Genome-wide association analysis (GWAS)
A diversity panel, consisting of 220 B. napus inbred lines was used for the GWAS in this study (Xu et al., 2021). More specifically, the population included winter, semi-winter and spring oilseed rape. The accessions originated from Asia, Europe, and North America. The B. napus population was grown at the Farm Station in Yangling, Shaanxi province, China (107°59′–108°08′E; 34°14′–34°20′N), where the local temperature ranged from −15 to 10 °C in winter (https://lishi.tianqi.com/xianyang/202101.html). Low-temperature resistance was measured in the field in January of 2017 and 2018. The grade of low-temperature resistance was evaluated with criteria including grade 1 (the plants are normal, and the leaves are green), grade 2 (a small part of leaves are necrotic), grade 3 (a half of leaves are necrotic), grade 4 (most of leaves are necrotic), and grade 5 (all leaves are necrotic). The association analysis for low-temperature resistance was carried out using a MLM with the software package TASSEL 5 (https://www.softpedia.com/get/Science-CAD/TASSEL.shtml). The population structure was calculated using PCA. The software PopLDdecay (https://github.com/BGI-shenzhen/PopLDdecay) was used to calculate LD. The parameter r2 =0.2 was read as LD length. The threshold of the GWAS was set to P -value < 10–6 .