Direct induction of somatic embryogenesis and plant regeneration from cotyledon explants of Myrica rubra Sieb. & Zucc.

Somatic embryogenesis was induced on woody plant medium (WB) supplemented with Thidiazuran (TDZ) alone or in combination with 2,4-D from mature cotyledon explants of Myrica rubra. All concentrations of TDZ except 1.0 mgL-1 induced somatic embryos and adventitious shoots simultaneously within two months of culture. Addition of 2,4-D in the medium significantly improved induction of somatic embryos. Frequency of embryogenesis was only 3.34% with 7.00 embryos per explants when TDZ was fortified as a single growth regulator which was improved to 22.00% with the addition of 0.1 mgL-1 2,4-D in the media. Repetitive embryogenesis was induced on optimized concentrations (0.5 mgL-1 BA and 0.05 mgL-1 TDZ) of two cytokinins in combinations with various concentrations of 2, 4-D. Continuous culture of the explants with cluster of embryos on the induction media did not induce repetitive embryogenesis. On repetitive embryogenesis induction media, most of the embryos induced were smaller in size than those of the primary embryos during their induction stage.  TDZ in combination with IBA induced adventitious shoots on the surface of somatic embryos explants. TDZ (0.2 mgL-1) plus IBA (1.0 mgL-1) was the most effective combination with maximum number (8.5) of shoots per explant. Shoot elongation was achieved on the media supplemented with 0.5 mgL-1  BA concentration plus 0.1 mgL-1 NAA. Root induction on micro-shoots was directly related to the media strength.  Microshoots rooted on BW medium fortified with 0.5 mgL-1 IBA with highest rooting efficiency. Rooted plants were successfully hardened and grown in the greenhouse. The protocol reported here for M. rubra is efficient, reproducible and could be used for genetic transformation experiments.    Key words: Myrica rubra, Red bayberry, direct somatic embryogenesis, cotyledon explants, Thidiazuran (TDZ)