Azospirillum spp. from native forage grasses in Brazilian Pantanal floodplain: biodiversity and plant growth promotion potential

Abstract

A sustainable alternative to improve yield and the nutritive value of forage is the use of plant growth-promoting bacteria (PGPB) that release nutrients, synthesize plant hormones and protect against phytopathogens (among other mechanisms). Azospirillum genus is considered an important PGPB, due to the beneficial effects observed when inoculated in several plants. The aim of this study was to evaluate the diversity of new Azospirillum isolates and select bacteria according to the plant growth promotion ability in three forage species from the Brazilian Pantanal floodplain: Axonopus purpusii, Hymenachne amplexicaulis and Mesosetum chaseae. The identification of bacterial isolates was performed using specific primers for Azospirillum in PCR reactions and partial sequencing of the 16S rRNA and nifH genes. The isolates were evaluated in vitro considering biological nitrogen fixation (BNF) and indole-3-acetic acid (IAA) production. Based on the results of BNF and IAA, selected isolates and two reference strains were tested by inoculation. At 31 days after planting the plant height, shoot dry matter, shoot protein content and root volume were evaluated. All isolates were able to fix nitrogen and produce IAA, with values ranging from 25.86 to 51.26 mg N mL and 107-1038 µmol L, respectively. The inoculation of H. amplexicaulis and A. purpusii increased root volume and shoot dry matter. There were positive effects of Azospirillum inoculation on Mesosetum chaseae regarding plant height, shoot dry matter and root volume. Isolates MAY1, MAY3 and MAY12 were considered promising for subsequent inoculation studies in field conditions.

Azospirillum brasilense INOCULATION AND MANAGEMENT OF FERTILIZER NITROGEN IN MAIZE

“…The nitrogen levels on inoculated plants with action combined with the diazotrophic bacteria are also related by other authors, which can be consequence of the growth promotion mechanisms, which can improve the capacity of the plants of absorbing nitrogen and fostering the productivity growth (DOBBELAERE et al, 2001). The results with the use of the strain MAY1 corroborates with this affirmation once it presents, according to Souza et al (2017) Abv8 strain, who obtained gains of productivity on the order of 17% and 9% respectively, with the use of the bacteria Azospirillum spp. in maize associated with fertilization.…”

“…inoculant containing the bacteria of the species A. brasiliense, strain MAY1 (with 2x10 8 cells/mL) isolated from the grass Hymenachene amplexicaulis which grows naturally on the sub-region of Nhecolândia Pantanal Sul Mato-grossense (SOUZA et al, 2017). This strain was used for presenting high production of indol acetic acid in vitro (1038,61 µM).…”

Azospirillum brasilense and macronutrients in the initial establishment of brachiaria

“…Studying three forages (Axonopus purpusii, Hymenachne amplexicaulis and Mesosetum chaseae) inoculated with Azospirillum, Souza et al (2017) report that the inoculation of A. purpusii, H. amplexicaulis resulted in higher root volume and higher aerial dry mass, and that the inoculation of M. chaseae reflected in higher plant height, dry mass and root volume. Potassium solubilizing bacteria used together with stone powder in U. brizantha cv.…”

Mitigation of Mombasa Grass ( Megathyrsus maximus ) Dependence on Nitrogen Fertilization as a Function of Inoculation with Azospirillum brasilense

“…The root mass of inoculated plants in the absence of N reached 96 % increment in comparison to non-inoculated plants, indicating the high efficiency of A. brasilense in promoting root growth of the plants, also justifying the higher forage production in the absence of N. In addition, increased root development allows a greater area of water and nutrient absorption, reflecting on biomass production, besides promoting tolerance to environmental stresses such as drought (Souza et al, 2017).…”