Effect of Deficit Irrigation Regimes and Foliar Application of Jasmonic Acid and Ascorbic Acid on Some Secondary Metabolites, Oil Yield and Grain Yield of Safflower Genotypes

Safflower is an annual plant native to the Mediterranean countries and cultivated in Europe and U.S. Safflower petals are very important as a source of medicinal preparations, natural food color and dyes for coloring fabrics. Water deficit stress severely limits crop growth especially in arid and semiarid regions of the world as it affects all stages of plant growth and development. Exposure to environmental stresses such as drought stress, heat stress, cold stress, salt stress and plant diseases often leads to the production of reactive oxygen species and other toxic compounds that diminish a plant’s performance. Reactive oxygen species (ROS) are highly toxic to plant cells and in an absence of any protective mechanism they can react with proteins, lipids and DNA and this can inactivate an antioxidant defense system. Plants have an elaborate system of enzymatic and non-enzymatic scavenging pathways or detoxification systems that working together function as an extremely efficient system to counter the deleterious effects of ROS. Higher plants have active oxygen-scavenging systems consisting of several antioxidant enzymes, and some low molecules of non-enzyme antioxidants, such as phenolic compounds, flavonoids, anthocyanins and ascorbic acid. Water deficit is considered to be a major abiotic factor affecting many aspects of plant physiology and biochemistry causing a significant reduction in agricultural production and changes its behavior regarding the biosynthesis of bioactive compounds such as phenolic compounds, flavonoids and anthocyanins in safflower. Ascorbic Acid is a major metabolite in plants. It is an antioxidant, in association with other components of the antioxidant system, protects plants against oxidative damage resulting from aerobic metabolism. Jasmonic acid (JA) is a plant-signaling molecule that shows a wide range of plant responses, with effects at the morphological to molecular levels. Many morphological, physiological, and biochemical processes occurring within the plants can be regulated by jasmonic acid. Previous studies have documented that foliar application of JA and ascorbic acid could modulate plant physiological responses towards abiotic stress tolerance. Considering the importance of safflower plant in terms of quantity and quality of oil, and its various applications in the oil, dyeing and pharmaceutical industries in the semi-arid regions of the world, it seems that increasing yield per unit area in low-irrigated conditions is a good way to increase the production of this plant and improve the economic conditions of farmers. Compared to breeding methods that are often long-term and costly, some agricultural management practices, such as the use of chemicals like ascorbic acid, jasmine acid and other compounds, are easier, cheaper and faster. Therefore, the aim of this study was to determine the effects of jasmonic acid and ascorbic acid on grain yield and Changes in antioxidant compounds of safflower genotypes under drought stress conditions.

This experiment was carried out as a split-split plot in a completely randomized block design with three replications at Shahrekord University Agricultural Research Station during spring planting season 2017. The main plots consisted of three levels of irrigation of 100%, 75% and 50% of the plant's water requirement of safflower and sub-plots including safflower genotypes including Sinai, Isfahan local and Faramanand sub-sub sub-plots including foliar application with three levels including ( control, foliar application of jasmonic acid with 0.5mM concentration and foliar application of ascorbic acid with 20 mM concentration. In this study, the amount of total flavonoid, total phenol, antioxidant activity, ammonialase enzyme activity, grain yield and oil yield were measured.

The results showed that simple effects of low irrigation treatment, genotype and foliar application were significantly in all traits studied in this study. The highest grain yield (1609 kg.ha-1) and oil yield (430 kg.ha-1) obtained in 100% of the plant's water requirement and the least of grain yield (1382 kg.ha-1) and oil yield (335 kg.ha-1) obtained in 50% of the plant's water requirement. The interaction of genotype × deficit irrigation treatments on total phenol content, total flavonoid content, phenylalanine ammonialase enzyme activity and oil yield as well as interaction of low irrigation treatment × foliar application on the amount of antioxidant activity, total phenol, total flavonoid content were significant. The results show that the highest total phenol content (35.4 mg GA. g-1 DW), total flavonoid content (12.1 mg quercetin .g-1 DW), phenylalanine ammonialase enzyme activity (28.6 µmol.g -1FW. min) obtained in interaction 50% of the plant's water requirement and sina genotype and the least amount oftotal phenol content (17.6 mg GA. g-1 DW), total flavonoid content (5.2mg quercetin . g-1DW), phenylalanine ammonialase enzyme activity (8.4 µmol.g -1FW. min ) obtained in interaction 100% of the plant's water requirement and Isfahan genotype. Foliar application with jasmonic acid and ascorbic acid increased antioxidant activity, total phenol, total flavonoid, phenylalanine ammonialase enzyme activity, oil yield and grain yield. So that, the highest amount of antioxidant activity (85.9 % inhibition of linoleic acid), total phenol (31.7 mg GA. g-1 DW) and total flavonoid (11.7 mg quercetin . g-1 DW) related to 50% of the plant's water requirement and foliar application with ascorbic acid and the least amount of antioxidant activity (54.7 antioxidant activity), total phenol (17.6 mg GA. g-1DW) and total flavonoid (5.2 mg quercetin . g-1 DW) related to 100% of the plant's water requirement and without foliar application.

Results indicated that deficit irrigation stress could increase antioxidant activity, Phenylalanine ammonia lyase (PAL) activity, Total phenol, total flavonoid and anthocyanin content in safflower genotype but, grain yield decreased. The increase in tolerance to drought in sina genotype is associated with antioxidant enzyme and non-enzyme activity. Also foliar application of jasmonic acid and ascorbic acid increase antioxidant activity, Phenylalanine ammonia lyase (PAL) activity, Total phenol, Total flavonoid, anthocyanin content and grain yield. According to these results, it may be suggested that increased activity of antioxidant enzymes and non-enzymes can reduce the harmful effects of reactive oxygen species and improve plant drought tolerance, therefore antioxidant enzymes and non-enzymes can be taken as indices of drought tolerance in plants.