Effects of drought stress on yield and yield-related traits, antioxidant enzymes and essential oil content of some Cumin (Cuminum cyminum L.) ecotypes

Cumin is one of the most important medicinal plants in Iran, which needs a lower irrigation to complete the growth stages. Therefore, cumin is one of the most valuable plants for cultivation in arid and semiarid regions of the world, especially in drought conditions. For this purpose, the present study was conducted to evaluate the key morphological and physiological parameters as well as the factors involved in oxidative stress and essential oil content in some ecotypes under drought stress and normal conditions. The experiment was arranged as factorial based on a completely randomized design with three replications and conducted in Saravan University's research greenhouse. Experimental factors included drought stress (stress and non-stress) and different ecotypes (eight ecotypes). The measured traits were plant height, number of secondary branches per plant, number of umbel per plant, number of umbellate per umbel, number of seeds per umbrel, 1000-seed weight and seed yield per plant, chlorophyll a, b and carotenoid content, and activity of biochemical factors (catalase, superoxide dismutase, peroxidase, malondialdehyde) and also seed essential oil. The results showed that drought stress reduced yield, yield components and photosynthetic pigments content. In general, Birjand ecotype had the highest grain yield per plant (1.37 g). Also, the activity of catalase, peroxidase and superoxide dismutase antioxidant enzymes was determined in this valuable medicinal plant. The drought stress increased the activity of these enzymes as well as the level of malondialdehyde, from 1.31 u/mgpro*min, 2.34 mg/g, 1.29 u/gFW and 21.87 µmol/gFW to 33.44, 4.37, 6.90 and 66.66, respectively. Finally, the tolerance of the studied ecotypes to drought stress was identified according to the measured indexes and Birjand ecotype was recognized as superior ecotype.