In vitro direct organogenesis of the Cretan dittany (Origanum dictamnus L.), an important threatened Greek endemic species

Abstract

Dittany of Crete (Origanum dictamnus L.) is a threatened medicinal-aromatic plant of Lamiaceae family which is a local endemic to the Island of Crete, Greece. Its high culinary use and increasing demand in the pharma, perfumery, cosmetic and food industry along with its overexploitation from its natural habitat has threatened this species and has necessitated its large-scale production for industrial exploitations using advanced technologies. Micropropagation is considered a good tool for ex situ conservation of endangered species with reduced populations in the wild, low germination rates and low seed production. In this study, moderate germination percentages (40-41.38%) were exhibited for seeds after 40 days of culture at 21-23 oC in MS medium regardless of photoperiod regime (16h light/ 8h dark, 24h darkness), without significance difference. In the proliferation and rooting stage, three basal culture media (MS, WPM, Gamborg B5) were tested in combination with two concentrations of 6-benzyladenine (BA) (1.1, 2.2 μM) and indole-3-butyric acid (IBA) (0.125, 0.25 μM), all supplemented with 0.3 μM gibberellic acid (GA3), 20 g L-1 sucrose and 6 g L-1 Plant Agar (pH: 5.8). The results showed that the MS medium + 2.2 μM BA + 0.25 μM IBA was the most effective treatment for micropropagation of shoot nodal explants in a single stage within a 30-day culture period, exhibiting 85% shoot formation, 1.8 new shoots/ explant 2.8 cm long with a 3.2 proliferation rate, 100% rooting, 16.5 roots/ rooted explant 2.1 cm long. Rooted plants obtained in vitro from MS medium enriched with 2.2 μM BA + 0.25 μM IBA gave 100% ex vitro survival rate on a peat: perlite (1:1 v/v) substrate mixture after 2 months in the greenhouse mist. In this study, an efficient in vitro propagation system of O. dictamnus is described for the first time through optimization of direct organogenesis stages (seed germination, proliferation, rooting, ex vitro acclimatization), as a means to facilitate domestication procedure, ex-situ conservation and future sustainable exploitation strategies, thus promoting wider usability of this local endemic with significant commercial potential.