Callus formation from stem internodes of the apple rootstocks M.9, M.25, M.26, M.27 and the cherry rootstock Colt, and from pith of Nicotiana tabacum cv. Wisconsin 38 was initiated on 4 c~-naphthaleneacetic acid (NAA)-based media (2.0-10.0mgl-~). Transfer of callus to corresponding media lacking NAA allowed regeneration of shoots from callus of M.25, M. 27, Colt and tobacco but not of M.9 and M.26. With M.25 phloroglucinol (PG) depressed regeneration from 30 to 10% and no regeneration was observed in cultures grown in the presence of casein hydrolysate (CH) and glutathione (GSH).
Organogenesis was also obtained from leaf discs of M.27 employing 6-benzylaminopurine (BAP) at 5.0mg1-1 and 2,4-dichlorophenoxy acetic acid (2,4-D) at 0.1 mg 1-~. The regenerated shoots have been multiplied and rooted.
Organogenesis also occurred in M.26 from small (1-2mm), green, compact embryoid-like structures derived from stem and leaf surfaces of excised axiUary shoots. These structures differentiated into shoots at a low frequency (< 1%) on media containing BAP (1.0 mg 1 -~ ) and indole-3-butyric acid (IBA) (0.1 mg 1 -~ ) and could also be micropropagated by subsequent axillary shoot proliferation.