## 4 Discussion
Through a combination of expression and volatile content analysis, we selected six volatiles: \(\alpha\)-calacorene (C15H20), which has a woody aroma, \(\alpha\)-cubebene (C15H24), rose-oil scented _cis_-\(\beta\)-farnesene (C15H24), pungent himachala-2,4-diene (C15H24), apple blossom scented nerolidol (C15H26O), and slightly herbaceous linalool (C10H18O). _Alpha_-calacorene and _alpha_-cubebene are currently less studied. It is known that the former can be obtained from the rhizomes of _Acorus calamus_ L., while the latter can be isolated from _Mentha canadensis_ L., and both are commonly used as flavoring constituents. Nerolidol, a naturally occurring sesquiterpene, serves as a volatile signal that induces plants to defend themselves against insects and pathogens [36]. Additionally, nerolidol can enhance the activity of enzymes responsible for degrading juvenile-protecting hormones in plants and inhibit the growth and development of insects, providing a new perspective for the development of novel pesticides with potent antimicrobial activity [37]. Linalool is a natural compound resistant to microorganisms [38], which can boost the supply of GPP as a precursor to enhance the efficiency of GPP in linalool biosynthesis [39] and achieve potent antibacterial activity [40]. A comparative study of volatile content revealed that the GJ and HDL varieties possess higher levels of \(\alpha\)-calacorene, \(\alpha\)-cubebene, _cis_-\(\beta\)-farnesene, and himachala-2,4-diene compared to GLD608. Thus, they exhibit stronger herbal and pungent flavors. A study by [PERSON] et al. [41] highlighted that the most notable difference between _C. annuum_ and _C. chinense_ is that the latter has a volatile pungent odor and a distinctive spicy flavor [42], which is consistent with our findings. Furthermore, it was observed that the less spicy varieties exhibit a more pronounced aromatic odor, and the content of \(\alpha\)-cubeene in HDL varieties is significantly higher than that in GJ varieties. Previously known differences were observed in the expression of enzyme genes related to metabolic pathways across various varieties and developmental periods. Furthermore, the content of volatile substances exhibited differing trends, suggesting a potential delayed effect on the synthesis of chili flavor compounds at various developmental stages. Negative correlations between volatiles and gene expression levels suggest that these genes may play a balancing or regulatory role in terpenoid synthesis. When gene expression levels are elevated, the synthesis of the final compound may be reduced by inhibiting the flow of specific precursor materials. Conversely, the positive correlation between gene expression and volatile content implies that these genes may be directly or indirectly involved in the synthesis of target compounds, either by promoting the generation of key precursor substances or by stimulating the accumulation of downstream metabolites, thereby enhancing metabolic pathway activity. Several potential reasons for the inconsistency between some genes and volatile organic compounds include, but are not limited to, the insufficient expression level of a single gene to significantly affect the concentration of final metabolites, inadequate substrate supply, shunting in metabolic pathways, or the necessity for constructive interaction among multiple genes. Thus, to assess these hypotheses, it is essential to further investigate the specific functions and regulatory mechanisms of these genes in the synthesis of aroma compounds through gene silencing or knockout experiments. Substantial progress has been made in understanding gene expressions linked to plant terpenoid metabolic pathways, including biosynthetic processes and molecular markers associated with terpene content [43]. However, the regulation of secondary metabolite synthesis through the synergistic control of related enzymes is still underexplored.