Rapeseed (Brassica napus L.) is an important oil crop, providing a wealth of edible oil with high nutritional values for human.However, rapeseed often suffers from a variety of diseases, including sclerotinia, viral diseases, downy mildew, white rust and bacterial black spot, soft rot, black spot and so on.In every year plant diseases may cause a global crop production loss by 12%. Downy mildew is an important disease in Brassica napus L. which may occur in the whole growth period. In some areas, downy mild...