The Effect of Foliar Spraying TiO2 Nanoparticles on Biochemical Responses, Growth, Yield and Essential Oil Content of Ajowan (Carum copticum) under Salinity Stress

Salinity is one of the most common abiotic stresses that affects growth and secondary metabolism in medicinal plants. In this study, the effects of two times foliar application of nano titanium dioxide on some agronomic traits of ajowan (Carum copticum) under salinity stress was investigated in a pot experiment. This study was conducted as a factorial experiment with completely randomized design and three replications. The factors included three levels of salinity (0, 50, and 100 mg L-1) and 5 concentrations of TiO2 nanoparticles (0, 10, 20, 40, and 80 mg L-1). Salinity treatments were implemented by adding NaCl to irrigation water of pots containing clay soil three times per week. The results showed that long-term irrigation with slightly saline water significantly decreased dry matter yield, height, total chlorophyll, weight of 100 seeds, number of seeds per plant, and seed yield and increased lipid peroxidation and the activities of catalase ( CAT ) and peroxidase (POX). Impact of 50 mg L-1 salt was not significant on essential oil percentage and essence yield; but 100 mg L-1 salt significantly (33.1%) decreased essential oil content. Foliar spraying of plants with 20 and 40 mg L-1 nano titanium dioxide had the most positive impact on growth and seed yield and significantly lowered lipid peroxidation via enhancing the activities of antioxidant enzymes under salt stress. Foliar spraying with 40 mg L-1 nano titanium dioxide significantly improved essential oil concentration (43.3%) and total essential oil yield (59.7%) under 100 mg L-1 salinity condition. The effect of foliar spraying with 80 mg L-1 nano titanium dioxide on some of the measured attributes was less than the impact of applying 20 and 40 mg L-1 nano titanium dioxide. These results suggest that foliar application of nano titanium dioxide with appropriate concentration improves salt tolerance, seed yield and essential oil content in ajowan.