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Salt stress caused by sodic soils is an important constraint that impacts the production of crucial solanaceous vegetable crops globally. Halotolerant poly-extremophiles rhizobacteria can inhabit hostile environments like salinity, drought, etc. The present study was aimed to design a halotolerant micro-formulation using highly salt-tolerant bacterial strains previously isolated from salt-tolerant rice and wheat rhizosphere in sodic soil. Nine halotolerant isolates were examined for plant growth-promoting traits and biomass production in pot studies with sodic soil of pH 9.23 in tomato. Compatible, efficient isolates were aimed to be formulated into different consortia like PGPR-C1, PGPR-C2 and, PGPR-C3 for field evaluation in sodic soils of pH 9.14. Halotolerant rhizobacterial consortia (PGPR-C3) comprising Lysinibacillus spp. and Bacillus spp. were found to produce extracellular enzymes like amylase, protease, cellulase, and lipase, showing significantly enhanced vegetative parameters, yield and lycopene content of tomato hybrid NS585 under salt-stressed sodic soils. PGPR-C3 consortia also showed enhanced plant growth-promoting activities and halo tolerance like high Indole acetic acid production, 1-aminocyclopropane-1-carboxylic acid deaminase, and antioxidative enzyme activity over the uninoculated control. Further, inoculation with PGPR-C3 consortia resulted in the efficient exclusion of Na+ ions from the rhizosphere through increased absorption of K+. Results of the study reveal that inoculation with PGPR-C3 consortia could alleviate the salt stress and promotes the successful cultivation of tomato crop in sodic soils. It can be considered the best option for eco-friendly, sustainable cultivation of vegetables like a tomato in sodic soils with a high pH range of up to 9.14.

The implementation of sustainable agriculture encompasses practices enhancing the activity of beneficial soil microorganisms, able to modulate biogeochemical soil cycles and to affect soil fertility. Among them, arbuscular mycorrhizal fungi (AMF) establish symbioses with the roots of most food crops and play a key role in nutrient uptake and plant protection from biotic and abiotic stresses. Such beneficial services, encompassing improved crop performances, and soil resources availability, are the outcome of the synergistic action of AMF and the vast communities of mycorrhizospheric bacteria living strictly associated with their mycelium and spores, most of which showing plant growth promoting (PGP) activities, such as the ability to solubilize phosphate and produce siderophores and indole acetic acid (IAA). One of the strategies devised to exploit AMF benefits is represented by the inoculation of selected isolates, either as single species or in a mixture. Here, for the first time, the microbiota associated with a commercial AMF inoculum was identified and characterized, using a polyphasic approach, i.e., a combination of culture-dependent analyses and metagenomic sequencing. Overall, 276 bacterial genera were identified by Illumina high-throughput sequencing, belonging to 165 families, 107 orders, and 23 phyla, mostly represented by Proteobacteria and Bacteroidetes. The commercial inoculum harbored a rich culturable heterotrophic bacterial community, whose populations ranged from 2.5 to 6.1 × 106CFU/mL. The isolation of functional groups allowed the selection of 36 bacterial strains showing PGP activities. Among them, 14 strains showed strong IAA and/or siderophores production and were affiliated with Actinomycetales (Microbacterium trichotecenolyticum, Streptomyces deccanensis/scabiei), Bacillales (Bacillus litoralis, Bacillus megaterium), Enterobacteriales (Enterobacter), Rhizobiales (Rhizobium radiobacter). This work demonstrates for the first time that an AMF inoculum, obtained following industrial production processes, is home of a large and diverse community of bacteria with important functional PGP traits, possibly acting in synergy with AMF and providing additional services and benefits. Such bacteria, available in pure culture, could be utilized, individually and/or in multispecies consortia with AMF, as biofertilizers and bioenhancers in sustainable agroecosystems, aimed at minimizing the use of chemical fertilizers and pesticides, promoting primary production, and maintaining soil health and fertility.

O presente estudo objetivou avaliar a ocorrência de bactérias diazotróficas associadas ao sorgo, selecionar cultivares eficientes na associação com bactérias diazotróficas e identificar os isolados mais eficientes em fixar nitrogênio atmosférico (N²) e produzir ácido indol-acético (AIA). Utilizaram-se 14 cultivares de sorgo forrageiro em vasos, com dois níveis de N: 0 e 130kg ha-1 de N. A seleção de cultivares foi baseada na associação com bactérias diazotróficas e na eficiência de absorção de nitrogênio das cultivares. Para o isolamento das bactérias, foram utilizados diferentes meios de enriquecimento semi-sólido e, após o isolamento, foram quantificadas a produção de AIA e a quantidade de N² fixada pelos isolados. A ocorrência de bactérias diazotróficas foi constatada em todas as cultivares avaliados sendo que a distribuição das bactérias isoladas foi influenciada pelo genótipo da planta. Todos os isolados foram aptos em fixar N² e produzir AIA in vitro.The present study aimed to evaluate the occurrence of diazotrophic bacterial associated with sorghum plants, to select efficient sorghum cultivars associated with diazotrophic bacterial, as well as to identify isolates efficient on nitrogen fixation (N²) and indole acetic acid (IAA) production. Fourteen forage sorghum cultivars were cropped in jars under two levels of nitrogen fertilization: 0 and 130kg ha-1 of N. The selection of sorghum cultivars was based on the association with diazothophic bacterial and on the efficiency of nitrogen absorption. Semi-solid enrichment medium was used for the isolation of the diazotrophic bacterial. The occurrence of diazotrophics was verified in all cultivars of sorghum evaluated and, the distribution of the isolates was affected by the plant genotype. All the isolates were able to fix N² and to produce IAA in vitro.

O presente estudo objetivou avaliar a ocorrência de bactérias diazotróficas associadas ao sorgo, selecionar cultivares eficientes na associação com bactérias diazotróficas e identificar os isolados mais eficientes em fixar nitrogênio atmosférico (N2) e produzir ácido indol-acético (AIA). Utilizaram-se 14 cultivares de sorgo forrageiro em vasos, com dois níveis de N: 0 e 130kg ha-1 de N. A seleção de cultivares foi baseada na associação com bactérias diazotróficas e na eficiência de absorção de nitrogênio das cultivares. Para o isolamento das bactérias, foram utilizados diferentes meios de enriquecimento semi-sólido e, após o isolamento, foram quantificadas a produção de AIA e a quantidade de N2 fixada pelos isolados. A ocorrência de bactérias diazotróficas foi constatada em todas as cultivares avaliados sendo que a distribuição das bactérias isoladas foi influenciada pelo genótipo da planta. Todos os isolados foram aptos em fixar N2 e produzir AIA in vitro. The present study aimed to evaluate the occurrence of diazotrophic bacterial associated with sorghum plants, to select efficient sorghum cultivars associated with diazotrophic bacterial, as well as to identify isolates efficient on nitrogen fixation (N2) and indole acetic acid (IAA) production. Fourteen forage sorghum cultivars were cropped in jars under two levels of nitrogen fertilization: 0 and 130kg ha-1 of N. The selection of sorghum cultivars was based on the association with diazothophic bacterial and on the efficiency of nitrogen absorption. Semi-solid enrichment medium was used for the isolation of the diazotrophic bacterial. The occurrence of diazotrophics was verified in all cultivars of sorghum evaluated and, the distribution of the isolates was affected by the plant genotype. All the isolates were able to fix N2 and to produce IAA in vitro.