Assessment of phytochemical and agro-morphological variability among different wild accessions of Mentha longifolia L. cultivated in field condition

Mentha longifolia L. is one of the most important aromatic and perennial herbs of the Lamiaceae family, having potential sources of essential oils and compounds with interesting pharmacological and therapeutic properties. In this study, the variability of morphological parameters, essential oil composition, and phenolic compounds such as rosmarinic acid and caffeic acid content were assessed among twenty different accessions of Iranian horsemint at full flowering stage. The average of essential oil content illustrated a high variability, ranging from 0.38% to 4.33% (w/w), and the phytomass amounts varied from 471.5 g/m2 to 860.66 g/m2. Also, the clustering of morphological traits of the studied accessions generated two main groups. The characterization of the essential oils by GC-MS/FID analyses revealed a total of forty-two constituents in the horsemint accessions. Although all the accessions were classified as oxygenated monoterpenes-rich volatile oils (42.38–94.7%), they were divided into seven main chemotypes by cluster and principal component analysis (PCA). The major constituents in the essential oil of the twenty accessions were piperitenone oxide (0.27–75.39%) > pulegone (0.17–69.49%) > trans-piperitone epoxide (0.3–54.39%) > menthone (0.5–48.12%) > 1,8-cineole (1.27–44.7%) > piperitenone (0.35–36.71%) > (Z)-β-ocimene (14.11–21.27%) > menthol (0.13–20.98%), respectively. The rosmarinic acid content of the methanolic extracts using HPLC analysis showed significant quantitative variability, ranging from 36.95 mg/100 g to 302.97 mg/100 g (based on the dry matter). Since all the accessions were subjected to similar soil and climate conditions, it was evident the priority of genetic effects on ecological factors. The high intraspecific variability in Iranian horsemint directs a holistic approach to gain novel and homogeneous genetic materials, required for the breeding programs and pharmaceutical industries.