Abstract
The current research investigated three Iranian dill (Anethum graveolens L.) ecotypes from Ardabil, Bushehr, and Kerman to evaluate the effects of harvesting times on essential oil yield, composition, and chemotypic variation. Aerial parts of the ecotypes were collected at three diurnal times (6 am, 12 noon, and 6 pm). Following grinding, essential oils were extracted from the dried powder (50 g in 1:10 w/v distilled water) using a Clevenger-type apparatus for 4 h, then collected, dehydrated over anhydrous sodium sulfate, and stored in amber vials at 4 °C prior to GC-MS analysis. Factor analysis revealed four factors explaining of the variation, reflecting distinct chemotypic patterns: (i) a thujene-terpinene-germacrene-myristicin versus pinene-dominated axis, (ii) an oxygenated monoterpene and bioactive compound axis, (iii) a sesquiterpene versus monoterpene/phenylpropanoid trade-off, and (iv) a pinene-type monoterpene axis. These factors demonstrated coordinated and independent regulation of monoterpene, sesquiterpene, and phenylpropanoid pathways, highlighting both metabolic trade-offs and synergistic accumulation within biosynthetic modules. The treatment-by-trait biplot explained 74% of total variance and revealed strong treatment-by-trait interactions, indicating that ecotype and harvest time jointly determine essential oil profiles. Ardabil ecotype favored monoterpene hydrocarbons and carvacrol, especially at 6 am and 12 noon, while Kerman ecotype exhibited higher levels of sesquiterpenes and phenylpropanoids depending on collection time. Positive and negative correlations among compounds reflected coordinated biosynthetic fluxes and antagonistic relationships, enabling chemotype differentiation and identification of functionally enriched oils. The results emphasize the importance of integrating genetic, environmental, and temporal factors for optimizing essential oil composition in A. graveolens L.