Azospirillum Brasilense Ab-V5 Research Articles

Meta-omics integration approach reveals the effect of soil native microbiome diversity in the performance of inoculant Azospirillum brasilense.

Plant growth promoting bacteria (PGPB) have been used as integrative inputs to minimize the use of chemical fertilizers. However, a holistic comprehension about PGPB-plant-microbiome interactions is still incipient. Furthermore, the interaction among PGPB and the holobiont (host-microbiome association) represent a new frontier to plant breeding programs. We aimed to characterize maize bulk soil and rhizosphere microbiomes in irradiated soil (IS) and a native soil (NS) microbial community gradient (dilution-to-extinction) with Azospirillum brasilense Ab-V5, a PGPB commercial inoculant. Our hypothesis was that plant growth promotion efficiency is a result of PGPB niche occupation and persistence according to the holobiont conditions. The effects of Ab-V5 and NS microbial communities were evaluated in microcosms by a combined approach of microbiomics (species-specific qPCR, 16S rRNA metataxonomics and metagenomics) and plant phenomics (conventional and high-throughput methods). Our results revealed a weak maize growth promoting effect of Ab-V5 inoculation in undiluted NS, contrasting the positive effects of NS dilutions 10-3, 10-6, 10-9 and IS with Ab-V5. Alpha diversity in NS + Ab-V5 soil samples was higher than in all other treatments in a time course of 25 days after sowing (DAS). At 15 DAS, alpha diversity indexes were different between NS and IS, but similar in all NS dilutions in rhizospheric samples. These differences were not persistent at 25 DAS, demonstrating a stabilization process in the rhizobiomes. In NS 10-3 +Ab-V5 and NS 10-6 Ab-V5, Ab-V5 persisted in the maize rhizosphere until 15 DAS in higher abundances compared to NS. In NS + Ab-V5, abundance of six taxa were positively correlated with response to (a)biotic stresses in plant-soil interface. Genes involved in bacterial metabolism of riboses and amino acids, and cresol degradation were abundant on NS 10-3 + Ab-V5, indicating that these pathways can contribute to plant growth promotion and might be a result of Ab-V5 performance as a microbial recruiter of beneficial functions to the plant. Our results demonstrated the effects of holobiont on Ab-V5 performance. The meta-omics integration supported by plant phenomics opens new perspectives to better understanding of inoculants-holobiont interaction and for developing better strategies for optimization in the use of microbial products.

Foliar Spray Inoculation with Plant Growth Promoting Bacteria Associated with Nitrogen Doses in Megathyrsus maximus cv. BRS Zuri

This study evaluated the combined effect of foliar spray inoculation with plant growth-promoting bacteria (PGPB) and nitrogen doses on the yield, development, and nutritive value of Megathyrsus maximus cv. BRS Zuri. The experimental design was randomized blocks with four replications, with repeated measures in time. Foliar inoculation of two bacteria (Azospirillum brasilense Ab-V5 (CNPSo 2083) and Ab-V6 (CNPSo 2084) and Pseudomonas fluorescens (CNPSo 2799)) and 40 and 80 kg ha−1 N (urea) rates, in addition to the control (without inoculation and N fertilization), were applied. In the rainy season, at the level of 40 kg ha−1 of N, inoculation of both A. brasilense and P. fluorescens increased, respectively, the tiller number by 33% and 25% (22 February), and the N accumulated in tissues by 42% and 25% (22 January), while in the previous year (21 February) the beneficial effects of both bacteria were observed in the percentage of leaf blade and in the true digestibility in vitro. When the foliar spray was inoculated with A. brasilense Ab-V5 and Ab-V6 and P. fluorescens CNPSo 2799, with 80 kg N ha−1, the root system of Zuri grass increased by 61% and 30%, respectively.

Effects of inoculation with plant growth-promoting rhizobacteria from the Brazilian Amazon on the bacterial community associated with maize in field

The objective of this study was to investigate the effects of the inoculation with the plant growth-promoting rhizobacteria Bacillus thuringiensis RZ2MS9 and Burkholderia ambifaria RZ2MS16, both from the Brazilian Amazon, on the bacterial community of the rhizobiome and leaves of maize grown in field. For comparison, we analysed the effects of inoculating Azospirillum brasilense Ab-V5, a strain that is commercialized as inoculant for maize, as well as the combinations RZ2MS16 + Ab-V5 and RZ2MS9 + Ab-V5. The treatment RZ2MS9 + Ab-V5 yielded the highest plant height and stalk diameter, which were significantly different from the non-inoculated control (p < 0.05). The core microbiome of maize was mainly composed of the bacterial classes Gammaproteobacteria, Betaproteobacteria, Actinobacteria, Alphaproteobacteria, Cytophagia, and Bacilli. Overall, the inoculation process had no effect either on the composition of the maize-associated bacterial community or on the total bacterial biomass. However, we detected significant differences in the richness and in the community structure among the plant niches analysed. Linear discriminant analysis identified that the class Actinobacteria, and the order Actinomycetales were enriched in leaf and root of plants treated with RZ2MS16 + Ab-V5 and in rhizosphere of plants treated with RZ2MS9 + Ab-V5. Functional analysis of the soil samples revealed significant differences in the abundance of predicted genes encoding proteins related to respiration and solubilization of Cu, Mg, and K among treatments. Furthermore, the NMDS ordination showed association between different functional gene categories and some plant traits. Our findings contribute to understanding the efficacy of microbial inoculants for maize in field conditions.

Meta-analysis of maize responses to Azospirillum brasilense inoculation in Brazil: Benefits and lessons to improve inoculation efficiency

The inoculation of maize with the plant-growth-promoting bacteria (PGPB) Azospirillum brasilense Ab-V5 and Ab-V6 strains has impressively increased in Brazil in the last decade. In the present study, we conducted a meta-analysis with 60 studies published between 2010 and 2021, comprising 103 field trials in 54 locations in Brazil, aiming to assess the benefits and factors that affect the efficiency of A. brasilense inoculation of maize. Results showed that bacteria inoculation increased 12.1% of root mass, 4.3% N leaf concentration, 5.4% grain yield, and 3.6% of N in grains. The analysis of cultivars, edaphoclimatic conditions, and others detected positive effects of inoculation on maize under all the study conditions and yield ranges. However, inoculation benefits were higher at yields ≤3000 kg/ha (+21%) than between 3000 and 12,000 kg/ha (+1.5% to +6.2%), and yield responses tend towards greater increases at lower N rates (≤ 50 kg/ha, +8%) that at higher ones (> 200 kg/ha, +3.8%). Seed inoculation was more efficient than inoculation via leaf spray, especially by applying solid (peat) inoculants (+9.5%) than liquid formulations (+5.5%). Leaf-spray inoculation showed positive effect on grain yield (+3.1%) only when performed at the initial vegetative growth stages (V2–V3). A. brasilense inoculation represents an important biotechnology tool to increase yields and nutritional value of maize crops under most agronomic and environmental tropical and subtropical conditions.

Bacillus thuringiensis RZ2MS9, a tropical plant growth-promoting rhizobacterium, colonizes maize endophytically and alters the plant's production of volatile organic compounds during co-inoculation with Azospirillum brasilense Ab-V5.

The beneficial features of Bacillus thuringiensis (Bt) are not limited to its role as an insecticide; it is also able to promote plant growth interacting with plants and other plant growth-promoting rhizobacterium (PGPR). The PGPR Bt strain RZ2MS9 is a multi-trait maize growth promoter. We obtained a stable mutant of RZ2MS9 labelled with green fluorescent protein (RZ2MS9-GFP). We demonstrated that the Bt RZ2MS9-GFP successfully colonizes maize's roots and leaves endophytically. We evaluated whether RZ2MS9 has an additive effect on plant growth promotion when co-inoculated with Azospirillum brasilense Ab-V5. The two strains combined enhanced maize's roots and shoots dry weight around 50% and 80%, respectively, when compared to the non-inoculated control. However, non-differences were observed comparing RZ2MS9 alone and when co-inoculated with Ab-V5, In addition, we used co-inoculation experiments in glass chambers to analyse the plant's volatile organic compounds (VOCs) production during the maize-RZ2MS9 and maize-RZ2MS9-Ab-V5 interaction. We found that the single and co-inoculation altered maize's VOCs emission profile, with an increase in the production of indoles in the co-inoculation. Collectively, these results increase our knowledge about the interaction between the Bt and maize, and provide a new possibility of combined application with the commercial inoculant A. brasilense Ab-V5.

Inoculation with plant growth-promoting bacteria and reduction of nitrogen fertilizer in herbage accumulation and nutritional value of Mavuno grass

Strategies that improve the use of nitrogen (N), by tropical forage grasses, can bring environmental and social gains. Thus, this study aimed to evaluate the forage productivity and the nutritional value (NV) of the hybrid Urochloa spp. cv. ´Mavuno`, under inoculation with plant growth-promoting bacteria (PGPB) and doses of N. The experiment was carried out in the field, for a period of 14 months, in a randomized block design, with nine treatments and four replications in plots of 9 m². Seed inoculations were tested with: Azospirillum brasilense Ab-V5 and Ab-V6 strains; Pseudomonas fluorescens CCTB 03 and co-inoculation with Rhizobium tropici CIAT 899 and A. brasilense Ab-V6, combined with 50 and 100 kg ha-1 of added mineral N; fertilization with N-mineral with these doses, without inoculation and the control treatment, without N and without inoculation. The bacteria were inoculated to the grass seeds. The forage was evaluated by determining the shoot dry weight yield (SDWY) and the levels of crude protein (CP), neutral detergent insoluble fiber (NDF), acid detergent insoluble fiber (ADF) and in vitro dry matter digestibility (IVDMD). The results were subjected to analysis of variance by the F test (p ≤ 0.05) and compared to each other by the Scott-Knott test at 5% probability. Inoculation with PGPB resulted in greater SDWY when associated with a dose of 50 kg ha-1 of N. In plants inoculated with A. brasilense Ab-V5 + Ab-V6 and P. fluorescens CCTB 03, associated with a dose of 50 kg ha-1 of N-mineral, SDWY was similar to that obtained with double the dose of N in the absence of inoculation. The inoculation with PGPB resulted in an increase in the NV of Mavuno grass, with emphasis on A. brasilense Ab-V5 + Ab-V6 and P. fluorescens CCTB 03, associated with the dose of 100 kg ha-1 of N-mineral that improved the nutritional value in all evaluated items. The inoculation with A. brasilense Ab-V5 + Ab-V6 was the most promising, followed by P. fluorescens CCTB 03, mainly in association with 50 kg ha-1 of N.

Initial development of upland rice plants inoculated with the MAY12 strain of Azospirillum spp.

ABSTRACT: The purpose of this study was to evaluate the contribution of the inoculation of the strain Azospirillum MAY12 to the development of rice plants of the cultivar BRS Esmeralda. A completely randomized experiment was performed in a greenhouse, with 8 treatments and 6 repetitions, namely, commercial inoculant (CI) containing strains of Azospirillum brasilense ABV5 and ABV6 (T1), MAY12 (T2), nitrogen control with 50 mg of N or full dose (T3), CI + 30% of N (percentage referring to full dose) (T4), CI + 60% N (T5), MAY12 + 30% N (T6), MAY12 + 60% N (T7) and absolute control (T8). There was a significant increase in the fresh and dry mass of the shoot and roots, height, root volume, and the number of tillers and leaves of plants with the MAY12 inoculation (with and without N added) compared to T8. Treatments containing MAY12 + N increased the total dry mass by ~920% compared to T8, matching the T3 yield. The inoculation of MAY12 in isolation was as efficient as the application of the full dose of N, resulting in an increase of ~115% in height and 373% in root volume of the plants compared to T8. The MAY12 strain demonstrated good performance in the development of the cultivar, which was comparable to the CI in the variables tested. Therefore, inoculation with the MAY12 strain is promising for the partial reduction of nitrogen fertilizers in upland rice cultivation.

Forage Mass, Tillering, Nutritive Value and Root System of Ruzigrass Inoculated with Plant Growth Promoting Bacteria Associated with Doses of N-Fertilizer

The aim of this study was evaluating the effect of the inoculation of plant growth promoting bacteria (PGPB) in forage mass, tillering, nutritive value and root system of ruzigrass (Urochloa ruziziensis (R. Germ. &amp; Evrard) Crins (syn. of Brachiaria ruziziensis) associated with doses of N-fertilizer. The bacteria inoculated were Azospirillum brasilense Ab-V5, Pseudomonas fluorescens CCTB03 and Pantoea ananatis AMG 521, plus the control treatment (non-inoculated), associated with doses of N-fertilizer (0, 50 and 100 kg N ha-1). The experiment was performed in a randomized block design, in a 4x3 factorial scheme, with four replicates, totaling 48 plots (12 m2). There were no effects of the PGPB and the use of N-fertilizer on the leaf blade, stem+sheath, forage mass, daily and yearly accumulation of forage mass. The PGPB did not have influence on the density of tillers. The doses of 50 and 100 kg of N ha-1 increased the amount of tillers. The AMG 521 strain associated with N-fertilizer provided heavier tillers. There was no effect of the PGPB on crude protein (CP), neutral detergent fiber (NDF), as well as acid detergent fiber (ADF), and in vitro digestibility of the dry matter (IVDDM). The use of 100 kg of N ha-1 contributed to an increase in CP and a decrease in NDF. The AMG 521 strain contributed to a smaller diameter of the root. Strains CCTB03 and AMG 521 demonstrated a smaller area, length and root density when associated with the dose of 50kg of N ha-1. In general, the PGPB were not efficient in promoting productive increments in ruzigrass.

Maize growth and yield promoting endophytes isolated into a legume root nodule by a cross-over approach

Rhizobia can colonize the roots of grasses in the Brazilian semiarid region; however, studies to isolate these bacteria for growth promotion of maize via unconventional isolation approaches have not been conducted. This study aimed to isolate, characterize (biochemically and molecularly) and assess the potential of cowpea nodulating/maize associated rhizobia for plant growth promotion. Extracts of surface-disinfected maize root were inoculated onto cowpea seeds in axenic conditions. Rhizobia were isolated and classified by sequencing of the 16 S rRNA and nodC genes, and recA and atpD were specifically assayed for Bradyrhizobium. The in vitro ability of rhizobia to produce auxin and siderophores, solubilize calcium phosphate, exhibit antagonism against the growth of the pathogen Fusarium verticillioides, and undergo endophytic colonization were evaluated. The ability of rhizobia to promote the growth of both potted cowpea and maize and to promote the growth and yield of maize under field conditions was also evaluated. Thirteen isolates were obtained, including six Rhizobium, four Agrobacterium, and three Bradyrhizobium isolates, which exhibited high genetic variability and low similarity with the type strains. All bacteria showed at least one plant growth promotion mechanism. Six bacteria stood out regarding the promotion of maize growth, and one bacterium showed the best performance in cowpea. The results of the field assay with maize indicated that Bradyrhizobium sp. ESA 114 and Rhizobium sp. ESA 116 induced the same maize grain yields as those observed in plants inoculated with the commercial strain of Azospirillum brasilense Ab-V5. Maize harbors a community of putative facultative endophytic rhizobia that are genetically diverse and have the potential to be used in inoculant production.

Root exudate supplemented inoculant of Azospirillum brasilense Ab-V5 is more effective in enhancing rhizosphere colonization and growth of maize

This study was aimed to evaluate inoculants of Azospirillum brasilense strain Ab-V5 supplemented with root exudates (collected from maize seedlings) for improving the inoculation response of maize, by stimulation of root colonization by the bacterium. Root exudates collected from seedlings of two commercial maize genotypes were evaluated, and their effects on seeds, seedling colonization and plant development under greenhouse conditions were addressed. Compared with seeds treated with water, seeds soaked with maize root exudate extract (MREE) increased mean bacterial count by three log-unity. Plantlets inoculated with MREE-supplemented inoculant suspensions showed 0.4 log-unity higher mean counts than those inoculated with non-supplemented bacterial suspension. The plant biomass for inoculants supplemented with MREE increased by 50% and the root area and number per plant increased by 19% when compared to non-supplemented bacterial suspensions. Photosynthetic physiological responses were also observed when the MREE inoculants were used, although these effects varied according to the plant genotype and MREE source. The results demonstrate that soluble compounds exuded by maize seedlings can increase the colonization of maize plants by A. brasilense Ab-V5 and suggest a strategy to improve the effectiveness of plant–PGPB associative systems by introducing chemoattractant molecules into inoculant formulations.

Morphogenetic and structural characteristics of Urochloa species under inoculation with plant-growth-promoting bacteria and nitrogen fertilisation

Ineffective management of pastures still constitutes the main problem in the Brazilian livestock industry, in which recovery of soil fertility is a determinant for soil restoration. In this context and in combination with the adoption of sustainable technologies, the use of plant-growth-promoting bacteria (PGPB) may represent an alternative to the use of chemical fertilisers that would reduce costs and environmental impacts. In this study, morphogenetic and structural characteristics were evaluated in three Urochloa (syn. Brachiaria) varieties. Urochloa is a genus that is present in the most degraded pastures in Brazil. The three varieties were inoculated with five PGPB (Azospirillum brasilense Ab-V5 and Ab-V6, Pseudomonas fluorescens CCTB 03 and ET76, and Pantoea ananatis AMG521) and treated with different doses of nitrogen (N) fertiliser (0, 50 and 100 kg N ha–1) in pots filled with sandy soil under greenhouse conditions. In general, for Marandu grass U. brizantha cvv. BRS Paiaguás and Xaraés, the best performances for leaf and stem elongation rates and number of basal tillers were obtained with strains CCTB 03 and AMG521. For U. ruziziensis, the best performance in the duration and rate of renewal of leaves and leaf senescence was observed with strains AMG521, Ab-V5 and Ab-V6. This result indicated the specificity of the effects of bacterial strains on different genotypes of Urochloa. Differences in the interactions between PGPB and N fertilisation were also verified. In U. brizantha, interaction effects were additive, whereas in U. ruziziensis, they were competitive. The results indicate the feasibility of inoculation of Urochloa with elite strains of PGPB that positively affect the production of forage biomass and allow reductions in N fertiliser usage.

Effect of Nitrogen Topdressing Fertilization and Inoculation of Seeds with Azospirillum brasilense on Corn Yield and Agronomic Characteristics

Biological nitrogen fixation and plant hormone synthesis promoted by Azospirillum spp. bacteria play a role in enhancing crop productivity and reducing losses. This may constitute a strategy to enhance crop productivity and reducing losses, thereby increasing nitrogen fertilization efficiency. This research aimed to evaluate the effects of Azospirillum brasilense Ab-V5 and Ab-V6 strain inoculation and nitrogen fertilization on the agronomic characteristics and productivity of two maize hybrids (Zea mays L.) AS 1572 and AG 9030. Experiments were carried out at Santa Maria, RS, Brazil in the 2013/2014 and 2014/2015 growing seasons using a 2 × 2 × 5 factorial arrangement to distribute two maize hybrids, inoculated, or not, with Azospirillum brasilense, and five nitrogen doses (0, 60, 120, 240, and 480 kg ha−1). Kernel yield, mass, and dimensions, as well as kernel number on the cobs, stalk diameter, plant height, ear insertion height, prolificacy, nitrogen use efficiency (NUE), and their correlations were measured. Compared to uninoculated plants, higher kernel yield (p &lt; 0.05) was observed for AS 1572 hybrid when inoculated with A. brasilense, with an increase of 0.978 Mg ha−1 or 10.95%. This effect was primarily due to the higher NUE rate and the increase (p &lt; 0.05) in the number of kernels per cob. The AG 9030 hybrid showed no response to inoculation. A. brasilense inoculation increased the NUE rate of the AS 1572 hybrid in the condition N zero dose at N 60 kg ha−1 dose. Nitrogen fertilization increased crop productivity, notably by raising kernel mass and other productivity components, but reduced the NUE rate. The maximum technical efficiency obtained for the AS 1572 hybrid was of 10.705 Mg ha−1 with a N dose of 342 kg ha−1, whereas the AG 9030 hybrid produced a maximum grain yield of 10.089 Mg ha−1 with a dose of 350 kg ha−1 of N. We conclude that the inoculation with A. brasilense increases NUE, maize grain yield, and agronomic characteristic in the AS 1572 hybrid.

Development of biodegradable coatings for maize seeds and their application for Azospirillum brasilense immobilization.

The objective of this study was to develop biodegradable coatings for agriculture crop seeds based on starch, gelatin, and polyvinyl alcohol (PVA). Developed materials were characterized according to their microstructures, barrier properties, influence on germination of maize seeds, and ability to sustain Azospirillum brasilense Ab-V5 viability in coated maize seeds. The coatings were obtained employing different proportions of starch, gelatin, and PVA, ranging from 0 to 3.0g/100g of each material, respectively. Samples formulated with the pure polymers showed the highest values of water absorption capacity, solubility, and water vapor permeability, and the ternary mixtures showed the lowest values. Single polymer formulations and the binary starch-gelatin mixture (CS50GL50) favored maize seeds germination compared to the uncoated maize seeds. In addition, seed coating obtained from CS50GL50 formulation resulted in A. brasilense Ab-V5 viability in coated seeds up to 15days after bacterial immobilization, being considered a promising low-cost, biodegradable, and renewable source material to be used in agriculture.

Screening of plant growth promotion ability among bacteria isolated from field-grown sorghum under different managements in Brazilian drylands.

Sorghum [Sorghum bicolor (L.) Moench] is a multipurpose grass cultivated in drylands due to its adaptation to drought. However the characteristics of sorghum-associated bacteria are not known in the Brazilian drylands. The aim of this study was to isolate and evaluate the plant growth promotion potential bacteria from field-grown sorghum under two irrigation and manure application levels in a Brazilian semi-arid reagion. Sorghum was irrigated with 3 or 1mm day-1 and fertilized or not with liquid goat manure. Bacteria were obtained from surface-disinfected roots applying two nitrogen-free semi-solid media. The bacteria were evaluated for the presence of nifH gene, 16S rRNA sequences, calcium-phosphate solubilization, production of auxins and siderophores and for sorghum growth promotion. We obtained 20 out of 24 positive bacteria for nifH. The isolates were classified as in six different genera. All isolates produced auxins "in vitro", six bacteria produced siderophores and three Enterobacteriaceae solubilized calcium-phosphate. At least ten bacteria resulted in the increased total N content in the sorghum shoots, comparable to fertilization with 50mg N plant-1 week-1 and to inoculation with Azospirillum brasilense Ab-V5. Enterobacter sp. ESA 57 was the best sorghum plant-growth promoting bacteria isolated in this study.

English

One of the most prominent strategies to increase maize grain yield with a higher benefit/cost ratio and a lower environmental impact is the inoculation of plant growth-promoting bacteria. Among other factors, the success of the interaction plant-microorganism depends on genetic traits, therefore, selection of plant genotypes compatible with this association is extremely important to the viability of this technology. This article presents an innovative study that investigates the interactions between Azospirillum brasilense Ab-V5 and 27 genotypes of maize, including 24 experimental hybrids from a partial diallel (denotated Hij as a result of the crosses among the parental inbred lines Li and the tester breeding lines Tj), the variety ST0509 from UEL and the commercial hybrids DKB390 and DKB390H from Monsanto. The plots consisted of treatments with or without inoculation in three replicates and the 27 maize genotypes were randomly distributed in the sub-plots. The inbred lines L2, L3, L6, L11, T2 and T3 present the highest general combining ability, producing the best hybrid combinations. The additive effects of genes are more important than the non-additive effects for all traits evaluated. The most promising experimental hybrids are H2 3’, H3 2’, H11 2’, H11 3’ and H12 3’. Significant effect for inoculum was not verified when performed at the seedling stage in the experimental conditions of this study. Key words: Zea mays L., Azospirillum brasilense, inoculation, biological nitrogen fixation, combining ability.

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.

English

In order to optimize the use of nitrogen (N), the aim of this work was to evaluate the efficiency of foliar application of Azospirillum brasilense Ab-V5 strain, as regards the productivity of wheat plantations combined with different N doses. The experiments were carried out in four municipalities in Minas Gerais (Brazil) under randomized block design with four replications. Forty percent of the N dose was applied at planting time and 60% as topdressing at tillering stage of the crop. Azospirillum brasilense was applied as foliar spray at a dose of 500 ml/ha. The treatments consisted of: (1) Control-without N or Ab-V5; (2) 50% of the N recommended; (3) 100% of the N; (4) Application of Ab-V5 strain; (5) 50% of N and Ab-V5 strain; (6) 100% of N and Ab-V5 strain; (7) 100% of N and seed inoculation with a commercial product (Master Fix). For all the locations, productivity increased with application of 100% of N recommended and foliar spray containing A. brasilense compared to the treatment that had only 100% of N recommended. &nbsp; Key words: Foliar spray, nitrogen fertilization, diazotrophic bacteria, Triticum aestivum L.

Agronomical Performance of Upland Rice Cultivars Inoculated with Azospirillum brasilense Depends on the Plant Genotype

Plant growth–promoting bacteria may play an important role on rice development; however, its interaction with different genotypes is still uncertain. This work aimed to assess the effect of inoculation of Azospirillum brasilense AbV5 strain on the agronomical performance of different rice cultivars under field conditions during two consecutive years and to determine the response of rice cultivars to indole-acetic acid (IAA) rates under in vitro conditions using for both conditions a randomized block design. Field experiments evaluated the productivity components and grain yield of inoculated and noninoculated cultivars and in vitro assays monitored the plantlet growth under different IAA rates. Field experiments showed that the general average grain yield of rice cultivars inoculated with A. brasilense AbV5 strain was significantly greater. Fifty percent of the evaluated cultivars had statistically significant increase in yield varying from 40 to 108 percent upon inoculation with A. brasilense AbV5 strain, while 35 percent showed no significant change in yield (−6 to −28 percent). In vitro assays showed rate- and cultivar-dependent responses of upland rice to exogenous IAA. These results show a cultivar-dependent response of rice to inoculation with A. brasilense AbV5 strain, which can be related with IAA production by AbV5 strain.