Seed germination, micropropagation from adult and juvenile origin explants and address of hyperhydricity of the Cretan endemic herb Calamintha cretica

Abstract

The optimum range of temperature for germination (96-100%) of Calamintha cretica, an herb with potential pharmaceutical and horticultural uses, was 15 to 20 °C, with 10 and 30 °C cardinal temperatures. Storage up to one year did not affect germination. The effect of zeatin (ZEA), 6-benzyladenine (BA), kinetin, and 6-γ-γ-(dimethylallylamino)-purine added in MS medium at concentrations from 0.0 to 8.0 mg L-1 was tested for shoot proliferation of both adult- and seedling-origin nodal explants at first- and sub-culture. Both explant types responded similarly during in vitro culture. At cytokinin concentrations up to 1 mg L-1 explant response was high (over 85%) but shoot number per explant was low (1.2-2.2). Increasing cytokinin from 2.0 to 8.0 mg L-1 resulted to an analogous decrease of explant response and shoot length, and an increase of shoot number, particularly when ZEA or BA was used (5.0-6.6 shoots per explant, 0.5-1.0 cm long) with simultaneous though increase of hyperhydricity (up to 50%). The addition of 0.1 mg L-1 naphthaleneacetic acid into the 8.0 mg L-1 BA medium almost eliminated hyperhydricity and increased explant response, while the increase of agar concentration from 8.0 to 12.0 g L-1 eliminated hyperhidricity and induced the highest shoot proliferation (93-95% explant response, 11.2-12.3 shoots per explant, 0.8-1.0 cm long). Microshoots and microshoot clusters rooted (88-96%) on half-strength MS medium either hormone free or supplemented with 1 to 4 mg L-1 indole-3-butyric acid. Plantlets survived at 80% to 100% after ex vitro acclimatization in peat: perlite 1:1 (v/v).