Cytogenetic studies in six populations of Silybum marianum (L.) Gaertn.

This investigation was carried out on six populations of Silybum marianum (L.) Gaertn. in Isfahan Research Center for Agriculture and Natural Resources, 2009. Karyotype of mitotic cells in metaphase of root apical meristem was studied. The base number of chromosomes for all populations was x = 17 and all populations were diploid. Based on Stebbin's two- way table, all populations were located in class 2B indicating the same evolutionary status. Analysis of variance showed significant differences for the length of the smallest chromosome, asymmetric index, and coefficient variation of centromic index (p < 0.01), total chromosome length, sum of small arms, sum of long arms and the largest length of chromosome (p < 0.05). Factor analysis introduced two factors that justified more than 94 percent of total variation. In the first factor, total chromosome length (TL) and sum of long arms (SLa) were identified as the most important factors while asymmetric index (AI) and coefficient variation of centromic index (CVci) in the second factor were highly effective. All populations were classified in four groups by cluster analysis. The least Euclidean distance was between Ahvaz and Sary populations and the highest Euclidean distance was observed between Ahvaz and Amol. Analysis of variance showed significant differences for all traits among groups. Populations of Ahavaz, Sary and Esfahan in the first group were superiour in terms of TL, SSa, SLa, LC and SC compared to other goups. Population of Amol in the second group showed the lowest SC, Cvci, and AI. Maximum CVci and AI were observed in population of Kordestan while TL, SSa, SLa and LC were the least in this population. Population distribution diagram was drawn based on the first and the second component values that would confirm the results of the cluster analysis.