Protocols for Micropropagation of Woody Trees and Fruits

122
D. EWALD
Root development. After the induction period, shoots were placed directly in JIFFY
7 peat pellets and saturated with water. The peat pellets were placed into small
plastic greenhouses. Growing peat moss (Sphagnum spec.) placed in-between the
peat pellets avoided a fungi attack which otherwise occurred very often. The period
of root development lasted 5–7 months until roots were visible outside the peat
pellets (Figure 1D). For that reason, moisture content of the peat pellets had to be
checked weekly (to avoid drying out).
2.5. Hardening and Transfer to the Field
After rooting, the plants were transferred into rootrainers (RONAASH Ltd. Scotland, 4.5
× 4.5 cm, 20 cm high, each for 40 plantlets) in propagation compost (EINHEITSERDE
type VM) and placed under high pressure fog (95% air humidity). Conditioning was
carried out by successive reduction of the air humidity over a period of 1 month.
Like for other conifers, two main different forms of growth behaviour were visible
after transfer to the soil, orthotropic growth and plagiotropic growth. In Taxus this
growth behaviour was closely related to the position of needles on the elongating
shoot. A radial position of needles around the shoot was an indicator for orthotropic
growth, similar to normal seedlings. A needle arrangement on two sides only, often
v-shaped along shoots, was an indicator for a branch-like or plagiotropic growth
(Figure 1E). These two growth characters were observed on shoots within propagation
culture in vitro for several clones. Small shoots (20 mm)
showed an almost equal relation (1:1). The amount of shoots forming the v-shaped
needle position increased during shoot elongation. There was a close correlation of
growth (orthotropic or plagiotropic) and the needle position on the shoot (radial or
v-shaped). With increasing shoot length after transfer to the soil (>40 mm), shoots
with radial needles on base of shoots often formed at the top of the shoot the
v-shaped needle position. Nevertheless, the relation of shoots with different needle
positions was approximately 1:1. Observations in the future will give information if
some of the trees produced will express an orthotropic growth demonstrating a
partial rejuvenation. Examinations of rooted cuttings from adult trees led to the
conclusion that orthotropic growth of the plants has not yet been achieved after a
period of 6 years in the field. This may indicate that the physiological differentiation
of Taxus tissues is fixed in material from cutting propagation. The comparison of
cutting-propagated versus micropropagated Taxus plants (Figure 1F) will allow
conclusions about the capacity for the micropropagation cycle to restore a seedlinglike
(rejuvenated) growth behaviour, which would be very important from the point
of view of utilisation of the material in forestry plantations.