Somatic Embryogenesis in Cymbidium through In Vitro Culture of Inner Tissue of Protocorm-Like Bodies

Abstract

Embryogenic callus (EC) was initiated from inner tissue (IT) of protocorm-like bodies (PLB) of Cymbidium orchid cultured on Murashige and Skoog (MS) media supplemented with 1-naphthaleneacetic acid (NAA) or 2, 4-dichlorophenoxyacetic acid (2, 4-D). EC was obtained within 15 days on a MS medium containing 2 mg•liter^-1 NAA or 0.5 mg•liter^-1 2, 4-D which was the most effective among the concentrations tested. When EC were transferred to a hormone-free MS medium, they produced protocorms within one month and complete plants in another 3 months. In contrast, the EC, in the presence of BA or NAA, produced light green, hairless, string-like structures in one month. These string-like structures grew 2 to 3 cm in length and died within three months. IT produced no callus in hormone-free MS medium or in a medium to which BA and NAA were added. After 5 days of culture, with NAA or 2, 4-D, a small mass of EC differentiated from the parenchyma cells of the vascular bundle on the basal cut end of IT sections. These ECs produced proembryoid-like structures after 10 days of culture; they became globular embryos 5 days later. The globular embryos differentiated into protocorms and plantlets after being transplanted to the hormone-free MS medium. These findings demonstrate that Cymbidium plantlets can be obtained from IT of PLB through somatic embryogenesis by manipulating the culture conditions.