## 2 Materials and Methods
### Mode of Action of VOCs on _B. cinerea_  
To determine the mode of action of VOCs on _B. cinerea_, the integrity of the membrane and wall cell and the generation of oxidative stress were analyzed.  
The integrity of the pragmatic membrane and the cell wall of _B. cinerea_ was determined using the SYTOX Green (Molecular Probes, Eugene, OR, USA) or Calcofluor White (Sigma-Aldrich, St Louis, MO, USA), respectively. The formation of reactive oxygen species (ROS) was evaluated using the dichloro-dihydro-fluorescein diacetate (DCFH-DA) (Santa Cruz, Biotechnology Inc, Dallas, TX, USA). For these assays, the same procedure as for spore germination was used.  
For the SYTOX Green stain, cultures were incubated at 22 \({}^{\circ}\)C for 6 h to allow the germination of the conidia. After this period, germinated conidia of _B. cinerea_ were exposed to VOCs as described above. The cultures were incubated at 22 \({}^{\circ}\)C for 6, 16, and 24 h under continuous agitation at 140 rpm. As a positive control, germinated conidia were incubated for 10 min with 70% _v/v_ ethanol. For the negative control, the same test was carried out, but using a PDA plate without inoculating with the endophytic yeast. After the incubation time, _B. cinerea_ hyphae adhered to glass were stained with SYTOX Green as described [27]  
For the Calcofluor White stain, the cultures were incubated at 22 \({}^{\circ}\)C for 16 and 24 h with agitation at 140 rpm. As a positive control, _B. cinerea_ was treated with hydrolytic enzymes from _Trichoderma harzianun_ (Sigma-Aldrich, St Louis, MO, USA) at 5 mg L\({}^{-1}\) (in 0.7 M KCl, buffer PBS pH 5.8) for 1 h at 20 \({}^{\circ}\)C. Additionally, for the negative control, the same test was carried out, but using a PDA plate without inoculating with the endophytic yeast. After the incubation time, _B. cinerea_ hyphae adhered to glass coverslips were stained with Calcofluor White as described in [27].  
To study the effect on the formation of reactive oxygen species, cultures were incubated at 22 \({}^{\circ}\)C with agitation at 140 rpm for 16 and 24 h. As a positive control, _B. cinerea_ was treated with 300 mM H\({}_{2}\)O\({}_{2}\) for 1 h at 20 \({}^{\circ}\)C. Additionally, a negative control was conducted, excluding the presence of the endophytic fungus. The samples were treated with 10 uM of DCFH-DA for 20 min. Subsequently, a washing procedure, similar to those described for the SYTOX Green assay was carried out. The fluorescence of _B. cinerea_ hyphae stained with DCFH-DA was visualized under an epifluorescence microscope at an excitation wavelength of 488 nm and an emission wavelength of 540 nm.  
Oxidative stress in the plasmatic membrane produced by Ec2 VOCs was determined by malondialdehydedehyde (MDA) formation as a marker of lipid peroxidation. For this purpose, the thiobarbituric acid reactive substances (TBARS) assay was carried out as in [PERSON] et al. [28] with some modifications. In total, 50 mg of fresh _B. cinerea_ mycelium treated with VOCsemitted by the endophyte Ec2 as mentioned, above were recovered and sonicated with 0.1% _w/v_ trichloroacetic acid (TCA). The samples were then centrifuged at 10,000\(\times\)\(g\) for 15 min at 4 \({}^{\circ}\)C. In total, 150 \(\upmu\)L of supernatant was added to 450 \(\upmu\)L of 0.5% _w/v_ thiobarbituric acid (TBA) in a 20% _w/v_ TCA solution. The solution was incubated at 95 \({}^{\circ}\)C for 20 min, then was cooled to room temperature, and centrifuged at 16,000\(\times\)\(g\) for 5 min. The absorbance of the supernatant was measured at 532 nm. MDA equivalents were determined using a molar extinction coefficient of 155 mM\({}^{-1}\) cm\({}^{-1}\), as described in [PERSON] et al. [29]. Results were expressed as MDA equivalents (nM g\({}^{-1}\) fresh weight). A negative control was conducted without incubation with the endophytic yeast.  
To determine the mode of action of VOCs on _B. cinerea_, three independent experiments were carried out, each one in triplicate.