Vegetative propagation of Syringa vulgaris L. in vitro.

Excised shoot tips from adult Syringa vulgaris L. plants were rejuvenated by repeated subculturing in vitro. The number of subcultures required to rejuvenate the shoots was strongly dependent on the age and genotype of the plant material. Three rootstocks (K8, A2 and A3) and 5 cultivars (Mademoiselle Marie Legray, Madame Florent Stepman, Maréchal Foch, Hugo Koster and Herman Eilers) were studied in vitro. The basic culture medium for isolation, subculture and shoot elongation contained: Murashige and Skoog (MS) macro-salts 1.5 strength, MS micro-salts (except Fe), NaFeEDTA 50 mg/1, saccharose 3.5°2iP 0.8 mg/1, Difco Bacto-agar 0.8°pH 6.0 and distilled water. The cultures were incubated in a growth room at 21°C and a day/night schedule of 16 h fluorescent light/8 h darkness. After rejuvenation, cloning was realized by repeated single-node culture. The application of a cytokinin and low irradiance (4–5 W m-2) induced stem elongation from pre-formed buds in the axils of the leaves. Zeatin(riboside) was most effective for stem elongation, followed by 2iP. The cytokinins, BA and kinetin, were not very effective in inducing stem elongation. Stem elongation was dependent on the genotype used. High cytokinin levels (2–5 mg/1) induced axillary branching but hardly any stem elongation and the leaves were strongly curled. Single-node culture and stem elongation in a medium containing 1.0 mg/1 2iP was definitely the best method of propagating lilac in vitro. Shoots were easy to root on a cytokinin-free medium with auxin or on an artificial substrate (rock wool) after an auxin dip. Acclimatization of in vitro rooted shoots to greenhouse conditions was successful when at low irradiance and high relative humidity for the first 2 weeks after transfer