Modulation in Growth, Yield, Water Relations, and Mineral Nutrients of Canola ( <i>Brassica napus</i> L.) by Foliar Application of Melatonin and Ascorbic Acid Under Salinity Stress

Salinity stress is a major abiotic factor that inhibits plant growth and yield. This study's objective was to evaluate how foliar applications of melatonin and ascorbic acid affected canola varieties under salt stress. The treatments of the study were as follows: canola varieties (a) (Oscar and Super), (b) melatonin (MT) and ascorbic acid (AsA) (control, 100 µM MT, 1 mM AsA, and 100 µM MT + 1 mM AsA), and (c) salt stress (0 mM NaCl, 75 mM NaCl, and 150 mM NaCl) levels were used. Under saline conditions, plant height was reduced by 27.8% in both varieties while the combined effect of MT and AsA improved the plant height up to 22.9% and 54.3% in Oscar and Super, respectively. Seed yield and biological yield significantly declined under salinity stress up to 74%, and 44.6% in Oscar and 81.3%, and 34.1% in Super. The cumulative effect of MT and AsA improved all these by 152.3%, and 31.1% in Oscar and 212%, and 35% in Super, respectively. Melatonin and AsA improved the water relations attributes and root and shoot Ca 2+ and K + and decreased the accumulation of Na + ions. Overall results Oscar outer‐performed Super, and MT and AsA role in improving plant salt tolerance.