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A growing body of evidence demonstrates the potential of various microbes to enhance plant productivity in cropping systems although their successful field application may be impaired by several biotic and abiotic constraints. In the present work, we aimed at developing multifunctional synthetic microbial consortia to be used in combination with suitable bioactive compounds for improving crop yield and quality. Plant growth-promoting microorganisms (PGPMs) with different functional attributes were identified by a bottom-up approach. A comprehensive literature survey on PGPMs associated with maize, wheat, potato and tomato, and on commercial formulations, was conducted by examining peer-reviewed scientific publications and results from relevant European projects. Metagenome fragment recruitments on genomes of potential PGPMs represented in databases were also performed to help identify plant growth-promoting (PGP) strains. Following evidence of their ability to coexist, isolated PGPMs were synthetically assembled into three different microbial consortia. Additionally, the effects of bioactive compounds on the growth of individually PGPMs were tested in starvation conditions. The different combination products based on microbial and non-microbial biostimulants (BS) appear worth considering for greenhouse and open field trials to select those potentially adoptable in sustainable agriculture.

A simple method is described for the determination of the ionic content of vegetable samples by ion chromatography with suppressed conductivity detection. Extracts of leaves of cucumber (Cucumis sativus), leaves and cotyledons of watermelon (Citrullus lanantus), cotyledons of zucchini (Cucurbitapepo), and leaves and roots of olive (Olea europaea) obtained at room temperature yielded chromatographic profiles with substantial differences in the relative contents of Cl-, NO3-, HPO4(2-) and SO4(2-) as well as of Na+, NH4+, K+, Mg2+ and Ca2+. Although NO3-, Cl- and K+ were common to each extracted sample and accounted for most of the ions present, two additional anion peaks (i.e. malate and oxalate) were detected. Among the vegetable tissues investigated, olive roots contained a considerable amount of oxalate (37 mg/g dry weight), while Na+, which is present in very low amount in extracted samples of leaves and cotyledons, represented ca. 30% of the cationic content of olive roots. In all the examined tissue extracts, K+ was the main cation (16-55 mg/g dry weight) and NO3-, Cl- and HPO4(2-) were the main inorganic anions.