Evaluation of reaction of sunflower (Helianthus annuus L.) genotypes in terms of yield and yield components under water stress conditions

Introduction Sunflower is known as the world's second largest hybrid plant and it is the fifth important oil plant in the world. Having of high percentage of unsaturated fatty acids along with a significant amount of protein (about 07-27%) increase the nutritional value of this oil seed. Drought stress is one of the main challenges for global crop production. So that about 40% of the world's land is located in arid and semi-arid regions and in these areas, water is the main limiting factor for production. In Iran, the limitation of water resources and the shortage of precipitation is a major challenge for crop cultivation. Thus, evaluation of response of different genotypes of a crop to deficit irrigation conditions and selection of more tolerant genotypes as well as improving advanced and resistant cultivars for arid and semi-arid regions, can achieve higher yields and more crop productions. In sunflower, despite there are deep and wide roots, the intense moisture stress significantly reduces the diameter of head, the number of seeds per head and the seed yield. Therefore, the aim of this study was to investigate the responses of sunflower genotypes under water stress conditions in order to select the superior genotypes under this stress. Materials and methods The present study was carried out to identify sunflower tolerant genotypes at Research Station of Dryland Agricultural Research Institute (Sararood) in Kermanshah. The experiment was carried out in the form of a lattice square design. In this study, 64 sunflower genotypes with 8 x 8 arrangement were compared in two conditions of non-stress and applying water stress (irrigation cut off at flowering stage). At the end of growing season, five plants per plot were harvested and after transferring them to the laboratory, traits of head diameter, number of seeds per head and weight of 1000 seeds were measured. In the bottom half of each plot that was dedicated to yield evaluation, the plants were harvested after removing the margin and counting the number of heads per m2 and then, after separation of seeds, seed yield of genotypes were measured, separately. Results and discussion The results showed that between genotypes as well as water stress treatment levels, there was no significant difference in number of heads per area. For head diameter in water stress conditions, in 27 genotypes head diameter was more than 11.4 cm and in 16 genotypes, head diameter did not reach even 10 cm. In non-stress conditions, Sil-96 genotype was shown the highest number of seeds per head by producing more than 842 seeds per head. However, 12 other genotypes were placed in a statistical group with this genotype. By applying water stress in 11 genotypes (including the Sil-96), the number of seeds per head was more than 630 and in 16 genotypes, the number of seeds per head was less than 400. In terms of weight of 1000 seeds, there was no significant difference between sunflower genotypes in both conditions of non-stress and water stress application. But by comparing two conditions of stress and non-stress, it was found that water stress caused a significant reduction in the weight of 1000 seeds in amount of 8.62%. Sil-96 genotype showed the highest seed yield in both stress and non-stress conditions. Although in each of the conditions of the water treatment, were placed into a statistical group with four other genotypes. Also, Sil-96 genotype had the highest stress tolerance index. Conclusions It seems that this genotype is recommended for cultivation in both conditions of stress and non-stress.