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Sugarcane production in Brazil for the 2019/20 harvest is estimated at approximately 615 million tons. However, in the state of Rio Grande do Sul, it is estimated at only 42.5 thousand tons. It is assumed that the use of diazotrophic bacteria can contribute to the expansion of sugarcane cultivation in the state through increased productivity; hence, this study aimed to evaluate the effects of diazotrophs on the growth of sugarcane. The study was conducted using sugarcane varieties: RB867515, RB92579, RB966928, and RB975932 that were either treated with diazotrophic bacteria or left as a control. The application of diazotrophic bacteria resulted in increased leaf area and stem number in variety RB867515 (cane plant cultivation cycle), and an increase in the relative chlorophyll content of all the varieties of sugarcane except of RB92579. Furthermore, most varieties responded positively in terms of biomass, dry matter, total nitrogen, and soluble solids. These results suggest that the application of diazotrophs assists in the growth and development of sugarcane varieties in Rio Grande do Sul. [ABSTRACT FROM AUTHOR]

Aims: This study was performed to determine if the contribution of biological N2 fixation (BNF) associated with Brazilian sugarcane cultivars could be increased by the inoculation with N2-fixing bacteria. Methods: The field experiment was planted with two sugarcane cultivars, inoculated or not, with five N2-fixing bacteria. All plant tissues, including belowground, were harvested for determination of dry matter, N accumulation and 15N abundance at five occasions until 450 days after planting. Results: Inoculation significantly increased total N accumulation in the aerial tissue of cultivar RB867515 from 147 to 199 kg N ha−1 and cultivar RB92579 from 126 to 192 N kg ha−1. At final harvest 15N abundances of entire sugarcane plants compared to that of plant-available N indicated that BNF inputs were over 64%. Total N derived from BNF and the soil was increased by inoculation, by 50 and 17 kg N ha−1 and 36 and 67 kg N ha−1, for the two cultivars respectively. Conclusions: Without inoculation, the two sugarcane cultivars obtained over 65% of N from BNF. Inoculation with the five component inoculant increased N accumulation from soil and BNF but with little impact on the proportion of N derived from BNF. [ABSTRACT FROM AUTHOR]

Aims: We examined the influence of inoculation with five species/strains of diazotrophic bacteria on the modulation of two enzymes involved in the assimilation of N and on the soluble N fractions in the sugarcane varieties RB867515 (adapted for low fertility soils) and IACSP95-5000 (adapted for medium to high fertility soils) under high- (3 mM) and low (0.3 mM)-N conditions in hydroponic cultivation for 59 days. Methods: The sugarcane plants were produced in three steps to obtain the hydroponic cultivation: the supply of 3 mM N for 30 days (first harvest), N depletion for 72 h (second harvest), and cultivation in high- and low-N conditions over 26 days (final harvest). Inoculation was performed by immersion of the minisetts in a diluted solution of five diazotrophic bacteria. After the final harvest, plants were divided into roots and shoots to assess their dry weight and N, P, and K accumulation. Results: The variety played an important role in the interaction with diazotrophs, each showing distinct behavior in the activity of their N-assimilation enzymes. The nitrate reductase activity (NRa—EC 1.7.1.1) was increased in var. RB867515 by 26% in the shoots and by 48% in the roots after 72 h under N depletion, while var. IACSP95-5000 showed a reduced enzymatic activity in the roots (by 62%) but not in the shoots. Under high-N conditions, the inoculated IACSP95-5000 plants showed 31% higher glutamine synthetase activity (GSa—EC 6.31.2) compared with 19% in RB867515. Under low-N conditions, the GSas were 21% and 16% higher in the inoculated RB867515 and IACSP95-5000 plants, respectively, compared with that of the control. The content of nitrogen in the form of nitrate (N-nitrate) confirmed these varietal differences, but the soluble sugar content did not. Conclusions: The varieties utilized N sources differently, and inoculation modified the activity of two N-assimilation enzymes as well as the biomass accumulation, with the highest improvement seen in the low fertility-adapted variety RB867515; it showed a greater response to inoculation compared with that of the high fertility-adapted variety IACSP95-5000, with an increase in biomass and nutrient accumulation (N, P, K), especially when cultivated under low-N conditions. This suggests that the best response to inoculation with diazotrophs will be achieved using low fertility-adapted sugarcane varieties under low-N conditions. [ABSTRACT FROM AUTHOR]

Sugarcane is a crop of great economic, social, and environmental relevance in Brazil. The country is the largest sugar producer and the second largest bioethanol producer in the world. The goal of this study was to evaluate the efficiency of a sugarcane inoculant composed of five diazotrophic bacterial strains, as well as nitrogen fertilization of two sugarcane varieties. Two experiments were carried out on two varieties using an experimental design composed of complete randomized blocks in a factorial of two varieties and three treatments with four replicates. The treatments can be described as: inoculation with the consortium of five diazotrophic strains, or N fertilization with 120 kg ha−1, and one control treatment. The following parameters were then evaluated: stem yield, accumulation of total dry matter, nitrogen content, quality of the sugarcane juice, and15N natural abundance on flag-leaves. Inoculation and N fertilization on the Sapucaia plantation promoted increases of stem yield equivalent to 22.3 and 26.5 Mg ha−1in the RB867515 variety, in comparison to the control, respectively. Inoculation and N fertilizer used for the Coruripe plantation increased stem yield of 38.0 and 42.4 Mg ha−1, respectively, with the RB867515 variety, while RB72454 showed increases of 16.7 and 37.5 Mg ha−1, both compared to the control. Biological nitrogen fixation was not affected by the treatments, however, both treatments increased the total recoverable sugar yield. Benefits from inoculation appeared to promote plant growth due to the plant–bacteria interaction. [ABSTRACT FROM PUBLISHER]

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Summary Although some sugarcane cultivars may benefit substantially from biological nitrogen fixation (BNF), the responsible bacteria have been not identified yet. Here, we examined the active diazotrophic bacterial community in sugarcane roots from Africa and America by reverse transcription (RT)-PCR using broad-range nifH-specific primers. Denaturing gradient gel electrophoresis (DGGE) profiles obtained from sugarcane showed a low diversity at all sample locations with one phylotype amounting up to 100% of the nifH transcripts. This major phylotype has 93.9-99.6% DNA identity to the partial nifH sequence from a strain affiliated with Rhizobium rosettiformans. In addition, nifH transcripts of this phylotype were also detected in spruce roots sampled in Germany, where they made up 91% of nifH transcripts detected. In contrast, in control soil or shoot samples two distinct nifH transcript sequences distantly related to nifH from Sulfurospirillum multivorans or Bradyrhizobium elkanii, respectively, were predominant. These results suggest that R. rosettiformans is involved in root-associated nitrogen fixation with sugarcane and spruce, plants that do not form root-nodule symbioses. [ABSTRACT FROM AUTHOR]

It is well described that the beneficial interactions between plants and bacteria are genotype and site specific. Brazilian sugarcane varieties can obtain up to 70% of their nitrogen requirement from biological nitrogen fixation (BNF), and this contribution is related to the Brazilian breeding and selection processes, by example of the variety SP70-1143. In this study the effect of two inoculation mixtures containing diazotrophic bacteria in our earlier pot experiment was evaluated with two sugarcane varieties, a known responder, SP70-1143, and a newly selected variety, SP81-3250, to investigate the sugarcane genotype effect and the role of the mixtures. The sugarcane varieties SP70-1143 and SP81-3250 were grown under commercial field conditions at three sites with contrasting soil types: an Alfisol, an Oxisol and an Ultisol that means a low, medium and high natural fertility respectively. The stem yield and BNF contribution in response to bacterial inoculation were influenced by the strain combinations in the inoculum, the plant genotype, and the soil type and nitrogen fertilization, confirming the genetic and environmental influence in PGP-bacteria interactions. Inoculation effects on the BNF contribution and stem yield increased in the variety SP70-1143 grown in the Alfisol without nitrogen fertilization for three consecutive crops, and it was equivalent to the annual nitrogen fertilization. The plants grown in the Oxisol showed small increases in the productivity of the variety SP70-1143, and in the Ultisol the sugarcane plants presented even decreases in the stem productivity due to inoculation with diazotrophic bacteria mixtures. The results demonstrate the feasibility of the inoculation technology using diazotrophic bacteria in micropropagated sugarcane varieties grown in soils with low to medium levels of fertility. In addition, the results also indicated that specific plant – bacteria – environment combinations are needed to harness the full benefits of BNF. [ABSTRACT FROM AUTHOR]

The adoption of bioinputs in agriculture has aroused great interest in recent years and, in this scenario, the inoculation of crops with synthetic microbial communities (SynComs) has shown to be promising. In sugarcane crop, inoculation with nitrogen-fixing bacteria (NFB) in consortium with arbuscular mycorrhizal fungi (AMF) has shown positive results on plant development and nutrition. However, considering that the microbiota plays a fundamental role in the growth and health of the host plant, especially the endophytes, which are closely associated, few studies have explored the effects of SynCom inoculation on the endophytic microbiota of sugarcane. This study aimed to evaluate the impact of SynCom inoculation on the structure of the endophytic microbiota of sugarcane. The results of the analyses revealed that the microbiota diversity remained unchanged due to the inoculation treatment, while differences in microbial communities were found between the two evaluated commercial cultivars, RB867515 and RB92579, and between the two plant organs, roots and culms, under field conditions at the end of the first crop growth cycle (~360 days). Furthermore, microbes specifically detected in roots or culms present potential valuable applications in sugarcane cultivation in the future. Altogether, our data support that the inoculated microorganisms exerted their beneficial effects during the initial stages of plant development, which opens up space for new research with SynComs in these primordial stages of cane cropping. • Inoculation of a SynCom onto sugarcane does not alter its microbiota after 360 days. • There are differences in alpha diversity of bacteria between two commercial cultivars. • There are differences in beta diversity of bacteria and fungi between roots and stems. [ABSTRACT FROM AUTHOR]