An unique system of somatic embryogenesis in the tree fern Cyathea delgadii Sternb.: the importance of explant type, and physical and chemical factors

Abstract

The effect of explant type (etiolation, age, length), physical (photoperiod, darkness) and chemical (sucrose and mineral salt concentrations) factors on somatic embryogenesis efficiency and sporophyte development in Cyathea delgadii was evaluated. Five-month-old cultures of sporophytes, which had developed 4–5 leaves, were used as a source of explants. The percentage response of stipes and the average number of somatic embryos were calculated after 2 months of culture. Etiolation of sporophytes used for culture initiation, was a critical factor in SE induction. Other factors studied significantly affected the production of somatic embryos. Optimum results were obtained when explants measuring 2.5 mm in length were excised from the youngest leaf of an etiolated sporophyte. Maximum SE efficiency (84.0 % response in explants; 42.3 somatic embryos per explant) was obtained on half-strength Murashige and Skoog medium supplemented with 1 % sucrose, under photoperiod conditions. However, light stimulated two different morphogenetic responses in explant cells: SE and apospory. In darkness, the number of somatic embryos was reduced to 32.9 per explant, but this was the only morphogenetic response observed. The presence of light alone was sufficient for somatic embryos growing on plain agar gel to reach maturity, but further development stopped shortly thereafter. The presence of both light and sucrose was necessary for the development of an embryonic leaf and root. For further sporophyte growth, mineral salts were essential. The micropropagation system described here is the first investigation into factors responsible for SE in ferns.