Research article EFFECT OF INCREASING SEVERITY OF DROUGHT STRESS ON MORPHOLOGY AND ESSENTIAL OIL OF POT MARIGOLD

Flower heads of Calendula officinalis L. are used for medicinal or culinary purposes. To evaluate effect of water deficit stress on morphology and yield of Calendula officinalis, a split plot experiment was carried out based on randomized complete block design with three replications in 2011. Treatments were irrigation (irrigation after 30, 60, 90 and 120 mm evaporation from class A pan) as main plots and gradual rise intensification of water deficit (increasing the irrigation intervals after first irrigation cycle amounted 0, 5, 10 and 15 mm evaporation) as sub plots. Results of ANOVA showed significant interaction between irrigation and increasing stress strength on capitulate diameter, percentage of essential oil, yields of dried flower and essential oil. The highest yields of flower (934.7 kg/ha), essential oil (4.92 kg/ha) and single dried flower weight were obtained from irrigation after 30 mm evaporation, and control treatment of water deficit strength (0 mm evaporation). The highest essential oil percent (0.77%) belonged to irrigation after 120 mm and increasing of 15 mm evaporation. In conclusion, increasing water deficit caused to reduction all traits, except the essential oil content that it raised along with sever stress.