Plasmodiophora brassicae Inoculum Density and Spatial Patterns at the Field Level and Relation to Soil Characteristics

Abstract

Clubroot, caused by Plasmodiophora brassicae, is an important soilborne disease of the Brassicaceae. Knowledge of the spatial dynamics of P. brassicae at the field level and the influence of soil properties on pathogen spatial patterns can improve understanding of clubroot epidemiology and management. To study the spatial patterns of P. brassicae inoculum density and their relationship to different soil properties, four clubroot-infested fields in central Alberta, Canada, were sampled in 2017 and 2019, and P. brassicae inoculum density, soil pH, and boron, calcium, and magnesium concentrations were quantified. Spatial autocorrelation of the inoculum density was estimated for each of the fields in both years with the Moran’s I and semi-variograms. A Bayesian hierarchical spatial approach was used to model the relationship between P. brassicae inoculum density and the soil parameters. Patchiness of the pathogen was detected, with most patches located at the field edges and adjacent to the entrance. Infested patches grew in size from 2017 to 2019, with an average increase in diameter of 221.3 m and with this growth determined by the maximum inoculum density and active dispersal methods such as movement by machinery and wind. Soil pH, boron, calcium, and magnesium concentrations were not found to have an important effect on the inoculum density of P. brassicae.

Canola with Stacked Genes Shows Moderate Resistance and Resilience against a Field Population of Plasmodiophora brassicae (Clubroot) Pathotype X

“…Despite the gradual reduction in soil inoculum by these resistant hybrids, the resting spore concentration remained >10 5 spores/g in all of the soil samples ( Figure 3 ), which is sufficient to cause severe clubroot on susceptible canola [ 43 ]. This initial inoculum level, however, was higher than those found in most of the infested commercial fields on the Canadian Prairies [ 40 , 44 ], indicating the potential for moderate resistance to deter inoculum buildup in those fields. On the flip side, lower soil inoculum levels would likely cause lighter clubroot infection [ 43 ], resulting in a smaller number resting spores going back into the soil.…”

“…Under field conditions, severe clubroot on a single crop can contribute up to10 10 spores/g soil (Hwang et al, 2013). Resistant cultivars, with fewer and smaller clubroot galls, can decrease the inoculum buildup in soil [ 5 , 6 , 40 ]. In the current study, where inoculated plants were given only six weeks for clubroot development, galls were smaller ( Figure S3 ) relative to those on mature field plants, likely returning fewer resting spores into the soil.…”

Advances in Biological Control and Resistance Genes of Brassicaceae Clubroot Disease-The Study Case of China

“…(1) Field management: P. brassicae is spatially aggregated in soil, with high incidence at entrances and field margins [35]. The viability and longevity of P. brassicae are closely related to soil properties, and it has been shown that alkaline addition in soil can reduce the germination rate of dormant spores, decrease root-hair infection, and inhibit the maturation of sporangia and Zoosporangium [36].…”

Control Strategies of Clubroot Disease Caused by Plasmodiophora brassicae

“…In soil, the pathogen survives as extremely robust, thick-walled resting spores. Those spores can be easily transported from field to field via infested soil on machinery, by animals, water, or wind [ 9 ]. In this way, the spread of the disease can occur rapidly within a region.…”