CUTTING PROPAGATION OF ZELKOVA SERRATA^©

Zelkova serrata is a deciduous tree in Ulmaceae from Japan, Taiwan, and eastern China. It is used for bonsai, shade tree, or park landscape because of its attractive habit, foliage colors, and heat and drought tolerance. Typically the plant reaches to 15-24 m tall with a spreading, upright-branching, vase-shaped crown (Fleme, 1983). Zelkova gained popularity because it was utilized to substitute American elm for its Dutch elm disease resistance and no elm leaf beetle (Dirr, 2011).
How to propagate this beautiful plant? Seed germination does not require pretreatment, and germination percentage would increase with prechilling at 4°C for 60 days (Ishii, 1979). However uniform Z. serrata seedlings can rarely be obtained by seed germination. Tissue culture had been successful, leaves and axillary buds were cultured on Murashige and Skoog (1962) medium containing half strength nitrogenous compounds to regenerate Z. serrata plants (Tomita, 1991), but tissue culture usually has high production cost and high technical requirement.
To regenerate uniform plants with lower cost for commercial production, rooting of stem cuttings is the most common application (Dirr and Heuser, 2006). Dirr and Frett (1983) rooted Z. serrata semi-hardwood cuttings treated with 0, 0.8, 1.6, and 3.2% IBA-quick dip and obtained rooting percentages at 32, 48, 62, and 54%, respectively. In our experiments, softwood and hardwood stem cuttings from 1-year-old seedlings treated with different types of rooting hormones at various concentrations were investigated in 2013-2014 hoping to regenerate Z. serrata all year round for market demand by rooting different types of cuttings.