No abstract

Some forage species, such as pangolão grass (Digitaria eriantha Steud. cv. Survenola), are resilient in tropical semiarid regions. A possible reason for this is the presence of endophytic and rhizospheric microorganisms. Thus, this study evaluated the diversity of associative bacteria in pangolão grass. Bacteria associated with the roots, culm, leaves, and rhizospheric soil were isolated and characterized in three municipalities of Pernambuco, Brazil. An initial phenotypic characterization was followed by a genotypic assessment by based repetitive extragenic palindromic-polymerase chain reaction (BOX-PCR) and partial sequencing of the 16S rRNA gene. We obtained 325 phenotypically-characterized isolates grouped into 243 strains with 100% similarity by BOX-PCR. The most diverse sampling environment was Araripina, and all factors affected bacterial diversity. There were 135 groups with 90% similarity, that were represented by a single strain each for sequencing. Among the sequenced strains, 118 showed 96.84-99.9% similarity with previously described strains, whereas 17 could not be identified. The following 18 genera were identified from three phyla, five classes, seven orders, and 13 families: Achromobacter,

The search for sustainable agriculture has increased interest in using endophytic bacteria to reduce fertilizer use and increase stress resilience. Stress-adapted plants are a potential source of these bacteria. Some species of these plants have not yet been evaluated for this, such as pangolão grass, from which we considered endophytic bacteria as potential plant growth promoters. Bacteria from the root, colm, leaves, and rhizospheric soil were isolated, and 132 strains were evaluated for their in vitro biological nitrogen fixation, IAA and siderophores production, and phosphate solubilization. Each mechanism was also assessed under low N availability, water stress, and low-solubility Fe and P sources in maize greenhouse experiments. All strains synthesized IAA; 63 grew on N-free media, 114 synthesized siderophores, and 46 solubilized P, while 19 presented all four mechanisms. Overall, these strains had better performance than commercial inoculant in all experiments. Still, in vitro responses were not good predictors of in vivo effects, which indicates that the former should not be used for strain selection, since this could lead to not testing strains with good plant growth promotion potential. Their heterologous growth promotion in maize reinforces the potential of stress-adapted plant species as potential sources of strains for inoculants.

N deficiency is one of the significant causes of tropical pasture degradation, and including legumes may be a sustainable strategy to prevent pasture degradation in tropical environments. The objective of this study was to investigate the use of forage peanut (Arachis pintoi), butterfly pea (Clitoria ternatea), calopo (Calopogonium mucunoides) and stylosanthes (Stylosanthes sp.) intercropped with signal grass to determine soil biomass and microorganismal activity in a tropical subhumid zone. Soil sampling was performed at the legume rows and, three meters away from them and in the soil of pastures with single signal grass with or without an application of N-fertilizer, two years after legume implantation and during the dry and rainy seasons. The estimate of carbon and nitrogen of microbial biomass, C-CO2 emission, and soil metabolic quotient of each legume were compared between the dry and rainy seasons, at two distances and with both single signal grass treatments. Although the rainy season decreased soil basal respiration in all treatments, forage peanut (~332 mg kg -1 ), and butterfly pea (~280 mg kg -1 ) showed pronounced soil microorganismal biomass, surpassing 27% and 14% the estimate for single signal grass not fertilized, respectively. The soil microorganisms with forage peanuts and stylosanthes also emitted more C-CO2 (~1.0 mg kg −1 h −1 ) in the dry season, indicating an effective microorganismal activity in these soils, mainly due to the absence of disturbances, as noted in the low metabolic quotients in both climatic seasons (less than 1%).