Improving growth indices and productivity of phytochemical compounds in Lemon balm (Melissa officinalis L.) via Induced Polyploidy

The induction of polyploidy using mutagenic chemicals is one of the plant breeding methods to enhance the production of secondary metabolites. In the current research, to induce polyploidy in lemon balm (Melissa officinalis) plants, seeds were treated with different concentrations of colchicine for various exposure times. A factorial experiment was performed using a randomized complete block design with two factors: colchicine concentrations with four levels (control, 0.05%, 0.1%, and 0.2%) and exposure times with three levels (24, 48, and 72 h) and three replicates. The physiological and phytochemical traits of plants were measured at a 4–6 leave stage. The results indicated that different concentrations of colchicine had a significant effect on the chlorophyll a (Chl.a), chlorophyll b (Chl.b), carotenoid, phenol, flavonoid, and rosmarinic acid contents. The exposure times of colchicine also caused significant changes in Chl.a, Chl.b, carotenoid, phenol, flavonoid, and rosmarinic acid amounts (P # 0.01). Increasing the colchicine concentration significantly increased the physiological and phytochemical traits at 0.05% and 0.1% concentration in comparison to the control (P # 0.01). In contrast, the interaction of colchicine concentration and exposure time had a significant effect on Chl.a, Chl.b, carotenoid, and rosmarinic acid amounts. The findings of this study indicate that one of the effective methods in primary screening of polyploidy plants in the polyploidization breeding program is the estimation of the physiological changes, the contents of chlorophyll a and b, and the total amount of chlorophyll and secondary metabolites. Flow cytometry is recommended to be used for the accurate identification of the ploidy level in M. officinalis.