Callus was initiated from cultured immature inflorescences of Hosta plantaginea Asch. ‘Grandiflora’ in darkness on a basal medium containing Murashige and Skoog salts, vitamins, glycine, i-inositol, sucrose, agar, and 10 mg/liter naphthaleneacetic acid (NAA) and 0.1 mg/liter 6-benzylamino purine (BA). Reculture of the callus onto a medium containing 0.01 mg/liter NAA and 5 mg/liter BA, resulted in the formation of numerous adventitious shoots. Adventitious shoots were initiated also from leaves and segments of leaves from shoots formed in vitro when cultured on a medium supplemented with 0.01-1 mg/liter NAA and 5 mg/liter BA. Root formation was achieved when individual shoots were excised and transferred to a medium containing the basal constituents without growth regulator supplements. Rooted plants were successfully transferred to soil.
Shoot tips proliferated in vitro were used as explants to determine the effects of various nutrient medium components and environmental conditions on shoot multiplication of Hosta decorata L. H. Bailey ‘Thomas Hogg’. The rate of axillary shoot multiplication was stimulated by the addition of either 0.01 or 0.10 mg×liter α-naphthaleneacetic acid (NAA) to medium containing 5 mg×liter 6-benzylamino purine (BA). Indoleacetic acid (IAA) and indolebutyric acid (IBA) did not promote axillary shoot formation. All 3 auxins were effective in promoting adventitious shoot initiation. In medium with 0.1 mg/liter NAA, BA at 5 mg/liter stimulated a higher number of shoots of axillary origin than did N6-isopentenylaminopurine (2iP) or N6-furfurylaminopurine (kinetin). However, equivalent or greater proliferation of adventitious shoots was achieved with 2iP or kinetin. Sucrose was essential for shoot multiplication and 30 g×liter was optimum. Inorganic phosphate (NaH2PO4 · H2O) and adenine sulfate stimulated growth and shoot multiplication while i-inositol, although not essential, enhanced shoot formation at 30 mg×liter. Axillary and adventitious shoot multiplication was optimum under photosynthetkally active radiation (PAR) of 70 or 130µE m-2s-1 at 21°C and under PAR of 70 µE m-2s-1 at 26°C. Rooting of shoots in vitro was obtained on basal medium without growth regulators or on medium containing 0.01 mg/liter NAA, and the plants were successfully established in soil. Plants obtained from culture which had lost leaf margin variegation regained it after receiving a cold room treatment of 3-6°C for 20 weeks.