Genetic Investigations on Silybum marianum and S. eburneum with Respect to Leaf Colour, Outcrossing Ratio, and Flavonolignan Composition

Abstract

In crossing experiments between S. marianum and S. eburneum the number of fruits produced was relatively high as compared to the two parental species. All the F₁-plants showed the variegated leaf characteristic of S. marianum, whereas after selfing the F₂-plants had completely green and variegated leaves in a ratio of about 3:1 indicating that the leaf colour is monofactorially inherited. This proves that the two species are only variants. Using leaf colour as the genetic marker, the outcrossing rate in field experiments was studied. Since the outcrossing rate on average is only about 2%, Silybum is predominantly a self-pollinator. From 11 randomly selected plants, three inbred generations were produced and their silymarin composition (silibinin, silidianin, silichristin) was studied. Two types of lines could be distinguished based on the relative values of three flavonolignans: Lines with approximately 70% silibinin, 30% silichristin, and traces of silidianin in all inbred generations and those with the relative contents of the compounds 30%, 57%, and 13%, respectively.

Key words

Silybum - Asteraceae - interspecific hybridization - outcrossing ratio - inbred lines - silymarin composition