## 2 Results
### Comparison of the VOCs of Hybrids and Parental Species in F. hybrida  
In our previous breeding work, we collected 9 representative hybrids with different aroma qualities, which were offspring from the intervarietal crossing of 9 cultivars (WR, HJ, CA, RR, DH, HTG, RP, RX and GR). The comparison of VOC characteristics with hybrids and parental species was made to analyze the hybridization results of the _F. hybrida_ flower scent.  
Figure 5 shows the quantitative comparison between parental species and hybrids. As a whole, 9 hybrids stably inherited a total of 16 compounds from both of their parents, and they contained steady VOCs with a range from 6 (in WR-HJ)-01, RR-DH-03 and HTG-RR-02) to 9 (in GR-RP-05 and GR-RP-02), including linalool, (_E_)-\(\beta\)-ocimene, d-limonene, \(\beta\)-myrcene, cosmene and alloocimene and so on (Table 2). These VOCs were all monoterpenes; linalool, (_E_)-\(\beta\)-ocimene, d-limonene and \(\beta\)-myrcene were observed in each overlap between parents and hybrids, of which linalool showed high relative contents above 30% in most hybrids except HTG-RR-02 (6.03%). (_E_)-\(\beta\)-ocimene was higher than 6%, except in WR-HJ-01 (1.86%) and CA-WR-01 (0.89%). Conversely, d-limonene and \(\beta\)-myrcene emitted low levels under 1.50%. In addition, numbers of unique compounds in hybrids differed from 4 in GR-RP-05 and GR-RP-06 to 19 in RP-RX-01 when compared with their parents, such as cyperene in WR-HJ-01, sabinene in RR-DH-02, durenol in RP-RX-01 and so on. These specific substances in hybrids were almost always lower than 2.80%, excluding ethanol (17.92%) in HTG-RR-02.  
Figure 4: HCA dendrogram of VOCs of 34 _F. hybrida_ germplasms.  
Figure 6 showed the relative contents of total VOCs and some important compounds of parents and hybrids. It was observed that different parental species groups generated various results, and the relative contents in most hybrids were near to, or higher than, parental species. Firstly, in WR-HJ-01, CA-WR-01 and RR-DH-03, the VOC proportions of hybrids were closer to the parents, with the advantage of high VOCs relative content, mainly due to an increase in copaene, linalool and (\(E\))-\(\beta\)-ocime, respectively. Secondly, the percentage of HTG-RR-02 was observed in evident proximity to RR, the female parent with low VOC relative content, as a result of a decrease in linalool percentage and a substantial increase in ethanol percentage. Thirdly, heterosis was present in RP-RX-01, GR-RP-05 and GR-RP-06. This occurred in RP-RX-01 mainly because of the increase of occime. However, as the offspring of the same parents (GR and RP), GR-RP-02 contained the lowest VOCs, even less than parents, which was also observed via linalool relative content decrease and ethanol content increase.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**No.** & **Name** & **Frequency** \\ \hline
1 & Linalool & 6 \\
2 & \(\beta\)-Myrcene & 6 \\
3 & D-Limonene & 6 \\
4 & (E)-\(\beta\)-Ocimee & 6 \\
5 & \(\alpha\)-Terpineol & 4 \\
6 & (+)-\(\alpha\)-Pinene & 3 \\
7 & Alloocimene & 3 \\
8 & Terpinolene & 2 \\
9 & (\(E\))-Dehydroxylinalool Oxide & 2 \\
10 & Rosefuran & 1 \\
11 & (\(E\))-Linalool Oxide (Pyranoid) & 1 \\
12 & Ethanol & 1 \\
13 & Cosmemee & 1 \\
14 & Dihydro-\(\beta\)-Ionone & 1 \\
15 & \(\beta\)-Elemene & 1 \\
16 & Selina-4(15),7(11)-Diene & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Frequency of the VOCs of freesia hybrids inherited from both parental species.  
Figure 5: Venn diagrams of numbers of VOCs of 8 freesia hybrids with their parental species.