## 2 Results  
### Volatile Organic Compounds of Single-Petal Phenotype Rosebuds at Different Stages  
A total of 74 volatile compounds were detected by using the SPME + GCMS (Table S1). These compounds belong to 10 categories, including alcohols, aldehydes, ketones, esters, ethers, phenols, terpenes, aliphatic hydrocarbons, aromatic hydrocarbons, and furans. Richness by category and total content at different flowering stages are shown in Table S2; RW1 to RW3 is composed of 8-10 categories (Figure 1) and the total richness of VOCs is (47 \(\pm\) 2) species. Terpenes were the most abundant group in all stages (34.94% in RW1, 27.32% in RW2, and 28.77% in RW3), followed by alcohols (26.70% in RW1, 30.20% in RW2, and 35.28% in RW3) (Figure 2). Terpenoids were highest in RW1 and alcohols increased with flower blooming. The contents of aldehydes and aliphatic hydrocarbons decreased gradually with flower blooming. On the contrary, ester content gradually increased with flower blooming (3.3%, 11.15%, and 14.86%, respectively). The contents of others were present at low levels--less than 5% in total.  
The contents of the main chemical components of _Rosa willmottiae_ at different flower stages are shown in Figure 3, and changes vary. Geranyl acetate (0%, 6.01%, 8.47%) gradually accumulates with flowers blooming; Although 2-phenylethanol has a similar trend, there is no significant difference between the initial stage and flowering stage (\(p\) > 0.05). On the contrary, the contents of \(\beta\)-maaliene (11.43%, 8.32%, 8.66%), (+)-\(\alpha\)-longipinene (9.49%, 6.19%, 6.13%), (E)-\(\beta\)-farnesene (6.36%, 5.01%, 4.95%), and benzaldehyde (7.50%, 6.08%, 5.62%) decreased, also with no significant difference between the initial stage and flowering stage. Additionally, pentadecane (6.96%, 5.49%, 1.99%) decreased to an extreme extent with flower blooming. Benzyl alcohol (10.02%, 6.85%, 10.69%) content was the lowest in the initial stage.  
There were 30 common components in the third stage of _Rosa willmottiae_ (Figure 4A), including four alcohols (mainly 2-phenyl ethanol and benzyl alcohol), three kinds of aldehydes (mainly benzaldehyde and trans-2-hexenal), two aliphatic hydrocarbons (pentadecane and n-heptadecane), o-methyl benzene as the only common aromatic hydrocarbon, three esters (phenethyl acetate, benzyl acetate, and hexyl formate), one ether (anisole), and one ketone (2-methyl-4-undecanone). There were 15 common terpen (mainly pinene and \(\beta\)-elemene). The unique components in bud stage were the most prevalent, up to 13 (\(\beta\)-bisabolene; \(\alpha\)-muurolene; 1,3,5-trimethoxybenzene; methyl isoeugenol; tetrade-cane; trans-2,4-decadien; 2-methyl-1-indanone; 1,3-cyclohexadiene, 5-butyl-; nonanal; (E)-2-octanel; (1S)- (1)-beta-pinene; 2-ethylfuran), and methyl isoeugenol (2.45%) had the highest content. The composition of alpha-gurjunene and isocayophyllene is unique in the initial flowering stage, while 1, 2, 3, 4, 6, and 8 alpha-hexahbro-1-isopropyl-4, 7-dimethylnaphthalene, and \(\beta\)-humulene are unique to the full flowering stage. The initial and full flowering stages have common components, up to 85%.  
Figure 1: The substances’ richness of different kinds in _Rosa willmottiae_ (RW1: bud stage, RW2: initial flowering stage, RW3: full flowering stage of single-flower phenotype).  
Figure 2: Ten kinds of VOCs’ accumulation in _Rosa willmottiae_ at different stages.