## 3 Discussion  
Richness of VOCs in numbers and relative contents reflects the diversity of different resources. We obtained the most floral scent compounds from 34 _F. hybrida_ germplasms so far. There are more VOCs detected in _F. hybrida_ than other species, such as _Prunus mume_, which emitted 31 VOCs in 8 cultivars [24]. As the most abundant floral scent volatiles, terpenoids widely exist in many scented plants, including \(\beta\)-ionone and linalool in _Osmanthus fragrans_[25]. In most detected _F. hybrida_, monoterenes contribute the majority of VOCs. There are also sesquiterpenes serving as the chief compounds in some freesia cultivars, including ZMG and 'Rose Marie' [26]. Similar results were reported that fatty acid derivatives may play a certain role in _Freesia_ fragrance [21]; and some wild _Dianthus_ also emit them as principal VOCs [27]. Though benzenoids and phenylpropanoids have no evident effects on _F. hybrida_, they are the primary VOCs in _Petunia axillaris_[28], _Antirhinum majus_[29], and _Hedychium coronarium_[30]. In addition, these results are nearly consistent with the result that linalool is the predominant VOC with a range from 33.60% to 82.51% in most _F. hybrida_ in previous reports [18; 26; 31]. Linalool is also a primary volatile substance in many species, which occurs in more than half of the families of seed plants [2]. Other compounds like terpionolene and alloocimene, the important volatiles firstly reported in _F. hybrida_, contribute specificity to the germplasm. The scent of VOCs is closely related to their composition. It was demonstrated that the number of VOCs had little effect on a sensory evaluation survey, suggesting that the floral odor was predominated by the principal volatile compound and its content [32]. Lower content and higher odor threshold values lead to weaker perceptions of floral scent [33]. Among the germplasms dominated by linalool, RR is almost without fragrance, due to the low content proportion of linalool compared to the other germplasms. Moreover, the principal VOCs of LL and SO are \(\alpha\)-terpineol and (+)-\(\alpha\)-pinene, whose odor value thresholds are 0.01-110 mg/m\({}^{3}\) and 0.0053-23 mg/m\({}^{3}\), respectively. These substances were observed in low proportions and their odor value thresholds were much higher than linalool (0.0004-6 mg/m\({}^{3}\)), so their scent was imperceptible [34]. Based on PCA and HCA, there are various composition patterns of VOCs of F. hybrida. Undoubtedly, linalool significantly contributes the floral scent of most germplasms. Interestingly, there are also other types of VOC composition observed in _F. hybrida_, including those which are dominated by (_E_)-\(\beta\)-ocimene, predominant in (_Z_)-\(\beta\)-ocimene, linalool and copaene simultaneously, and predominant in \(\alpha\)-terpineol, d-limonene and eucalyptol and other substances, respectively. (_Z_)-\(\beta\)-ocimene are even higher than linalool in TW. These substances were first observed as the major components in _F. hybrida_. As an inherited  
Figure 6: Relative content of total and important VOCs of parental species and hybrids. trait, the similar VOC compositions in the same group may possess a close evolutionary relationship [14; 35], so the high scent similarity of LL and JHH may be due to close ancestors. Having various major VOC compositions is beneficial to the diversity of floral scent. According to scent classification, 29 _Tulipa_ cultivars were classified into 9 groups, including anise, citrus, fruity and six other scented groups [36]. These above findings will enhance the understanding of the floral scent of _F. hybrida_ and are helpful to exploit the developmental potential of different _F. hybrida_ scent types in future. Intervarietal crossing is frequently used as an important method to breed new varieties for important commercial flowers including _Freesia_. As a showy trait, excellent floral scent is also considered as a key breeding purpose in _Freesia_.