In vitro tissue culture: Towards conservation of threatened desiccation sensitive Encephalartos cycads seeds

Approximately 62% of the 355 cycad species in the world are classified as threatened with extinction. The African genus, Encephalartos, has a total of 65 species, approximately 70% of which are threatened. This status emphasizes the need to conserve these species; however, the recalcitrant nature of cycads seeds makes it difficult to conserve using conventional seed banking methods. Recalcitrant seeds have a short lifespan and cannot be dried or stored for prolonged periods as they become non-viable when they lose moisture. While studies on cryopreservation for conserving cycad germplasm and banking these desiccation-sensitive seeds has made some advances, cycad conservation is still limited to ex situ living plant collections. In vitro tissue culture is a promising technique for conserving cycads. While attempts have been made, there have been few reported successes and, to date, there has been no successful regeneration of Encephalartos species. As such, this study was aimed at developing an efficient and successful in vitro regeneration protocol for two Encephalartos species. Embryo regeneration of E. altensteinii and E. manikensis was assessed, testing the effects of plant growth regulators (PGRs) - 0.5 mg/L Kinetin and 0.5 mg/L 6-BAP, alone or in combination, sucrose (0, 15 and 30 g/L) and light. Within six weeks of culture, embryos of both species were able to regenerate, however, each responded differently to the tested variables. While shoot regeneration was evident for both species during this period, this was however not explained by any of the variables assessed in this study. Rooting was highest in the treatments with 0.5 mg/L Kinetin for E. altensteinii, after subculture rooting was favoured by the treatments with 0.5 mg/L Kinetin + 0.5 mg/L 6-BAP. Encephalartos manikensis rooting was significantly higher in PGR-free treatment in the first six weeks of culture. After subculture, rooting was enhanced by the treatment with the highest PGR concentration of 1.0 mg/L Kinetin + 1.0 mg/L 6-BAP. Darkness ...