Breeding Objectives and Selection Criteria for Milk Thistle [Silybum marianum (L.) Gaertn.] Improvement

Milk thistle [Silybum marianum (L.) Gaertn.] is an important medicinal-industrial plant. The medicinal compounds of milk thistle are derived from its seeds. The plant is commercially cultivated for the production of silymarin. Cultivation offers the opportunity to optimise achene yield and silymarin content. Furthermore, efforts should be made to develop new cultivars. The main objective of milk thistle breeding is to develop high yielding cultivars with elevated silymarin content. There are few developed cultivars of milk thistle (e.g. Argintiu, Budakalaszi, Szibilla, Khoreslo, Babak Castle, Mirel, Silma and Silyb). Different genotypes of milk thistle have variable amount of silymarin e.g. a ‘Royston’ genotype is rich in silymarin (6-10%). Further progress can be made by using the genetic diversity available in abundance in different genotypes. The main concern of the breeder should be to increase the yield and silymarin contents of the seeds. Asynchronous flowering and seed shedding are also major problems in milk thistle cultivation. At the time of harvest, the plants have flower heads at all stages of development resulting non-uniform maturation of seeds. Therefore, a breeding effort in milk thistle should be planned to obtain plants with simultaneous flowering and reduced crop losses. The developed cultivar Argintiu is characterised by simultaneous seed maturation in flower heads. The wild populations, as valuable gene pools, could be exploited for the improvement of milk thistle crop.