Abstract
Stem segments with well-developed and dormant axillary buds of 30 Davidia involucrata
trees were collected as explants for a micropropagation study in January~February 2009 and
2010. These trees, originally from Beichuan Qiang Autonomous County, Sichuan Province,
China, were numbered and planted at Fushan Botanical Garden, Taiwan in 2008. Bud
dormancy breaking and new shoot production were achieved using axillary buds cultivated on
Woody Plant Medium (WPM) supplemented with 0.1~0.5 mg L-1 benzyladenine (BA), 1.6 g L-1 polyvinylpyrrolidone (PVP), or 100 mg L-1 ascorbic acid (AA). For the shoot multiplication,
shoot elongation, and rooting study, 5-mo-old in vitro shoot tips and nodal segments from trees
no. 22 and 28, which produced relatively more buds, were used. Among the different media
tested for shoot multiplication, the best result was obtained on WPM basal medium
supplemented with 2~3 mg L-1 BA. Averages of 5.3~5.6 shoots (shoot tip)-1 and 7.6~7.8
shoots (nodal segment)-1 were produced. WPM with low concentrations of BA (0.1~0.5 mg L-1) helped shoot elongation. On the best 3 medium compositions (i.e.,WPM with 3 mg L-1 indole-3-butyric acid (IBA), 1/2 Murashige and Skoog (MS) medium with 2 mg L-1 IBA, and WPM with
2 mg L-1 IBA and 0.2 mg L-1 α-naphthaleneacetic acid (NAA) for in vitro rooting, elongated
shoots had 100% rooting rates with averages of 9.6~10.6 roots explant-1. Among different individuals, great variations existed in shoot proliferation, elongation, and rooting rates when
explants were cultured under the foregoing best medium compositions. Tree nos. 6, 15,
28, and 30 easily produced plantlets by micropropagation, while tree no. 16 had the lowest micropropagation rate. After being acclimatized for 3 wk in a growth chamber (with a survival
rate of 95%) and then transferred to a greenhouse at Taipei Botanical Garden for 2~4 mo, some
of these 355 surviving plantlets were transplanted to a greenhouses at the Lienhuachih Research Center (63 plantlets) and Meifeng Farm (42 plantlets). After 1 yr, the survival rate at Meifeng
was the highest (97.6%), followed by those at Lienhuachih (57.1%) and in Taipei (43.6%).
Average heights of plantlets at the 3 sites were similar, at 5.1~5.9 cm. Tissue culture plantlets
of tree no. 30 had the highest survival rate and average height among different individuals at
all sites.