Ethephon and secondary shoot induction in Gentian (Gentiana spp.) hybrids in vitro

The potential effect of ethylene on the production of secondary shoots of in vitro explants of two cultivars of gentian (Gentiana sp.) with different branching habit, 'Little Pinkie' (naturally highly branched) and 'Showtime Diva' (naturally less branched), was evaluated by supplementing the medium with ethephon ([2-chloroethyl]phosphoric acid). An almost constant concentration of ethylene (60 nL L−1) in the headspace of the culture vessels was measured when the medium was supplemented with ethephon. The number of secondary shoots arising from single node explants of 'Little Pinkie' after 8 weeks increased five times as a result of ethephon application in vitro, whereas branching did not increase in explants of 'Showtime Diva'. Microscopic observation supported the hypothesis that secondary shoots additional to those arising from pre-existing axillary buds were adventitious in origin. Future research strategies will be to investigate the mechanism of action of ethephon/ethylene on branching, and determining the basis of genetic differences between cultivars.