Waterlogging and Sclerotinia stem rot are major constraints on rapeseed yield and quality in the rice-rapeseed rotation system of the Yangtze River Basin. This study aims to elucidate the physiological mechanisms by which pydiflumetofen, a novel succinate dehydrogenase inhibitor (SDHI), synergistically controls Sclerotinia stem rot and promotes growth, stress tolerance, yield, and quality in rapeseed (Brassica napus).

Field and laboratory experiments were conducted from 2023 to 2025 in Jingzhou, Hubei Province, using the B. napus cultivar ‘Changshuang 1’. This study investigated the effects of pydiflumetofen, prochloraz, tebuconazole, boscalid, and their mixture (pydiflumetofen + prochloraz) on seedling growth and physiological indices under normal growth, waterlogging and polyethylene glycol (PEG)-simulated drought conditions; endogenous hormone contents and balance at the full flowering stage; and Sclerotinia stem rot resistance, yield components and grain quality at the maturity stage.

(1) Under normal growth conditions, pydiflumetofen significantly promoted seedling growth, with root length, lateral root number, seedling height, and fresh weight increasing by 65.8%, 84.2%, 39.0%, and 20.0%, respectively, compared with the control. Chlorophyll a, chlorophyll b, and carotenoid contents increased by 19.3%, 28.1%, and 28.9%, respectively. The promoting effects were significantly greater than those of other fungicide treatments. (2) Under stress, pydiflumetofen pre-treatment significantly enhanced seedling tolerance. Under waterlogging, relative root length significantly increased by 48.3% compared with the control, and the activities of superoxide dismutase (SOD) and peroxidase (POD) were increased by 26.2% and 26.3%, respectively. Under PEG-simulated drought, relative seedling height, relative fresh weight, and vigor index significantly increased by 40.3%, 36.0%, and 113.8%, respectively, compared with the control. (3) At the full flowering stage, foliar application of pydiflumetofen significantly optimized endogenous hormone balance, indole-3-acetic acid (IAA) and gibberellic acid (GA₃) contents increased by 27.5% and 45.5%, respectively, while abscisic acid (ABA) content showed no significant difference compared with the control. (4) At the maturity stage, pydiflumetofen treatment achieved synergistic disease control and yield increase. The disease index of Sclerotinia stem rot was decreased by 58.3%-59.9%, while silique number per plant, seeds per silique, yield, and seed oil content were increased by 13.9%-14.1%, 7.0%-7.3%, 34.4%-34.9%, and 5.1%, respectively, outperforming other fungicide treatments. The mixture of pydiflumetofen and prochloraz exhibited antagonism, reducing yield by 16.1%-16.9%, compared with pydiflumetofen alone.

Pydiflumetofen synergistically improves rapeseed growth, stress tolerance, disease resistance and grain quality by optimizing root architecture, activating the antioxidant system and regulating the endogenous hormone balance. Its integrated benefits are superior to those of conventional fungicides such as prochloraz, tebuconazole and boscalid.

Rapeseed (Brassica napus L.) is the first major oil-bearing crop in China. Enhancing rapeseed yield per unit area is the key to increase its effective supply and economic benefits. Under the condition of mechanical direct seeding, further clarifying the impacts of major technical factors, such as variety selection, overwintering regulation, and disease and pest control, on the yield per unit area could provide a theoretical basis for the improvement of rapeseed yield per unit area in China.

Nine high-yield and high-quality rapeseed varieties were selected, and mechanical direct-seeding experiments were conducted at 22 experimental sites (major rapeseed-producing counties) over 2 years from 2021 to 2023. A systematic study was carried out to investigate the impacts of factors such as rapeseed variety, seed treatment, overwintering regulation, and Sclerotinia sclerotiorum control on the yield per unit area under the condition of reduced topdressing application of nitrogen fertilizer.

The application of three combined treatment techniques, namely seed treatment (Maishuping coating for pest prevention, D1), overwintering regulation (D2), and novel Sclerotinia sclerotiorum control (fluxapyroxad, D3), all significantly increased the yield per unit area of rapeseed under reduced nitrogen topdressing (urea 45 kg·hm^-2). Compared with the traditional loss-reduction technology mode (uncoated seeds+no overwintering regulation and prochloraz for Sclerotinia sclerotiorum control+urea topdressing, CK), with a yield of 112.5 kg·hm^-2, the yields under D1, D2 and D3 treatments increased significantly by 6.2%, 6.4%, and 10.9%, respectively, while the corresponding yields reached 2 594.2, 2 600.4 and 2 708.9 kg·hm^-2, respectively. However, only the incidence of Sclerotinia sclerotiorum was extremely significantly reduced by 49.1% under the D3 treatment. Different technical combinations exhibited significant interaction effects on yield per unit area improvement. When seed treatment and overwintering regulation were combined with the novel Sclerotinia sclerotiorum control technology respectively, the yields were significantly 15.7% and 16.1% higher than those under the traditional technology, respectively, reaching 2 820.0 and 2 834.2 kg·hm^-2, respectively, while the incidence of Sclerotinia sclerotiorum decreased by 55.6% and 55.3%, respectively. Additionally, there was a significant interaction effect between rapeseed variety genotypes and technology. The application of new technologies could exceed the national regional trial yields of the corresponding varieties. For instance, the regional trial yields of Yangguang 131, Dadi 199 and Zhongyouza 39 were 2 341.2, 3 085.5, and 2 982.0 kg·hm^-2, respectively. Under optimized combinations of regulatory technology, the yields were 11.7%, 5.0% and 3.5% higher than their respective regional trial yields, respectively. A multiple stepwise regression analysis was conducted between the experimental yield and factors including the regional trial yield, disease resistance of rapeseed varieties, as well as different technological combinations, and the results revealed that the critical factors determining yield levels were the 1000-seed weight in regional trials, regional trial yield of varieties, novel Sclerotinia sclerotiorum control, and reduced winter urea topdressing rate. Canonical correlation analysis further confirmed that the regional trial yield, regional trial 1000-seed weight, and regional trial silique number of varieties determined the yield levels. Meanwhile, fluxapyroxad and Maishuping played a very important role in enhancing yield increase rates. Additionally, the novel Sclerotinia sclerotiorum control technology and overwintering stress resistance regulation were related to reducing the incidence of Sclerotinia sclerotiorum.

In the mechanical production of rapeseed, the regional trial yield of varieties was a key factor affecting the rapeseed yield levels. The use of fluxapyroxad to control Sclerotinia sclerotiorum was an effective factor for reducing the yield loss caused by Sclerotinia sclerotiorum at present. The combination of seed treatment, overwintering regulation and the novel Sclerotinia sclerotiorum control technology could further exert the yield potential of rapeseed varieties. It was suggested that in practical production, high-yield and high-quality varieties should be selected, and loss-reduction technologies, such as supporting seed treatment, overwintering regulation and fluxapyroxad, should be matched to achieve a significant improvement in rapeseed yield per unit area.

As a new Plant growth regulator, 14-hydroxylated brassinosteroids (14-HBR) increase biological activity by 50% than the traditional Brassicin sterols, while the relation effect of 14-HBR on rapeseed growth, yield and seed coating pesticide were not clear.

In this study, 14-HBR regulator and pesticide are used to treat the seeds in mid-duration winter rapeseed variety (Yangguang 2009) and early-duration variety (Yangguang 131), investigated germination, seedling growth, insect resistance, and yield, to reveal the interaction effects of environment, variety genotype and 14-HBR.

0.0075 and 0.015 mg·L^-1 14-HBR treated seed increased significantly germination potential in medium duration rapeseed, but decreased germination potential and germination rate significantly as mixed with pesticide. 14-HBR treated seed had no significant effect on germination rate and germination potential in short duration rapeseed. The 14-HBR showed better biological activity in seedling growth and yield than that of Brassinolide, 0.0075 and 0.015 mg·L^-1Brassinolide increased by an average of 5.19% and 8.15%, 0.0075 and 0.015 mg·L^-1 14-HBR increased by an average of 11.98% and 5.50%, respectively. 14-HBR mixed with seed pesticide of Clothianidin and Thiamethoxam, also increased seedlings weight and yield. The yield of Thiamethoxam and Clothianidin seed treatments increased by 4.7% and 4.6% independently. The yield of mixed with 0.0075 and 0.015 mg·L^-1 14-HBR to Clothianidin increased 6.8% and 3.3%, mixed to Thiamethoxam increased by 3.5% and 8.2%, respectively. 14-HBR did not affect insecticidal activity of Thiamethoxam and Clothianidin to peach bud nymphs and phyllotreta striolata fabricius.

The study revealed seed treatment with 14-HBR regulator has a positive effect on early growth of rapeseed and increased yield of rapeseed significantly, interacted with planting environment, pesticide type and varieties genotype as traditional regulators, it is necessary to optimize seed treatment technology of 14-HBR regulator to obtain higher harvest yield.