The Effect of Drought Stress on Yield and Agrophysiological Characteristics of Bread Wheat (Triticum aestivum L.) Genotypes under Irrigated and Rainfed Conditions

This study was carried out in a split plot experiment based on randomized complete block design with three replications at Sarableh Agriculture Research Station in Ilam. Irrigation and non-irrigation (rainfed cultivation) were assigned to the main plots and 20 wheat genotypes to the sub plots. The amount of total SOD, CAT, and APX activities, RWC, prolin and yield were measured. Irrigated condition showed a significant difference effect on grain yield, yield, 1000 grain weight, grain number per spike, relative leaf water content, prolin content and anti-oxidant enzymes activities. Relative water content of leaves decreased by 33% and 21% compared to optimal irrigation conditions in the first and second years of experiment, respectively. Prolin content increased by 81% in rainfed conditions. Catalase, Superoxide Dismutase and Ascorbate peroxidase activities were also increased under rainfed condition. Significant variation was observed among genotypes for traits under study and the rate of variation of traits under dryland conditions was not similar for different genotypes. Cultivation under rainfed conditions decreased grain number per spike (24%) and grain weight per spike (16%). Cultivation under rainfed conditions reduced grain yield by 29 and 41% in the first and second year, respectively. But, the percentage of yield losses in both two years of experiment were not similar for different genotypes. The results showed that the rainfed condition affected the crop yield, and all of traits under experiment. Thus, the means of traits of genotypes under irrigated and rainfed conditions were significantly different. The activity of antioxidant enzymes (catalase and superoxide dismutase and ascorbate peroxidase), relative water content of leaf and proline percentages in rainfed conditions were significantly increased as compared to irrigated condition.