Integrated evaluation of morphophysiological, phytochemical, and cytogenetic diversity in eight Iranian spearmint ( Mentha spicata L.) accessions

Spearmint (Mentha spicata) is a substantial plant widely used in the food, pharmaceutical, traditional medicine, cosmetic, and personal care industries, and it is also commonly consumed fresh as part of the daily diet. In hybrid plant species with outcrossing reproductive systems, genetic diversity is typically high. In a country such as Iran, which has considerable climatic diversity, the diversity of hybrids resulting from gene expression can be even greater. Therefore, investigating the diversity of spearmint accessions (a hybrid, outcrossing, open-pollinated plant grown under different climatic conditions) is of great importance for identifying and introducing accessions with specific targeted traits. This study aimed to evaluate variations in morphophysiological and phytochemical traits, macro- and microelements, heavy metals, leaf anatomy, and cytogenetics among eight accessions of Mentha spicata L. from Iran. The data were analyzed using a completely randomized nested design with three replications, principal component analysis (PCA), biplot, and cluster analysis. The results revealed a significant difference (p ≤ 0.01) among accessions in all morphological traits, including fresh and dry flowering shoot yields, essential oil (EO) content and yield, concentrations of heavy metals, and levels of macro- and microelements. Additionally, significant differences were recorded in carotenoid, chlorophyll, flavonoid, and phenol contents. Mean comparisons showed that the range of variation for selected traits was as follows: dry flowering shoot yield ranged from 1,537 to 3,453 kg ha−1; EO percentage, from 0.94% to 2.36%; EO yield, from 21.3 (Guilan) to 54.8 (Qom) kg ha−1. Cytogenetic analysis revealed that the Qom, Zanjan, Qazvin, Alborz, Kermanshah, and Lorestan accessions were diploid (2n = 24); the Guilan accession was triploid (3n = 36); and the Kerman accession was tetraploid (4n= 48). These findings indicate significant variation in both the quality and quantity of traits among the accessions, underscoring the importance of selecting appropriate accessions for specific applications, such as food, spices, processing, and pharmaceutical uses. Moreover, the difference of 2 tons per hectare in the yield of flowering shoots and 33.5 kg of EO per hectare is of considerable economic importance, and the observed variation at the ploidy level indicates a high potential for breeding and the development of hybrids with superior quantity and quality.