The objective of this work was the optimization of the conditions of in vitro
culture for callus production of Silybum marianum
(L.) Gaertn. ( Asteraceae
). Sections of cotyledons, previously disinfected by washing successively with ethanol 70°, NaClO (10% w/v) and Tween 20 (0.05% v/v) and rinsing with sterile distilled water, were used as explants. For its initial culture, B5 medium supplemented with BA and 2,4-D solidified with phytagel was used, and a 63% survival was achieved. To obtain callus, two solid media were assayed (S1 and S2) using B5 medium supplemented with growth regulators (BA and 2,4-D or NAA and BA, respectively). The calli were grown at 25°C during 45 days in darkness. Growth kinetics was studied using S1 medium obtaining a typical growth curve with an exponential phase after 14 days of incubation (rate of growth 0.005 gdry weight/ day) and stationary phase after 35 days. The rate of growth in S2 medium was slower, and rhizogenesis was observed starting on the fifth week of incubation. From these results, the best culture medium for callus production of Silybum marianum
was S1 medium.