Impact of Plasmodiophora brassicae on Canola Root and Rhizosphere Microbiomes and Its Implications for Clubroot Biocontrol.

Clubroot, caused by the obligate parasite Plasmodiophora brassicae, is a soilborne disease affecting canola (Brassica napus) and other crucifers. Although planting resistant cultivars remains the primary strategy for managing clubroot, the emergence of resistance-breaking P. brassicae pathotypes continues to threaten canola production. In this context, soil and root microorganisms may play a role in suppressing the disease. This study investigated the impact of P. brassicae infection on the microbial communities of soil, seeds, roots, and the rhizosphere in susceptible and resistant canola lines, with the aim of analyzing host-pathogen-microbiome interactions and identifying microbial taxa potentially associated with disease resistance. Our findings showed that resistant canola lines inoculated with P. brassicae (pathotype 3A) exhibited reduced disease severity compared to their susceptible counterparts. Diversity analyses of microbial communities revealed that clubroot-resistant canola lines tended to maintain more stable and diverse fungal communities, with a higher Shannon index than susceptible lines. Inoculation with P. brassicae induced more pronounced changes in the root microbiome than in the rhizosphere. Additionally, the seed microbiomes of resistant and susceptible lines displayed distinct bacterial and fungal profiles, suggesting that clubroot susceptibility may influence seed-associated microbial community composition. Differential abundance analysis of root and rhizosphere microbiomes indicated that certain microbial taxa, including bacterial genera such as Acidovorax, Bacillus, Cupriavidus, Cytophaga, Duganella, Flavobacterium, Fluviicola, Luteimonas, Methylotenera, Pedobacter, and Peredibacter, as well as fungal genera such as Aspergillus, Candida, Fusicolla, Paecilomyces, and Rhizophlyctis, may be recruited or enriched in resistant canola lines following P. brassicae inoculation, potentially contributing to reduced clubroot severity.