In vitro multiplication and genetic improvement of tuberose (polianthes tuberosa linn.)

Abstract

Investigations on in vitro propagation and genetic improvement of tuberose (Polianthes tuberosa Linn.) were carried out in the Department of Pomology and Floriculture, College of Horticulture, Vellanikkara during 1999-2002. The main objectives were to develop techniques for in vitro regeneration of commercial varieties of tuberose, viz., Single, Double, Shringar and Suvasini from different explant sources and attempt to create variability through mutation breeding for cormnercial exploitation. The scale stem sections from bulbs Were found to be the ideal explant for the enhanced release of axillary buds.Inflorescence segments containing immature flower buds were ideal for somatic organogenesis, whether direct or callus mediated. The best sterilization treatment was treating with Bavistin 0.1 per cent for 30 minutes, followed by ethyl alcohol 50 per cent for 3 minutes and mercuric chloride 0.10 per cent for 30 minutes for scale stem sections. For inflorescence segments treatment with 0.10 per cent mercuric chloride for 10 minutes alone was enough. Early release of buds and further growth of buds were better in MS medium supplemented with BAP 6.0 mg r' + KIN 4.0 mg r', in all the varieties. On subculturing elongated buds onto the same medium, high rate of multiple axillary bud production was observed. The rate of axillary bud production and callusing were low with BAP in combination with NAA. Elongation of multiple -axillary buds was obtained in half strength MS medium devoid of growth regulators. The elongated shoots produced maximum number of roots in MS medium supplemented with IBA 4.0 mg r' + 0.2 per cent activated charcoal. Plantlet survival was maximum when the cultures were left in the culture vessels till the media dried out partially and planted out in disposable cups containing cocopeat under mist chamber. Field performance of plants derived from tissue culture was comparable with the plants produced by conventional methods. Direct organogenesis could be obtained from immature inflorescence segments in MS medium supplemented with NAA 0.2 + BAP 2.0 + KIN 1.0 to 3.0 I -I mg . Among the various explants tried for callus mediated organogenesis, the inflorescence segments containing immature flower buds were the most ideal for callus initiation, growth and differentiation. Callus index was maximum when inoculated into the modified MS medium supplemented with NAA 15.0 to 20.0 mg r' + adenine sulphate 10.0 mg r'. The callus differentiated into shoots in MS medium supplemented with BAP in combination with KIN. Mutation breeding has been attempted to induce variability via. in vitro mutagenesis and in vivo methods. For in vitro mutagenesis, safest dose of irradiation at culture establishment stage, shoot proliferation stage and callusing stage were 15 Gy, " 15 Gy and 10 Gy, respectively. Some variations noticed in the plantlets reverted to normal behaviour after planting out. Considering the efficacy of different doses of mutagens in creating variability through in vivo methods, gamma rays at 15 Gy and 20 Gy as well as EMS at 1.0 and 2.0 per cent, were most effective. Morphological variants like chlorophyll mutants, branched flower stalk mutants compact inflorescence mutants and non flowering mutants were observed at different levels of mutagens. Based on growth parameters and floral characters, mne mutants were isolated, viz., dwarf mutants, high tiller mutants, non tillering mutants, compact inflorescence mutants, tall mutants, long leaf mutants, broad leaf mutants, large flower mutants and large inflorescence mutants. They retained the characters in V:rxh generation also and were evaluated for genetic parameters. High estimates of heritability coupled with high genetic gain were noticed for number of flowers per spike, spike length, flower diameter, leaf length and leaf width which indicate that the observed variability is heritable and that there IS considerable scope for genetic improvement with respect to these traits. Comparisons made between parents and mutants based on Isozyme analysis revealed differences in banding pattern. The banding pattern of esterase, peroxidase and catalase were different in mutants and their parents.