Ayşe Betül Avci, Özlem Alan, Merve Göre, Bintuğ Öztürk
Harvest timing is a critical agronomic factor influencing both yield and phytochemical quality in aromatic plants. This study evaluated the effect of different harvest stages on biomass production, essential oil (EO) yield, chemical composition, and chemotype variation in parsley (Petroselinum crispum (Mill.) Fuss). Field experiments were conducted under Mediterranean conditions (Ödemiş/İzmir, Türkiye), and plants were harvested at four distinct developmental stages (Pet-1 to Pet-4, May to September). Essential oils were extracted by hydrodistillation and analyzed using GC-MS, while multivariate analyses (HCA and PCA) were applied to assess compositional variation. Biomass yield increased progressively with delayed harvest, whereas EO content showed a non-linear pattern, peaking at the second harvest (0.73%) and declining thereafter, indicating a trade-off between yield and oil concentration. GC-MS analysis identified 55 volatile compounds across all harvest stages (identification rate: 94.47%-96.47%). Early harvests were characterized by higher proportions of monoterpene hydrocarbons (particularly β-phellandrene), while later stages showed increased accumulation of phenylpropanoids (apiol reaching 43.69% at Pet-4) and, notably, sesquiterpenes (caryophyllene (Z): 20.86% at Pet-3, the accumulation of which may be associated with prevailing summer conditions). Principal component analysis (PC1 = 62.1%, PC2 = 30.6%; cumulative = 92.7%) clearly separated harvest stages based on chemical profiles, supporting the presence of two distinct chemotypes: a monoterpene-balanced type (Chemotype A: Pet-1, Pet-2) and a phenylpropanoid-dominant type (Chemotype B: Pet-3, Pet-4). These findings demonstrate that harvest timing plays a decisive role in shaping both EO composition and chemotype in parsley. Moreover, the observed variation in key constituents, particularly caryophyllene and myristicin, may influence the functional properties of the oil, as these compounds are associated with antioxidant and antimicrobial activities. Optimizing harvest stage is therefore essential not only for maximizing biomass yield but also for improving the qualitative and potential bioactive value of parsley essential oil under specific environmental conditions.