Assessment of Growing Degree-Days Values of Phenological Stages in Iranian Bread Wheat Cultivars and Landraces

In studying the phenological stages of crops, the growing degree-days (GDD) gradients is considered as an alternative to counting the calendar days. Genetic diversity of 86 Iranian cultivars and 184 Iranian wheat landraces were studied based on the phenological stages (day to booting, day to flowering, day to maturity and GDD of these stages) along with grain filling period, thousand grain weight and grain yield during the 2013-14 and 2014-15 growing seasons. The results revealed that there is a significant difference between cultivars and landraces and studied traits were able to effectively distinguish between cultivars and landraces. On the other hand, the results indicated that genotypes with different growth habits have a significant difference in terms of most of the phenological traits. That is implied that either directly or indirectly has been occurred on increasing the length of the grain filling period along with grain yield. Since the diversity of phenological traits was higher in landraces, they can be a valuable source of choice for improving these traits. Finally, due to the importance of the phenological stages, it is recommended that these traits be taken into account in terms of yield and yield components and GDD index can be used to obtain more accurate results.