Effects of Planting Date and Plant Density on Physiological Indices, Quantity and Quality Traits of Two Varieties of Marigold (Calendula officinalis L.)

Introduction\ud Marigold (Calendula officinalis L.) is originated from North West Africa and Mediterranean area, is a medicinal plant used for several purposes. It is an annual herb or short-lived perennial from the Asteraceae family with yellow or orange flowers. The Marigold has been used as a traditional medicine and food dye, but is currently used as an anti-inflammatory and wound healer. It is grown for drug, obtained from the flowers. The flowers blossom during summer three or more times per year. The essential oil of yellow or orange petals of Calendula officinalis L. is one of the important yield components which is used for food and medicine. Moreover, the seed has an oil content of 5-20 %. Seed oil could be used as a binder in paints, coating and cosmetics. \ud Growth, development and production of medicinal plants, as well as other plants are affected by genetic and agronomic factors. Planting date and plant density are two most important factors that can affect yield and yield components. Planting date affects the quantity and quality of secondary metabolites of medicinal plants. The optimum sowing date and plant density can improve the light and temperature absorption and other factors during the growing season. The positive effects of optimal planting date and plant density has been described by a number of researchers. The Plant population is dependent on the plant characters, growth period, time and method of cultivation. Also, the suitable sowing date has advantages for maximum production. Early sowing in the spring causes weakly establishment of plant and late planting date shortens growth period and simultaneous flowering period due to high temperature in summer. In this study, the effects of plant density and planting date on physiological indices, quantity and quality of two varieties of spare and compact marigold has been evaluated.\ud Materials and Methods\ud In order to determine the effects of planting date and plant density on physiological indices, quantity and quality traits of two varieties of marigold (Calendula officinalis L.), a split-factorial experiment with three replications was carried out in agricultural research station in Arak (latitude: 34o 5' N; longitude: 29o 42' E; 1757 m altitude) in 2010 the growing season. Soil was silty-loamy with pH of 7.5 and EC of 0.8 Ds ms-1. The experimental factors included two planting dates (22 April and 2 May), four planting densities (26, 32, 41 and 57 plants/m2) and two varieties (sparse and compact petal). Thinning was performed 20 days after cultivation. Irrigation was carried out in 7 days intervals. For determination of growth indices, ten plants from each plot cut from crown and dried for 48 h in oven at 70°C and then weighted. The plant height, number of flowers per plant, leaf chlorophyll, leaf area index, total dry matter, seed yield, 1000 seed weight, essential oil and grain oil were measured. The extraction of the essential oil of the flower was performed using the Clevenger apparatus by steam distillation (1). Extraction of grain, oil was accomplished according to the soxhelet standard method. The data were analyzed using the statistical analysis system (SAS 9.1) and means were compared using Duncan test at P ≤ 0.05 probability.\ud Results and Discussion\ud Results showed that, planting date and plant density had significant effects on physiological indices, plant height, and number of flowers per plant, 1000 grain weight, chlorophyll index, oil percent and essential oil percentage of marigold. Late planting and decreasing plant density, reduced leaf area index (LAI), total dry weight (TDW) and crop growth rate (CGR) indices. The compact petal variety showed the highest growth indices compared with spare petal plants. On the other hand, early planting, high plant density and compact petal variety increased the growth and development of plants. The first planting date had higher leaf area index compared to second sowing date. It seems that first sowing date made adequate leaf area indices for light and radiation absorption for photosynthesis. Number of 57 plants per square meter in the first and second planting dates improved plant height by 25.1 % and 34.4 %, compared to 26 plants per square meter, respectively. It is noticeable that delay in planting date reduced the mention plant traits. The second planting date (2 May) with 57 plants per square meter in comparison to the first planting date (22 April) decreased chlorophyll index by 18.4%. The compact petal variation showed the highest number of flower and oil percent in comparison with sparse petal variety. The compact petal variety in the number of 57, 41, 32 and 26 plants densities increased essential oil percentage by 9.8, 6.8, 3.5 and 9.1 % compared to sparse petal, respectively. Martin and Deo (32) showed that the highest flower yield in Calendula officinalis L. was observed in 40 plants/m2 density and April 15 sowing date. \ud Conclusions\ud The present study showed that the best result for different traits with the exception of number of flower per plant achieved in the first sowing date (22 April) with a compact petal variety and 57 plants per square meter. Therefore, this treatment is suitable for marigold cropping in Arak situation and areas with similar climate and weather