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Plant growth-promoting bacteria (PGPB) are a broad group of microorganisms that offer a huge, unexplored potential. We assessed the genetic diversity of endophytic bacteria that were isolated from corn and wheat plants in 3 different types of soils: A1 (Red Argisol), A2 (Red Latosol) and A3 (Red Nitossol). Endophytic bacteria were isolated from seedlings using 7 solid culture media and were further analyzed by 16S gene sequencing. IAA (Indole-3-acetic acid) production and PSI (Phosphorus solubilization index) bacteria capacity were tested in a randomly scheme in triplicate. In vitro association was assayed with 6 randomly selected endophytic strains. The experiment design was arranged in a randomly scheme with 10 replications. In vivo assays were performed to evaluate plant growth promotion using a low-fertility soil in different inoculation and/or fertilization conditions. The experiment design was arranged in a factorial 3x4 scheme in triplicate. The following characteristics were evaluated in both experiments in triplicate: plant biomass, total nitrogen content (TN) and endophytic population. As results, a total of 136 isolates were collected, and from these isolates, 41 strains were sequenced and classified into 4 major phylogenetic categories. There was a 38-fold variation between the highest (Ensifer adhaerens) and the lowest (Agrobacterium larrymoorei) IAA producer, and only 14% of strains were high phosphate solubilizers. In vitro assays identified both positively (Burkholderia ambifaria) and negatively (Pantoea ananatis) associative strains. In vivo assays showed that plant genotype can limit or induce the endophytic microbiota and that plant microbiota are highly influenced by soil fertility.

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Growth promoting bacteria are a potential option for sustainable cultivation with lower costs, among them Burkholderia ambifaria, whose importance is mainly due to the endophytic root colonization capacity. The objective of this work was to evaluate the effect of the inoculation of growth promoting bacteria in corn plants, in vitro and in greenhouse, with different levels of nitrogen fertilization. The PIONEER® 30F53 YH maize genotype was inoculated with Burkholderia ambifaria, with 106 CFU per seed, in 12-liter polyethylene pots, filled with commercial substrate, prepared with the different nitrogen contents (N), resulting in treatments with different doses of fertilization, associated or not with bacterial inoculation. After 30 and 45 days, it was evaluated: growth promotion, epiphytic and endophytic population and nitrogen accumulation. In the in vitro experiment, inoculated seeds were cultured in test tubes containing culture medium with absence and presence of nitrogen, evaluated after 7 days. The data were submitted to analysis of variance and the means were compared by the Tukey test at 5% of probability and regression. Increased nitrogen doses in inoculated plants resulted in better morphological parameters at 45 days. In vitro bacterial inoculation, in vitro, influenced the accumulation of fresh weight of shoot, root growth and development of root hair. The endophytic potential and the accumulation of nitrogen were higher in the absence of nitrogen, but lower than the absence of bacteria and the presence of nitrogen.