Arbutus unedo L., A. andrachne L., and their natural hybrid, A. ×andrachnoides Link, are the three Arbutus species of the Eastern Mediterranean Macchia. A. unedo is used as an ornamental plant and as cut foliage, whereas the other two species have the potential to be introduced to the floricultural industry. This study was carried out to clarify whether the seeds of these Arbutus species possess dormancy to determine the temperature range for their germination and the effects of storage period on germination. Seeds of the three species, which were stored dry at 25 °C for either three or 11 months, germinated at very high percentages (82% to 99%) and in a short period of time (24 to 46 days) when incubated at 15 or 10 °C without any pretreatment proving that they do not possess dormancy; germination was faster at 15 °C. At 20 °C only seeds of A. unedo and A. andrachne stored for three months germinated (29% to 34%), whereas at 25 °C, there was practically no germination. Seeds stored for three months germinated (61% to 75%) when incubated at 5 °C, but the germination was delayed and the seedlings did not grow further than the appearance of the radicle unless transferred at a higher temperature (10 to 25 °C). After 27 months of dry storage at 25 °C, seeds did not germinate when incubated at the range of 10 to 25 °C even after pretreatment with cold stratification.
Konstantinos F. Bertsouklis and Maria Papafotiou
Georgia Vlachou, Maria Papafotiou and Konstantinos F. Bertsouklis
Seed ecophysiology and micropropagation of Clinopodium nepeta, an aromatic Mediterranean plant with pharmaceutical and horticultural uses was investigated. The optimum germination temperature of seeds stored at room temperature for 0, 6, or 12 months was 15 to 20 °C (100% germination completed in 10 to14 days) and cardinal temperatures were defined at 10 and 30 °C (80% to 82% and 62% to 76% germination, respectively). Six or 12 months of storage did not seem to affect germination, although 12-month-old seeds germinated at higher percentage and completed germination earlier at 15 °C than at 20 °C. Concerning micropropagation, shoot multiplication at subcultures of both adult plant- and seedling-origin nodal explants was tested on Murashige and Skoog (MS) medium supplemented with various cytokinin types, i.e., zeatin (ZEA), 6-benzyladenine (BA), kinetin (KIN), and 6-γ-γ-(dimethylallylamino)-purine (2IP), at various concentrations from 0.0 to 8.0 mg·L−1. Both explant types presented a rather similar response during in vitro culture. Increasing concentration of all cytokinin types resulted in an increase in shoot number per responding explant (1.1–5.3) and in most cases a decrease in shoot length (0.6–3.4 cm). Increasing cytokinin concentration induced hyperhydricity to a number of shoots (0.1–6.5) per explant, mostly when ZEA and BA were used. Supplementing the MS medium with 8.0 mg·L−1 BA combined with 0.1 mg·L−1 1-naphthaleneacetic acid (NAA) led to almost elimination of hyperhydricity and very satisfactory shoot production (80%/88% explant response and 6.5/7.5 shoot number per responding explant for seedling- / adult-origin explants, respectively). Alternatively, increasing the agar concentration to 12.0 g·L−1 and supplementing the medium with 8.0 mg·L−1 BA only, resulted in the same effect on eliminating hyperhydricity, such as the addition of NAA, and in the best shoot multiplication response achieved in this study (100% explant response, 9.4/9.9 shoots per explant for seedling-/adult-origin explants, respectively). Microshoots rooted abundantly (92% to 100%) on half-strength MS medium, either Hf or supplemented with 0.5 mg·L−1 to 4.0 mg·L−1 indole-3-butyric acid (IBA). The addition of IBA to the rooting medium, regardless of its concentration, affected only the root length by increasing it 2- to 3-fold. Microshoot clusters produced on multiplication media rooted at 96% when cultured on Hf half-strength MS medium. Rooted microshoots and shoot clusters survived at 80% to 100%, respectively, after ex vitro acclimatization in peat:perlite 1:1 (v/v).