Simultaneous Selection for Oil Yield and other Agronomic Traits in Rapeseed Genotypes using Genotype × Trait and Genotype by Yield × Trait Biplots

Extended Abstract Background: Oilseeds are one of the most important sources of energy in the world. As one of the most important oilseed plants in the world, rapeseed has nutritional and economic value, with its seeds containing 40% oil and its oilseed meal containing more than 35% protein. This plant has higher adaptability to diverse climatic conditions. Given the need to supply edible oil in Iran, the selection of high-yielding genotypes with desirable characteristics in this plant is very important for sustainability in production. Moreover, examining the relationship between yield and other agronomic traits improves the efficiency of breeding programs by determining appropriate selection criteria, such that some breeders prefer to select varieties indirectly using yield-related traits to achieve high yield. Among the methods that provide more appropriate characteristics of the status of genotypes and traits are graphical methods that allow for visual examination of correlations and relationships between traits and evaluation and identification of desirable genotypes based on the values of yield-trait combinations. Therefore, this study aimed to compare different genotypes of rapeseed in terms of several traits and analyze the correlation between their different traits, as well as to select superior rapeseed genotypes based on the combination of agronomic traits with oil yield using genotype × trait biplot and genotype × yield × trait biplot methods. Methods: In this study, 15 new lines along with two cultivars were evaluated in a randomized complete block design with three replications in the Agriculture Research Station of Gonbad during 2019-2020. The phonological, morphological characteristics, and yield components including days to flowering starting, days to physiological maturity, plant height, the number of lateral branches, the number of pods per plant, the number of seeds per pod, 1000-seed weight (TSW), oil content, and oil yield were measured in the sample plants. In this study, the genotype × trait (GT) and genotype by yield × trait biplot (GYT) methods were used to identify interrelationships between different traits and selection of the best rapeseed genotypes. Results: The results showed that the genotype by yield × trait biplot method was more efficient than the genotype × trait biplot method. Based on the biplot and the genotype by yield × trait biplot index, a positive correlation was observed between all yield-trait combinations, and genotype 17, followed by genotypes 11 and 4, respectively, were identified as the best genotypes in the combination of oil yield with days to flowering, days to physiological maturity, plant height, the number of lateral branches, the number of pods per plant, the number of seeds per pod, TSW, and oil percentage. Genotypes 2 and 15, respectively, were identified as the weakest genotypes by being located at the end of the horizontal axis of the average tester coordinate diagram. Moreover, the results of the genotype by yield × trait biplot showed a high positive correlation between oil yield × the number of lateral branches, oil yield × the number of seeds per pod, oil yield × TSW, oil yield × plant height, oil yield × oil percentage, oil yield/days to flowering, and oil yield/days to physiological maturity, indicating the usefulness of combining the number of lateral branches, the number of seeds per pod, TSW, oil percentage, plant height, and maturing time (the number of days to flowering and maturing) with oil yield to increase the production of genotypes in rapeseed. Conclusion: In general, the results showed that the genotype by yield × trait biplot method was a more suitable tool for investigating relationships between traits and evaluating, comparing, and selecting different rapeseed genotypes in terms of multiple traits than the genotype × trait biplot method. Based on the display of the average tester coordinates of the genotype × yield × trait biplot, genotypes 17, 11, and 4 were identified as the best genotypes with genotype × yield × trait biplot values of 2.22, 1.33, and 1.01, respectively, and genotypes 2 and 15 were identified as the weakest genotypes with genotype × yield × trait biplot values of -1.78 and -1.01, respectively, in terms of oil yield and other agronomic traits. Furthermore, the number of lateral branches, the number of seeds per pod, TSW, plant height, and maturing time (the number of days to flowering and maturing) are the traits that can be used as appropriate indicators in breeding programs to select high-yielding genotypes in rapeseed.