Effects of Foliar Application of Citric Acid on Morphological and Phytochemical Traits of Calendula officinalis L. under Drought Stress Conditions

The experiment was performed to study the effect of foliar application of citric acid on reducing the effects of drought stress on Calendula officinalis L., the effect of citric acid (0, 50 and 100 mg l-1) and different levels of drought (no stress: control, 25, 50 and 75% field capacity) was studied as a factorial experiment based on a completely randomized design with three replicates in 2018 in greenhouses in northern Iran. The foliar application was applied in three stages with an interval of about 20 days, including the six-leaf stage, full tillering and the appearance of the first bud. The results showed that drought stress and foliar application of CA significantly affected the parameters evaluated. The highest fresh and dry weight of shoots and roots, carotenoids, phenol and flavonoid were obtained in 75% FC + CA 50 mg l-1. The maximum plant height, root length and number of flowers were for control irrigation + CA 50 mg l-1 and the highest longevity of the flower on the plant, total carbohydrate, rutin and total antioxidant activity was observed in 75% FC + CA 100 mg l-1. In addition, treatment of control irrigation + CA 100 mg l-1 had the highest total chlorophyll and vitamin C and the 25% FC treatment had the highest proline content. In general, irrigation of pot marigolds with 75% FC and spraying with citric acid 100 mg l-1 had positive effects on plant growth and biochemical parameters