The effect of humic acid foliar application on yield and some quality traits of Lolla rossa lettuce (Lactuca sativa L.) under salt stress

Salinity stress is one of the important stresses in reducing the yield of plants, especially leafy plants, and it is very important to provide solutions to deal with it. For this purpose, a factorial experiment was conducted in the form of a completely randomized design in four replications in a greenhouse located in Naziabad, Karaj on llolaroza lettuce hydroponically under salt stress conditions. The factors of this research included humic acid in four concentrations 0 (control), 500, 1000 and 1500 mg/l and salinity stress at two levels no stress (control) and 30 mM. The results showed that application of salinity stress decreased the yield of Lolla rossa lettuce. The application of humic acid and increasing its concentration increased the quantitative and qualitative performance of this plant and reduced the negative effects of salinity stress. The highest yield of fresh weight of lettuce was 682.27 g/m2, related to the mutual effects of humic acid treatments of 1500 mg/l and salinity stress. The application of humic acid and increasing its concentration decreased the activity of catalase enzyme and ascorbate peroxidase enzyme. Salt stress increased the activity of catalase enzyme and ascorbate peroxidase enzyme. The lowest activity of catalase enzyme (0.004 µmole FW/min) and ascorbate peroxidase enzyme (0.41µmol H2O2 min-1.mg-1 protein), related to the interaction of humic acid 1500 mg/l and control of salinity stress. The highest activity of catalase enzyme (0.024 µmole FW/min) and ascorbate peroxidase enzyme(0.81 µmol H2O2 min-1.mg-1 protein) were observed in humic acid control under salt stress condition.