Key Factors of Yield Formation and Comprehensive Evaluation of Breeding Materials in Brassica napus L. Spring Rapeseed

To provide theoretical basis and elite germplasm support for high-yield breeding of spring rapeseed ( Brassica napus L.), this study systematically dissected the key growth characteristics, internal structural relationships of agronomic traitsunderlying yield formation. A total of 23 spring rapeseed varieties (lines) were tested across five ecological sites, with systematic observations of growth period, major agronomic traits and yield performance. Correlation analysis, principal component analysis and variety stability evaluation were employed to characterize trait correlations and genetic diversity. The results showed that the effect of environment on the growth period of spring rapeseed was much greater than that of genotype. Seedling emergence was highly consistent among genotypes within the same site (variation < 5 d), while significant genotypic differentiation occurred at the bolting stage. Qinza5_CK, Qingza9 and Yuyou35 exhibited stable growth periods across sites; PCA extracted four principal components with a cumulative contribution rate of 65.547%, representing yield capacity factor, plant height (PH)-inflorescence factor, pod-grain number factor and branching factor, respectively. Yield differed significantly among sites with prominent environmental effects. Yield per plant (YPP) was significantly and positively correlated with total pods per plant (TPS), seeds per pod (SPS) and thousand-seed weight (TSW), indicating that increasing effective pod number was the primary approach to boost yield. Qin 21BP191 and Qingza9 combined high yield potential and wide adaptability, making them suitable for extension in Gansu and similar ecological regions. Yield formation in spring rapeseed is coordinately regulated by multiple relatively independent traits. High-yield breeding should prioritize germplasm with stable growth period, high TPS and high TSW, and optimize plant type architecture to balance sink-source relationships for yield breakthrough.