In vitro shoot multiplication of eastern white cedar (Thuja occidentalis)

A protocol for clonal propagation of eastern white cedar (Thuja occidentalis L.) was enhanced by optimizing the shoot multiplication stage using unbranched in vitro-produced shoots. This was achieved by careful selection of different medium components. An optimum range of 10 to 14 axillary shoots was obtained when shoots were cultured on half-strength Quiorin and LePoivre medium containing 10μM filter-sterilized zeatin for 3 wk. Transfer of the treated shoots to cytokinin-free medium containing 0.05% activated charcoal improved both the number and quality of the axillary shoots produced. Maximum axillary bud induction was also accomplished when shoots were pulsed in 1 mM liquid, filter-sterilized zeatin for 3 h, and then transferred to half-strength Quiorin and LePoivre, charcoal-containing medium. Inclusion of 4% sucrose improved the number of axillary shoots obtained. Half strength of the major salts produced an optimum response. Shoots obtained from different cultures (1 to 5 yr old) responded similarly to the applied cytokinin; however, newly induced shoots (4 mo. old) gave a significantly higher response.