Abstract: Since the 1950s, with the introduction and application of winter rapeseed (Brassica napus) in China, it has led to the rapid transformation, i.e., replacing winter turnip rape by winter oil rape, in the Yangtze River Basin being the main production areas of winter rapeseed in China. In the late 1980s, with the continuous breakthroughs in cold tolerance breeding, the planting area of winter oil rapeseed continued to extend northward. Winter oil rapeseed had raplaced winter turnip rapeseed in the main production areas in China, such as the Huanghuai River Basin, Weihe River Basin, and Weibei Dry Plateau. In recent years, strong cold resistant cabbage type winter oil glycerol 4 and other varieties have been developed, which can replace winter turnip rapeseed in arid and cold regions of northern China, achieving doubled yield of winter rapeseed, "double low" quality, and suitable machine harvesting for lodging resistance. The essence of the successful northward migration of winter rapeseed was the northward migration of winter oil rapeseed in China, namely cold resistant varieties of winter oil rapeseed replaced winter turnip rapeseed in the original production area, which have greatly promoted the development of winter rapeseed industry. Nevertheless, the northward migration of winter turnip rapeseed faces completely different difficulties. Since 1955, the northward migration trial of winter turnip rapeseed has been terminated by the introduction of spring oil rapeseed into the planting regions of spring turnip rapeseed at the same time. In the subsequent trial, there is a deviation in the research direction on techlonogies of the northward migration, i.e., solely paying close attention to the cold resistance, while ignoring drought tolerace of varieties been migrated into the northward migration area with further reduction in precipitation. There was resulting in technology output not meeting the actual needs of the industry. As a result, the northward migration practice has been carried out for decades and has not yet formed a stable winter rapeseed planting area outside of traditional production areas. In recent years, the original planting area has also continued to shrink, and the northward migration of winter turnip rapeseed has had little effect. In practical condition, the main challenge faced by the northward migration of winter turnip rapeseed is water limitation and the combination of drought and cold stress. The low comparative efficiency is the leading factor in the predicament of industrial development. In recent years, the strong cold-tolerant verieties of winter oil rapeseed developed can stably overwinter in northern cold and arid regions, replacing the varieties of winter turnip rapeseed, significantly improving yield, quality, planting efficiency of winter rapeseed, etc., which is the hope for winter rapeseed in strong winter regions to break through industrial difficulties. We have reviewed the history of winter rape northward-extension in China, achievements and existing problems. The reasons for the dilemma of northward extension were analyzes, and suggestions were made. The revolution of replacing winter turnip rape with winter oilseed rape should be promoted to meet the challenges in winter rape industry development in north China.

Key words: winter rapeseed, drought tolerance, strog cold toerance of winter rapeseed, introduction