## 2 Results
### Odor Classification and OAVs of Volatile Compounds  
Major volatile compounds were divided into seven groups (herbal, woody, spicy, floral-rose, floral-lily, fruity-sweet, and fruity-citrus) according to their odor descriptions (Table S5). The total content of seven groups and their percentage in the total volatile content of 17 cultivars were shown in Figure 5A,B. Herbal, floral-rose, and floral-lily were the three groups with the highest proportion and contents.  
Figure 4: Main volatile compounds of floral fragrance released by 17 herbaceous peony cultivars. 1\(-\)17 represents 17 cultivars, and numbers assigned as described in Figure 2. **(A)** The relative contents of 26 main volatile components from 17 cultivars. **(B)** The proportion of 26 main volatile components from 17 cultivars. **(C)** Trend comparison of relative content and sensory evaluation score. Data represent means and standard errors of three biological replicates, and the relative content is calculated using the internal standard method. Detailed data were shown in the Supplementary Table S4.  
However, there is no direct relationship between the content of volatile compounds and their aroma contribution, and the odor threshold should also be considered. OAV is the ratio of the volatile contents to its odor threshold, which is an important indicator to measure the aroma contribution [40]. The greater the volatile OAVs, the greater the contribution to aroma [41].  
Volatile compounds with OAV \(\geq 1\) were generally considered as effective contributors to overall aroma [41]. As shown in Table S5, the OAV of 17 volatiles was greater than 1, indicating that they were contributors to the aroma of herbaceous peony. Compounds with OAV \(\geq 10\) were considered as the important aroma substances [41]. Eight compounds were the important components contributing to the aroma of herbaceous peony. Four compounds had very high OAVs (\(>80\)) and may be the most important odor compounds for the overall aroma, including linalool, citronellol, geraniol, and 2-PE.  
Figure 5: The odor classification, content, and OAV of 26 main volatile compounds from 17 cultivars. The numbers \(1-17\) represent 17 cultivars, and numbers are assigned, as described in Figure 2. **(A)** The relative contents of main volatile compounds in seven groups. **(B)** The proportion of main volatile components in seven groups. **(C)** The relative contents of 26 main volatile compounds. **(D)** The OAVs of 26 main volatile compounds. Data represent means and standard errors of three biological replicates. The detailed data were shown in Supplementary Tables S4 and S5.  
Combined with the contents of 26 volatile components of 17 cultivars (Figure 5C), some substances, such as fatty acid derivatives, were found with a high odor threshold. Although their content was high, the contribution to aroma is small. In addition, the content of fatty acid derivatives in 17 cultivars was concentrated in 1000-1500 ng/g with no significant difference, and they were distributed in six types (hexanal, 2-hexanal, 3-hexen-1-ol, trans-2-hexenol, 1-hexanol, 1-hexanol, and 2-ethyl-). Most of these types release grass fragrance, which is not considered a component of flower fragrance. The reason for the sensory difference of flower fragrance among herbaceous peony cultivars was mainly due to the different contents of terpenoids and benzenoids/phenylpropanoids.  
Linalool and citronello were the main aroma contribution components of most strong-scented herbaceous peony cultivars, and geraniol and 2-PE were also the main aroma contribution components of a few cultivars based on the OAVs of volatile compounds (Figure 5D).