Abstract
Here, we grow two different varieties of lentil (lentil-2009 and lentil-93) under different drought levels and with different applications of melatonin. Increasing the levels of soil water deficit significantly decreased numerous morphological and biochemical characteristics, including shoot length, total chlorophyll content, and transpiration rate, in both varieties of lentil. Contrastingly, drought stress increased the concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2), and electrolyte leakage, an indicator of oxidative damage to membrane-bound organelles. The activities of enzymatic antioxidants and osmolytes were initially increased up to a drought level of 80% water field capacity (WFC) but gradually decreased with higher levels of drought stress (60% WFC) in the soil. At the same time, the results also showed that the lentil-2009 is more tolerant to drought stress than lentil-93. The negative impact of drought stress can be overcome by the application of melatonin. Melatonin increased plant growth and biomass, photosynthetic pigments, gas exchange characteristics, and enhanced the activities of various enzymatic and non-enzymatic antioxidants and proline content by decreasing oxidative stress. We conclude that foliar application of melatonin offers new possibilities for promoting lentil drought tolerance.