Salinity is one of the major environmental threats to plants because a large number of plants are intolerant to NaCl stress. One such plant, Justicia vasica, which is the subject of our study, is said to have great medicinal properties. However, the natural occurrence and cultivation of this species has been constrained due to various factors including its poor seed germination rate under its normal conditions of habitat, and a low availability of seeds. This study was undertaken to examine the efficiency of callus formation and regenerative tendencies of Justicia vasica under saline conditions. The leaf, shoot tips and inter nodal cuttings were employed for this study using MS media formulated with several concentrations of different kinds of hormonal combinations. This study also tested the effects of different concentrations of NaCl on callus induction and growth. Each experiment was conducted thrice with 12 replicates. A superior level of callus formation was achieved by treating shoot tips with 2.0 mg/l α-naphthalene acetic acid (NAA) and 0.5 mg/l 6-benzyladenine purine (BAP) in combination. From this study, it was concluded that there was no inhibitory action from the medium supplemented with 0.05 mg/l NaCl. The optimal hormonal combination also exhibited highest rate of callus induction and growth with 0.05 mg/l NaCl added. There was no callus necrosis at this saline concentration after 60 days of inoculation. Furthermore, some somatic embryogenic callus displayed the organogenesis of leaf like structures after 75 days of inoculation. The development of salinity tolerance of plants by genetic application has been a vital area on modern agriculture as well as medicinal plant research because more land has been salinized through poor local irrigation practices. The present investigation assumed that the NaCl tolerance of this plant could be effectively obtained in vitro.
Keywords: callus necrosis; explant browning; NaCl stress; salinity tolerance; somatic embryo; tissue culture
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