P-340 - The breakdown of resistance in clubroot-resistant cultivars of canola

Clubroot on canola caused by Plasmodiophora brassicae Wor. has seriously threatened the canola industry wherever canola is grown. In North Dakota, the primary management practice opted by the growers is the use of commercially available clubroot-resistant canola cultivars. However, the frequent deployment of resistant cultivars generally results in the selection of increased virulence in the pathogen population, leading to resistance breakdown. The annual clubroot survey in canola fields conducted in 18 counties of North Dakota revealed a breakdown of first-generation resistance to clubroot in three resistant canola cultivars in Cavalier County. This breakdown was observed in the fields where resistant canola cultivars were planted in frequent rotations. However, the implementation of proactive measures, such as the practice of longer crop rotations (one in four years) in acidic soils, the use of multi-gene clubroot-resistant canola cultivars, and proper equipment sanitation in endemic areas can play a crucial role in the management of clubroot on canola. Likewise, opting for growing multiple canola cultivars in different fields of a grower can spread out the risk and provide some insurance for canola production. The resistance breakdown indicates an urgent need for pathotype evaluation and identification of shifts or mutations among the pathotypes.