Brasilense Ab-V5 Research Articles

Seed size and <i>Azospirillum brasilense</i> Ab-V5 and Ab-V6 inoculation influences germination and early seedling vigor of <i>Acacia mearnsii</i>

Acacia mearnsii is an Australian native tree species commercially grown in Africa and South America that produces tannins and woodchips. Its seed size varies, which may impact the germination and initial growth of seedlings. In its turn, Azospirillum brasilense inoculation is known to improve the growth of several crops. However, there are few studies the effects of A. brasilense inoculation on the germination and initial growth of forestry species. The present study evaluated the influence of seed size and A. brasilense Ab-V5 and Ab-V6 inoculation on germination and initial growth of A. mearnsii. Small seeds reduced the mean germination time (MGT) by 5.2% and the time to 50% germination (T50) by 23.8% in comparison to large seeds. On the other hand, seedlings that originated from large seeds had a seedling vigor index (SVI) 18.6% higher than those that originated from small seeds. Azospirillum brasilense inoculation increased the germination percentage by 20.9%, germination speed by 91.8%, root length (RL) by 35.8%, and root fresh weight by 20.5%. Additionally, it decreased MGT by 8.2% and T50 by 37.6%. The combination of large seeds and A. brasilense inoculation increased RL by approximately 50% and SVI by 62.1%. Thus, the use of A. brasilense inoculation favors germination and seedling vigor in A. mearnsii, showing to be a promising strategy for obtaining more uniform seedlings in forest nurseries.

Thermal and salt stress effects on the survival of plant growth-promoting bacteria Azospirillum brasilense in inoculants for maize cultivation.

The plant growth-promoting bacteria (PGPB) Azospirillum brasilense is widely used as an inoculant for important grass crops, providing numerous benefits to the plants. However, one limitation to develop viable commercial inoculants is the control of PGPB survival, requiring strategies that guarantee their survival during handling and field application. The application of sublethal stress appears to be a promising strategy to increase bacterial cells tolerance to adverse environmental conditions since previous stress induces the activation of physiological protection in bacterial cell. In this work, we evaluated the effects of thermal and salt stresses on the survival of inoculant containing A. brasilense Ab-V5 and Ab-V6 strains and we monitored A. brasilense viability in inoculated maize roots after stress treatment of inoculant. Thermal stress application (> 35 °C) in isolated cultures for both strains, as well as salt stress [sodium chloride (NaCl) concentrations > 0.3 mol L-1], resulted in growth rate decline. The A. brasilense enumeration in maize roots obtained by propidium monoazide quantitative polymerase chain reaction (PMA-qPCR), for inoculated maize seedlings grown in vitro for 7 days, showed that there is an increased number of viable cells after the salt stress treatment, indicating that A. brasilense Ab-V5 and Ab-V6 strains are able to adapt to salt stress (0.3 mol L-1 NaCl) growth conditions. Azospirillum brasilense Ab-V5 and Ab-V6 strains had potential for osmoadaptation and salt stress, resulting in increased cell survival after inoculation in maize plants. © 2024 Society of Chemical Industry.

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.

Azospirillum brasilense AbV5/6 encapsulation in dual-crosslinked beads based on cationic starch

The main challenge of agriculture is feeding the growing population and at the same time providing environmental sustainability. Using Azospirillum brasilense as a biofertilizer has proved to be a promising solution. However, its prevalence in soil has not been efficient due to biotic and abiotic stresses. Thus, to overcome this drawback, we encapsulated the A. brasilense AbV5 and AbV6 strains in a dual-crosslinked bead based on cationic starch. The starch was previously modified with ethylenediamine by an alkylation approach. Then, the beads were obtained by a dripping technique, crosslinking sodium tripolyphosphate with a blend containing starch, cationic starch, and chitosan. The AbV5/6 strains were encapsulated into the hydrogel beads by a swelling diffusion method followed by desiccation. Plants treated with encapsulated AbV5/6 cells showed an increase in the root length by 19 %, shoot fresh weight by 17 %, and the content of chlorophyll b by 71 %. The encapsulation of AbV5/6 strains showed to keep A. brasilense viability for at least 60 days and efficiency to promote maize growth.

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.

Co-inoculation and inoculation methods of plant growth-promoting bacteria in wheat yield performance

Several studies have reported the beneficial effects of inoculation of Azospirillum brasilense in wheat, but only a few of them have related the co-inoculation of A. brasilense and Rhizobium sp. and the evaluation of different inoculation methods. This study aimed i) to verify the efficiency of plant growth-promoting bacteria (PGPB) in subtropical environments, ii) to verify the efficiency of co-inoculation of A. brasilense and Rhizobium sp., and iii) to verify the efficiency of the management of different inoculation methods in the wheat crop. The experiments were carried out in Londrina and Apucarana, State of Paraná, Brazil, under a complete randomized block design, with four replications and nine treatments: T1) absence of nitrogen (N) topdressing, T2) 30 kg ha−1 of N topdressing, T3) 60 kg ha−1 of N topdressing, T4) A. brasilense Ab-V5 in the seeds, T5) A. brasilense Ab-V5 in post-emergence, T6) A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 in the seeds, T7) A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 in post-emergence, T8) commercial inoculant (A. brasilense Ab-V5 + Ab-V6) in the seeds, and T9) commercial inoculant (A. brasilense Ab-V5 + Ab-V6) in post-emergence. The number of ears per linear meter, number of spikelets, number of grains per spikelet, number of grains per ear, thousand-grain weight, number of spikelets to ears ratio, leaf nitrogen content, and grain yield were evaluated. Leaf N content and yield components showed no alterations due to the inoculation and co-inoculation performed both in the seed and in the post-emergence of seedlings. Treatments T3, T7, and T9 showed the highest means of grain yield (2077.50, 1743.12, and 1660.62 kg ha−1, respectively), demonstrating that co-inoculation with A. brasilense Ab-V5 + Rhizobium sp. 53GRM1 and inoculation with A. brasilense Ab-V5 + Ab-V6, both in post-emergence of seedlings, have the potential to replace the topdressing nitrogen fertilization in wheat.

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.

Biomass Yield, Nitrogen Content and Uptake, And Nutritive Value of Alfalfa Co-Inoculated with Plant-Growth Promoting Bacteria

Alfalfa (Medicago sativa L.) has high forage yield potential, protein quality, palatability, and digestibility, and low seasonality. The aim of this study was to evaluate the effects of strains of Sinorhizobium meliloti and Azospirillum brasilense on the nutritive content, bromatological composition (crude protein [CP], neutral detergent fiber [NDF], acid detergent fiber [ADF], and in vitro digestibility of dry weight [IVDDW]), and shoot dry weight (SDW), relative chlorophyll index (RCI), number of tillers (NT), plant height (PH), and root dry weight (RDW) and volume (RV), of alfalfa grown in a Typic Ultisol. The experiment consisted of eight combinations of plant-growth promoting bacteria (PGPB). The treatments were as follows: T1:non-inoculated control without N-fertilizer (NI); T2: NI + N-fertilizer, and inoculated with T3: Sinorhizobium (=Ensifer) meliloti SEMIA 116 + N-fertilizer; T4: S. meliloti SEMIA 116 + A. brasilense Ab-V5 + Ab-V6 + N-fertilizer; T5: S. meliloti SEMIA 134 + N-fertilizer; T6: S. meliloti SEMIA 134 + co-inoculation + N-fertilizer; T7: S. meliloti SEMIA 135 + N-fertilizer; and T8: S. meliloti SEMIA 135 + co-inoculation + N-fertilizer. S. meliloti strains are used in commercial inoculants for the alfalfa, and A. brasilense for several non-legumes and legumes in Brazil. The experiment was performed for three successive cuts under greenhouse conditions. Application of N-fertilization increases the production cost, making alfalfa cultivation unviable. Inoculation with three strains of Sinorhizobium meliloti highly promoted alfalfa growth, considering several parameters, including PH, RCI, NT, SDW and RDW, nutritive value, and with an emphasis on RV, and total N content and total N accumulated in shoots and roots. No further increases were observed with the co-inoculation with the PGPB A. brasilense. Studies in field and greenhouse conditions are necessary to verify the benefits of the use of PGPB in the cultivation of alfalfa.

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.

Inoculation and co-inoculation of growth promoting rhizobacteria in irrigated rice plants

Aiming at obtaining high productivity and reduction of production costs, new techniques have been studied in rice crops, such as the use of plant growth promoting rhizobacteria (PGPR). The objective of this study was to evaluate the efficiency of inoculation and co-inoculation of rhizobia and Azospirillum brasilense in promoting the growth of irrigated rice plants cultivated in the field. Two experiments were conducted in the field, in the 2014/15 and 2015/16 crops, at the Rio Grande do Sul Rice Experiment Station. The experiment was composed of seven treatments, with two control treatments, without inoculation (81 kg ha-1 N and 135 kg ha-1 N, equivalent to 60% and 100%, respectively, of the recommended nitrogen dose). The other five treatments received only 60% of the N dose and were inoculated with the UFRGS Vp16 (Burkholderia sp.) and UFRGS Lc348 (Mesorhizobium sp.) Rhizobia, and with the commercial product containing the A. brasilense AbV5 and AbV6 strains. Inoculation and co-inoculation with PGPR may represent a viable alternative to reduce the amount of nitrogen fertilizers in rice crops.

The ammonium excreting Azospirillum brasilense strain HM053: a new alternative inoculant for maize

We evaluated the effect of Azospirillum brasilense strain HM053 inoculation on maize seeds, a spontaneous mutant that excrete ammonium and fix nitrogen constitutively. 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. 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. The new strain HM053 showed to be a great biofertilizer for maize seeds and a new alternative for a more sustainable agriculture.

Azospirillum brasilense promotes increases in growth and nitrogen use efficiency of maize genotypes.

The development of cultivars with an improved nitrogen use efficiency (NUE) together with the application of plant growth-promoting bacteria is considered one of the main strategies for reduction of fertilizers use. In this sense, this study: i) evaluated the effect of Azospirillum brasilense on the initial development of maize genotypes; ii) investigated the influence of A. brasilense inoculation on NUE under nitrogen deficit; and iii) sought for more NUE genotypes with higher responsiveness to A. brasilense inoculation. Twenty-seven maize genotypes were evaluated in three independent experiments. The first evaluated the initial development of maize genotypes with and without A. brasilense (strain Ab-V5) inoculation of seeds on germination paper in a growth chamber. The second and third experiments were carried out in a greenhouse using Leonard pots and pots with substrate, respectively, and the genotypes were evaluated at high nitrogen, low nitrogen and low nitrogen plus A. brasilense Ab-V5 inoculation. The inoculation of seeds with A. brasilense Ab-V5 intensified plant growth, improved biochemical traits and raised NUE under nitrogen deficit. The inoculation of seeds with A. brasilense can be considered an economically viable and environmentally sustainable strategy for maize cultivation.