## 3 Results
### Volatile Compounds Produced during the Interaction of _A. pullulans_-_C. acutatum_  
Among the two endophytes tested, _A. pullulans_ showed the greatest biocontrol potential against _C. acutatum_. The results from the dual culture of _A. pullulans_-_C. acutatum_ show that the endophyte inhibits the growth of the pathogen before mycelial contact and that none of the isolates were able to overgrow the other (data not shown). Thus, it is likely that this inhibitory effect was due to diffusible and/or volatile compounds with antimicrobial activity produced by _A. pullulans_. Therefore, during the in vivo interaction between _A. pullulans_ and _C. acutatum_, the production of VOCs after 2, 8 and 16 days of olive inoculation with the pathogen was studied. These sampling times were selected based on results from the bioassay that showed changes in the inhibitory effect of _A. pullulans_ over anthracose progression with time: 2 days (no inhibition), 8 days (moderate inhibition with statistical significance) and 16 days (maximal inhibition). Overall, a total of 38 compounds were detected, 37 of which were putatively identified by comparison to the NIST library of mass spectra (Table 1). The identified compounds belong to seven different chemical classes (Table S1). Alcohols, aldehydes and ketones were the most diversified chemical classes, with 14, 8 and 7 different compounds, respectively (Table S1), while the most abundant ones were alcohols followed by alkanes, accounting for 62% and 17% of the total VOC abundance, respectively (Figure S1). Figure 4: Sporulation (**a**) and spore germination (**b**) of _Colletotrichum acutatum_ in the presence of the endophytes _Aureobusidium pullulans_ (Ap + Ca) and _Sarocladium summerbellii_ (Ss + Ca) and in control (_C. acutatum_—Ca control), in olive bioassays, after 21 days of pathogen inoculation. Bars with different lowercase letters indicate significant differences (\(p<0.05\), \(n=5\)). \begin{table}
\begin{tabular}{l l l r r r r r r r r r r r} \hline \hline \multicolumn{1}{c}{**N**} & \multicolumn{1}{c}{**Compound**} & \multicolumn{1}{c}{**A. Pullinature**} & \multicolumn{1}{c}{**A. Pullinature C. Academia**} & \multicolumn{1}{c}{**C. Academia**} & \multicolumn{1}{c}{**C. Academia**} & \multicolumn{1}{c}{**Toven**} & \\ \cline{2-13}
**N** & **Compound** & \multicolumn{1}{c}{**2. Days**} & \multicolumn{1}{c}{**10. Days**} & \multicolumn{1}{c}{**2. Days**} & \multicolumn{1}{c}{**3. Days**} & \multicolumn{1}{c}{**5. Days**} & \multicolumn{1}{c}{**10. Days**} & \multicolumn{1}{c}{**2. Days**} & \multicolumn{1}{c}{**8. Days**} & \multicolumn{1}{c}{**10. Days**} & \multicolumn{1}{c}{**2. Days**} & \multicolumn{1}{c}{**5. Days**} & \multicolumn{1}{c}{**10. Days**} \\ \hline
1 & 2.4408+1-spanned & - & - & 12.2 \(\pm\) 4.02 & 58.8 \(\pm\) 0.90 & 7.6 \(\pm\)  
The emitted VOCs by the inoculated olives were qualitatively and semi-quantitatively different among the four treatments (Table 1; Figure S2a), with the type of treatment accounting for 13% of the total VOC variance (PERMANOVA, \(p<0.001\); Table S2). Overall, olives inoculated with C. _acutatum_ or Tween showed the highest number of volatiles (30 and 33, respectively). By contrast, the total number of VOCs produced in olives inoculated with _A. pullulans_ or _A. pullulans_ + _C. acutatum_ was lower (25 and 26, respectively). Around 53% of the detected compounds were common to all four treatments, with five VOCs exclusively identified in olives inoculated with Tween and one volatile (2-undecanone) in olives inoculated with C. _acutatum_. Curiously, four VOCs (2-hexanone, 2-heptanone, 2-octanone and limone) were exclusively identified in olives inoculated with _A. pullulans_ + _C. acutatum_ or _C. acutatum_. 1-Hexanol was the most abundant compound in olives inoculated with _A. pullulans_, while in the other treatments, it was 2-methyl-1-butanol. In comparison to the control (i.e., olives inoculated with Tween), both _A. pullulans_ + _C. acutatum_ and _C. acutatum_ showed greater changes in the volatile profile than _A.