## 2 Results
### Volatile Compounds of the Flower Petals of N. 'Eldorado' at Different Development Stages
#### 2.1.3 Hierarchical Cluster Analysis and Principal Component Analysis of the Volatile Compounds  
Hierarchical cluster analyses (HCAs) were used to analyze the data for 60 volatile compounds obtained from the four flowering stages of \(N\). 'Eldorado', and three samples  
Figure 3: Percentages of alkenes, alcohols, esters, aldehydes, ketones, alkanes, and other volatile compounds released from different development stages of \(N\). ’Eldorado’ flower.  
were used to perform analyses for each stage (Figure 4). The 12 \(N\). 'Eldorado' samples could be divided into four groups. The first group was the S3 group, which was characterized by high concentrations of hexadecane, 2,6,10-trimethyltridecane, methyl salicylate, p-anisaldehyde, 4-methoxybenzyl alcohol, anisyl acetate, benzyl acetate, benzaldehyde, and cis-3-hexenyl hexanoate. The second group included three samples of plants at S1, with high concentrations of tetradecanal, isocaryophyllene, (Z6),(Z9)-pentadecadien-1-ol, 1-methyl-4-(6-methylhept-5-en-2-yl)cyclohexa-1,3-diene, (E)-\(\alpha\)-farnesene, pentadecane, and 6-tridecene. The third and fourth groups contained plants at S2 and S4, respectively, and the main volatiles in the S4 group included dihydrocurcumene, c-terpinene, o-cymene, 1-(1,5-dimethyl-4-hexen-1-yl)-4-methyl-1,3-cyclohexadiene, \(\alpha\)-pinene, sabinene, and D-limonene.  
Figure 4: Hierarchical clustering analysis (HCA) and heatmap of volatile compound levels at four flowering stages of \(N\). 'Eldorado'. Values of all studied volatile compounds per stage are shown on the heatmap, colors of the heatmap cells indicate a low (blue) and high (red) abundance of a particular compound. The HCA and dendrogram of samples were according to Euclidean distances. S1-1, S1-2, and S1-3 indicate the three samples of S1, and the same is true of S2, S3 and S4; the same labels are used in Figure 5.  
Principal component analysis (PCA) was used to identify which volatiles contributed the most to the differences among the different flowering stages of \(N\). 'Eldorado' using the data of 60 volatile compounds (Figure 5A) and the seven classes of volatile compounds (Figure 5B). Using the factor scores, the tested \(N\). 'Eldorado' samples were positioned in a two-dimensional space that was divided into four groups based on the scores. As shown in Figure 5A, the volatiles of benzyl alcohol, 1-methoxy-4-methyl-benzene, methyl salicylate, p-anisaldehyde, benzyl acetate, benzaldehyde, 4-methoxybenzyl alcohol, cis-3-hexenyl hexanoate, and anisyl acetate were highly positively correlated with the S3 samples. Isocaryophyllene, (E)-\(\alpha\)-farnesene, (6Z,9Z)-pentadecadien-1-ol, 8-heptadecene, pentadecane, heptadecane, 1-methyl-4-(6-methyl-5-en-2-yl)cyclohex-1,3-diene, and 2-phenyl-undecane were positively correlated with the S1 samples. However, the S2 group was characterized by only \(\alpha\)-ionone. The S4 group was characterized by high amounts of D-limonene, levoverbenoeno, \(\alpha\)-bergamotene, zingiberene, and others. Figure 5B shows that alcohols, esters, and aldehydes were the most important volatile compounds in the S3 samples; alkanes, alkenes, and ketones were the predominant volatiles in the S4, S2, and S1 samples, respectively.