Ploidy status and karyotype variation in two Mentha L. species

Mentha L. is a valuable source for cytological investigations due to its pronounced polymorphism and diverse chromosomal races within species. Chromosome numbers have been studied in many species, but detailed karyotype analysis remains unexplored for the studied species. This study analyzed Mentha arvensis and M. viridis using aceto-orcein and DNA-based fluorochrome staining to elucidate their ploidy and karyotypic variation. The somatic chromosome formulae were 2n=6x=72m in M. arvensis and 2n=3x=36m in M. viridis. M. viridis showed comparatively larger chromosomal lengths, higher CVCI and CVCL values than M. arvensis, indicating greater variation in chromosomal length and centromeric dispersion. The GC-specific stain, chromomycin A3, revealed 5 and 2 CMA+ve chromosomes in M. arvensis and M. viridis, respectively. The AT-specific stain, 4,6-diamidino-2-phenylindole, showed 6 DAPI+ve chromosomes in M. viridis only. This unique banding pattern found in the CMA/DAPI staining highlights the distribution of AT- and GC-rich regions.