Changes in essential oil yield and fatty acid contents in black cumin (Nigella sativa L.) genotypes in response to drought stress

[Display omitted] •Effect of three drought levels on yield, oil and essential oil contents of black cumin genotypes were examined.•Yield and oil content reduced while essential oils content increased by drought conditions.•Mashhad under normal irrigation, Arak under moderate drought and Semirom under severe drought stress produced the greatest yield.•Shahrekord genotype was the best genotype for essential oil production. Black cumin (Nigella sativa L.) is a medicinal and aromatic plant whose essential oil and fatty acid composition may be affected by drought stress. The present study was conducted in Isfahan, Iran during 2017 and 2018 growing seasons to investigate the effects of three irrigation regimes (I1, 40 %; I2, 60 %; and I3, 80 % soil permissible moisture depletion representing normal, moderate, and severe stress levels, respectively) on the seed yield, essential oil percentage, and fatty acid composition of ten black cumin genotypes (namely, ‘Arak’, ‘Isfahan’, ‘Semirom’, ‘Shahreza’, ‘ShahrKord’, ‘Mashhad’, ‘Afghanistan’, ‘Pakistan’, ‘India’, and ‘Syria’). Drought was found to decrease seed yield, essential oil yield, oil content, and oil yield of the genotypes but enhanced their essential oil percentage. However, the effects were depend on drought-level and genotype, ‘Mashhad’ under I1, ‘Arak’ under I2, and ‘Semirom’ under I3 had the highest seed yield while ‘Shahrekord’ produced the greatest essential oil yields under all the irrigation regimes. Moreover, ‘Mashhad’ under I1, ‘Arak’ under I2, and ‘Shahrekord’ under I3 recorded the highest oil yields. Linoleic (46.43 %), oleic (24.40 %), and palmitic (15.04 %) acids were found to be the main fatty acids produced by the species. Saturated and polyunsaturated fatty acid proportions increased while those of monounsaturated fatty acids decreased with increasing drought level but the polyunsaturated fatty acids exhibited far greater increases than did the saturated ones. Overall, results indicated that black cumin genotypes were both qualitatively and quantitatively affected by drought level; hence, proper irrigation regimes might be used to optimise fatty acid compositions in the selected genotypes.