ASSESSMENT OF CROP ROTATION, CULTIVAR RESISTANCE AND BACILLUS SUBTILIS BIOFUNGICIDE FOR CONTROL OF CLUBROOT ON CANOLA

This study was conducted to assess additional management strategies potentially complimentary to cultivar resistance for control of clubroot on canola. New Bacillus subtilis formulations were developed to deliver the biofungicide into canola fields. In 2011, a granular formulation was applied in furrow during seeding at 50 kg/ha to clubroot resistant (CR) and susceptible (CS) canola cultivars in three field trials. A seed treatment delivering approximately 1×10⁵ to 5×10⁶ cfu/seed doses of the biocontrol agent was evaluated on the CS cultivar seeded to different crop-rotation conditions where the plots had a 1-year, 3-year, or 11-year break from previous canola. In 2012, CS, CR, and a moderately susceptible (MS) canola cultivar were seeded to the plots with 0 to 4 year break from a previous canola. None of the biocontrol treatments reduced clubroot impact, while the CR cultivar showed consistent efficacy, doubling the yield over that of the CS cultivar. Plots of varying rotations showed a pattern of clubroot pathogen pressure, with those of longer rotations being up to 10-fold lower in inoculum loads. Under high disease pressure, longer crop rotation reduced root gall size slightly, showed milder above-ground disease impact, and generally increased canola seed yield relative to a short rotation, even on the CR cultivar. A 2- to 3-year break, however, will not reduce clubroot enough to allow a CS or MS cultivar to reach its yield potential. In areas of heavy clubroot infestation, a resistant cultivar should be the first line of defense and when possible, accompany it with a 3-year crop rotation (>2-year break).