In vitro propagation ofSalix tarraconensis Pau ex Font Quer,an endemic and threatened plant

Summary Salix tarraconensis Pau ex Font Quer, an endemic willow species from northeast Spain, was micropropagated with nodal segments. Shoot multiplication was obtained with different cytokinins, either on Murashige and Skoog medium or woody plant medium. Best results for shoot formation were obtained on Murashige and Skoog medium containing 4.9 μM of 6-γ-γ-dimethylallylaminopurine. Shoots showed strong apical dominance, and some cultures displayed apical necrosis. Benzyladenine gave the worst results; shoots displayed very slow growth, deformed leaves, and hyperhydrity. Good rooting of shoots was obtained with different auxins or without plant growth regulators on woody plant medium. The best results (90-100%) were obtained within 20 d. On rooting media with indole-3-butyric acid or indoleacetic acid, shoot elongation was good (35-40 mm length). Apical necrosis was observed in elongating shoots on rooting medium, but this disturbance favored axillary bud sprouting and formation of new shoots. Shoot length and quality of roots decreased gradually as the concentration of naphthaleneacetic acid increased. Plant survival was 90% 4 weeks after removal fromin vitro conditions.