In vitro propagation and cardenolide profiling of Digitalis ferruginea subsp. schischkinii, a medicinally important foxglove species with limited distribution in Northern Turkey

Cardenolides isolated from genus Digitalis are natural compounds used in treating cardiac insufficiencies. Recent investigations have also suggested the use of cardenolides in oncology. Due to the medicinal importance of the genus Digitalis, in vitro regeneration techniques would be useful for propagating the best genotypes selected from natural sources. To achieve this, Digitalis ferruginea subsp. schischkinii (Ivanina) K. Werner was collected from different locations along the Black Sea region of Turkey. In the cardenolide analysis, samples from Giresun and Trabzon showed a greater diversity than those from other locations, and thus, the Trabzon population was selected for plant tissue culture studies. In vitro regeneration was performed using cotyledonary leaves and hypocotyl segments on Murashige and Skoog (MS) medium containing various concentrations (0.5, 1.0, or 2.0 mg L−1) of 6-benzyladenine (BA), kinetin (KIN), or thidiazuron (TDZ) alone or in combination with indole-3-acetic acid (IAA) at 0.5 or 1.0 mg L−1. Among the media used for shoot regeneration, the highest frequency of shoot organogenesis was obtained from MS medium containing 2.0 mg L−1 TDZ and 0.5 mg L−1 IAA, producing 11.0 shoots per explant with 100% regeneration frequency from hypocotyl explants after 4 wk. For successful rooting, IAA was the most effective at 1.0 or 2.0 mg L−1, producing 16.3 or 17.3 roots per shoot, respectively, after 4 wk. Regenerants from several medium types were grown in a greenhouse for 6 mo, and all displayed similar cardenolide contents, i.e., the lanatoside C level was around 0.3% (w/w) while the levels of lanatosides A and B, digoxin, and digitoxin were less than 0.08% (w/w), similar to plants grown from seeds collected from Trabzon district.