Evaluation for grain yield in regional preliminary yield trials and selection in segregating generations in bread wheat genotypes under limited water conditions in cold regions

Terminal drought stress is one of the limiting factors of wheat production in cold regions of Iran. Selection and introduction of terminal drought tolerant cultivars is one of the major goals of wheat breeding program for cold dry areas of Iran. Considering the importance of terminal drought stress and shortage of water at terminal growth stage of wheat cultivars, different types of yield trails are conducted under optimum and limited water conditions to identify and introduce cultivars which have the ability to produce expected high grain yield under limited water conditions. The objectives of this study were 1) to select terminal drought tolerant wheat lines with high grain yield and good adaptability in Uniform Preliminary Regional Wheat Yield Trial (URPWYT) and 2) to evaluate and select for agronomical characters effective in yield of bread wheat in segregating populations under limited water conditions in cold regions. This study was conducted in two series of experiments as follows: A-Evaluation and selection in F2 and F3 Segregating Populations (SP): In the first series of experiments, 19 (F2) and 44 (F3) entries of segregating populations were evaluated at Karaj station. Necessary data such as plant height, kernel size, leaf length, days to heading and maturity and resistance to environmental stresses were recorded. Modified bulk selection method was used to handle segregating populations. B- Uniform Preliminary Regional Wheat Yield Trial (UPRWYT) were conducted with 76 wheat lines including three checks (Gaspard, Cross Shahi and Toos) under late season limited water conditions in 5 experimental stations (Karaj, Ardabil, Hamedan, Miandoab and Mashad) in 2004-2005 cropping seasons. Due to the large number of lines, these experiments had no replication. The water stressed trials were irrigated by just the heading stage. During cropping seasons, morpho-physiological and agronomical characters associated with drought tolerance such as plant height, growth habit, no of kernels/spike, 1000 kernel weight, no of days to heading and maturity, and grain yield were recorded. From F2 and F3 segregating population grown at Karaj station, 11 and 18 entries were respectively selected for planting in further generations in the next growing season. Comparisons of grain yield of new lines in UPRWYT in each station and determination of their yield stability was carried out, using non-parametric ranking statistic method (rank method). Based on results, most of new lines were superior to the check cultivars. However, considering both the recorded data, and the grain yield of wheat lines under limited water conditions, 32 superior lines were selected. These selected lines will be assessed for terminal drought tolerance in replicated advanced yield trials in next year’s cropping season.