Karyotypic Study and Chromosome Evolution in Some Iranian Local Onion Populations

Abstract
A karyotypic study was performed on 12 Iranian local onion (Allium cepa L.) populations. A number of mitotic cells at metaphase stage for each population were prepared. Chromosomes of suitable mitotic cells were counted and various parameters, including long arm (L), short arm (S), total length of chromosome (TL), relative length of chromosome (RL), arm ratio (AR), r-value, total chromosome volume (TCV) and centromeric index (CI), were measured. All populations were diploid with 2n=2x=16 and they were differentiated by their karyotype formula and parameters. Chromosome length varied in the populations and the highest quantity of chromatinic material was found in BehdashtShahrud onion. The onion populations under study occupied classes 1A and 2A of Stebbins’ karyotype classification, indicating the presence of a primitive symmetrical karyotype in these populations. The mean chromosome length ranged from 8.54 to 11.97 µm. Haploid genome length was in the range of 67.79 to 96.65 µm and mean centromeric index (CI) of complements varied from 41.1 to 43.7%.The chromosome types were detected as mostly metacentrics “m” and some submetacentrics “sm”, showing the karyotype formula of 8m (two populations), 7m+1sm (eight populations) and 6m+2sm (two populations). The cluster analysis using chromosomal parameters and based on Ward’s minimum variance algorithm assigned the populations into two groups.