Improving productivity of steviol glycosides in Stevia rebaudiana via induced polyploidy

The polyploidy induction using mutagenic chemicals is one of the breeding approaches to improve enhancing productivity of yield and secondary metabolites in medicinal plants. In the present research, to induce polyploidy in Stevia rebaudiana plants, the seeds were treated with four concentrations of colchicine (control, 0.05%, 0.1% and 0.2%) for 12, 24, 36 and 48 h in a factorial experiment based on randomized complete block design with three replicates. The morphological and phytochemical traits of plants were measured before the flowering stage. The results indicated that different concentrations of colchicine had a significant effect on the plant height, number of leaves, number of branches, mean of leaf length, stomata size and stomata density. The exposure times of colchicine also caused significant changes in the plant height, number of branches, leaf width and length (P ≤ 0.01). Enhancement of colchicine concentration, significantly increased the above mentioned morphological traits, along with stomata size and rebaudioside-A, while significantly decreased stomata density in comparison to the control (P ≤ 0.01). In contrast, the interaction of colchicine concentration and exposure time had a significant effect on leaf length. The findings of this study indicated that estimation of physiological changes and secondary metabolites amount is one of the effective methods in primary screening of polyploid plants in polyploidisation breeding program and flow cytometry is recommended to be used for accurate identification of ploidy level in Stevia rebaudiana.