## 3 Discussion

Table 2: Identification of major chemical signals detected in mVOCs, based on GC–MS analysis and comparison with the NIST database, with acceptance of SI \(\geq\) 800.  
of the gene expression of peroxidase, catalase, nitrite reductase, and vegetative storage protein, whereas the HKT1 transporter pyrroline-5-carboxylate synthase and polyphenol oxidase were down-regulated [65]. In another study, the VOCs emitted by _Acaligenes faecalis_ promoted _A. thaliana_ grown under salt stress conditions by the regulation of the auxin and gibberellin pathways involved in the modulation of root and shoot growth and development [66], along with the regulation of ion transporters [67]. Moreover, the PGPR _Paraburdholderia phytofirmanus_ VOCs reduced the accumulation of sodium within leaf tissues. Similarly, 2R-3R-butanediol, produced the closure of the stomata, generating a decrease in water evaporation [68]. mVOCs from _Rahntella aquatilis_ JZ-GX1 ameliorated the salt stress effects on acacia seedlings by a decrease in malondialdehydehyde, superoxide anion and hydrogen peroxide content, and an increase in the proline level, superoxide dismutase, peroxidase and glutathione reductase activities [69]. mVOCs may also play an important role in bacteria through phytopathogenic fungi interaction. There are many reports where PGPR VOC blends have shown antifungal properties against a wide range of phytopathogenic fungi [70], although the mechanisms involved in such processes remain poorly understood. Recent studies have suggested that VOCs affect phytopathogens by modulating the activity of specific enzymes and altering motility and protein production, which subsequently influence growth, cell morphology and virulence factors [53]. VOCs from _Pseudomonas_ sp. have been shown to cause DNA damage to the sugarcane pathogen _Thielavopsis ethacetica_[71]. Structural damage on hyphae and down-regulation in the expression of virulence factors in _Ralstonia solanacearum_ are other mechanisms by which VOCs act [72]. In the present study, inhibition of _A. alternata_ and _S. rol/sii_ growth by mVOCs emitted by both bacterial strains was observed under control conditions (0 mM NaCl). In agreement with our results, it has been shown that some mVOCs produce the inhibition of the vital activity of fungi in the soil, thereby negatively affecting the germination and growth of fungi [73; 74]. [PERSON] et al. [75] also showed this effect, when two fungal strains _Rhizoctonia solani_ AG2.2 IIIB and _Fusarium culmorum_ PV were used against the _Pseudomonas donghunensis_ strain P482, with the same being reported for the _P. fluorescens_ ZX strain against _Pencilium italicum_[76]. However, in the present study, it was observed that the presence of stress did not limit the production of VOCs, but modified the biocontrol capacity. When PGPR SJ46 and SJ04 were grown under salt stress conditions, mVOCs only inhibited the mycelial growth of _A. alternata_, with mVOCs emitted under salt stress not affecting _S. rol/sii_ growth, suggesting that the fungi response to mVOCs is species-specific and depends on the concentrations of certain compounds rather than their composition, since we did not find any new compound in the headspace obtained from salt treatments. Moreover, we showed that SJ46 VOC emissions under salt stress conditions (75 or 100 mM NaCl) promoted greater _S. rol/sii_ mycelium growth in comparison with SJ46 VOC emissions at 0 mM NaCl (Figure 5). The above results suggest that the same mVOC blends may have different effects on the receptor organism, as in the case of the different fungi used in this study (_A. alternata_ and _S. rol/sii_). Similar results were observed by [PERSON] et al. [77], where the mVOCs produced by different avocado rhizobacteria belonging to the genus _Bacillus_ were able to suppress the growth of _Fusarium_ sp., but not all inhibited _Colletotrichum gloeosporoides_, and none reduced the diameter of the mycelial growth of _Phytophthora cinnamomi_. The mVOC profiles of the two _P.