Comparative Study of Chromosome Morphology in Silybum marianum

Abstract

Karyotype and morphology of mitotic chromosomes in four populations of medicinal plant Silybum marianum collected from various geographical locations of Iran and two cultivars of this species were studied. Chromosome characteristics were measured from 10 complete metaphase cells using Micromeasure software. Results showed that S. marianum is a diploid species with 2n=2x=34 chromosomes. The karyotype consisted of six pairs of metacentric, ten pairs of submetacentric, and one pairs of acrocentric chromosomes. One of the chromosomes (chromosome 1) had a secondary constriction on centromeric region of its short arm. Karyological characteristics of all materials studied were similar to each other, however, among different genotypes some variations were observed on chromosome arm ratios and relative lengths. According to Stebbin's asymmetry index, S. marianum is placed at 2B category.