Foliar application of ascorbic acid enhances growth and yield of lettuce (Lactuca sativa) under saline conditions by improving antioxidant defence mechanism

Lettuce (Lactuca sativa L.) production is low because of different environmental stresses. Salt stress significantly reduces lettuce growth and yield. Foliar application of ascorbic acid is considered as a possible way to mitigate the adverse salinity effects on plants. This current study investigated the effect of foliar spray of ascorbic acid (control, 100, 200, 300 and 400 mg/L) to mitigate negative effects of salinity (0, 50, 100 and 150 mM NaCl) in lettuce plants in 2019 and 2020. Salinity level of 200 mM NaCl significantly reduced growth and yield traits; i.e. leaf length and diameter, number of leaves, fresh plant weight, number of roots, root length and root dry weight and these traits increased under foliar application of ascorbic acid concentration of 400 mg/L. Two salinity levels (150 and 200 mM NaCl) x 400 mg/L ascorbic acid enhanced superoxide dismutase (SOD) content in lettuce plants. Peroxidase (POD) content increased in 200 mM NaCl and 400 mg/L ascorbic acid. Catalase (CAT) content increased in 100, 150 and 200 mM NaCI and 400 mg/L ascorbic acid. Ascorbic acid was significantly greater in 200 mM NaCl and 400 mg/L ascorbic acid. Phenolic content was the maximum in 200 mM NaCl and 300 mg/L and 400 mg/L ascorbic acid. Titratable acidity was higher in 0, 50, 100, 150 and 200 mM NaCl and control of ascorbic acid. We conclude that ascorbic acid had potential to mitigate the adverse effects of salinity by reducing oxidative injury in agricultural crops especially lettuce.