Selection of the most effective traits on yield of sunflower under normal irrigation and drought stress conditions in Birjand region

In order to evaluate crop yield and its components and determination of the most important traits influencing yield, seven genotypes of sunflower were planted under normal irrigation and drought stress conditions in two separate experiments based on randomized complete block design with three replications at Birjand University Research Farm in the cropping season of 2010-2011. Treatments included two levels of stress and normal conditions. Measured traits included yield, seed per head, seed weight, head diameter, plant height, leaf width, leaf length, leaf number, top diameter of the stem, bottom diameter of the stem, petiole length, the distance between ground and head, and the distance between ground and the highest point of the stem. Results of the simple analysis of variance showed that the distance between the ground and head, bottom diameter of the stem, leaf number, plant height, 1000-seed weight and seed yield were significantly different amongst cultivars under both conditions. Compound analysis of variance showed that all traits except the leaf length were significantly different amongst genotypes studied under two conditions and stress effects were significant on yield, 1000-seed weight and head diameter. The correlation between crop yield and seed per head, leaf width, petiole length, top and bottom diameter of the stem, head diameter, 1000- seed weight and the distance between ground and the highest point of the stem was significant under normal condition, while under stress conditions, crop yield merely had significant correlation with seeds per head. Multiple regression results showed that the seeds per head, diameter of head, 1000-seed weight and petiole length were the most influential traits under both conditions. The path analysis showed that the seed per head is the most influential trait in crop yield. Factor analysis identified three and five factors under normal (explained 79.37% of the total variations) and stress conditions (explained 86.88% of the total variations), respectively. Cluster analysis classified genotypes in two and three categories under normal and stress conditions, respectively.