Enhancement of direct somatic embryogenesis and plantlet growth from leaf explants of <Emphasis Type="Italic">Phalaenopsis</Emphasis> by adjusting culture period and explant length

Two Phalaenopsis orchids, Phalaenopsis amabilis and Phalaenopsis ‘Nebula’, were used to test the effects of induction period (30, 45 and 60 days), subculture period (30, 45 and 60 days), and explant length (1, 1.5 and 2 cm) on direct somatic embryogenesis from different regions (leaf tip, adaxial side, abaxial side and cut end) of leaf explants from in vitro grown seedlings. The results showed that the cut end had a highest competence to form embryos than the other regions of the leaf explants from both orchids. In addition, the suitable culture conditions were 60 days for induction period in darkness, 45 days for subculture period in light and 1 cm for explant length. Besides, the combinations of N⁶-benzyladenine (BA) and naphthaleneacetic acid were tested on their effects on plantlet conversion and further development of leaf-derived embryo. It was found that 0.5 mg/l of BA showed the highest response on plantlet conversion rate and the lowest browning rate of explants. In this communication, the embryo structures and development were proved by scanning electron microscopy.