## 2 Materials and Methods
### Analysis of the Fungicidal or Fungistatic Effect of VOCs  
The fungicidal or fungistatic effect of VOCs was analyzed using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazololium bromide (MTT) assay (Thermo Fisher Scientific Inc., Waltham, MA, USA). For this, a double Petri dish assay was carried out as mentioned above. The assay was carried out in _B. cinerea_ mycelium exposed to VOCs emitted by the endophyte Ec2. _B. cinerea_ mycelium without VOC exposure served as a negative control, while mycelium treated with 70% _v/v_ ethanol was used as a positive control. In total, 50 mg of mycelium of _B. cinerea_ were incubated with nine \(\upmu\)L of 5 mg mL\({}^{-1}\) of MTT reagent stock in 300 \(\upmu\)L of 100 mM buffer sodium phosphate pH 7.0 at 30 \({}^{\circ}\)C in the dark for 3 h at 140 rpm. Mycelium was then centrifuged for 10 min at 4000\(\times\)\(g\). The produced formazan in the mycelium was extracted with 500 \(\upmu\)L of acidified isopropanol. The solution was incubated for 30 min at room temperature, and centrifuged for 10 min at 4000\(\times\)\(g\). Finally, the absorbance of the supernatants was measured at 570 nm.  
To determine whether the VOCs emitted by the endophyte had a fungicidal or fungistatic effect, _B. cinerea_ mycelium exposed to VOCs using the double Petri dish assay was re-inoculated onto a fresh PDA medium. Radial mycelial growth of these treated samples was compared to a control consisting of mycelium not previously exposed to VOCs.  
The fungistatic effect of 2-phenylethylanol, the most abundant volatile compound emitted by the endophyte Ec2, was analyzed on _B. cinerea_ mycelium. For this, pieces of _B. cinerea_ mycelium were inoculated in the center of Petri dishes containing PDA and incubated for 48 h at 22 \({}^{\circ}\)C. After this initial incubation, the lids of the plates were replaced with base plates containing filter papers with different amounts of 2-phenylethylanol (Merck, Santiago, Chile). The concentrations of 2-phenylethylanol used in each treatment are shown in Table 1. The plates were sealed with Parafilm and incubated at 22 \({}^{\circ}\)C for an additional 48 h. A control treatment used filter paper without 2-phenylethylanol. After this second incubation period, the mycelial growth inhibition was determined using Formula (1), but _R_x represents the radial mycelial growth of _B. cinerea_ in the presence of 2-phenylethylanol. A log-probit analysis with linear regression was used to determine the concentration of 2-phenylethylanol that caused 50% inhibition of mycelial growth (IC\({}_{50}\)). Additionally, plugs of _B. cinerea_ mycelium treated and not treated with 2-phenylethylanol were re-inoculated in a fresh PDA medium. After 36 h of incubation at 22 \({}^{\circ}\)C, the mycelial growth was evaluated.  
\begin{table}
\begin{tabular}{c c c}
**Amount** & **Double Petri Dish Volume** & **Concentration** \\ **(\(\upmu\)L)** & **(mL)** & **(\(\upmu\)L mL\({}^{-1}\))** \\ \hline
0 & & 0.00 \\
5 & & 0.03 \\
15 & 160 & 0.09 \\
30 & & 0.19 \\
50 & & 0.31 \\ \end{tabular}
\end{table}
Table 1: Concentration conversion of 2-phenylethylanol.  
In these experiments, three independent experiments were performed, each one in triplicate.