Rapid identification of waterlogging tolerance and selection of high waterlogging tolerance germplasm resources of rapeseed (Brassica napus L.)

The middle and lower reaches of the Yangtze River constitute the main rapeseed-producing region in China, characterized by a wet and rainy climate that frequently leads to waterlogging. This environmental stress severely affects both the yield and quality of rapeseed. Therefore, developing a rapid and reliable method for identifying waterlogging tolerance and screening waterlogging-tolerant germplasm is of great importance. In this study, we established a fast and effective method to assess waterlogging tolerance during the germination stage by subjecting seeds to 24 hours of waterlogging, followed by a graded evaluation based on growth vigor, survival rate, and the development of cotyledons and root systems after recovery. Using this method, 152 rapeseed germplasms were evaluated, resulting in the identification of 10 highly tolerant, 34 moderately tolerant, 53 generally tolerant, and 55 sensitive germplasms. To validate the reliability of this approach, 32 germplasms previously classified by the rapid method were assessed using the root waterlogging tolerance index during indoor germination, following the “Code of Practice for Identification of Waterlogging Tolerance in Rapeseed”. The results showed that highly tolerant germplasms identified by the rapid method exhibited significantly higher root waterlogging tolerance indices compared to generally tolerant and sensitive ones. Furthermore, 54 germplasms identified by the rapid method were subjected to field validation. A comprehensive field waterlogging tolerance index (D value) was calculated using principal component analysis (PCA) and membership function analysis based on four indices: plant height waterlogging tolerance index, number of primary effective branches waterlogging tolerance index, number of siliques per plant waterlogging tolerance index, and number of seeds per silique waterlogging tolerance index. The results revealed significant variation in field waterlogging tolerance among germplasms, with the D values of highly tolerant lines significantly exceeding those of the generally tolerant and sensitive ones. These findings indicate that the rapid identification method is highly reliable and enables large-scale, efficient screening of waterlogging-tolerant germplasm. Finally, by integrating results from both the rapid identification method and field evaluations, three highly tolerant, ten moderately tolerant, and eight sensitive germplasms were confirmed. These results provide a valuable genetic resource and practical reference for future breeding efforts aimed at improving waterlogging tolerance in rapeseed.