Evaluation of Temporary Immersion System for in vitro propagation of Stevia rebaudiana Bertoni
- Acta Horticulturae, 1083, p.327-333, 2015 .
Stevia rebaudiana Bertoni belongs to the Asteraceae family and it is native of Paraguay and Southern Brazil. It is one of 154 species belonging to the genus Stevia, but it is the only important for the presence of stevioside (3-10 percent of the dry weight of the leaves)and rebaudioside (1-3 percent)that are sweetening compounds alternative to sucrose. Studies indicate that the culture is not only suitable for cultivation in tropical and sub-tropical areas but also in temperate ones (including Italy). A micropropagation protocol has been established starting from selected material and the liquid culture has been evaluated with the aim to improve plant quality and enhance micropropagation efficiency. Two Temporary Immersion Systems (TIS)have been compared (RITAź and PLANTFORM)towards the culture in agarized medium (AM). After the establishment of the vitro cultures, 3 media were compared with the 2 TIS systems: MS hormone-free base medium, MS base with BA (0.3 mg/L)or MS base with IAA (0.5 mg/L). Nutrition was performed with three minutes of flooding every three hours and, only for PLANTFORM, the flooding frequency was changed to 3 min of flooding every 8 hours. All the cultures were grown at 23±1°C under a 16 h d-1 photoperiod provided by cool-white fluorescent lights at 35 ?mol m-2 s-1 (photosynthetic photon flux density). Results showed that already inabsence of GRF interesting multiplication rate could be achieved (5.33 in agar and about 8 in liquid media); the addition of BA increased the number of shoots per explants per month until 14 inPLANTFORM and RITAź systems. It was possible to achieve in RITAź vessels the highest explant height (9.58 cm), a total absence of basal callus and a good explant quality. In PLANTFORM the flooding every 3 hours induced callus and hyperhydricity in all explants, whereas with the flooding every 8 hours the shoots displayed a good behaviour and quality.