Meta-topolin improved micropropagation in Syzygium cumini and acclimatization to ex vitro conditions

Abstract

An efficient micropropagation system was developed for a recalcitrant woody tree Syzygium cumini (L.) Skeels using nodal explants excised from 15-d-old aseptic seedlings. The explants were employed on an Murashige and Skoog (MS) medium supplemented with different concentrations (1.0 - 10.0 μM) of cytokinins, such as benzyladenine (BA), kinetin (Kin), meta-topolin (mT), or 2-isopentyl adenine (2ip), either alone or in combination with different concentrations (1.0 - 3.0 μM) of auxins, such as indole-3-acetic acid (IAA), indole-3-butyric acid (IBA), or α-naphthalene acetic acid (NAA). Of the cytokinins tested, mT proved to be best for shoot bud induction and proliferation. Among the tested combinations, a maximum regeneration (90 %) with a mean shoot number of 25.33 ± 0.33 and a shoot length of 5.20 ± 0.11 cm were recorded on the MS medium containing 5.0 μM mT + 2.0 μM NAA after 12 weeks of incubation. Further 4-week incubation on optimum 5.0 μM mT before transfer to a secondary medium consisting of MS + 5.0 μM BA + 2.0 μM NAA yielded up to 51 microshoots with an average length (6.53 cm). For in vitro rooting, healthy shoots (about 5 cm) were excised and incubated on the half or full strength MS medium enriched with different concentrations (1 - 7.5 µM) of NAA. A substantial increase in rhizogenic competency (15 %) was observed in shoots raised on a medium with mT with a mean root number of 6.33 ± 0.10 and a mean length of 5.13 ± 0.21 cm on the half MS supplemented with 5.0 µM NAA after 4 weeks. A maximum of 95 % plantlets regenerated on the medium with mT was successfully acclimatized and established in earthen pots under field conditions. The consistent increases in activities of superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase during acclimatization indicate that mT raised plantlets response well to the stress induced by ex vitro conditions.