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Strawberries (Fragaria × ananassa Duch.) are widely demanded by the consumers because they contain several bioactive compounds, mainly vitamin C and anthocyanins, which may be increased by biofertilization with some plant growth promoting bacteria. In this work we have analysed two bacterial strains, PEPV15 and PEPV16, from genera Phyllobacterium and Rhizobium, respectively, which under microcosms conditions were able to promote the strawberry growth, increasing the content of some bioactive compounds, such as vitamin C or organic acids. Here we have analysed the effect on bioactive compounds in strawberries from plants biofertilized with the strains PEPV15 and PEPV16 in field conditions. Under these conditions, the anthocyanin content was increased when plants were biofertilized with the strain PEPV15 and the pelargonidin-3-O-rutinoside content significantly increased. Besides, citric acid, vitamin C and epicatechin contents were significantly higher when either of the two strains was used as biofertilizer. Our results showed that the inoculation with Phyllobacterium and Rhizobium strains is a good agronomical practice, which improve the content of several bioactive compounds of strawberries increasing the beneficial effects on human health., (Copyright © 2018. Published by Elsevier Ltd.)

Hispaniola Island was the first stopover in the travels of Columbus between America and Spain, and played a crucial role in the exchange of Phaseolus vulgaris seeds and their endosymbionts. The analysis of recA and atpD genes from strains nodulating this legume in coastal and inner regions of Hispaniola Island showed that they were almost identical to those of the American strains CIAT 652, Ch24-10 and CNPAF512, which were initially named as Rhizobium etli and have been recently reclassified into Rhizobium phaseoli after the analysis of their genomes. Therefore, the species R. phaseoli is more abundant in America than previously thought, and since the proposal of the American origin of R. etli was based on the analysis of several strains that are currently known to be R. phaseoli, it can be concluded that both species have an American origin coevolving with their host in its distribution centres. The analysis of the symbiovar phaseoli nodC gene alleles carried by different species isolated in American and European countries suggested a Mesoamerican origin of the α allele and an Andean origin of the γ allele, which is supported by the dominance of this latter allele in Europe where mostly Andean cultivars of common beans have been traditionally cultivated., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Rhizobium spp. is a well-known microbial plant biostimulant in non-legume crops, but little is known about the mechanisms by which rhizobia enhance crop productivity under drought stress. This work analyzed the mechanisms involved in drought stress alleviation exerted by Rhizobium leguminosarum strains in wheat plants under water shortage conditions. Two (LBM1210 and LET4910) of the four R. leguminosarum strains significantly improved the growth parameters (fresh and dry aerial weight, FW and DW, respectively), chlorophyll content, and relative water content (RWC) compared to a non-inoculated control under water stress, providing values similar to or even higher for FW (+4%) and RWC (+2.3%) than the non-inoculated and non-stressed control. Some other biochemical parameters and gene expression explain the observed drought stress alleviation, namely the reduction of MDA, H2O2 (stronger when inoculating with LET4910), and ABA content (stronger when inoculating with LBM1210). In agreement with these results, inoculation with LET4910 downregulated DREB2 and CAT1 genes in plants under water deficiency and upregulated the CYP707A1 gene, while inoculation with LBM1210 strongly upregulated the CYP707A1 gene, which encodes an ABA catabolic enzyme. Conversely, from our results, ethylene metabolism did not seem to be involved in the alleviation of drought stress exerted by the two strains, as the expression of the CTR1 gene was very similar in all treatments and controls. The obtained results regarding the effect of the analyzed strains in alleviating drought stress are very relevant in the present situation of climate change, which negatively influences agricultural production.

The legume nodules are a rich source not only of rhizobia but also of endophytic bacteria exhibiting plant growth-promoting mechanisms with potential as plant biostimulants. In this work we analyzed the genomes of Phyllobacterium endophyticum PEPV15 and Rhizobium laguerreae PEPV16 strains, both isolated from Phaseolus vulgaris nodules. In silico analysis showed that the genomes of these two strains contain genes related to N-acyl-homoserine lactone (AHL) and cellulose biosynthesis, involved in quorum sensing and biofilm formation, which are essential for plant colonization. Several genes involved in plant growth promotion such as those related to phosphate solubilization, indole acetic acid production, siderophore biosynthesis and nitrogen fixation were also located in both genomes. When strains PEPV15 and PEPV16 were inoculated in lettuce and carrot in field assays, we found that both significantly increased the yield of lettuce shoots and carrot roots by more than 20% and 10%, respectively. The results of this work confirmed that the genome mining of genes involved in plant colonization and growth promotion is a good strategy for predicting the potential of bacterial strains as crops inoculants, opening new horizons for the selection of bacterial strains with which to design new, effective bacteria-based plant biostimulants.

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The legume nodules are a rich source not only of rhizobia but also of endophytic bacteria exhibiting plant growth-promoting mechanisms with potential as plant biostimulants. In this work we analyzed the genomes of Phyllobacterium endophyticum PEPV15 and Rhizobium laguerreae PEPV16 strains, both isolated from Phaseolus vulgaris nodules. In silico analysis showed that the genomes of these two strains contain genes related to N-acyl-homoserine lactone (AHL) and cellulose biosynthesis, involved in quorum sensing and biofilm formation, which are essential for plant colonization. Several genes involved in plant growth promotion such as those related to phosphate solubilization, indole acetic acid production, siderophore biosynthesis and nitrogen fixation were also located in both genomes. When strains PEPV15 and PEPV16 were inoculated in lettuce and carrot in field assays, we found that both significantly increased the yield of lettuce shoots and carrot roots by more than 20% and 10%, respectively. The results of this work confirmed that the genome mining of genes involved in plant colonization and growth promotion is a good strategy for predicting the potential of bacterial strains as crops inoculants, opening new horizons for the selection of bacterial strains with which to design new, effective bacteria-based plant biostimulants. [ABSTRACT FROM AUTHOR]

• Newly isolated Pseudomonas brassicacearum subsp. neoaurantiaca has an assortment of PGP actions. • Rhizobium + Pseudomonas inoculation improved common bean yield by 15 % compared with single rhizobia. • Both endophytes localise inside the nodules intracellular (Rhizobium) or intercellular (Pseudomonas). • Rhizobium + Pseudomonas produced a gross margin increase of 488 euro ha−1 compared with single rhizobia. Microbial inoculants are gaining prominence in technologically advanced agri-systems due to the need for alternatives to the most pollutant agricultural inputs. The objective of this work was to improve the agronomic performance of the rhizobial inoculants for common bean, based on the superior native strain Rlp-LCS0306 of Rhizobium leguminosarum bv. phaseoli (R), through co-inoculation with non-rhizobial partners, namely the autochthonous isolate RVPB2-2 from Pseudomonas brassicacearum subsp. neoaurantiaca (P) and the type strain of Azotobacter chroococcum. It has been reported that co-inoculation improves nodulation, nodule functions and plant growth, although there is a lack of field testing in technologically advanced agri-systems. This work bridges this gap. In the field trial which was carried out in two different environments, the consortium R + P was the most successful, because it increased the N 2 fixation by 51.7 kg ha−1 (87 %) and the yield by 1337 kg ha−1 (59 %), compared with the uninoculated and unfertilised control. In addition, the increased yield observed following inoculation with the above indicated consortium was 16.7 %, compared with the single rhizobia inoculation, and this increase was also superior to that observed with other consortia. The superiority of the R + P consortium could partially be explained because in this study, there was an increased tendency for improved nodule biomass and function following co-inoculation. While this increase was not deemed to be statistically significant, it is noteworthy that nodule biomass increased by 25 % in average and N-fixed by more than 20 %, which, in turn, could be explained by the indole-3-acetic acid (IAA) production and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity of the P strain. However, further delineation of the system is required in order to explain the yield improvement exerted by the consortium. Here, we observed, i) the strong plant growth-promoting potential displayed by the P strain; ii) the colonisation of the nodules by the P strain; and iii) the strategy of colonisation of complementary spaces inside the nodules by P (intercellular) and the rhizobia (intracellular), by confocal microscopy. [ABSTRACT FROM AUTHOR]