In Vitro Germination of the Mediterranean Xerophytes Thymelaea hirsuta and Thymelaea tartonraira ssp. tartonraira as Affected by Scarification, Temperature, Photoperiod and Storage

Aim: ing to develop an efficient propagation method for the exploitation of Thymelaea hirsuta and T. tartonraira ssp. tartonraira in xeriscaping and pharmaceutical industry, the effect of: i) pretreatment (mechanical and chemical scarification or immersion in hot water, ii) incubation temperature (5-30 oC), iii) incubation light conditions (16 h photoperiod or continuous darkness) and iv) storage period at room temperature and darkness (up to 24 months), was examined on in vitro germination of their seeds. Seeds collected for two years from the same wild plants in Greece were surface sterilized with commercial bleach solution (15% for 15 min) after the abovementioned treatments and placed for germination in Petri dishes with half-strength MS medium in growth chambers. The rate and final percentage of germination were recorded. For both species, scarification after dipping in concentrated H2SO4, preferably for 20 min, was necessary for seed germination, which indicates coat dormancy. Higher germination percentages were observed at temperatures of 10-20 oC, under continuous darkness for T. hirsuta (79-100%) and regardless of photoperiod for T. tartonraira (73-90%). Storage time reduced the germination of only T. tartonraira seeds (54-68%, at optimum temperatures, 23 months after collection). For both species, an effective seed propagation protocol suitable for their exploitation as ornamental and landscape plants was developed.