## 3 Results
### Volatile Compounds Produced during the Interaction of _A. pullulans_-_C. acutatum_
pullulans_ (Figure S3). Overall, the abundance of most VOCs emitted in the control (around 53%) was significantly reduced (up to \(p<0.05\)) in fungal-inoculated olives, with only 16% increasing in abundance. In particular, 1-heptanol, 2-hexenal and methoxy-phenyl-oxime were the most depleted in olives inoculated with _A. pullulans_, _A. pullulans_ + _C. acutatum_ and _C. acutatum_, respectively, while Z-3-hexen-1-ol (in _A. pullulans_) and 2,2,4-trimethyl-pentane (in both _A. pullulans_ + _C. acutatum_ and _C. acutatum_) were the most enhanced. Similarly, differences were found in VOC production over the pathogen-endophyte interaction, with the sampling time accounting for 42% of the total variance in the VOCs emitted (PERMANOVA \(p<0.001\); Table S2). The results show a decrease in the number of VOCs produced throughout the experiment, from 30 VOCs on day 2, to 28 VOCs on day 8 and 19 VOCs at the end of the assay (Table 1; Figure S2b). Some VOCs were detected at a specific time point. Overall, a total of eight VOCs were exclusively detected on day 2 and, afterwards, reduced to four (on day 8) and two (on day 16). The main VOC emissions also varied over time, with hexanal, 2,2,4-trimethyl-pentane and 2-methyl-1-butanol being the most abundant on days 2, 8 and 16, respectively. Differences in the individual VOC amount between olives inoculated with Tween (control) and fungi were noticed mostly on days 2 and 8 of the experiment (Figure S4). At these two sampling times, the abundance of 63% of the total VOCs emitted in fungal-inoculated dives decreased significantly (at least \(p<0.05\)) when compared to the control. In contrast, at the later stages of the assay (day 16), the fold change in the VOC amount between olives inoculated with fungi and the control was negligible, with only a few VOCs increasing their amount in the presence of fungi. To identify which VOCs are characteristic of each treatment, principal component analysis (PCA) was performed with VOCs analyzed after 2, 8 and 16 days of pathogen inoculation (Figure 5). The PCA showed a high variance, around 80%, 80% and 60% for days 2, 8 and 16, respectively, considering the two principal components (PC1 and PC2). For day 2, the PCA grouped the _C. acutatum_ (Ca) and _A. pullulans_ + _C. acutatum_ (Ap + Ca) treatments together, which were characterized by the VOCs 2-methyl-1-propanol, 2-methyl-1-butanol, 2-hexanone, 1-hexanol, 2-heptanone and limone. These two treatments were separated from the _A. pullulans_ (Ap) and Tween treatments, which correlated positively with an array of VOCs, with hexanal, benzeneacetaldehyde, [1S-(1\(\alpha\),2\(\alpha\),5\(\beta\))]-cyclohexanol and 5-methyl-2-(1-methylethyl) being the most discriminant. The PCA for day 8 showed a similar trend, with treatments Ca and Ap + Ca being clearly separated from the other treatments due to the production of 2-methyl-1-propanol and 2,2,4-trimethyl-pentane. On day 16, this pattern changed, with a separation between the Ca, Ap + Ca and Ap/Tween treatments being noticed based on the volatiles produced. On this day, the most characteristic VOCs of the Ca treatment were 6-methyl-5-hepten-2-one and 2-nonanone, while the Ap + Ca treatment was positively correlated with an array of compounds, particularly Z-3-hexen-1-ol, benzyl alcohol and nonanal. The Ap and Tween treatments were positively related to the production of 2,2,4-trimethyl-pentane. Figure 5: Principal component analysis score plots obtained from the volatile profile of divines inoculated with _Aureusisilium pullulans_ and _Calletrichum acutatum_ (Ap + Ca), or solely with \(A\). _pullulans_ (Ap), \(C\). _acutatum_ (Ca) or _Toven_, after 2, 8 and 16 days of pathogen inoculation. Each number corresponds to a particular volatile compound, as indicated in Table 1. The gradient color represents the contribution of each variable (i.e., volatile compounds) to the explanation of the greatest variance in the dataset. Each circle represents treatments, with the ones with the greater size representing the average.