Phenolics and Antioxidant Capacity of Basil (Ocimum basilicum L.) Genotypes Across Locations and Developmental Stages

Basil (Ocimum basilicum L.) is a globally consumed herb whose hydroxycinnamic acid esters and flavonoids contribute to dietary antioxidant intake. This study aimed to characterise the phenolic composition, antioxidant capacity, and developmental-stage variability of twelve Turkish basil genotypes grown across three ecologically contrasting sites. Twelve genotypes were evaluated in a two-year field experiment (Year 1 and Year 2) at three ecologically contrasting locations in Türkiye: Bursa, Eskişehir, and Tokat. Agronomic performance, nine-compound HPLC-TOF phenolic profiles (Year 1), total phenolic content (TPC), and antioxidant capacity (ABTS, DPPH, and FRAP) were measured. The effects of developmental stage on the phenolic composition of plants from Bursa (Year 1) were characterised. Location was the dominant source of variation in phenolic quality. Plants from Tokat ranked highest for individual phenolic concentrations (Year 1 HPLC-TOF data) and for all three antioxidant assays (two-year means). Rosmarinic acid varied 4.4-fold (59.0-261.8 mg 100 g⁻¹ DW; Year 1), with the highest values recorded for genotypes R-3k, R-19, R-15, and R-4 from Tokat. ABTS antioxidant capacity was 113% higher in plants from Tokat than in those from Bursa (two-year means: 483 vs. 227 µmol TE g⁻¹ DW). Analysis of rosmarinic acid in plants from Bursa showed an irregular, stage-dependent pattern, whereas TPC remained broadly stable across developmental stages (vegetative to full flowering: +3.9%). The genotype × stage interaction accounted for 44-50% of the total variance. PCA explained 89.3% of the variance across two components, with Tokat combinations separating clearly from those of the other sites. Under the tested field conditions, genotypes R-23 and R-4 emerged as strong candidates for phenolic-acid-targeted cultivation, while Y-15 recorded the highest two-year mean TPC at Tokat.