Elicitation strategies for the improvement of essential oil content in Rhododendron tomentosum (Ledum palustre) bioreactor-grown microshoots

Rhododendron tomentosum Harmaja, previously Ledum palustre L., is a fragrant plant growing in swampy areas, which is characterized by well-known repellent properties and the anti-arthritic potential. In the present study, R. tomentosum microshoots cultivated in RITA. bioreactor, providing the alternative, environment-independent source of the valuable essential oil, were treated for 7 days with copper and nickel salts, methyl jasmonate, chitosan, ergosterol, lysates of: Candida aibicans, Escherichia coli, Enterobacter sakazaki, Pectobacterium carotovorum and Dickeya dadantii, to stimulate the production of secondary metabolites. Moreover, for the first time, the aphid ethanol extract was tested as an elicitor of insect origin. Suspensions of all pathogens added to in vitro culture reduced significantly the biomass growth parameters. The application of the aphid extract and lysate of P. carotovorum increased the volatile fraction content by 14%, while Ni2+ and ergosterol by 8%. The influence of the studied elicitors on the chemical composition of R. tomentosum essential oils was presented and discussed thoroughly, taking into account a percentage of 22 main terpenoid compounds, determined by GC/MS (i.a. p-cymene, geranyl acetate, delta-cadinene, shyobunone, methyl eveminate, ledene oxide (II) and alloaromadendrene). The biosynthesis of monoterpenes was primarily proven to be affected by the elicitation. The conducted experiments suggest that R. tomentosum is rather resistant to elicitation strategies, both abiotic and biotic as well as methyl jasmonate.