Innovative applications of flamingo explants and TDZ in Digitalis purpurea L. organogenesis

Digitalis purpurea L. is a valuable medicinal and ornamental species, but its conventional propagation is constrained by low seed germination and high genetic variability. The present study aimed to develop an efficient and reproducible in vitro regeneration system for D. purpurea through both direct and indirect organogenesis by optimizing explant type and plant growth regulator (PGR) combinations. Among the explants evaluated, hypocotyl-cotyledon (flamingo) explants exhibited the highest morphogenic competence, whereas leaf and root explants showed no regenerative response under any treatment. In direct organogenesis, MS medium supplemented with 0.25 mg L⁻¹ thidiazuron (TDZ) was the most effective, producing the maximum shoot length (6.3 mm) and shoot number (8.6 shoots per explant). Indirect organogenesis was strongly influenced by auxin type, with callus induction reaching 100% in flamingo explants cultured on media containing 0.5-1 mg L⁻¹ NAA, while 2,4-D was markedly less effective. Shoot regeneration from callus was significantly enhanced by cytokinin-polyamine interactions, with the highest shoot proliferation (up to 28 shoots per callus) and superior shoot elongation obtained on MS medium supplemented with 0.25-0.5 mg L⁻¹ BAP in combination with 50 mg L⁻¹ putrescine. Root induction was optimized on half-strength MS medium containing IBA, where 0.25 mg L⁻¹ IBA resulted in the highest rooting frequency (91%), maximum root number, and well-developed roots. Overall, this study highlights the critical role of explant selection and tailored PGR-polyamine combinations in establishing a high-efficiency micropropagation protocol for D. purpurea, providing a reliable platform for large-scale propagation and future biotechnological applications.