## 4 Discussion
Soil irrigation with 150 or 300 mM NaCl water solutions, in the case of quinoa seedlings (CC150 and CC300), had an opposite effect respect to maize; in fact, they even showed a superior growth on saline soils, probably because, as stated by [PERSON] et al. [39], \"the expression of salt stress-responsive genes, which are inducible in glycopytes, is, on the other hand, a salt tolerance trait in haplotypes, as precisely quinoa is.\"Since the abiotic stress, induced by high salt irrigation to the assayed crops, was relevant, we supposed that a similar stress has been applied also to the rhizosphere microbial community as selection pressure and, consequently, allowed us to isolate the highly NaCl-tolerant rhizo-bacterial strains. Many laboratories all around the world are isolating bacterial strains tolerant to NaCl, or salt in general. Halo-tolerant bacterial strains have been isolated from both balk and rhizosphere soils [40; 41; 42; 43], but also from endophyte bacterial communities [44; 45; 24]. Several of these bacterial strains have proven some plant growth capabilities such as, indole acetic acid (IAA) and siderophore synthesis, solubilization of phosphate, 1-aminocyclopropane-1-carboxylate (ACC) deaminase [45; 46; 24]. The bacterial strains we isolated from maize and quinoa rhizosphere showed very high tolerance to NaCl between 2.0 and 4.0 M as in the case of the strains QB13 (3.5 M--_Bacillus stratosphericus_ strain MPF-B2a) or MD6 (4.0 M--_Staphylococcus succinus_ strain JM40), demonstrating that selection we applied to the rhizosphere community of the assayed crops and vegetables, amended with compost, was extended for a long time and strong enough to select highly NaCl tolerant bacterial strains. Among 13 bacterial strains identified by 16S rDNA, we isolated 10 different species, suggesting the presence of a very heterogeneous bacterial community that populates the compost amended root soils of both maize and quinoa. Out of the 13 halo-tolerant strains, 9 were selected from quinoa rhizosphere, as well as the most represented bacterial genus, namely _Halomonas_. This observation would suggest that quinoa can establish and select a specific rhizosphere microbiome, enriched by compost, able to better tolerate high soil NaCl concentration when compared with that of maize. This consideration is supported also by the fact that all the assayed crop species had higher biomass when amended with compost and compared with the control (Group C), even when soils were irrigated with solutions containing high NaCl concentrations. All the halotolerant NaCl bacterial species, we selected, belong to species and genera well known to be resistant to salts and have been isolated from different and peculiar environments as in the case of: _Halomonas alkaliantarctica_, originally isolated from the saline lake Cape Russell in Antarctica in 2001. It is an alkalophilic moderately halophilic, exopolysaccharideacharide-producing bacterium [47]; _Halomonas titanicae_ isolated in 2010 from a sample of rustictic obtained from the RMS Titanic, collected during an oceanic expedition in 1991, for its peculiar characteristics it could also have the potential to be used in bioremediation to accelerate the decomposition of shipwks litterting the ocean and sea floor; [48]_Bacillus majorensis_, whose name suggests the place where it was collected and isolated, such as the Mojave Desert in US [49]. It belongs to the _Bacillus_ genus, in particular to the subgroup including _Bacillus amyliquefaciens_, _B. atrophaeus_, _B. licheniformis_, _Brevibacterium haltolerans_, _P. penillicanthus_, and _P. popilliae_, which have peculiar features such as: salt tolerance, resistance to metals and high temperatures, but also able to colonize the root vascular tissues and therefore considered as bacterial endophytes (_B. majorensis_) [50]. It is relevant that we isolated also other two species belonging to this subgroup of the genus _Bacillus_ as _B. licheniformis_ and _Brevibacterium_ spp (two strains).