In double-cropping rice areas in the Yangtze River Basin (YRB), ensuring the yield of late-seeded rapeseed is essential to reduce the winter fallow fields. Additionally, promoting the accumulation of dry matter before winter and improving cold resistance during the overwintering period are effective ways to increase the yield of late-seeded rapeseed. Soaking seeds with exogenous substances is an effective measure to improve the cold resistance during the overwintering period and promote the rapid growth before winter. In this experiment, the early maturing rapeseed variety Huayouza 137 was selected, while soaking-seed treatments of water (CK); 0.01 mmol L-1, 0.05 mmol L-1, 0.10 mmol L-1 betaine (T1-1, T1-2, T1-3); 0.1 mmol L-1, 0.5 mmol L-1, 1.0 mmol L-1 proline (T2-1, T2-2, T2-3); 0.03%, 0.15%, 0.30% hydrogen peroxide (T3-1, T3-2, T3-3); 0.001 mmol L-1, 0.01 mmol L-1, 0.05 mmol L-1 malic acid (T4-1, T4-2, T4-3); 25 mg L-1, 100 mg L-1, 300 mg L-1 nano zinc oxide (T5-1, T5-2, T5-3); 0.5 mmol L-1, 1.0 mmol L-1 polyamines (T6-1, T6-2) were conducted between 2021 and 2023 rapeseed growing season. We studied the effects of soaking seeds with different exogenous substances and their levels on the cold resistance in winter and yield of late-seeded rapeseed. The results showed that the different exogenous substances and their levels of soaking seeds affected the germination rate of late-seeded rapeseed, and part of them, such as T3-3, T4-2, and T5-3, significantly increased by 19.2%, 15.3%, and 17.3% versus CK. Soaking seeds with some exogenous substances significantly improved the cold resistance of late-seeded rapeseed in winter. On the one hand, the activities of peroxidase, catalase, and the content of glutathione were improved, and the contents of hydrogen peroxide, active oxygen and MDA reduced; on the other hand, the contents of soluble sugar, proline, malic acid, polyamine, and mannitol were increased; at the same time, the content of membrane cold response protein kinase was increased. The increase of leaf cold resistance was beneficial to the accumulation of leaf biomass and the increase of effective branches and pod number per plant, thus promoting yield. In addition, 9 positive and 3 negative cold resistance indicators were comprehensively evaluated. The results showed that the two-year average yield ranking and the comprehensive evaluation value ranking of cold resistance were basically the same over the two years. While the soaking-seed treatments with the best yield and cold resistance were T5-3, T5-2, T2-3, and T1-2. These results of this study provide theoretical and technical support for the cultivation of late-seeded rapeseed seedlings before winter and the improvement of cold resistance in the YRB, and provide a basis for the stress resistance and stable production of late-seeded rapeseed and the development and utilization of winter fallow fields.
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