Development of encapsulation techniques for the production and conservation of synthetic seeds in ornamental plants

Abstract

The synthetic seed (synseed) technology, initially developed through the encapsulation of somatic embryos, is now available for the use with non-embryogenic in vitro-derived explants, such as buds and nodal segments. For ornamental plants, to date there are few reports dealing with the production and the conservation of synseeds. Hence, the present study was conducted to develop an efficient encapsulation protocol for apical and axillary buds from various ornamental shrubs, i.e., oleander (Nerium oleander L.), photinia (Photinia fraseri Dress.), and lilac (Syringa vulgaris L.). For encapsulation, apical and axillary buds were excised, directly immersed in a Na-alginate solution, and then released dropwise in 100 mM CaCl2 center dot 2H(2)O for bead hardening. With photinia, best results were achieved when the synseeds were prepared using 3% Na-alginate, beads hardened for 30 min and germinated on hormone-free or BA-containing gelled MS medium. Thus, up to 92% of synseeds germinated and converted to shoots in a period of 10-11 days. The synthetic seeds of lilac, containing apical buds, showed a shorter germination time when 10-30 g 1(-1) sucrose was included in their artificial endosperm. Successful medium-term conservation was then achieved with the storage of synthetic seeds at 4 degrees C in the dark on gelled MS medium, where up to 75% (oleander) and and 9 1 % (photinia) synseeds still germinated after 2 or 3 months of cold storage, respectively. Moreover, promising results have been obtained with the cryopreservation of photinia apical buds by means of the technique of encapsulation-dehydration.