Improved organogenesis and micro-structural traits in micropropagated plantlets of Caralluma umbellata Haw. in response to Meta-Topolin

Caralluma umbellata Haw. is a rare and endemic xerophyte with astonishing therapeutic properties. It is used as an appetite suppressant and in weight loss management program. The natural population of this plant is decreasing due to overharvesting from the forests as an ethnomedicine. Therefore, an effective in vitro propagation system was developed using 6-(3-hydroxybenzylamino) purine ( Meta -Topolin; m T) for rapid clonal production of C. umbellata planting material. The highest shoot induction frequency (93.0%) and multiple shoot regeneration (6.0 shoots/nodal explants) was achieved on Murashige and Skoog’s (MS) medium fortified with 2.0 mg L −1 of m T in 4 weeks. The synergistic impact of 1.0 mg L −1 m T and 0.25 mg L −1 NAA (α-Naphthalene acetic acid) was evident in shoot proliferation (43.6 shoots per nodal explant with 6.2 cm length after 3rd subculture) as compared to 6-benzylaminopurine (BAP) and NAA combinations. The structural traits concerning optimized plant growth regulators (PGRs) were enumerated from the in vitro raised shootlets. Microscopic results revealed that m T and NAA combination promoted the structural developments in shoot systems with well-developed cuticle, epidermis, and the presence of a large area of ground and vascular tissues. Whereas, the shoots developed on BAP and NAA had poorly developed tissue systems with thin cuticle, underdeveloped epidermis, reduced cortex, xylem, and phloem tissues. The shoots derived from m T and NAA supplemented medium exhibited 100% rooting averaging with 4.0 roots per shoot and 2.7 cm in length on half-strength MS medium containing 1.0 mg L −1 indole-3-butyric acid (IBA). In contrast, BAP and NAA-derived shoots exhibited 75% rooting with 3 roots per shoot averaging 1.9 cm in length on 1.0 mg L −1 IBA. The plantlets were hardened and acclimatized well in greenhouse and shade-net. The plantlets derived from m T and NAA presented a significant increase in survival rate (94%) after transplantation in the field as compared to BAP and NAA-derived plantlets (81%). The presence of m T in the medium reduced structural abnormalities and mortality that may better serve the purpose of germplasm conservation, large-scale production, and the sustainable utilization of C. umbellata as a medicinal plant. Key message An improved shoot proliferation with well-developed tissue systems could be obtained in Caralluma umbellata by selecting 6-(3-hydroxybenzylamino) purine as a growth regulator, which reduced in vi