The effect of late season drought stress on some morphophysiological characteristics of Iranian safflower varieties in Karaj region

Introduction The importance of oil crops such as safflower has increased in recent years. Due to that safflower, can resistance in drought condition without reduction in yield, it can be a promising alternate crop in dryland agro-ecosystems. Plant have developed a wide variety of drought tolerance mechanisms in morphological and physiological levels. There are wide variations among the safflower genotypes with respect to seed and oil yields at drought stress condition. Materials and methods In order to investigate the effects of late-season drought stress on some morphophysiological characteristics of Iranian safflower varieties, an experiment was conducted in the research field of Karaj Seed and Plant Improvement Research Institute. This study included two irrigation levels; normal irrigation (control) and drought stress from grain filling stage (main plot), and five Iranian safflower varieties including Sofeh, Goldasht, Golmehr, Padideh and Parnian (sub-plot), which conducted as a split-plot experiment in a randomized complete block design with three replications during the 2016-17. Results and discussion The results showed that drought stress had a significant effect on morphophysiological traits and seed yield of safflower varieties and decreased plant height, heads per plant, head diameter, seeds per head, 1000-seed weight and seed yield. Moreover, drought stress reduced relative water content, leaf area index and increased canopy temperature of safflower varieties. Late season drought stress reduced the growth duration of safflower varieties by 6-days compared with normal irrigation (control). Plant height of safflower varieties decreased under drought stress by an average of 8.2 cm. The highest plant height was observed in Parian variety (140.6 cm) in normal irrigation treatment. In contrast, under drought stress conditions, the highest plant height was observed in Golmehr (128.3 cm). In the present study, late season drought stress increased three degrees Celsius at safflower canopy temperature. The highest and lowest canopy temperatures were observed in Goldasht and Parian varieties (34.1 and 30.6 °C, respectively). Also, late season drought stress reduced leaf area index (LAI) by 34% in safflower varieties. The highest and lowest leaf area index were observed in Parnian and Goldasht varieties (2.4 and 0.7, respectively). Under non-stress conditions, the highest relative leaf water content (RWC) was observed in Parnian variety. In addition, in drought stress treatment, Parnian and Padide varieties had the highest RWC (67.4% and 66.1%, respectively). Drought stress reduced seed yield and seed oil content by 14.9 and 2.7%, respectively. Due to the number of heads and 1000-seed weight, Parnian variety had the highest seed yield at both control and drought stress conditions by 2150 and 1773 kg.ha-1, respectively. The highest seed yield loss due to drought stress was observed in Sofeh variety by 24.8%. Conclusion Overall results of this study showed that Parnian variety was significantly superior to other varieties in terms of morphophysiological characteristics such as LAI, RWC and seed yield under late season drought stress. According to this, in terms of morphophysiological traits affecting drought tolerance, this variety performed better than other varieties.