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

Terminal drought stress is one of the limiting factors of wheat production in cold regions of Iran. Development of new cultivars with high grain yield stability and good agronomic characteristics under both terminal drought stress and normal irrigation conditions is one of the major goals of wheat breeding program for cold dry areas of Iran. The objectives of this study were :1) to select terminal drought tolerant wheat lines with high grain yield and good adaptability in Preliminary Regional Wheat Yield Trial (PRWYT) 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: APreliminary Regional Wheat Yield Trials (PRWYT) were conducted with forty nine newly improved wheat pure lines including two checks (Alvand\\ and Toos CVs) under late season limited water conditions at Miandoab and Mahad experimental stations, respectively in 2006-07 cropping seasons. B- Evaluation and selection in F2 segregating populations, F4 and F5 families. In the segregation populations nurseries, eleven (F2), seven (F4) families and sixty three F5 lines were evaluated at Karaj station. Necessary data such as plant height, kernel size, days to heading and maturity and resistance to environmental stresses were recorded. Selected bulk method was used to handle the segregating populations and families. Preliminary Regional Wheat Yield Trials 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 early growth vigor, plant height, no of kernels/spike, kernel size, 1000 kernel weight, no of days to heading and maturity, resistance to yellow rust and grain yield were recorded. Considering both the recorded data, and the grain yield of new wheat lines in the PRWYT trials under limited water conditions, 20 superior pure lines were selected from Mashad and Miandoab stations. These selected new improved lines will be assessed for terminal drought tolerance in replicated advanced yield trials in the next year s cropping season. From eleven F2 segregating populations grown at Karaj, 5 populations had good agronomic performance. Selected individual plants from each family were bulked for planting in the further generations in the next growing season. Because of the yellow rust epidemic disease and therefore the susceptibility of F4 families to yellow rust, individual spikes were selected only from two families for planting in the F5 families in the next growing season. Of the sixty three F5 lines, twenty five inbred lines with good agronomic performance were selected for planting in the further generations.