Efficient in vitro germination and shoot proliferation of chilling-treatedwater chestnut (Trapa japonica Flerov) embryonal explants

Embryonal explants from water chestnut (Trapa japonica Flerov) seeds germin ated with high efficiency following a 40-d cold treatment at 5 degreesC on half-strength MS (Murashige and Skoog) medium supplemented with 2.7 muM N-6 -benzyladenine (BA), 0.5 muM 1-naphthaleneacetic acid (NAA) and 0.5 muM gib berellic acid (GA(3)). Control and chill-treated (different durations) embr yonal explants were cultured onto media which contained half-strength MS me dium supplemented with different concentrations and combinations of cytokin ins [BA, thidiazuron (TDZ), kinetin, zeatin], auxin (NAA) and GA(3). A liqu id half-strength MS medium with 1.1 muM BA and 0.5 muM NAA resulted in the best shoot proliferation of control or chill-treated explants, and the addi tion of 0.5 LM GA3 stimulated axillary shoot elongation. Germination and sh oot proliferation were always greater for chill-treated explants compared w ith control explants under the same culture conditions. Shoots produced in vitro rooted 100% of the time in a liquid half-strength MS medium with 1.1 muM BA, 0.5 muM NAA and 1.1 muM indole-3-butyric acid, and the regenerated plantlets were established successfully in a water chestnut paddy field.