Effect of salicylic acid on some physiological traits and yield of Black cumin medicinal plant (Nigella sativa L.) under different humidity regimesconditions

Drought stress is one of the major factors limiting plants growth. Salicylic acid (SA) is a natural phenolic compound playing an important regulatory role in plant different processes. Studies have indicated that external application of SA increased plant tolerance to several abiotic stresses, including osmotic stress, drought, salinity, ozone or UV radiation. The purpose of this study was to evaluate the interactive effects of different humidity regimes and application methods of SA on some physiological and biochemical parameters, grain yield and determination of the most suitable application method of salicylic acid in black cumin.

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 (rainfed), 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 (with 0.5 mM concentration), foliar spraying (with 0.5 mM concentration) were studied. After applying of treatments, some traits including total chlorophyll content, antioxidant enzymes activity (catalase, peroxidase and ascorbate peroxidase), leaf relative water content, leaf water saturated deficiency, 1000 grain weight, grain yield, biological yield and harvest index were evaluated.

The results showed that interaction effects of irrigation and salicylic acid on all evaluated traits were significant except for biological yield. Salicylic acid foliar spraying increased activity of peroxidase and ascorbate peroxidase antioxidant enzymes in all irrigation treatments while not significantly affecting catalase enzyme activity. Means comparison revealed that the highest total chlorophyll content (26.2 mg/g FW), RWC (72.44%) and seed yield (1329 kg/ha) obtained from SA foliar spraying application and double irrigation treatment.

Results indicated that SA application especially foliar spraying activated antioxidant system and also improved plant moisture condition and chlorophyll content which finally resulted in enhanced growth and desirable yield under different humidity treatments. Therefore, application of SA can be introduced as an effective approach for regulation and decrease of stress effects and desirable yield production in areas subjected to water deficit.