Induction and development of nodular cluster cultures in Vriesea reitzii (Leme and Costa), an endangered bromeliad from the Brazilian Atlantic Forest

The present work studied the induction, multiplication and development of nodular cluster cultures (NCC) of Vriesea reitzii, an endangered bromeliad species native to the Brazilian Atlantic Forest Biome, in different culture media under different culture conditions. Leaf basal segments of in vitro-grown plantlets were used as explants and inoculated into Murashige and Skoog (MS) liquid medium supplemented with different types and concentrations of plant growth regulators (PGRs) in the presence or absence of light, followed by sub-culturing in or on PGR-free liquid or solidified culture media to promote multiplication. The induction of NCC, which occurred from the basal region of the explants, was observed in all culture media tested. Morphological features and regenerative efficiency were ascribed to the different culture media, based mainly on medium type, and the concentration and combination of PGRs, as well as on exposure to light or dark conditions. Green-coloured NCC with a granular texture showed a high regenerative efficiency in response to MS culture medium supplemented with 4 µM -naphthaleneacetic acid (NAA) plus 2 µM N⁶(2-isopentenyl) adenine (2-iP), or plus 2 µM 6-benzylaminopurine (BAP), in cultures incubated under a 16 h photoperiod. Throughout the multiplication stage, regenerative efficiency showed a direct correlation with the composition of the induction medium in which the NCC had originated. Thus, NCC that originated from MS culture medium supplemented with 4 µM NAA and 2 µM 2-iP showed the highest regenerative efficiency (7.2 g g–¹ of NCC). NCC that originated from MS culture medium supplemented with 2 µM NAA plus 4 µM BAP showed the highest number of regenerated microshoots (140.0 microshoots g–¹). Therefore, the competence of NCC for having a high regenerative efficiency was related to the culture environment and to the type, concentration, and combination of PGRs added to the basal MS culture medium. In vitro-shoot elongation was obtained on filter paper bridges over PGR-free basal MS (BMS) liquid medium. Fully-developed and acclimatised plants were obtained in an ex vitro environment. Taking together, the results of the present study provide new and useful information on an in vitro protocol for the endangered bromeliad, V. reitzii, based on regeneration from nodular cluster cultures.