Evaluation of genetic diversity of Iranian bread wheat genotypes considering germination related traits under normal and osmotic stress

Common wheat (Triticum aestivum L.) is an important crop in Iran and world which many new cultivars with improved agricultural traits are developed by plant breeders every year. In order to evaluate the genetic diversity of 30 bread wheat genotypes considering germination related traits under normal and osmotic stress released during 1930-2010 in Iran, an experiment was carried out as factorial in a randomized complete block design with three replications. The studied factors were 30 wheat genotypes and four drought stress conditions simulated by PEG (0, -2, -4 and -6 bar). The results showed that the old winter cultivar, Omid, had the highest biomass dry weight in both control and -6 bar drought stress conditions. According to the sensitivity index calculated based on biomass dry weight, the cultivars Sabalan, Zare and Tabasi were the most tolerant and Navid, Moghan-2 and Golestan were the most sensitive genotypes. In cluster analysis under -6 bar drought stress conditions, the genotypes Sabalan and Omid, away from the other genotypes, were grouped in a separate cluster. Comparison of the genetic variance between old released cultivars and new cultivars showed that the genetic variance has significantly decreased in new cultivars for shoot length, shoot dry weight and root to shoot dry weight ratio. This result indicated that the new cultivars had less variation than the old cultivars. Therefore, it is recommended that more diverse genetic resources be used in breeding programs to avoid genetic homogeneity.