Meta-Topolin Mediated Improved Micropropagation, Foliar Micro-Morphological Traits, Biochemical Profiling, and Assessment of Genetic Fidelity in Santalum Album L.

An improved in vitro propagation system has been developed for Santalum album L. using meta-Topolin for the first time. Direct organogenesis (100 %) was achieved by induction of axillary buds and a maximum of 8.2 shoots with 4.0 cm length was developed from nodal explants on Murashige and Skoog's (MS) medium containing 1.0 mg L-1 meta-Topolin (mT). The MS medium supplemented with 0.5 mg L-1 mT and 0.25 mg L-1 alpha-naphthalene acetic acid (NAA) exhibited maximum shoot proliferation potential (135 shoots with 7.9 cm length per explant) after the 3rd subculture. Further, the combination of mT and NAA resulted in the production of higher levels of free amino acids [33.6 mg g(-1) dry weight (DW)], soluble sugar (37.4 mg g(-1) DW), and reducing sugar (45.0 mg g(-1) DW) in the leaves than the BAP and NAA combinations. The efficiency of mT has also been highlighted in the foliar structural developments. Comparative anatomy of leaves showed the presence of structural variations influenced by the type of cytokinins used. BAP and NAA-derived leaves revealed the presence of under-developed cuticle, unorganized tissue systems, undifferentiated mesophyll tissues, and under-developed mechanical and vascular tissues. Whereas, mT and NAA-derived leaves exhibited comparatively thick cuticle, collenchymatous hypodermis, well-differentiated mesophylls, and increased vascular elements. Roots were induced ex vitro under the greenhouse conditions when the shoot-bases were treated with 500 mg L-1 indole-3-butyric acid (IBA) for 10 min. These plantlets were hardened in soilrite (R) and cocopeat (1:1) mixture and a 100 % survival rate was achieved in the field. Additionally, the Start codon targeted (SCoT) markers analysis demonstrated that the genetic homogeneity was maintained during in vitro development of plantlets. The application of mT can be an effective growth regulator for in vitro propagation of S. album, as it favoured enhanced and quick production of genetically uniform clones.