Variations of phytochemical properties of Calendula officinalis L. under salinity stress and treatment with humic acid and selenium

The present study was designed to investigate the phytochemical composition and yield of essential oil of Calendula officinalis L. (Marigoldisa) under NaCl-induced salinity stress using humic acid and selenium as a factorial experiment in the form of a completely randomized design with two factors of NaCl-induced salinity stress (50 and 100 ppm) as the main factor and foliar application with selenium (at both S and 10 ppm levels) as well as soil application of humic acid (at both 50 and 100 ppm levels) as side factors and their interactions. The experiment consisted of 19 treatments each with 3 replicates, each replicate containing 3 plants and a total of 171 pots. In this study, Calendula officinalis L. seeds were cultivated in a tray containing cocopeat and then transferred to a pot of size 15 after 20 days (six-leaf stage) with the pot soil containing loamy soil, sand, and compost with a 1-1-1 ratio. The treatments were applied after 20 days of transfer to the main pot (early stage of stem emergence). The humic acid was added at the time of bed preparation with sodium chloride applied in combination with irrigation water twice in three consecutive weeks. Foliar application with selenium was also performed after each irrigation with sodium chloride. Fertilization with the required elements was normally performed for plants with the pots treated without control. Sampling and evaluation of traits were done about 20 days after flowering stage. The experiment was repeated for two consecutive years for greater confidence and better results. The results revealed that in both years, the control treatment had the highest effect on traits including fresh and dry weight of aerial parts and root, plant height and flower number, petal carotenoid content and total leaf chlorophyll content, protein content, phenol and flavonoid content, and it lead to longer longevity. The highest proline content was associated with the NaCl 100ppm treatment and the highest activity of super-oxide dismutase and peroxidase enzymes as well as highest percentage of essential oil were observed in the NaCl 50 ppm + H 200ppm + Se 10ppm treatment. In addition, in the first and second years, the control treatment with 10.9 and 11.2 days, respectively, had the highest while NaCl 100ppm with 5.4 and 6.1 days had the lowest longevity of Calendula officinalis L. flowers on the plant.