Cytogenetic study of some populations of the genera Alyssum L. and Malva L.

Background and Objectives: The genera Alyssum L. and Malva L., belonging to the Brassicaceae and Malvaceae families, respectively, comprise annual and perennial plant species with considerable medicinal and ecological importance. These genera are widely distributed throughout Iran and have long been used in traditional medicine because of their expectorant, antitussive, and laxative properties. However, cytogenetic information regarding the chromosome number, ploidy level, and karyotype characteristics of native populations remains limited or incomplete. Therefore, the present study aimed to determine the somatic chromosome number, assess ploidy diversity, and characterize the karyotypic features of selected populations of Alyssum and Malva in order to provide fundamental cytogenetic information for taxonomic studies, conservation, and future breeding programs.
Materials and Methods: Seeds of eight populations representing Alyssum stapfii, A. hirsutum, Malva sylvestris, and M. parviflora (two populations of each species) were obtained from the Gene Bank of Natural Resources of Iran and grown under controlled conditions following appropriate seed germination treatments. Root-tip meristems were collected for chromosome preparation using the squash technique after pretreatment, fixation, hydrolysis, and hematoxylin staining. Chromosome observations were performed using an Olympus BX40 light microscope, and high-quality metaphase plates were photographed for subsequent analyses. Chromosomal parameters, including long arm length (LA), short arm length (SA), and total chromosome length (TL), were measured using Micro-Measure software. Cytogenetic indices, including the centromeric index (CI), intrachromosomal and interchromosomal asymmetry indices (A1 and A2), total form percentage (TF%), arm ratio (AR), difference in relative chromosome length (DRL), symmetry index (SI), centromeric gradient (CG), and dispersion index (DI), were calculated using Microsoft Excel and standard cytogenetic formulas. Karyotype symmetry was classified according to the systems proposed by Stebbins and Levan. Statistical analyses were performed using SAS software.
Results: In the genus Alyssum, the basic chromosome numbers were x= 7 and x= 8, with tetraploid (2n=4x = 32) and hexaploid (2n=6x = 42 and 48) cytotypes identified among the studied populations. According to Stebbins’ karyotype classification, all Alyssum populations were assigned to symmetry class 1C, with metacentric chromosomes predominating. Analysis of variance revealed that only the centromeric gradient (CG) differed significantly among populations (P≤ 0.01), whereas the remaining cytogenetic parameters showed no significant differences. Based on the values of A1, A2, TF%, SI, and the karyotypic formula, population 30546 (Khalkhal) of A. stapfii exhibited the most symmetrical karyotype. Mean comparison indicated that the greatest total chromosome length (1.31 μm) was recorded in population 23372 (Taft) of A. stapfii. In the genus Malva, the basic chromosome numbers were x=7 and x=14, with hexaploid chromosome complements of 2n=42 and 2n=84 observed among the populations. The Malva populations were classified into Stebbins’ symmetry classes 1B, 1C, and 2C, with metacentric chromosomes predominating in all populations. Significant differences were detected among populations for DRL, A2, and DI (P ≤ 0.01). Among the evaluated populations, population 012 (Tangestan) of M. parviflora exhibited the greatest total chromosome length (1.22 μm).
Conclusion: The results of this study demonstrate substantial cytogenetic diversity among the evaluated populations of Alyssum and Malva, particularly with respect to chromosome number, ploidy level, and karyotype structure. Such diversity is likely associated with adaptation to the diverse ecological conditions of their natural habitats. The cytogenetic information generated in this study provides a valuable foundation for taxonomic revision, evolutionary and phylogenetic investigations, germplasm conservation, and the development of breeding programs for these medicinally important genera.