E. Shahbazi - Department of Plant Breeding and Biotechnology, College of Agriculture, Shahrekord University, Shahrekord ۸۸۱۸۶-۳۴۱۴۱, Islamic Republic of Iran.
B. Safipor - Department of Plant Breeding and Biotechnology, College of Agriculture, Shahrekord University, Shahrekord ۸۸۱۸۶-۳۴۱۴۱, Iran.
k. Saeidi - Department of Horticultural Sciences, College of Agriculture, Shahrekord University, Shahrekord ۸۸۱۸۶-۳۴۱۴۱, Islamic Republic of Iran.
P. Golkar - Department of Natural Resources, Isfahan University of Technology, Isfahan ۸۴۱۵۶-۸۳۱۱۱, Islamic Republic of Iran.

Nigella damascena and Nigella sativa are two important species of the genus Nigella that have many medicinal and industrial applications. Both species are widely cultivated in arid and semi-arid areas, and are affected by abiotic stresses, especially drought stress. In the present study, the effect of water deficit stress on seed yield, oil percentage and yield, total phenolics and flavonoids content, and antioxidant activity of both species were investigated during two growing seasons (۲۰۱۸ and ۲۰۱۹). In this experiment, different levels of irrigation (severe stress, mild stress, and control) and two species (N. sativa and N. damescena) were studied as the main plots and subplots, respectively. Seed and oil yields decreased sharply due to drought stress in both species. Means of the seed and oil yields in N. sativa were ۵۴۰.۶۵ and ۲۰۶.۹۲ kg ha-۱, respectively, and seed and oil yields in N. damascena were ۲۸۶.۳۷ and ۱۰۰.۲۹ kg ha-۱, respectively. Mild stress increased the oil content in both species, but severe stress significantly decreased the oil content in N. sativa. Linoleic acid had the highest percentage in both species, followed by oleic and palmitic acids, in the order of their appearance. Drought stress decreased polyunsaturated fatty acids (linolenic acid and linoleic acid), but saturated ones (stearic and palmitic acids) increased under drought stress with increasing drought stress, and the amount of phenolics and flavonoids in both species increased (P< ۰.۰۵). Furthermore, the IC۵۰ level decreased with increasing phenolics and flavonoids contents. In general, drought stress negatively affected seed and oil yields and edible oil quality in these species. Considering the acceptable seed and oil yields of N. damascena and its beneficial fatty acid compositions, it can be used in plant breeding programs and edible oil production.

Medicinal plants, Oil yield, Seed yield.