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The co-inoculation of Bradyrhizobium with other non-bradyrhizobial strains was already assessed on cowpea, but the co-inoculation of two Bradyrhizobium strains was not tested up to now. This study aimed to evaluate the cowpea growth, N accumulation, and Bradyrhizobium competitiveness of the elite strain B. pachyrhizi BR 3262 when co-inoculated with other efficient Bradyrhizobium from the Brazilian semiarid region. Three potted-plant experiments were carried out. In the first assay, 35 efficient Bradyrhizobium isolates obtained from the semiarid region of Brazil were co-inoculated with the elite strains B. pachyrhizi BR 3262. The experiment was conducted in gnotobiotic conditions. The plant growth, nodulation, N nutritional variables, and nodular occupation were assessed. Under gnotobiotic and non-sterile soil conditions, ten selected bacteria plus the elite strain B. yuanmingense BR 3267 were used at the second and third experiments, respectively. The cowpea was inoculated with the 11 bacteria individually or co-inoculated with BR 3262. The plant growth and N nutritional variables were assessed. A double-layer medium spot method experiment was conducted to evaluate the interaction among the co-inoculated strains in standard and diluted YMA media. The co-inoculation treatments showed the best efficiency when compared to the treatments inoculated solely with BR 3262. This strain occupied a low amount of cowpea nodules ranging from 5 to 67.5%. The treatments with lower BR 3262 nodule occupancy showed the best results for the shoot nitrogen accumulation. The culture experiment showed that four bacteria inhibited the growth of BR 3262. In contrast, seven strains from the soils of Brazilian semiarid region were benefited by the previous inoculation of this strain. In the second and third experiments, the results indicated that all 11 co-inoculated treatments were more efficient than the single inoculation, proofing the best performance of the dual inoculation of Bradyrhizobium on cowpea., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© King Abdulaziz City for Science and Technology 2020.)

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 1 mm 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 50 mg 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.

Drought is one of the environmental factors that most affects peanut cultivation in semi-arid regions, resulting in economic losses to growers. However, growth promoting bacteria are able to reduce water deficit damage in some plant species. In this context, this study aimed to evaluate the interaction of Bradyrhizobium strains reducing water stress effects on peanut genotypes by antioxidant enzymes activities, leaf gas exchanges and vegetative growth, as well as to determine the taxonomic positioning of strain ESA 123. The 16S rRNA gene of ESA 123 was amplified by PCR and sequenced by dideoxy Sanger sequencing method. An experiment was performed in greenhouse with three peanut genotypes (BRS Havana, CNPA 76 AM and 2012-4), two Bradyrhizobium strains (SEMIA 6144 and ESA 123), a mineral source of N and an absolute control (without N) under two water regimes (with and without irrigation). Seeds of peanut were sown and the plants were grown until 30 days after emergence. On the 20th day, the water deficit plants group had their irrigation suspended for 10 days. At in silico analyzes, ESA 123 presented 98.97% similarity with the type strain of B. kavangense. Leaf gas exchange was affected by water deficit; as well as alteration of antioxidant activities and reduction of vegetative growth variables. However, some plants inoculated with SEMIA 6144 and ESA 123 strains presented lower reductions and increment of some evaluated variables, mainly the ones inoculated with the ESA 123 strain, Bradyrhizobium sp. from the semi-arid region of Northeast Brazil. This data suggests beneficial effects of the peanut-Bradyrhizobium interaction in a water stress condition, specially with the ESA 123 strain.

A sustainable alternative to improve yield and the nutritive value of forage is the use of plant growth-promoting bacteria (PGPB) that release nutrients, synthesize plant hormones and protect against phytopathogens (among other mechanisms). Azospirillum genus is considered an important PGPB, due to the beneficial effects observed when inoculated in several plants. The aim of this study was to evaluate the diversity of new Azospirillum isolates and select bacteria according to the plant growth promotion ability in three forage species from the Brazilian Pantanal floodplain: Axonopus purpusii, Hymenachne amplexicaulis and Mesosetum chaseae. The identification of bacterial isolates was performed using specific primers for Azospirillum in PCR reactions and partial sequencing of the 16S rRNA and nifH genes. The isolates were evaluated in vitro considering biological nitrogen fixation (BNF) and indole-3-acetic acid (IAA) production. Based on the results of BNF and IAA, selected isolates and two reference strains were tested by inoculation. At 31 days after planting the plant height, shoot dry matter, shoot protein content and root volume were evaluated. All isolates were able to fix nitrogen and produce IAA, with values ranging from 25.86 to 51.26 mg N mL -1 and 107-1038 µmol L -1 , respectively. The inoculation of H. amplexicaulis and A. purpusii increased root volume and shoot dry matter. There were positive effects of Azospirillum inoculation on Mesosetum chaseae regarding plant height, shoot dry matter and root volume. Isolates MAY1, MAY3 and MAY12 were considered promising for subsequent inoculation studies in field conditions.