Evaluating multiple resistance to major diseases in a core set of inbred lines of Brassica rapa at seedling stage

Years of continuous cropping of Brassica rapa crops in main producing areas in China lead to the outbreak of some diseases, such as downy mildew (DM), turnip mosaic virus (TuMV), black rot (BR), verticillium wilt (VW), and club root (CR), causing severe loss in yield and quality. Resistance to the aforementioned diseases of 302 inbred lines of Brassica rapa to DM, TuMV, BR, VW, and CR were evaluated under controlled conditions at seedling stage. Forty lines were identified to be highly resistant to DM, 13 to TuMV, 0 to BR, 30 to VW, and 24 to CR. Among the 302 lines, 121 exhibited high resistance to two diseases, 70 to three diseases, and eight to four diseases, but none of these lines showed comprehensive resistance to all the five diseases. Chinese cabbage lines XDYFX, 536S, 536Q, DY×T, and CR-C, and Pak choi lines DFAK×SH, NB, and SYHTC showed high resistance to four diseases and therefore represent elite materials in multiple-disease resistance breeding. In addition, different disease resistance tendencies were discovered in diverse Chinese cabbage groups which were classified in different ways, such as the ecotype, heading-type, and geographical origin.