Unlocking Petroselinum crispum (Mill.) Fuss's potential: A study of morphological, agronomic, biochemical, and nutritional diversity, alongside essential oil composition, to strengthen breeding programs

Despite the economic and medicinal importance of parsley, comprehensive multi‑trait studies of its germplasm remain limited, and the complex relationships governing trait expression have seldom been explored. In the present study, 83 morphological, agronomic, physiological, nutritional, and phytochemical traits—including volatile and medicinal compounds—were evaluated across 17 distinct parsley populations. Correlation analysis revealed strong positive relationships between seed yield and key photosynthetic pigments, as well as valuable essential oil compounds such as β‑bisabolol and carotol. Furthermore, a positive relationship was identified between mineral elements (particularly phosphorus, potassium, magnesium, calcium, iron, copper, and manganese) and bioactive volatile compounds (α‑thujone, α‑terpinolene, bicyclogermacrene), indicating that simultaneous selection for nutritional quality and medicinal compounds is feasible. Principal component analysis reduced the 83 traits to three biologically meaningful dimensions: productivity–nutrition–oil quality, morphology‑reproduction versus antioxidant capacity, and photosynthetic efficiency–seed yield. Heatmap clustering resolved two major population groups with contrasting trait profiles: one group (Poldokhetar, Tehran, Tabriz, Shiraz, Arak, Hamedan, and Kurdistan) characterized by superior mineral and essential oil profiles—ideal for pharmaceutical and nutritional applications—and the other (Crispum, Neapolitanum, Isfahan, and Shahr-e Rey) distinguished by enhanced photosynthetic pigments and seed yield—optimal for seed production. Overall, this study provides parsley breeders with three actionable outcomes: (1) simultaneous improvement of nutritional and medicinal traits is feasible without unfavorable trade‑offs; (2) reliable negative markers, particularly germacrene A, are identified for screening purposes; and (3) a reduced, low‑cost trait panel has been developed to support marker‑assisted selection in parsley breeding programs.