Population and phenotyping
A diversity panel of 505 B. napus accessions was grown in three different sites: Wuhan (WH; 114° 21′E, 30° 28′N) for 4 years (2015–2016, 2016–2017, 2017–2018 and 2018–2019), Hefei (HF; 117° 13′E, 31° 52′N) for 2 years (2016–2017 and 2017–2018) and Chengdu (CD; 104° 12′E, 30° 46′N) for 2 years (2016–2017 and 2019–2020). Additionally, a subset of 50 accessions, consisting of 25 high-plasticity lines and 25 low-plasticity lines, was grown in Wuhan and Ezhou (EZ; 114° 42′E, 30° 21′N) on three different planting dates in 2022. In Wuhan, the planting dates were September 27th, October 7th, and October 17th (WH1, WH2 and WH3); in Ezhou, the dates were October 8th, October 18th, and October 28th (EZ1, EZ2 and EZ3). The phenotypic data for WH2016, WH2017, WH2018, HF2017, HF2018 and CD2017 were obtained from a previous study (Tang et al., 2021). Mature open-pollinated seeds of the natural population were harvested and dried for SOC analysis with a Foss NIRSystems 5000 near-infrared reflectance spectroscope (Li et al., 2003). Six biological replicates per accession were used for analysis. Detailed phenotype and genotype data can be found in supplemental files (Supplementary Tables S3, S4) or in the previous study (Tang et al., 2021).