab-V5. Enterobacter sp. ESA 57 was the best sorghum plant-growth promoting bacteria isolated in this study.

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest

Abstract Erythrina velutina ("mulungu") is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of "mulungu" rhizobia are poorly understood. The aim of this study was to characterize "mulungu" rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45 °C to 0.51 mol L-1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

Phenotypic, genetic and symbiotic characterization of Erythrina velutina rhizobia from Caatinga dry forest.

Erythrina velutina ("mulungu") is a legume tree from Caatinga that associates with rhizobia but the diversity and symbiotic ability of "mulungu" rhizobia are poorly understood. The aim of this study was to characterize "mulungu" rhizobia from Caatinga. Bacteria were obteined from Serra Talhada and Caruaru in Caatinga under natural regeneration. The bacteria were evaluated to the amplification of nifH and nodC and to metabolic characteristics. Ten selected bacteria identified by 16S rRNA sequences. They were tested in vitro to NaCl and temperature tolerance, auxin production and calcium phosphate solubilization. The symbiotic ability were assessed in an greenhouse experiment. A total of 32 bacteria were obtained and 17 amplified both symbiotic genes. The bacteria showed a high variable metabolic profile. Bradyrhizobium (6), Rhizobium (3) and Paraburkholderia (1) were identified, differing from their geographic origin. The isolates grew up to 45°C to 0.51molL-1 of NaCl. Bacteria which produced more auxin in the medium with l-tryptophan and two Rhizobium and one Bradyrhizobium were phosphate solubilizers. All bacteria nodulated and ESA 90 (Rhizobium sp.) plus ESA 96 (Paraburkholderia sp.) were more efficient symbiotically. Diverse and efficient rhizobia inhabit the soils of Caatinga dry forests, with the bacterial differentiation by the sampling sites.

Mechanism and control of Genipa americana seed germination.

Genipa americana (Rubiaceae) is important for restoration of riparian forest in the Brazilian Cerrado. The objective was to characterize the mechanism and control of germination of G. americana to support uniform seedling production. Morphology and morphometrics of seeds, embryo and endosperm were assessed by light and scanning electron microscopy during germination. Imbibition and germination curves were generated and over the same time interval endosperm digestion and resistance were measured by puncture force analysis and activity assay of endo-ß-mannanase (EBM) in water and in abscisic acid (ABA). The gene encoding for EBM was partially cloned and its expression monitored by quantitative real-time-polymerase chain reaction. Embryos displayed growth prior to radicle protrusion. A two-phase increase in EBM activity coincided with the two stages of weakening of the micropylar endosperm. The second stage also coincided with growth of the embryo prior to radicle protrusion. Enzyme activity was initiated in the micropylar endosperm but spread to the lateral endosperm. ABA completely inhibited germination by inhibiting embryo growth, the second stage of weakening and expression of the EBM gene, but EBM activity was not significantly inhibited. This suggests that a specific isoform of the enzyme is involved in endosperm weakening. EBM may cause a general 'softening' of micropylar endosperm cell walls, allowing the embryo to puncture the endosperm as the driving force of the decrease in puncture force.