Potential of Silicon and Melatonin Amendments to Enhance the Tolerance of Lettuce Plants to Water Deficit Stress

Drought is one of the biggest problems nowadays and it will be mandatory to cultivate crops with limited irrigation in the upcoming days. A number of treatments are used to reduce the devastating effects of drought. Silicon and melatonin are popular treatments and, their efficacy was tested in lettuce under drought conditions for the purpose of this study. Thus, two doses of silicon (4 mM/ 8 mM), one dose of melatonin (150 µM), and their co-treatments were conducted in lettuce under two (full irrigation/drought) irrigation regimes. The physiological, photosynthetic, and basic growth parameters were measured in lettuce. Based on these data, 8 mM silicon treatment significantly mitigate the severity of drought stress. It was found that the 8mM silicon treatment had the similar leaf dry weights as the non-drought-treated and leaf fresh weight was also found to be slightly affected by drought. 8 mM silicon treatment also significantly improved the values of chlorophyll a, chlorophyll b, total chlorophyll, protein, and chlorophyll fluorescence in lettuce under drought stress. Additionally, melatonin treatments (150 µM) resulted in significant increases in the examined parameters of the non-drought-treated lettuce groups. Consequently, it was concluded that silicon fertilization alleviated the adverse effects of drought or limited irrigation conditions, whereas, under full irrigation conditions, silicon and melatonin treatments contributed significantly to lettuce cultivation.