The response of yield and some morphological characteristics of safflower cultivars to water stress

Introduction Oilseeds are the second main source of human food after cereals. Safflower is an oilseed crop with favorable and unique characteristics that make it a valuable oilseed crop. Safflower due to having long roots and the high ability for absorbing water from deep soil layers, is considered as a low water-tolerant plant; but after the rosette stage, it becomes more sensitive to water stress such that since the first signs of inflorescence emergence up to the middle of the grain-filling period, it shows more sensitivity to this kind of stress. Increasing need for oil production on one hand and increasing levels of drought due to world climatic changes on the other hand makes it necessary to seek for more water stress tolerant plants such as safflower with relatively high yield capacity under low water content areas. Meanwhile the area under cultivation of safflower should increase. Agricultural and environmental factors can affect safflower seed yield and seed oil content. Therefore, it is important to investigate different environmental factors and their effects on growth and yield performance of safflower plants. Limitations of water resources makes it more difficult to grow safflower plants. Furthermore increasing levels of per capita oil consumption in Iran indicates that oilseed production must increase. Therefore, One of the objectives of this research was to identify and evaluate species and cultivars resistant to water stress and to find the plant stages sensitive to water stress. Materials and methods In order to evaluate the effects of water stress on some morphological, yield and yield components of different safflower cultivars, an experiment was carried out as split plots based on randomized complete blocks design with three replications at the experimental field 56° 58' E; 30° 15' N; 1754 meters above sea level of Faculty of Agriculture, Shahid Bahonar university of Kerman, Iran during 2019-2020 growing season. Water stress applied at three levels including 40, 60 and 100% of full crop water requirement in the main-plots and 6 Iranian safflower cultivars including Faraman, Goldasht, Golmehr, Parnian, Padideh and Sina assigned to the sub-plots. Physical and chemical properties and nutrient elements content of the soil before planting were measured using samples taken from of 0-30 cm soil depth of experimental location. Seeds planted manually and plots fully irrigated immediately after planting. Thereafter, plants irrigated throughout the growth period based on the calculated values of the water requirement of the plant. Results and discussion Based on results, the treatment 40% of the plant water requirement had a significant reduction effect compared to other treatments of water stress on the studied traits in all investigated cultivars. The results Data analysis showed that water stress had not a significant effect on lateral branch number, but it causes a significant reduction in all traits, Including the plant height, number of heads per plant, number of seed per head, head diameter, 1000 seed weight, seed oil content, oil yield and seed yield. Significant differences found among cultivars in term of all other plant characteristics. Meanwhile, Highest values of 1000 seed weight (37.2 g), oil yield (461.8 kg.ha-1) and seed yield (1592.6 kg.ha-1) observed in Faraman cultivar. The Interaction effects between irrigation treatment and cultivar were significant in case of number of heads per plant, number of lateral branches, oil yield and seed yield. However, the Faraman cultivar had more grain yield potential in water stress conditions than the other investigated safflower cultivars. Conclusion Generally, results showed that the reaction of the six cultivars investigated in terms of plant height, number of heads per plant, number of seed per head, number of lateral branches, 1000 seed weight, head diameter, seed oil content, oil yield and seed yield were affected by water stress. The highest values of 1000 seed weight, oil yield and seed yield among the investigated safflower cultivars were related to Faraman cultivar. Meanwhile, cultivar Faraman showed higher seed yield potential under water stress conditions compared to the other cultivars. Therefore, to achieve higher yield, Faraman recommended to be grown under low soil water content condition.