Introduction: Oilseed rape, as one of the most important oilseed crops however, drought stress and water scarcity remain major challenges, posing significant risks to the expansion of oilseed rape cultivation and its successful production in the country. Drought-tolerant and high-yielding oilseed rape varieties are well-suited for water-limited enviroments. Given the limited availability of domestic rapeseed cultivars suitable for dryland conditions, identifying and selecting superior genotypes with tolerance to environmental stresses is essential for cultivation in the warm and temperate dryland regions of the country. Accordingly, this study aimed to identify the most promising spring rapeseed genotypes under dryland conditions using the Selection Index for Ideal Genotype (SIIG).
Methodology: In this study, 12 advanced spring oilseed rape lines, along with four cultivars—Dalgan, RGS003, Baharan, and Pishro—were evaluated under dryland conditions over two growing seasons (2023–2025). The experiment was conducted using a randomized complete block design (RCBD) with three replications at the National Agricultural Research Station and Dryland Seed Production of Gonbad-e Kavous. Seeds of each genotype were sown in an experimental plot of 4.8 square meters, each consisting of four 4-meter-long rows with a row spacing of 30 cm. Agronomic traits assessed included the days to flowering (DF), days to flowering ending (DFE), flowering period duration (FPD), days to physiological maturity (DPM), number of sub-branches (NSB), number of pods per plant (NPP), number of seeds per pod (NSPP), plant height (PH), branching height (BH), thousand-kernel weight (TKW), and seed yield (SY). Statistical analyses, included combined analysis of variance for traits, selection of the best genotypes using the SIIG method, and factor analysis of traits.
Research findings: Based on SIIG index values, genotypes G6, G3, G2, G11, G10, G13, G1, and G9, showing high SIIG values (0.752, 0.727, 0.721, 0.581, 0.576, 0.518, 0.508, and 0.508, respectively), were classified as superior genotypes. Conversely, genotypes G5, G4, G7, G15, G8, G12, G16, and G14, with lower SIIG values (0.319, 0.326, 0.334, 0.341, 0.358, 0.444, 0.489, and 0.492, respectively), were categorized as weaker genotypes based on the majority of evaluated traits. According to the two-dimensional scatter plot of genotypes based on SIIG index and grain yield, genotypes G2, G6, and G3—having grain yields above the overall mean and high SIIG values—were selected as ideal genotypes in terms of grain yield and other measured agronomic traits. In contrast, genotypes G15, G4, G5, and G7, with very low SIIG values and poor seed yields, were categorized among the weakest genotypes. Factor analysis extracted three factors that collectively accounted for 72% of the total variance in the dataset, with the first, second, and third factors explaining 38.98%, 20.94%, and 12.15% of the variance, respectively. The results indicated a positive correlation between plant height and the number of pods per plant with seed yield. These traits can serve as reliable selection criteria in breeding programs aimed at identifying rapeseed genotypes with economically viable yields under dryland conditions. |