Chromosomal Variation Studies in some Thymus Medicinal Plant Species

Eight accessions of Thyme medicinal plant, belonging to Iranian endemic Thymus daënensis, T. eriocalyx, T. migricus and an unknown Thymus spp species, were tested for karyotypic analysis, using squash technique and 2% (w/v) aceto-orcein staining method. Chromosomal parameters examined were: short arm (S), long arm (L), total length of chromosome (TL), arm ratio (AR), r-value, total chromosome volume (TCV), relative length of chromosome (RL), form percentage of chromosome (F%), Difference range of relative length of chromosome (DRL), total form percentage of karyotype (TF%), symmetry index (S%), centromeric index (CI), total chromatin length (X), dispersion index (DI) and coefficient of variation (CV%). ANOVA showed significant differences between accessions for S, TL and TCV. Six accessions were distinguished as diploids and two as tetraploids. The mean length of chromosomes ranged between 0.88 and 1.07 µm. The most common karyotype formula (KF) was 30m (5 accessions), followed by 28m, 56m and 58m+2sm (1 accession of each). Karyotypes were mostly symmetrical, falling in the Stebbins 1A category, except for A8 accession which fell in category. The present study indicated intra- and inter-specific variations in Thyme accessions.