Journal of Crop Breeding

Extended Abstract
Background: Rapeseed, scientifically known as Brassica napus L., plays a very important role in meeting food and biofuel needs. Increasing rapeseed yield is essential to improve the economic performance of this plant and ensure food security. Rapeseed yield has low heritability due to its influence on environmental conditions and various genetic traits. For this reason, improving its yield is possible by using yield components that have genetic diversity and high transferability to offspring. In rapeseed breeding programs, traits related to the silique are of great importance to increase yield, and breeding for silique-related traits and creating high-yielding varieties is one of the important goals of breeders. Therefore, this study aimed to gain knowledge about the gene function, heritability, and combinability of silique-related traits and the effect of these traits on seed and oil yields using line × tester analysis in spring rapeseed.
Methods: In this study, three high-yielding spring rapeseed genotypes (SPN34, RGS003, and SPN1) were crossed as testers with five genotypes recommended for cultivation in the warm climate of Iran (SPN3, SPN9, SPN36, SPN30, and DH4) as lines. The resulting hybrids were studied in a randomized complete block design with two replications at the Seed and Seedling Breeding and Production Research Institute in the 2014-2015 crop year. The studied traits included the number of silique, the number of seeds per silique, silique length, the length of the first silique from the ground, seed yield, and oil yield. The line × tester analysis was used for statistical analysis of the design, and the specific combining ability of the hybrids, the general combining ability of the parents, the mode of gene action, and the Broad-sense and narrow-sense heritability of the traits were estimated in this analysis.
Results: The interaction effects of line × tester were significant for all traits, except for the number of seeds per silique, indicating that the lines reacted differently in combination with different testers, showing the role of dominance and non-additive effects in controlling these traits. The estimated broad-sense heritability of all traits was high (85.72-95.56%), which indicates the higher importance of genetic variance than environmental variance in the studied traits. The value of narrow-sense heritability for seed oil yield was 55.77%. The high narrow-sense heritability of the number of silique in the secondary branches (43.87 %), the number of silique per plant (98.82 %), the number of seeds per silique (34.66 %), and the length of the first silique from the ground (72.69 %) confirmed the greater contribution of the additive variance to the genetic control of these traits than the other evaluated traits. Selection-based breeding methods are suggested to improve these traits, while the non-additive variance played a greater role than the additive variance for the number of silique on the main stem, silique length, seed yield, and seed oil yield traits. The degree of dominance of more than one in the number of silique on the main stem, silique length, seed yield, and seed oil yield traits indicates the action of gene dominance in controlling these traits, which is suggested as a result of hybrid production and exploitation of the effects of gene dominance in these traits. Among the genotypes studied, testers SPN1 and SPN34 and lines DH4 and SPN3 were good combiners in terms of silique-related traits. As a result, they can be used as one of the suitable parents in breeding programs based on hybrid seed production. Among the combinations of rapeseed cultivars, the RGS003 × DH4 hybrids were superior for the number of silique trait in secondary and main branches and the whole plant, DH4 × SPN1 for the number of seeds per silique, seed yield, and seed oil yield traits, RGS003 × SPN30 for the silique length trait, SPN1 × SPN9 for the length of the first silique from the ground, and SPN36 × RGS003 for the seed yield and seed oil yield traits. They can be used in hybrid cultivar production programs.
Conclusion: The results showed sufficient genetic diversity among the lines and testers in terms of silique-related traits, so that the diversity resulting from their crossing could be exploited for the introduction of new cultivars. Lines and testers with high general combining ability and parents of hybrids with high specific combinability are recommended to form a suitable population for producing offspring with superior silique-related traits and higher yields in future programs. Combining lines and testers with high general and specific combining ability can lead to the development of hybrids that not only have good grain yield but also show high heterosis and increase the yield of rapeseed seed and oil.