Clubroot, a persistent threat to Swedish oilseed rape production

Brassica oilseed crops have been grown by Swedish farmers since the early 1940s. Years of high market prices for vegetable oils resulted in intensive cultivation of Brassica oilseeds in various regions, which led to problems with soilborne pathogens including Plasmodiophora brassicae. This pathogen most likely was present in Swedish soils prior to the Brassica oilseed boom after World War II. Currently, reports of clubroot disease outbreaks in Sweden are frequent, with a trend of increasing incidence. Since 2012, DNA-based soil analyses for the presence of P. brassicae have been offered to farmers in order to improve their crop rotation planning. Other means of limiting the damage caused by P. brassicae also are presently under study, such as the effects of boron or different sources of nitrogen. The distribution and identification of different pathotypes/races of P. brassicae in Sweden could so far not be verified. To aid in race diagnostics, resistance breeding efforts, and in understanding the biology of this Plasmodiophorid, the sequencing of the P. brassicae genome has been initiated in Sweden.