Evaluation of salicylic acid application on the physiological responses of black cumin (Nigella sativa L.) under different irrigation conditions

Introduction Drought stress has different effects on morphological, physiological and biochemical processes of plants. Growth regulators play a crucial role during plant growth and development and utilizing of them can a possible approach to improving plants economic grain yield. Salicylic acid plays an essential role in regulating various physiological processes such as growth, plant development, ion absorption, photosynthesis and germination. The aim of this study was to determine the most suitable method for the application of salicylic acid as a drought tolerant inducer and to investigate the effect of salicylic acid on physiological traits and herb yield of black cumin under different irrigation regimes.   Materials and Methods This study was conducted based on randomized complete design with factorial arrangement of treatment and three replications at Gonbad Kavous university research field in 2018 growing season. Different irrigation regimes at four levels including no irrigation (dry farm), once irrigation at flowering stage, once irrigation at grain filling stage and double irrigation at flowering and grain filling stages and salicylic acid factor at three levels including non- application (control), seed priming (0.5 mM -1), foliar spraying (0.5 mM -1) were studied. In this study, some traits such as amount of chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, electrolyte leakage, proline, soluble sugars and grain yield were evaluated. Statistical calculations were performed using SAS software version 9.1 and the obtained measurements were compared using LSD test and probability level five.   Results and discussion The results showed that the effects of simple irrigation and salicylic acid and their interactions on all studied traits were significant.Salicylic acid spraying increased the content of proline and soluble sugars in all irrigation conditions. The lowest amount of membrane degradation was observed from salicylic acid priming treatment (39.67%) under irrigated conditions and the highest amount of membrane degradation was observed in salicylic acid (72.33%) absence in dry farm conditions. Salicylic acid spraying led to an increase in photosynthetic pigmentation at all levels of irrigation. Also, the highest grain yield was obtained from spray application (1329.66 kg/ ha-1) under irrigated conditions and the least grain yield belonged to non-salicylic acid treatment (817.33 kg/ ha-1) under dry farm conditions. It seems that spillage of silicic acid has been shown to be a retrograde process and, by increasing the antioxidant capacity of the cell, decreases the amount of peroxidation of the lipids and further protects cell membranes and photosynthesis and photosynthetic pigments and prevents chlorophyll catabolism. Reducing membrane damage due to the use of salicylic acid, known as the main way to increase drought resistance in the plant, may be associated with the production of antioxidants that the production of antioxidants is a response from the plant to reduce the oxidation damage. In other words, salicylic acid increases the membrane stability against oxidative stresses. Salicylic acid leads to proline accumulation in the plant by induction of protective interactions with aqueous humor hormones. According to the results, it is observed that the soluble sugars in sprayed plants were more than primed seeds and did not consume salicylic acid. In addition, drought stress increased the amount of soluble sugars, but the increase caused by spraying was higher than that in stress Is significantly higher. It seems that salicylic acid increases the amount of sugars in plants by increasing the amount of photosynthetic pigments, reducing oxidative stress and protecting chloroplast and cell membranes. Application of salicylic acid improved seed yield through positive effects on photosynthesis, photosynthetic material transfer, inoculation of flowers, preventing severe abortion of flowers and increasing grain filling time. The results also showed that salicylic acid could have a positive effect on grain yield in dry farm condition, so that the application of salicylic acid as spraying and priming increased the yield of 23.08 and 14.39 percent, respectively, than salicylic acid.   Conclusions According to the results of this study, it can be concluded that the application of salicylic acid as foliar spraying is a suitable strategy for increasing the resistance of black cumin to drought stress.