عنوان مقاله [English]
Introduction: The genus of African violet is the most common genus known among the plants of Gesneriaceae family. This genus has beautiful leaves and flowers that are zygomorph. African violet (Saintpaulia ionantha) is a famous ornamental plant due to its various colors and shapes that an excellent model system for in vitro regeneration studies because of its tissue culture amenability.Besides the importance of this plant in plant production industry and increasing need for new plant varieties with desired traits, more studies for creating African violet with new features by increasing the ploidy level under the in vitro conditions were not done until now. Polyploidy is a widespread phenomenon in the evolution of flowering plant and a key in plant speciation and diversification. Polyploid plants have been used in plant breeding programs for developing superior varieties and restoring the fertility of interspecific or intergeneric hybrids. Polyploidy in ornamental crops were successfully obtained under in vitro conditions. The chemical colchicine can be used as the most effective substance to obtain polyploid plants. In vitropolyploidization has number of advantages such as treatment of more plants with less material, control of test conditions, lower toxicity of chemicals and high success rate. This study with the aim of polyploid induction was carried out by different concentrations of colchicine at various periods under in vitro conditions.
Materials and Methods: The best treatment for the shoot regeneration and proliferation was MS medium with 2 mg/l BA after optimizing the tissue culture process. The study performed as follows: plantlets grown under in vitro in proliferation stage were treated with colchicine. The experiment was carried out in a 2-factorial manner based on a completely randomized design and factors were colchicine concentration at 0.02, 0.05, 0.1% and treatment duration for 18, 24, 48 hours. Evaluated characters of regenerated plants were as follows: plantlets survival percentage (the first month, the second month and the third month), morphological traits (include leaf number, petiole length, leaf length, leaf width, petiole diameter, leaf thickness and variation in form, vein, tip and margins leaf), reproductive traits (flower diameter (mm), number of petal, number of flower in inflorescence, height of inflorescence (mm)), microscopic epidermal cells in samples of diploid and tetraploid and ploidy levels. Assessment of flow cytometery was also used for all of the treated plants with colchicine and some diploid control plants and were expressed in the form of the percentage of diploid, mixoploid and tetraploid plants of African violet.
Results and Discussion: Results indicated that tetraploidy induction successfully was changed different morphological and cytological characteristics. Plantlets of treated with 0.02% colchicine in all three times only survived after three months, and with increasing treatment time, plantlets survival percentage was reduced. Thus 0.02% colchicine treatment for 24 hour found effective in inducing in vitro culture polyploidy of African violet. Comparison of the leaves of tetraploid with diploid plants indicated that the leaves of tetraploid plants in length and width were bigger than the diploid ones. The selected tetraploid plants showed a more compact shape than the control plants. Other results revealed that the treated plants with colchicine showed delayed growth. The assessment of microscopic indicated that the epidermal cells of tetraploid were larger than diploid. The results of flow cytometery evaluation showed that with increasing duration of colchicine, the number of diploid plants reduced and were added to mixoploid and tetraploid plants. Most plants were mixoploid.
Conclusion: The results of this study showed that the diploid and tetraploid plants indicated significant differences in term of morphological traits like leaf number, petiole length, leaf length, leaf width, petiole diameter, leaf thickness and variation in form, vein, tip and margins leaf, reproductive traits like flower diameter, number of petal, number of flower in inflorescence and also size of epidermal cells and flow cytometery evaluation. These differences can be suitable criterion for separating diploid and polyploid plants from each other. Generally, the combination of tissue culture methods and tetraploidy induction can be used as a rapid strategy for achieving new forms and properties of regenerates in vitro on African violet.