## 3 Results
### Multivariate Statistical Analysis of Petiole Volatile Profiles  
To assess the similarity/dissimilarity in the volatile profiles of the different celery varieties investigated here, PCA was applied separately to the relative (%) peak areas of the compounds collected from the petioles and leaves.  
PCA exploration of the volatile profiles of the celery petioles are shown in Figure 1, reporting the projection of the samples, and Figure 2, displaying the variable loadings, in the space of the first four PCs that accounted for 97% of the total variance (explained variance, EV). PCA was performed on the centered data, which did not alter the variance of the original variables. A clear separation of the WTC samples along the positive PC1 direction from the cultivated celery varieties can be observed in Figure 1a. This figure also displays a differentiation, approximately along PC2, of both WC and CC samples collected in June and in February. In addition, PC2 seems to describe a variability internal to the BC group. The four BC samples located in the second quadrant of the PC1-PC2 plane, in particular, come from outer petioles having a darker green color and being more fibrous compared to all the other petioles samples of the BC group that were extracted from the inner part of the plant. Interestingly, the outer and internal petioles of the BC variety are separated along the same direction discriminating the more and less mature samples of the WC and CC groups. The BC samples are isolated from the other varieties along PC3 (Figure 1b) while PC4 describes the different behavior of the BC samples according to the harvesting time (June vs. August). Figure 1b also displays a neat clustering of the CC and WC samples along PC3 according to the harvesting time, and a separation, although incomplete, between the samples of these two varieties for each of the two harvesting dates. Inspection of Figure 2 provides information on which petiole volatiles are responsible for the trends observed in the score plot. In particular, discrimination of the WTC group with respect to the cultivated varieties can be related to a higher content of \(\beta\)-myrcene (having a positive loading on PC1) and lower content of \(\gamma\)-terpinene and limone (both having negative loadings on PC1). The differentiation of BC from the other cultivated varieties along PC3 can be ascribed to higher contents of \(\gamma\)-terpinene, limonene, p-cymene e \(\beta\)-myrcene and lower contents of (\(Z\))-\(\beta\)-ocimene, (E,E)-1,3,5-Undecatriene and \(\alpha\)-pinene. A decrease in p-cymene and increase in \(\gamma\)-terpinene contents is responsible for the separation along PC4 of the BC samples harvested in August and in June. According to the reciprocal position along the PC2 and PC4 directions of WC and CC samples collected in different months, the relatively high positive loadings of limonene on both PCs suggest an increase of this volatile components in the samples of July compared to those of February, accompanied by a decrease in the contents of \(Z\)-\(\beta\)-ocimene, (E,E)-1,3,5-Undecatriene and \(\alpha\)-pinene (showing negative loadings on PC3). On the other hand, the effect of the sampling time on the content of p-cymene and \(\gamma\)-terpinene is not so obvious because the loadings of both variables on PC2 and PC3 have opposite signs.