Polyploidy increases tolerance to salt stress in Anise hyssop (Agastache foeniculum [Pursh.] Kuntze)

Salinization is one of the most serious environmental problems in agriculture. Polyploid induction could increase abiotic stress tolerance in plants. In this study, the effect of different NaCl concentrations (0, 50, 100 and 150 mM) was studied on diploid (2x) and tetraploid (4x) plants of anise hyssop (Agastache foeniculum) in vitro. The results indicated that salt stress reduced survival percent, stem length, leaf and shoot number in both tetraploid and diploid plants. However, tetraploid plants had better survival and growth rates compared to diploids. The highest antioxidant enzymes activity was observed in the plants treated with 100 mM NaCl, while increasing the salinity to 150 mM NaCl lowered the activity of antioxidant enzymes significantly. Essential oil content in diploid and tetraploid plants decreased as the concentration of NaCl was elevated. Also, salinity stress affected the chemical composition of essential oil in both diploid and tetraploid plants. In conclusion, the results indicated that tetraploids showed greater tolerance to salt stress compared to diploids, and polyploidy might be a useful breeding method in anise hyssop to amplify its tolerance to salt stress under soil salinity.