Background and Objectives: The Asteraceae family, with many genera and species, is one of the largest plant families. These plants are dispersed all over the world, except in tropical areas. They are used in traditional medicine. Studies conducted on this family showed that these plants, with basic chromosome numbers of x=9 and 15, exhibit different ploidy levels. The Lamiaceae family is also one of the largest flowering plant families, with global dispersion and medicinal species. The basic chromosome number is often x=12, and they are mainly diploid and tetraploid. The present study was conducted to document the chromosome number of different populations from the two families Asteraceae and Lamiaceae, to complement the data obtained from morphological and agronomic studies and to increase knowledge about the chromosome number and ploidy variation in these populations. Materials and Methods: The seeds of the superior populations studied belonged to the two families Asteraceae and Lamiaceae and seven genera (Achillea, Anthemis, Matricaria, Tanacetum, Tripleurospermum, Mentha, Nepeta), which were obtained from the Natural Resources Gene Bank of Iran. To break seed dormancy, various methods (chilling, removing the seed coat, diluted acid treatment, washing under running water) were used. For cultivation, 20 seeds from each population were separated and after disinfection, they were sown on wet filter paper and in Petri dishes and kept at a temperature of 4°C for four weeks. At the end of the chilling period, they were transferred to a germinator with regulated temperature and humidity. The roots were separated when their length reached 1.5 cm. Pretreatment, fixation, preservation, hydrolysis and staining were performed and finally, microscopic sample preparation was conducted using the squash method. Five metaphase plates were recorded for each population by a digital camera. Karyotypes of the populations were prepared using Photoshop software and their chromosome numbers and ploidy levels were determined. Micro Measure software was used to measure various karyotype parameters. Other indices, such as long arm (L%), short arm (S%), Intra-chromosome asymmetry index (A1), Inter-chromosome asymmetry index (A2), difference of relative length (DRL), total form percentage (TF%) and karyotype formula (KF), were calculated using Excel software and the relevant formulas. Results: In the genus Achillea, populations of A. millefolium (x=9) and A. wilhelmsii (x=15 and x=9) showed two ploidy levels (diploid & tetraploid). Total genome length (TL) values ranged from 53.12 μm in population 14198 of A. millefolium to 85.76 μm in population 23458 of A. wilhelmsii. All populations of both Anthemis tinctoria and Matricaria recutita were diploid with x=9 (2n=18). Chromosome lengths of M. recutita were longer than A. tinctoria, and the highest value of TL (65.40) belonged to M. recutita. Populations of Tanacetum parthenium and Tripleurospermum sevasnense with x=9 were diploid (2n=2x=18). For TL, there were no significant differences among Tanacetum parthenium populations. The longest total genome (TL=73.56 μm) belonged to population 1087 of Tripleurospermum sevanense. In the genus Mentha, the populations of M. longifolia (14161, 26436, 29910), and Nepeta, populations of N. catarica (15062, 21030, 33531), were all diploid with x=12 (2n=24). Total genome length (TL) values ranged from 17.64 μm to 19.88 in populations of M. longifolia. The highest and lowest values of TL were for population 29910 (Shahre Kord) and 26436 (Gazvin), respectively. These values ranged from 13.74 to 18.74 for populations of N. cataria. The populations of 21030 (Mehriz) and 15062 (Taft) showed the highest and lowest values of TL, respectively. In both species, the karyotype formula was short and more metacentric chromosomes. Conclusion: The superior populations (in terms of morphological and agronomic traits) were examined regarding chromosomal traits (number and type of chromosomes) and karyotypic traits (genome length, centromere position and symmetry traits). In the genera belonging to the family Asteraceae (Achillea, Anthemis, Matricaria, Tanacetum and Tripleurospermum), all species were diploid and tetraploid with x=9 (except for population 14930 of the species Achillea wilhelmsii with base chromosome number 15). The genera belonging to the family Lamiaceae (Mentha and Nepeta) were diploid with a base number of 12. |