Physiological Regulation of Pydiflumetofen on Rapeseed (Brassica napus) and Its Combined Effect with Prochloraz

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.