Abstract
ABSTRACTClubroot, caused by the obligate parasitePlasmodiophora brassicae, is one of the most devastating diseases affecting the canola/oilseed rape (Brassica napus) industry worldwide. Currently, the planting of clubroot-resistant (CR) cultivars is the most effective strategy used to restrict the spread and the economic losses linked to the disease. However, virulentP. brassicaeisolates have been able to infect many of the currently available CR cultivars, and the options to manage the disease are becoming limited. Another challenge has been achieving consistency in evaluating host reactions toP. brassicaeinfection, with most bioassays conducted in soil and/or potting medium, which requires significant space and can be labour intensive. Visual scoring of clubroot symptom development can also be influenced by user bias. Here, we have developed a hydroponic bioassay using well-characterizedP. brassicaesingle-spore isolates representative of clubroot virulence in Canada, as well as field isolates from three Canadian provinces, in combination with canola inbred homozygous lines carrying resistance genetics representative of CR cultivars available to growers in Canada. To improve the efficiency and consistency of disease assessment, symptom severity scores were compared with clubroot evaluations based on the scanned root area. According to the results, this bioassay offers a reliable, less expensive, and reproducible option to evaluateP. brassicaevirulence, as well as a means to identify which canola resistance profile(s) may be effective against particular isolates. This bioassay will contribute to the breeding of new CR canola cultivars and the identification of virulence genes inP. brassicaethat could trigger resistance and have been very elusive to this day.
Publisher
Cold Spring Harbor Laboratory