In vitro propagation of Rhododendron tomentosum - an endangered essential oil bearing plant from peatland

Rhododendron tomentosum Harmaja (formerly Ledum palustre L.) is a medicinal peat bog plant native to northern Europe, Asia and North America. This plant has a distinctive aroma thanks to the presence of essential oil, to which it also owes its anti-inflammatory, analgesic, antimicrobial and insecticidal properties. However, in Europe R. tomentosum is classified as an endangered species, mainly due to degradation of peatlands. In the present work, the micropropagation protocol for R. tomentosum was established for the first time, providing both an ex situ conservation tool and a means of continuous production of in vivo and in vitro plant material for further studies. R. tomentosum microshoots were initiated from leaf explants and further multiplied using Schenk- Hildebrandt (SH) medium supplemented with 9.84 μM 2iP and 1.00 μM TDZ. The shoots were elongated on the SH medium supplemented with 24.6 μM 2iP and subsequently rooted using the perlite substrate saturated with half-strength Woody Plant medium supplemented with 1.0% sucrose and 4.92 μM IBA. The regenerated plants were hardened on the phytohormone-free SH medium and acclimatized using 3:1:1 deacidified peat:perlite:gravel substrate. The identity of the mother plant was confirmed at morphological and molecular levels and Random Amplified Polymorphic DNA (RAPD) method was implemented to assess the genetic fidelity of the regenerants. The essential oil content of the maternal plant, in vitro shoots and the regenerants was determined by steamdistillation, and the obtained volatile fractions were analyzed by GC/MS.