P-337 - Microbial communities differ between the rhizosphere of clubroot-infected canola and bulk soil

Clubroot is a disease of Brassicaceae crops caused by the soil-borne Chromist  Plasmodiophora brassicae (Wor.). Soil microbes are known to influence plant growth and health, but the role of rhizosphere microbial communities is poorly understood. A field trial was conducted to compare microbial communities in bulk soil to the rhizosphere of clubroot-infected canola in organic soil (~70% OM) in the Holland Marsh, ON, Canada. Combinations and rates of soil amendments, gypsum, potassium bicarbonate, and hydrated lime, were applied prior to seeding clubroot-susceptible canola cv. L233P. Rhizosphere and bulk soil samples were collected 6 weeks post-emergence and sequenced by Metagenom Bio Life Science Inc (Waterloo, ON) using universal ITS (fungi) and 16S (bacteria) primers. Microbial communities of both soil types were unaffected by soil amendments. Rhizosphere soil consistently had lower microbial diversity compared to bulk soil. However, higher proportions of beneficial and pathogenic microbes were present in the rhizosphere. Gammaproteobacteria, Bacteroidia, and Olipidomycetes microbial classes, as well as Alternaria and Pseudomonas spp. were elevated in the rhizosphere. Trichoderma spp. were elevated in bulk soil and no differences were seen in Fusarium spp. among soils. Elevated rhizosphere proportions of specific microbes were consistent with host-driven recruitment for beneficial microbial functions such as disease suppression. However, the presence of pathogenic microbes in the rhizosphere may arise when infected plants fail to defend against opportunistic pathogens.