Effects of a Novel Waterlogging-Tolerant Growth-Promoting Pelletizing Agent on the Growth of Brassica napus

The Yangtze River Basin serves as the primary rapeseed-producing region in China, accounting for over 80% of the national output, yet it is severely impacted by waterlogging, resulting in yield reductions of 17–42.4%. This study investigated the effects of pelleting treatments on growth and waterlogging resistance in Brassica napus varieties Xiangzayou 787 and Fanmingyoutai. Conventional pelleting agents were augmented with waterlogging resistance agents, surfactants, and amino acids as growth-promoting reagents. The results demonstrated that melatonin at 5.0×10−5 mol/L significantly enhanced rapeseed growth and stress resistance. Specifically, for Xiangzayou 787, root fresh weight increased by 16.9% and stem diameter by 30.6%; for Fanmingyoutai, stem diameter increased by 16.9% and leaf length by 12.3%. The freezing injury index decreased by 90.9% for Xiangzayou 787 and 50% for Fanmingyoutai. The waterlogging injury index was reduced by 43.5% for Xiangzayou 787 and 30.4% for Fanmingyoutai, with stem diameter increasing by 30.6% and 16.5% in the respective varieties. The disease index decreased by 63.2% for Xiangzayou 787 (incidence reduced to 20.5%) and up to 57.1% for Fanmingyoutai (incidence reduced to 23.3%). Under this treatment, soluble protein content in Fanmingyoutai reached 20.37%, representing a 20.37% increase relative to the control. Peroxidase (POD) and superoxide dismutase (SOD) activities exceeded control levels, exhibiting an initial rise followed by a decline; malondialdehyde (MDA) content gradually increased; catalase (CAT) activity and soluble protein content showed an initial increase then decrease. The increase in relative electrical conductivity was reduced by 20.8% for Xiangzayou 787 and 17.3% for Fanmingyoutai. Yield per plant increased by 10.2% for Xiangzayou 787 and 35.6% for Fanmingyoutai. The newly developed pelleting formulation integrates waterlogging resistance agents, surfactants, and amino acids, unlike traditional agents, and proves effective for both hybrid and conventional rapeseed varieties. It enhances waterlogging resistance, promotes growth, improves disease resistance, and elevates seed quality while being cost-effective and simple for production and field application. This approach significantly boosts yield and supports productivity enhancement in southern rice fields, thereby improving rapeseed output and oil supply.