Responses of Safflower cultivars to irrigation treatments in spring and summer cropping seasons

Safflower (Carthamus tinctorius L.) is an oil-producing plant, which is considered to be a valuable source of seed oil due to its high oil quality and relatively high resistance to salinity and water-deficit conditions (Mozaffari and Asadi, 2006). In the regions where annual precipitation is low and also the distribution of rainfall is unpredictable, drought is the most important environmental stress that adversely affects crop plant performance. Identifying tolerant cultivars with high yield potential is of paramount significance for researchers under the condition with ever-decreasing rainfall, elevated air temperature and increased hot weather. Delayed sowing in the spring cropping of safflower causes accelerated development, reduced vegetative growth and decreased yield and yield components of the plant (Zimmerman, 1972). The objective of this work was to determine suitable cultivars for the spring and summer cropping seasons under water-shortage conditions.
This experiment was carried out as split-split plot in a randomized complete block design with four replications at agricultural research station of Kabutarabad in the 2016 growing season. The main factor consisted of two spring and summer sowing dates, the sub-factor comprised of three irrigation treatments (Full Irrigating from sowing to plant maturity as control, irrigation till the beginning of flowering and irrigation till the seed filling period) and the sub-sub factor included nine safflower cultivars: Sofeh, Goldasht, Sina, Faraman, and Mexican cultivars of Mec117, Mec295, Mec18, Mec11 and Mec7. Following seed sowing, and the initial irrigation for plant emergence and establishment, the plots were irrigated after 70 mm cumulative evaporation from evaporation pan class A and cessation of irrigation for plots occurred based on plant growth stage and the irrigation termination treatments.
The results indicated that there was a significance difference between spring and summer planting dates for all the measured traits. Plant height, plant dry matter at flowering stage, boll numbers, number of seeds in boll, seed weight and seed yield decreased in summer cropping as compared with spring cropping. There was no significant difference in plant dry matter at flowering stage, boll numbers and seed weight under irrigation treatments but other traits showed significant differences. The highest grain yield was obtained when the cultivars received full irrigation (control treatment). Termination of irrigation in the grain-filling period and at flowering reduced grain yield by 25 and 45% as compared to the control. Average seed yield of cultivars in the spring planting was 62% higher than summer planting. The highest seed yield in spring planting was obtained from Sofeh and Goldasht and Mec117 cultivars. But, the greatest seed yield in summer planting was obtained from Sofeh, Goldasht, Sina and Faraman cultivars (The cultivars are mentioned in descending order of yield). Mexican cultivars performed best in spring planting, however, they experienced a significant decline in their seed yield in summer planting. Crop seed yield is reduced when sensitive growth stages e.g. flowering and pollination coincides with adverse environmental conditions such as high temperature (Emami et al., 2011). The observed yield reduction in the safflower cultivars in the second planting date (summer season) is attributable to decreased duration of rosette and vegetative stages. This was due to rapid transition from vegetative to reproductive stage caused by environmental stressors, in particular, high temperature, which prevented the plant from achieving adequate yield- forming components.
In general, Iranian cultivars were more resistant to stress and had higher grain yield than Mexican cultivars. Iranian cultivars Sofeh, Sina and Goldasht are suitable cultivars for planting under normal and drought stress conditions for spring and summer cropping seasons.