Effects of Humic Acid and Salinity Stress on Some Germination and Morpho-physiological Indices of Iranian St Johns Wort in in Vitro Conditions

The use of compounds that can improve plant tolerance to abiotic environmental stress, including salinity, is important. To evaluate the adjustment of salinity stress using humic acid (HA), a factorial layout is conducted based on a complete randomized design with three replications on the Hypericum perforatum L. as an Iranian medicinal plant are collected from Hamadan province in the tissue culture laboratory of the Faculty of Agriculture, Sayyed Jamaleddin Asadabadi University during 2019. Experimental treatments include NaCl as salinity at three levels (such as 0, 50, and 100 mmol.L-1) and HA at four levels (control, 25, 50, and 100 mg.L-1). Results indicate that the plants treated with 50 mg.L-1 HA without salinity have had the highest germination percentage (98.65), germination rate (38.94) and root length (34.21 mm). The highest plant height, fresh and dry weight of both shoots and roots and total chlorophyll are obtained under control conditions and HA with a concentration of 100 mg.L-1. On the contrary, the highest amount of phenol in the treatment is 50 mmol.L-1 salinity and HA with a concentration of 50 mg.L-1. In the treatment of 100 mmol.L-1 salinity and HA with a concentration of 50 mg.L-1, the highest amount of total antioxidants (99.77 mg/g FW) and total flavonoids (2.39 mg/Qe g FW) and the lowest amount of hydrogen peroxide (9.12 µg/g FW) are obtained. Results show that the mitigating effect, especially the application of HA of 50 mg.L-1 levels, can affect the physiological processes and morphological traits of the Hypericum perforatum L. under salinity stress.