Odair José Andrade Pais dos Santos

Composition and activity of endophytic bacterial communities in field-grown maize plants inoculated with Azospirillum brasilense

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 N-fertilizers and plant inoculation did not have an additive effect and actually tended to decrease crop productivity.

Maize Inoculation with Azospirillum brasilense Ab-V5 Cells Enriched with Exopolysaccharides and Polyhydroxybutyrate Results in High Productivity under Low N Fertilizer Input

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.

Plant growth-promoting bacteria associated with nitrogen fertilization at topdressing in popcorn agronomic performance

The use of plant growth-promoting bacteria is a promising alternative with low environmental impact to increase the efficiency of use of chemical fertilizers, ensuring high yield with better cost-effective ratio. In maize crops, several studies have demonstrated an increased yield when Azospirillum-based inoculants are used. In the case of popcorn, there are no available studies related to use of inoculation and its response on yield parameters. Thus, the aim of this study was to evaluate the field performance of popcorn when inoculated with the commercial product Masterfix L (A. brasilense Ab-V5 and A. brasilense Ab-V6) and the non-commercial inoculant UEL (A. brasilense Ab-V5 + Rhizobium sp. 53GRM1) associated with nitrogen fertilization. The trials were conducted in Londrina and Maringa, Parana State, Brazil, in a randomized block design with four replications, in a split plot design with the inoculation treatments located in the plots (uninoculated, Masterfix L, and UEL) and the different N rates located in the subplots where ammonium sulphate was applied in the topdressing at the V6 stage (0, 50, 100, and 150 kg∙ha–1). 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.

Invasion ecology applied to inoculation of plant growth promoting bacteria through a novel SIMPER-PCA approach

AimsPlant growth promoting bacteria (PGPB) have been used on crops for years, but inoculants that are efficient in some locations may not be efficient in others. Here, we applied classical invasion ecology theory to PGPB inoculation in order to identify patterns that can be used to predict plant growth promoting (PGP) efficiency. The hypotheses that the inoculant that causes most impact will be the most efficient PGPB, and that the most invasible locations would have higher PGP efficiency, were tested. We also aim to present our statistical approach to analyze SIMPER results.MethodsUsing next generation sequencing targeting the 16S rDNA gene in metagenomics samples, we analyzed samples of pre-planting bulk soil and rhizosphere of inoculated maize plants. Bacterial communities of inoculated plants were compared to the non-inoculated controls, in order to estimate the inoculant invasion impact. Crop yield was compared to different indexes, and a novel data exploration approach was employed.ResultsThe most efficient inoculant was not the most invasive, and a nutrient per diversity ratio was unable to predict inoculant efficiency or invasion impact. However, the efficient inoculation treatment presented an enrichment of specific pre-planting taxa.ConclusionsInvasion ecology frameworks could not anticipate field results of inoculated plants. Nonetheless, our data exploration approach, which is explained in detail, can be useful to raise new hypothesis and improve the visualization of dissimilarity data.

Physiological, biochemical and morphoagronomic characterization of drought-tolerant and drought-sensitive bean genotypes under water stress

Water deficit is one of the main factors that reduce grain yield. A better understanding of the mechanisms related to this abiotic stress is a key aspect to design and act upon drought tolerance improvement in crop plants. Therefore, the major objective of this study was to investigate four common bean genotypes for drought tolerance and to establish their tolerance mechanisms. The experiment was carried out in a greenhouse, using the completely randomized design in a factorial arrangement (2 × 4), composed by 2 water conditions (well-watered and water deficit) and 4 cultivars, with six replicates per treatment. The four cultivars, two drought-sensitive (IAC Tybatã and BRS Pontal) and two drought-tolerant (IAPAR 81 and BAT 477), were evaluated for some physiological, biochemical and morphoagronomic traits. Drought promoted physiological and metabolic changes in the plants, reflecting on the morphoagronomic traits. Under water deficit, the genotype IAPAR 81 stood out from the others in terms of physiological characters, however, it presented a low efficiency concerning biochemical activities and a significant reduction in the morphoagronomic characters. The cultivar BAT 477 demonstrated to be drought-adapted presenting more efficient biochemical and morphoagronomic adaptions and the genotype BRS Pontal obtained morphoagronomic values similar to BAT 477, thus it may be classified as moderately tolerant to drought.

The influence of topdressing nitrogen on Azospirillum spp. inoculation in maize crops through meta-analysis

Bragantia, Campinas, v. 77, n. 3, p.493-500, 2018 ABSTRACT: The Azospirillum is considered one of the most studied plant growth promoter genus. These bacteria are capable of promoting plant growth through several factors. However, the effect of Azospirillum spp. associated to nitrogen fertilization on maize grain yield has brought about controversial results. Thus, the objective of this study was to verify the influence of topdressing nitrogen on the effect of Azospirillum spp. inoculation on maize crops through meta-analysis. Data were collected from articles published in scientific journals, obtained from the Web of Science®, Scopus® and Google Scholar® databases. The bibliographic review included only articles with direct comparisons between maize yield in the presence and absence of Azospirillum spp. under field conditions in Brazil. The meta-analysis SOIL AND PLANT NUTRITION Article