Effects of drought stress on some morphological characteristics and quercetin production levels of pot marigold at different stages of growth

Calendula officinalis L. belongs to Asteraceae and is an ornamental and medicinal plant. Since diagnosis of medicinal plants growth under different irrigation conditions and drought stress can be a guide for growing plants in dry and low water conditions, the aim of this study was investigating of the effects of drought stress on morphological characteristics and quercetin amount, in different stages of plant growth of C. officinalis L. This research was conducted in Gorgan in a completely randomized factorial design, each treatment with 3 replications. The experimental treatments included three levels of stress (no stress, mild stress and severe stress) in pots under greenhouse conditions, at vegetative, preflowering, flowering, and fruiting stages. After determining the soil field capacity in the pots, the water content was calculated for control pots, and then its content was set at 2/3 for mild and 1/3 for drought stress. The pots were irrigated with the specified amount. After the treatments, plants were pulled from soil and their morphological traits including plant height, root length, stem length, leaf length, number of flowers, and flower diameter were measured. Moreover, their predominant flavonoid production (quercetin) was measured by liquid chromatography. Statistical analysis was performed SPSS software and means were compared using Duncan's multiple range test at 5% level. The results showed decreased plant height, leaf number and area and flower number and diameter, and increased root length by decreasing of soil moisture content at all stages of growth. The amount of quercetin increased in mild stress condition and decreased in severe stress condition at flowering and fruiting stages. The highest level of quercetin (59.11 mg g -1 dry weight) was belonged to mild drought stress at fruiting stage and the lowest level (41.05 mg g -1 dry weight) was belonged to severe drought stress at flowering stage. It can be concluded that plants produce more secondary metabolites in response to stress, and in severe stress, they produce fewer secondary metabolites due to lower plant growth rate.