The rice–rice–rapeseed rotation is one of the predominant
cropping systems in the Yangtze River Basin. However, competition among late-season
rice, ratoon rice, and rapeseed often delays the sowing of rapeseed. This
postponement reduces the effective accumulated temperature before winter,
resulting in fewer leaves, limited dry matter accumulation, and weakened
lodging resistance, ultimately leading to low and unstable seed yields. The
foliar application of exogenous substances is a rapid, efficient, and
labor-saving agronomic strategy that can enhance lodging resistance and improve
yield in rapeseed. In this study, the cultivar Huayouza 137 was used as the
experimental material. Five types of exogenous substances were applied at the
seedling stage (four-leaf stage) in varying concentrations: triacontanol (0.5,
1.0, 1.5 mg L?1; A1, A2, A3), gibberellin (10, 20, 40 mg L?1;
B1, B2, B3), compound sodium nitrophenolate (10, 20, 30 mg L?1; C1,
C2, C3), 6-benzyladenine (10, 20, 30 mg L?1; D1, D2, D3), and uniconazole
(12.5, 25, 50 mg L?1; E1, E2, E3). Water treatment was used as the
control (CK). Yield and its components, lodging-related traits, reactive oxygen
species (ROS) accumulation, and antioxidant enzyme activities during the overwintering
period were evaluated. The results indicated the following: (1) Based on two
years of data on yield, agronomic traits, and cold resistance indicators, the exogenous
treatments that significantly enhanced cold tolerance, lodging resistance, and
yield in delayed-sowing rapeseed were 30 mg L?1 compound sodium
nitrophenolate, 30 mg L?1 6-benzyladenine, 40 mg L?1 gibberellin, and 1.0 mg L?1 triacontanol. Among these, 30 mg L?1 compound sodium nitrophenolate consistently produced the highest yield in both
years, increasing by 14.4% and 12.9% compared to the control. Treatments with
30 mg L?1 compound sodium nitrophenolate, 30 mg L?1 6-benzyladenine, and 40 mg L?1 gibberellin significantly increased
leaf area per plant at the seedling, budding, and flowering stages, and improved
dry matter accumulation at each stage. (2) Application of 1.0 mg L?1 triacontanol and 30 mg L?1 6-benzyladenine significantly enhanced
stem strength, reduced lodging angle, and improved lodging resistance in
delayed-sowing rapeseed. (3) Treatments with 1.0 mg L?1 triacontanol, 40 mg L?1 gibberellin, and 30 mg L?1 compound sodium nitrophenolate significantly increased soluble sugar content in
overwintering leaves, enhanced antioxidant enzyme activity, and reduced ROS
levels and malondialdehyde content, thereby improving cold tolerance during winter.
This study provides a technical basis for enhancing stress resistance and ensuring
stable yields of delayed-sowing rapeseed in the Yangtze River Basin.