Direct seeding of winter rapeseed in the Yangtze River Basin often coincides with low temperatures during establishment. The aim of this study was to test whether low-temperature (LT) germination performance predicts overwintering survival and yield under delayed sowing. Thirty accessions were evaluated in controlled germination at 20/14 °C (CK) and 12/6 °C (LT) and in two field seasons (2020–2021 and 2021–2022), with six sowing dates from 15 October to 4 December. Mean germination rate was 97.6% in CK and 88.0% in LT. Germination potential (GP) averaged 95.7% in CK and 41.9% in LT. Root and shoot length decreased from 7.63 and 5.02 cm in CK to 1.47 and 0.48 cm in LT. Overwintering survival declined with later sowing. In the colder season (2020–2021), survival for sowings after November fell below 20% for most accessions, whereas S1–S2 averaged above 80%. Yield decreased with delay. In 2021–2022, yield under S1 exceeded S2–S6 by 5.5%, 8.5%, 13.9%, 14.0%, and 23.3%. In 2020–2021, S1 was similar to S2, but 6.3–22.8% higher than S3–S6. Thousand-seed weight followed the same trend. LT GP and LT root length were positively correlated with yield at several sowing dates in the colder season, indicating that LT germination traits are predictive of late-sown performance under harsher winters. Seven accessions (3409, M417, Zheza0903, 86155, 3445, Zheyou50, and 3462) showed superior LT germination and comparatively better field performance. For the lower Yangtze site, a practical latest safe sowing window is late October, based on two seasons; November sowing substantially increases winter mortality and yield risk. Selecting genotypes with strong LT germination and managing for rapid autumn establishment can stabilize 1000-seed weight and yield when sowing is delayed.

Salinity stress progressively restricts rapeseed (Brassica napus L.) growth and productivity. However, the molecular mechanism underlying its tolerance remains poorly understood. This study aims to shed light on differential responses between shoots and roots, and further clarify the regulatory mechanisms of ion homeostasis and oxidative defense under early-and long-term salt stress. Under salt stress, the Na⁺/K⁺ ratio increased by 46.26% and 26.33% in shoots and roots, respectively. Activities of SOD and POD increased in both tissues, while CAT activity declined in shoots. MDA content was significantly higher in roots. Transcriptome PCA clearly separated samples of early-term (3–48 h for shoots, 3–24 h for roots) from long-term (72 h 25 d for shoots, 48 h 25 d for roots) salt stress. SOD2 and UGT72E1 were significantly up-regulated in shoots but down-regulated in roots. CAT2 exhibited strongly up-regulation in roots than shoots, whereas RBOHC was markedly down-regulated in roots relative to shoots. Additionally, CAT1 was mainly up-regulated at the early-term salt stress. Most DEGs involved in phenylpropanoid biosynthesis (CYP73A5, PAL2, CCR1/2, CAD1/5, COMT1 and PER66) were up-regulated in both tissues. Notably, HCT and CSE exhibited a striking tissue-specific antioxidant pattern, down-regulated in shoots but up-regulated in roots. PER34 was specifically induced at early-term, and PER31/63/169 were exclusively activated under long-term salt stress in roots. Moreover, we performed weighted gene co-expression network analysis (WGCNA) to describe tissue- and time-specific transcriptional dynamics that occur in rapeseed under salt stress. Several hub genes, including ABI5, MPK6, CAD5, NADK1 and LFG2, exhibited high correlations with early-term salt stress responses in roots. These genes are mainly enriched in transcription factors and hormone signaling pathways, and function in antioxidant defense and redox homeostasis. This study suggests distinct spatiotemporal salt stress response patterns in rapeseed and identifies key genes for salt-tolerance breeding.

Low-temperature stress inhibits seed germination in rapeseed. Nonetheless, the continuous dynamic changes in seed germination under low-temperature stress, particularly at the transcriptome level, remain poorly understood. In this study, two rapeseed lines with contrasting LTG phenotypes—HY7201 (cold-tolerant) and HY3404 (cold-sensitive)—were subjected to transcriptome analysis. In total, we identified 76,996 DEGs across 18 groups, with a greater number of DEGs detected in HY7201 compared to HY3404. Additionally, genes related to antioxidative metabolism were specifically upregulated in HY7201. Furthermore, WGCNA identified 29 hub candidate genes associated with specific time points. Gene expression changes during LTG were most pronounced between 18 and 96 h. The average fold change relative to the control was 4.74. Among these genes, some exhibited particularly high fold changes, such as LOC106407757 (HERK1) and LOC106437922 (FER), which were upregulated 11.6-fold at 24 h and 35.4-fold at 18 h, respectively. Finally, 17 key candidate genes specifically expressed in the two lines were identified. Among these, BnaRGL2 was of particular interest, as it is predicted to interact with ABI3 to modulate LTG through GA and ABA signaling pathways. The findings provide valuable insights for breeders aiming to utilize rapeseed germplasm resources to advance low-temperature resistance breeding.

To develop innovative, high-value utilization models for green manure rapeseed, this study investigated the effects of planting density (PD) and nitrogen (N) application rate on the yield and quality of rapeseed flowering stalks harvested at different plant heights. A factorial experimental design was employed, incorporating three factors, PD, N application, and harvesting height, each at three levels. Morphological traits, including stem diameter, fresh weight per plant, flowering stalk yield, and fresh biomass yield after stalk harvesting, were evaluated, together with biochemical traits comprising cellulose, soluble protein, soluble sugar, and vitamin C concentrations in the flowering stalks. The results showed that stem diameter, individual plant fresh weight, and flowering stalk yield generally declined with increasing PD and delayed harvesting height, whereas responses to N application varied depending on PD level. Flowering stalk yield ranged from low to high values across treatments, with the highest yields consistently recorded at a PD of 202,000 plants ha⁻¹ (PD2) across all N levels and at 303,000 plants ha⁻¹ (PD3) combined with 17.25 kg N ha⁻¹ (N1). Variations in PD and N application significantly influenced both yield performance and biochemical composition of the flowering stalks. Elevated concentrations of soluble protein, soluble sugar, and vitamin C were observed at a harvesting height of 25 cm under PD3N1 and at 30 cm under PD2N1 and PD2N2, whereas lower cellulose concentrations were detected at 30 cm under PD2N1 and PD2N2. Overall, these findings demonstrate that coordinated optimization of planting density, nitrogen input, and harvesting height can effectively balance yield and quality traits, providing a practical dual-purpose production strategy for rapeseed cultivated as both a vegetable and green manure in the Shanghai region.