Analysis of agronomic traits of winter rapeseed (Brassica campestris L.) in different ecological areas of North China

This study researched the growth and development characteristics of winter rapeseed (Brassica campestris L.) in different ecological areas in North China to clarify the suitable areas for northward movement of the planting area of winter rapeseed. An experiment involving 18 winter rapeseed varieties was conducted in 2008–2013 at 17 ecological sites and the results statistically analyzed for variations in agronomic traits. Then parametric method and variation coefficient method were used to analyze the stability of the traits of 18 varieties of winter rapeseed. Finally, agronomic traits of the rapeseeds were analyzed using synthetic subordinate function. The analyses showed that winter rapeseed grew normally with excellent agronomic traits in safe wintering areas in North China (dry and cold regions). Also the 18 winter rapeseed varieties performed better than other oil corps, such as spring rapeseed and flax. The agronomic traits of winter rapeseed were not significantly different among varieties and years, showing high stability. Temperature was the main factor influencing the agronomic traits of rapeseed. Also altitude, latitude and wintering rate significantly influenced the agronomic traits of rapeseed. Because average annual temperature and extreme minimum temperature were low, low temperatures occurred early and lasted for a long time, daytime and nighttime temperature difference was largely in the study area of North China, the agronomic traits of 18 rapeseed varieties in different ecological sites were significantly different. The plant height and branch length were shorter, while the number of branches was less in high latitude areas (latitude greater than 36°) than those in the north boundary of the original north planting region of winter rapeseed (Tianshui City, 36 °N). In high latitude areas, segmented siliques happened due to freeze injure during flowering stage. The length of main florescence was longer and the siliques of main florescence were shorter and mal-distributed. However, the 1000-grain weight and seeds per silique increased due to relatively longer postulation period and low temperature during pustulation period, while the large daytime and nighttime temperature difference also reduced respiration consumption. Urumqi, Tacheng and Baicheng Cities were the potential areas of cultivation of winter rapeseed as the extremely cold temperature in these areas provided enough snow both in winter and spring to protect the winter rapeseed from freeze injure in winter and drought stress in spring. Therefore it was not only possible to grow winter rapeseed in dry and cold regions of North China, but it was possible to have excellent agronomic traits of the crop. There was a huge potential for the development of winter rapeseed in North China, an area with huge advantages in terms of 1000-grain weight and seed per silique of winter rapeseed.