SOMATIC EMBRYOGENESIS AND SHOOT REGENERATION FROM EXCISED ADVENTITIOUS ROOTS OF THE ROOTSTOCK ROSA-HYBRIDA L MONEYWAY

Plants were regenerated from excised adventitious roots of the rose ro otstock 'Moneyway' via a three step procedure: callus induction, induc tion of somatic embryos and shoot development. Callus was induced on e xcised roots after incubation for 4 weeks in the dark on SH-medium (Sc henk and Hildebrandt) containing 50 mu M 2,4-dichlorophenoxyacetic aci d. For embryo induction, calluses were transferred to hormone-free SH- medium and incubated for 8 weeks. The use of Gelrite instead of agar d uring callus induction stimulated somatic embryogenesis (up to 16% of the explants formed organized structures), whereas the presence of 6-b enzylaminopurine in this phase inhibited subsequent regeneration. Yell ow solid calluses with embryo-like cotyledons or primordia and friable calluses with embryos were selected, and upon incubation in the light shoots developed. Shoot development was faster and more frequent on s olid callus than on friable callus (64% and 21% of the calluses finall y formed one or more shoots, respectively). Eleven out of thirteen reg enerants developed similarly to control shoots. Finally this regenerat ion method is compared with other systems for somatic embryogenesis an d opportunities for the production of transgenic rose rootstocks and r ose cultivars are discussed.