Factors influencing the growth of micropropagated shoots and in vitro flowering of gentian

Abstract

About 70% of the shoots developed from nodal explants ofGentiana triflora flowered in vitroondouble strength WPM medium containing 3% (w/v) sucrose, 0.5mg/l BA after 12 weeks of culture in a growth room at 22°Cwith continuous illumination (PPFD = 60μmolm⁻² s⁻¹). The influences oninvitro shoot development and flowering of several factors includingthe position of the explant, requirements for sucrose, cytokinin orGA₃, variations of pH and photosynthetic photon flux density (PPFD)were investigated. In vitro flowering but not shootdevelopment of G. triflora decreased notably withincreaseddistance from the apex of the shoot, indicating the presence of a “floralgradient” in the micropropagated shoots. Conversely, as little as 0.01mg l⁻¹ GA₃ in the medium promotedshootdevelopment but even up to 0.2 mg l⁻¹GA₃ did not induce in vitro flowering.Even though BA could substitute GA₃ for a high level of shootdevelopment, it also promoted a high level of in vitroflowering at the PPFD of 60 μmolm⁻² s⁻¹. Sucrose was required for shootdevelopment and flowering in vitro and higher levels ofPPFD could not compensate effectively for the omission of the sugar from themedium. In general, the effects of different concentrations of BA in the mediumor variations of pH on shoot development and flowering invitro were found to be influenced by PPFD. A novel observation isthat precocious flowering of micropropagated gentian shoots did not occur ifthey were first cultured for 5 weeks in the dark before transfer to the lightcondition.