Effect of cytokinins on in vitro blastogenesis of Thymelaea tartonraira ssp. tartonraira (L.) All.

Due to its particular morphology (much-branched, silvery-grayish, silkily hairy leaves and yellowish flowers) and tolerance to drought and poor rocky soils, Thymelaea tartonraira ssp. tartonraira is considered suitable for use as an ornamental landscape plant in xerothermic urban and suburban areas, green roofs and landscape restorations including archaeological sites. In the present study the effect of various cytokinins on in vitro establishment and shoot multiplication was examined in order to develop an effective micropropagation protocol, since seed germination is low and stem cuttings fail to root. Shoot tip and nodal explants, excised from in vitro grown seedlings were initially cultured on MS medium either hormone-free or supplemented with 0.25 mg L^‑1 benzyladenine (ΒΑ) or 1.0 mg L^‑1 zeatin. More shoots per explant were produced on a medium with 0.25 mg L^‑1 ΒΑ (4.9) or 1.0 mg L^‑1 zeatin (3.7) compared to hormone-free medium (1.6), while no differences were observed in shooting percentage (>90%) and shoot length (over 3 cm). Shoots derived from hormone-free medium were subcultured twice on MS medium with 0.5 mg L^‑1 zeatin and then became source of nodal explants, which were cultured on MS medium with 0.0, 0.25, 0.5, 1.0 or 2.0 mg L^‑1 ΒΑ or zeatin or 6-furfurylaminopurine (kinetin) or 6-γ-γ-(dimethylallylamino)-purine (2iP). Almost all (>92%) explants produced shoots. The most shoots per explant (7.0-9.5) were formed on media containing 0.25-2.0 mg L^‑1 BA or 1.0-2.0 mg L^‑1 zeatin. However, at 2.0 mg L^‑1 ΒΑ excess callus and hyperhydrated shoots were observed. Shoot length was greatest (2.9-3.3 cm) on media containing kinetin or 0.25 and 1.0 mg L^‑1 2iP or 0.5 mg L^‑1 zeatin. Considering explants productivity and shoots normality, ΒΑ at 0.25-0.5 mg L^‑1 and zeatin at 1.0-2.0 mg L^‑1 were considered the most appropriate for shoot multiplication.