ELONGATION, ROOTING AND ACCLIMATIZATION OF MICROPROPAGATED SHOOTS FROM MATURE MATERIAL OF HYBRID LARCH

Factors were defined for elongation, rooting and acclimatization of mi cropropagated shoots of Larix x eurolepis Henry initiated from short s hoot buds of plagiotropic stecklings serially propagated for 9 years f rom an 8-year-old tree. Initiation and multiplication were on Schenk a nd Hildebrandt (SH) medium supplemented with 5 mu M 6- benzyladenine ( BA) and 1 mu M indole-butyric acid (IBA). Stem elongation was obtained in 36% of the shoots on SH medium containing 0.5 mu M BA and 63% of t he remaining non-elongated shoots initiated stem elongation after tran sfer on SH medium devoid of growth regulators. Rooting involved 2 step s: root induction on Campbell and Durzan mineral salts and Murashige a nd Skoog organic elements, both half-strength (CD-MS/2), supplemented with 1 mu M of both naphthaleneacetic acid (NAA) and IBA, and root elo ngation following transfer to CD-MS/2 medium devoid of growth regulato rs. Repeating this 2-step sequence yielded up to 67% rooted shoots. Ac climatization of plantlets ranged from 83% to 100%. Over 300 plants we re transferred to the greenhouse; some showed plagiotropic growth.