Micropropagation of Salix pseudolasiogyne from nodal explants

The effect of phytohormones on the breaking of dormancy of axillary buds in Salix pseudolasiogyne and their subsequent proliferation from nodal explants were examined. Nodal explants obtained from a 20–year-old S. pseudolasiogyne tree were cultured either on woody plant basal medium (WPM) or WPM supplemented with benzyladenine (BA, 2.2/4.4 μM), zeatin (1.1/2.2 μM), gibberillic acid (GA₃, 2.9 and 14.5 μM), and GA₃ + BA (2.9 + 4.4 μM). Although axillary shoots developed in all the media, a higher percentage bud break occurred on BA supplemented media. To corroborate the results, endogenous levels of cytokinins Cks, N ⁶-isopentenyladenine (iP), zeatin riboside (t-ZR), dihydrozeatinriboside (DHZR)] and abscisic acid (ABA) were determined. On BA supplemented media, the levels of zeatin type (Z-type) of Cks were higher than those of isopentenyladenine type of Ck in the explants, while the ABA level was low. Axillary shoots did not grow well and became necrotic upon subculture to fresh basal WPM. In order to improve shoot growth, they were subcultured twice at a 4-week interval on to WPM supplemented with BA (2.2/4.4 μM), GA₃ (1.4 μM), or GA₃ + BA (1.4 + 4.4/2.9 + 4.4 μM). Maximal shoot growth (93%) was achieved on WPM supplemented with 2.2 μM BA. Comparative analyses of endogenous Cks revealed that higher Cks (Z-type Cks) were present in actively growing shoots. Rooting was readily achieved when the shoots were subcultured to WPM without phytohormones. The rooted plants were acclimatized well upon transplantation.