Vertical distribution of resting spores of Plasmodiophora brassicae in soil

Abstract

Resting spores of Plasmodiophora brassicae, the causative agent of clubroot in canola (Brassica napus) and other members of the Brassicaceae, can survive in soil for many years. Information on their vertical distribution in the soil profile is required to assess the efficacy of control measures and strategies for management of infested soil, for instance in road and pipeline construction. Vertical soil cores from the soil surface to 53-cm depth were collected from four naturally infested fields, one in Alberta and three in Ontario, and lateral cores, from the side of a trench, were collected at regular intervals down to 1-m depth at two infested fields in Alberta and one in Ontario. Genomic DNA of P. brassicae was assessed using quantitative polymerase chain reaction (qPCR) assays that included a competitive internal positive control to correct for inhibition. Genomic DNA of P. brassicae was detected to 1-m depth at one site, and moderate levels (up to 10⁵ spores g ⁻¹) of resting spores were detected below the plow layer at several sites. The concentration of resting spores was not uniform, vertically or horizontally, throughout the soil at any site. Results indicate that resting spores move downwards in the soil profile over time.