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Given the limited availability of domestic rapeseed varieties suitable for cultivation under the country's rainfed conditions, enhancing genetic diversity through hybridization within breeding programs is crucial. This process, followed by the selection of superior lines from segregating populations, plays a vital role in identifying and introducing high-potential genotypes optimized for rainfed agriculture. This study aims to enhance genetic diversity to develop rapeseed cultivars with optimal grain yield, drought tolerance, early maturity, and suitability for cultivation in warm and temperate regions under rainfed conditions. For this study, ten open-pollinated spring rapeseed cultivars were cultivated during the 2022–2023 growing season at the National Agricultural Research Stations and Dryland Seed Production of Gonbad-e Kavous, as well as in the greenhouse of the Dryland Agricultural Research Institute (Serarood branch), to maximize hybrid production. Crosses were performed using a full diallel mating design (10×10). For this study, the seeds of each cultivar were individually sown in three 3-meter rows at low density, with a 60-centimeter spacing between rows, across three planting dates at 20-day intervals. In total, 3,672 pods were collected from the 90 hybrids (excluding the ten parental cultivars) across the two experimental sites. During the 2023–2024 growing season, 90 hybrids and 10 parental cultivars were cultivated at the National Agricultural Research Stations and Dryland Seed Production of Gonbad-e Kavous using a randomized complete block design with two replications. The targeted traits were subsequently evaluated. The variance analysis results for all measured traits, except for the number of sub-branches, revealed statistically significant differences at the 1% and 5% levels. The four highest-yielding crosses in this study were, in order: Taban × Asa (5,872 kg/ha), Aram × Roshana (5,796 kg/ha), Roshana × Pishroo (5,617 kg/ha), and Asa × Aram (5,617 kg/ha). The lowest grain yield, recorded at 2,045 kg/ha, was observed in the Asa × RGS003 cross. Overall, most crosses derived from the maternal cultivars Safar, Taban, Dalgan, Asa, Aram, and Pishroo exhibited early maturity, whereas the majority of crosses originating from Shirali, Baharan, Roshana, and RGS003 demonstrated later maturity. The Shirali × RGS003 and Safar had the highest (205 cm) and lowest (148.5 cm) plant height, respectively. In terms of branching height, the Shirali × Asa had the highest value (73 cm), while the crosses RGS003 × Baharan and Dalgan × Safar had the lowest (13 cm). The self-pollinated populations obtained for the selection and development of lines adapted to rainfed conditions in warm and temperate climates will subsequently be incorporated into a project focused on managing segregating generations.
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