Protocols for Micropropagation of Woody Trees and Fruits

MICROPROPAGATION OF MATURE TREES 241
shoot forming capacity was higher in the apical part where the mean numbers of
shoots per apical segment explant were 5.5 ± 1.6. The basal parts responded to culture
on multiplication medium with the mean number 3.8 ± 1.8 of shoots per explant. In
the apical parts the new adventitious shoots arose from the meristemoids that were
formed in calluses on the bases of apical segments (Figure 2B). The removal of the
apex released the axillary buds from apical dominance and the adventitious shoots
formed on the elm shoot basal parts originated from axillary buds (Figure 2C).
2.4. Rooting of Shoots
Mixed samples of 50 microcuttings about 3–4 cm long from 15 clones of each elm
species were used for rooting and acclimatization. The rooting was performed in two
steps. Transferred shoots were cultured in black boxes in air-conditioned room at
25°C for 1 week on the agar medium with one-third strength MS enriched with αnaphthalenacetic
acid (NAA) as the sole growth regulator (Table 2). After 7 days the
shoots were transferred onto the hormone-free medium (one-third strength MS) and
exposed to 16 h photoperiod (white fluorescent light, 30 µmol m –2 s –1 ). Roots
appeared in all species after 7–8 days. The percentages of rooted U. minor and U.
laevis microcuttings were high, 95.8% ± 2.1% and 92.8% ± 3.6%, respectively, while
in U. glabra it reached only 85.6% ± 2.7%. After 3–4 weeks rooted shoots were
transferred into non-sterile substrate for acclimatization (Figure 3A).
A B
Figure 3. A) Rooted elm plantlet after 4 weeks cultivation in agar medium. B) An elm plantlet
growing in perlit for 15 days.