Effect of spermidine foliar application on some morphophysiological traits and secondary metabolites of marigold (Calendula officinalis L.) under drought stress

Drought stress is the most common abiotic stress that has the most negative effect on plant growth and production Polyamines are plant growth regulators that increase plant resistance to environmental stresses, including drought stress. The aim of this study was to investigate the effect of foliar application of spermidine on reducing the effects of drought stress on marigold (Calendula officinalis L.). For this purpose, foliar application of spermidine (0, 50, and 100 mg/l) was considered at different levels of drought stress (control, 25, 50, and 75% of field capacity) in a factorial experiment based on a completely randomized design with 3 replications in 2018 in a greenhouse located in northern Iran. The foliar application was applied at three stages with intervals of about 20 days including six visible leaves, complete tillering, and emergence of the first bud. Results showed that drought stress and foliar application of spermidine had a significant effect on the evaluated traits. The highest fresh and dry weight of shoots, number of flowers, and total chlorophyll contents were observed in the treatment with 75% of field capacity and spermidine 50 mg/l and the highest fresh and dry weight of roots and flowers on the plant were recorded in the treatment with 100% of field capacity and spermidine 100 mg/l. Also, the highest root length, plant height, total antioxidant activity (DPPH), rutin and quercetin were observed in the treatment with 75% of field capacity and spermidine 100 mg/l and the highest proline and polyphenol oxidase activity was observed in the treatment with 25% of field capacity. Therefore, according to the results of this study, foliar application of spermidine 100 mg/l with an irrigation level of 75% of field capacity is recommended for marigold.