Investigation of micropropagation of the Mediterranean xerophyte Thymelaea hirsuta (L.) Endl. (Thymelaeaceae)

Thymelaea hirsuta (L.) Endl. (Thymelaeaceae) is a dioecious and sometimes monoecious, perennial, evergreen, shrub, which is considered suitable for use as an ornamental landscape plant in xeriscaping, due to its particular morphology and tolerance to drought and poor rocky soils. In the present study the effect of various cytokinins on in vitro establishment and shoot multiplication, as well as of various auxins and techniques on rooting were examined in order to find 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 with 0.0-2.0 mg L^‑1 zeatin. The presence of cytokinin increased the number of shoots produced per explant compared to the control. After two subcultures on MS medium with 0.5 mg L^‑1 zeatin, explants were cultured on MS medium with 0.0, 0.25, 0.5, 1.0 or 2.0 mg L^‑1 ΒΑ or zeatin or kinetin or 6-γ-γ-(dimethylallylamino)-purine (2iP). Almost all explants produced shoots, excepting those cultured on medium with BA (>75%). More shoots explant^‑1 were produced in media containing 0.5-2.0 zeatin or kinetin or 0.25 ΒΑ (mg L^‑1), while shoot length was greater in media with 0.25-1.0 2iP or 0.25 zeatin (mg L^‑1). However, the produced shoots, excepting those cultivated in zeatin, exhibited a variety of morphological abnormalities, such as hyperhydration, deformation and dried appearance. Considering explant productivity and shoot normality, zeatin at 1.0-2.0 mg L^‑1 was accepted as the most appropriate for shoot multiplication, whereas rooting of microshoots was not achieved.