الفهرس 
Title : Induce genetic variability and selection for salt tolerance in stevia plant - Stevia rebaudiana, Bertoni
AbstractOnly 14 pages are availabe for public view
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Abstract
Tissue culture technique became one of the most important tools in plant breeding and in vitro culture could be used to enhance selection process for salt stresses. Callus is important for rapid mass multiplication, generation of variability, cell suspension culture, preservation of cell line culture and production of secondary metabolites. Therefore, this study was carried out on Stevia plant for establishing efficient methods of formation and regeneration of callus as well as in vitro evaluation of salt stress effects on callus induction, regeneration and biochemical constituents. Three different explants (shoot tips, leaves and nodal segments) and MS medium with different combinations of plant growth regulators (PGRs) as well as five levels of salt stresses (0.0, 2000, 3000, 4000, 5000 ppm of NaCl) were studied. Results showed that all studied media induced callus for all explants, but MSc4 (MS+1.0 mgl-1 2,4-D +0.75 mgl-1 NAA) gave the highest values of callus fresh weight. Only, calli obtained from MSc4 callus induction medium gave the best response to regenerate a sufficient number of shoots. Half strength MS medium with 1 mgl-1IBA was found to be the optimum medium for root formation. Adding NaCl salt to the media significantly decreased fresh and dry weights of callus, but it significantly increased callus production of Stevioside, Rebaudioside A and total SGs (Steviol Glycosides). There was no regeneration with salt concentration of 4000 and 5000 ppm. Adding 2000 and 3000 ppm had no effect on the regeneration and multiplication process, but plantlet growth parameters in terms of shoots number, shoots length, nodes number, leaves number, leaves fresh weight, leaves dry weight, roots number, roots length and survival rate% were decreased significantly with raising NaCl level up to 3000 ppm. Increase of salinity level up to 3000 ppm significantly decreased chlorophyll a, b and total chlorophyll contents, but significantly increased proline contents. Genetic variability in induced callus under salt concentrations was studied through Peroxidase isozyme and Poly phenyl oxidase banding patterns and the results indicated a difference between the various saline stress factors