Effects of drought stress, salicylic acid, and polyamines on plant growth yield and oil and essential oil content of Nigella sativa L.

To investigate the effects of drought stress, salicylic acid, and polyamines on plant growth yield and oil and seeds essential oil content in Nigella sativa L., a factorial experiment was conducted in a completely randomized design with three replications in the research greenhouse of Shirvan Azad University in 2020-21 cropping year. The experimental treatments included drought stress at four levels (25, 50, 75, and 100% of field capacity) as the first factor and foliar application of salicylic acid, putrescine, and spermidine each at two levels (0.5 and 1 mM) as the second factor. The results showed that the highest number of fertile capsules per plant (12.66), number of seeds per capsule (96.24), and harvest index (58.69%) were obtained in the 100% of field capacity treatment. Also, the highest seed yield per pot was obtained in the 100% of field capacity treatment (16.05 g) and 1 mM salicylic acid (11.46 g). On the other hand, the highest plant height (62.5 cm), dry weight of single plant (6.44 g), biomass in pot (32.2 g), oil content (31.21%), and oil yield (5.71 g.pot-1) were obtained in the treatment of 100% of field capacity + 1 mM salicylic acid and also, the highest essential oil content (0.09%) was obtained in the treatment of 25% of field capacity + 1 mM salicylic acid. Overall, the results showed that full irrigation (100% of field capacity) + 1 mM salicylic acid foliar application was the best treatment for N. sativa under greenhouse conditions. In general, the plant growth characteristics decreased with increasing stress severity, but the negative effects of drought stress were moderated with increasing the salicylic acid foliar application.