Although Azospirillum strains used in commercial inoculant formulations presents diazotrophic activity, it has been reported that their ability to produce phytohormones plays a pivotal role in plant growth-promotion, leading to a general recommendation of its use in association with regular N-fertilizer doses. In addition, a high variability in the effectiveness of Azospirillum inoculants is still reported under field conditions, contributing to the adoption of the inoculation technology as an additional management practice rather than its use as an alternative practice to the use of chemical inputs in agriculture. To investigate whether the content of stress-resistance biopolymers would improve the viability and performance of Azospirillum inoculants when used as substitute of N-fertilizers, biomass of A. brasilense strain Ab-V5 enriched in exopolysaccharides (EPS) and polyhydroxybutirate (PHB) was produced using a new culture medium developed by factorial mixture design, and the effectiveness of resulting inoculants was evaluated under field conditions. The culture medium formulation extended the log phase of A. brasilense cultures, which presented higher cell counts and increased EPS and PHB contents than observed in the cultures grown in the OAB medium used as control. An inoculation trial with maize conducted under greenhouse conditions and using the biopolymers-enriched Ab-V5 cells demonstrated the importance of EPS and PHB to the long term bacterial viability in soil and to the effectiveness of inoculation. The effectiveness of liquid and peat inoculants prepared with Ab-V5 cells enriched with EPS and PHB was also evaluated under field conditions, using maize as target crop along different seasons, with the inoculants applied directly over seeds or at topdressing under limiting levels of N-fertilization. No additive effect on yield resulted from inoculation under high N fertilizer input, while inoculated plants grown under 80% reduction in N fertilizer showed yields at levels compared to fully fertilized plants, regardless the inoculation method. The presented data highlights the feasibility to partially substitute the N-fertilizer demand in non-legume crops using high-quality inoculant formulations, prepared with diazotrophic bacteria enriched with stress-resistance biopolymers that confer increased viability an effectiveness to the bacterial cells.

The variance analysis showed significant effects (p < 0.05) of inoculation (Londrina environment) and N rates (both environments) only for grain yield. There was no inoculation effect in the grain yield when inoculants were applied together with N-fertilization at topdressing. In the absence of N-fertilization at topdressing, the inoculants Masterfix L. and UEL promoted higher grain yield as compared to the uninoculated plants, with resulting increases of 13.21 and 26.61% in yield, respectively.

Aims We evaluated the effect of Azospirillum brasilense strain HM053 inoculation on maize seeds, a spontaneous mutant that excrete ammonium and fix nitrogen constitutively. Methods Maize was grown with different nitrogen (urea) concentration and inoculated with A. brasilense Ab-V5 (Brazilian commercial strain) or HM053 strain in four field experiments, in three regions of Parana State, Southern Brazil. We evaluated yield components, nutrient content on leaves and grains and productivity during the crop cycle. Results Inoculation with A. brasilense strain Ab-V5 and HM053 associated with base fertilization (30 kg ha −1 N) improved crop yield in all trials. Ab-V5 increased production between 2.2 to 10.4%, or 178.0 to 759.9 kg ha −1 , respectively. HM053, by itself, increased production between 4.7 to 29%, or 460.5 to 1769.3 kg ha −1 , respectively. Conclusion The new strain HM053 showed to be a great biofertilizer for maize seeds and a new alternative for a more sustainable agriculture.

The application of agricultural practices in which non-leguminous plants are inoculated with growth-promoting diazotrophic bacteria is gaining importance worldwide. Nevertheless, an efficient strategy for using this inoculation technology is still lacking, and a better comprehension of the environmental factors that influence a plant's ability to support its associative bacterial community is indispensable to achieving standardized inoculation responses. To address the effects of nitrogen (N)-fertilization on the diversity of both the total and metabolically active endophytic bacterial communities of field-grown maize plants, we extracted total DNA and RNA from maize plants inoculated with Azospirillum brasilense strain Ab-V5 that were growing in Oxisol and treated with regular and low levels of N-fertilizers (RN and LN, respectively). Four clonal libraries were constructed and sequenced and the dominant populations analyzed. Partial description of the bacterial diversity indicated that plants receiving RN-and LN-treatments can maintain bacterial communities with similar diversity indexes for the total endophytic bacterial community, although the communities of Novosphingobium and Methylobacterium were unevenly distributed. Fertilization management had a stronger effect on the dominant populations of the metabolically active bacterial community, and 16S rRNA gene libraries from RN plants suggested a lower diversity of such populations in comparison with libraries from LN plants. The agronomic parameters obtained at the end of the crop season indicated that the inoculation treatment was efficient in promoting plant growth. However, the combination of regular treatments with Nfertilizers and plant inoculation did not have an additive effect and actually tended to decrease crop productivity.

The extrusion technology of blends formed by compounds with different physicochemical properties often results in new materials that present properties distinctive from its original individual constituents. Here, we report the use of melt extrusion of blends made from low-cost materials to produce a biodegradable foam suitable for use as an inoculant carrier of plant growth-promoting bacteria (PGPB). Six formulations were prepared with variable proportions of the raw materials; the resulting physicochemical and structural properties are described, as well as formulation performance in the maintenance of bacterial viability during 120 days of storage. Differences in blend composition influenced foam density, porosity, expansion index, and water absorption. Additionally, differences in the capability of sustaining bacterial viability for long periods of time were more related to the foam composition than to the resulting physicochemical characteristics. Microscopic analyses showed that the inoculant bacteria had firmly attached to the extruded material by forming biofilms. Inoculation assays using maize plants demonstrated that the bacteria attached to the extruded foams could survive in the soil for up to 10 days before maize sowing, without diminishing its ability to promote plant growth. The results presented demonstrate the viability of the new matrix as a biotechnological material for bacterial delivery not only in agriculture but also in other biotechnological applications, according to the selected bacterial strains.