Somatic embryogenesis and plantlet production using rejuvenated tissues from serial grafting of a mature Kalopanax septemlobus tree

An effective micropropagation technique via somatic embryogenesis has been developed using tissue from serially grafted shoots generated from a mature Kalopanax septemlobus tree (~40 y old). Callus was induced from leaf segments obtained from the grafts by culturing the explants in Murashige and Skoog (MS) medium supplemented with 2,4-D and 3% w/v sucrose under darkness. The effects of sucrose, coconut water, and polyethylene glycol (PEG-3350) were evaluated as factors to promote development of somatic embryos (SEs) from embryogenic callus. More than 90% of explants formed callus; however, only 2.5%, or 20 leaf segments out of 800 explants, formed embryogenic callus after 8 wk of culture. High sucrose concentrations (3% and 5% w/v) were effective in inducing SEs. Treatment with 2–10% v/v coconut water also had a positive effect on embryo induction. A synergistic effect on SE induction was obtained using sucrose and PEG, with presence of the latter compound resulting in smaller, more uniform SEs. Embryo germination and conversion to plantlets were significantly influenced by the gelling agents. In general, gelrite-gelled medium was superior to agar-gelled medium. In gelrite-gelled medium, gibberillic acid (GA3) enhanced embryo germination. Converted plantlets in an artificial soil mixture showed a 91% survival rate and displayed no distinct morphological variations. Our results indicate that reliable somatic embryogenesis and plant production can be achieved with rejuvenated tissues after repeated grafting of shoots derived from a mature Kalopanax septemlobus tree.