The effect of PlantformTM bioreactor on micropropagation of Quercus robur in comparison to a conventional in vitro culture system on gelled medium, and assessment of the microenvironment influence on leaf structure

Quercus robur L. was micropropagated by axillary bud proliferation testing two different shoot culture systems: (i) on gelled medium in Microbox (plastic vessel with a strip for ventilation) and (ii) in liquid culture in PlantformTM bioreactor (a temporary immersion system). Two different conditions of temporary immersion were assessed: 12 min/8 h (Plantform 1) and 8 min/16 h (Plantform 2). The effect of the two culture systems was evaluated also during subsequent rooting phase, carried out on gelled medium. Finally, the influence of the different culture conditions on leaf structure was considered, taking also into consideration the micromorphological characters of young leaves from in-field-grown oaks. Nodal segments, excised from established in vitro shoots and cultured on modified Woody Plant Medium, showed a higher Relative Growth Rate in Plantform than in Microbox, but culture conditions provided in Plantform 1 favored shoot and leaf hyperhydricity. Shoots cultured in Microbox or Plantform 2 presented the same percentage of rooting after their transfer on gelled rooting medium. Leaves developed in the two different microenvironments had large stomata with elliptical shape, which indicates good functionality, and formed hairs, and epicuticolar waxes. These leaf features are considered to provide a good adaptability to ex vitro conditions.