The effect of brassinosteroid foliar application on growth traits and content of sodium and potassium ions of Satureja hortensis under salinity stress

In order to investigate the effect of brassinosteroid foliar application on the growth characteristics and content of sodium and potassium ions of summer savory (Satureja hortensis L.) under salt stress, a factorial experiment was conducted based on randomized complete block design with three replications in the greenhouse of Payam Noor University in Lorestan in 2020. The factors were salinity stress at three levels (0, 40 and 80 mmol/L NaCl) and foliar sprays of brassinosteroid at three levels (0, 0.5 and 2 μmol/L). The largest mean values of plant height (32.56 cm), root length (22.02 cm), shoot fresh weight (5.89 g/plant), shoot dry weight (2 g /plant), root dry weight (0.87 g/plant), and potassium content in plant shoot (16.39 mg/g dry matter) were observed under control conditions (without salinity). These traits declined by 32, 21, 19, 17, 31, 23 and 79%, respectively, under salinity conditions (80 mmol /L NaCl). However, spray of brassinosteroid, especially at 2 μmol /L, increased mean plant height (30.46 cm), root length (21.7 cm), fresh and dry weights of shoot (5.95 and 2.06 g/plant, respectively), and potassium content of aerial organs (10.63 mg/ g dry matter).The interaction effects of the salinity and hormone spray indicated that increases in salinity level significantly improved sodium content of plants (sodium content was 10.93 mg/g dry matter in the treatment of applying 80 μmol/L NaCl and no hormone spray). This led to a drastic reduction in the potassium/sodium ratio (the mean value of this trait was 0.2 in the treatment of applying 80 mmol/L NaCl without hormone spray); however, spray of brassinosteroid somewhat reduced sodium absorption (the sodium content in the treatment of applying 80 mmol/L NaCl and 2 μmol/L of the hormone was 6.56 mg/g dry matter). In general, salinity decreased the studied plant growth traits by disrupting potassium absorption and strongly reducing plant potassium /sodium ratio, but brassinosteroid spray improved the fresh and dry weight of summer savory plants.