Propagation of Ornamental Plants
17(2): 55-63, 2017
EFFICIENT VEGETATIVE PROPAGATION OF TORENIA CULTIVARS BY LEAF CUTTING
Tanapoom Laojunta*, Takako Narumi-Kawasaki, and Seiichi Fukai
Horticultural Science, Faculty of Agriculture, Kagawa University, Ikenobe 2393,
Miki-cho, 761-0795 Kagawa, Japan, *Fax: + 81-87-891-3072,
The number of commercial Torenia cultivars including seed and vegetatively propagated genotypes has increased. For vegetatively propagated genotypes, an efficient propagation system with reduced production costs is required to meet demand for young plants in flower markets, which concentrates at rather short-term in spring. The aim of this study was to investigate the effect of leaf position and explant type for the propagation of Torenia by leaf cutting. ‘Summer Wave Blue’ apical shoot cutting (≈ 2 cm) and leaf explants (whole leaf without petiole) were cut and incubated in a medium (Metro-mix 350) at 20 ± 2°C, 25 ± 2°C, and 30 ± 2°C in June (summer) and November (winter). Regrowth of shoots in shoot cuttings and shoot regeneration and its growth in leaf cuttings were temperature dependent. Results showed that propagation efficiency of leaf cutting was much higher than those of shoot cutting, i.e. 4.6 shoots were obtained by leaf cutting in summer season. Leaves were taken from three positions (upper, middle, and lower) on the stem (about 15-20 cm). Four types of explants (whole leaf with petiole (W + P) or without petiole (W − P), and upper half (UH) or lower half (LH) of leaf) were made from the leaves and incubated for 25 days. Leaf explants taken from the upper and middle shoot positions showed higher regeneration with a higher number of adventitious shoots and longer shoots. Histological observation of leaf cuttings showed that a meristematic structure was observed in the sub-epidermal tissue of the swollen part near the vascular bundle at the distal end of the explants 10 days after cutting. Vegetative propagation by leaf cutting could be adapted for most of the tested 25 torenia cultivars. Twelve of the twenty-five genotypes showed high shoot regeneration capacity (>85%).
Key words: explants, histological observation, leaf primordial, meristematic tissue, shoot regeneration