Spatial distribution of cabbage root maggot (Delia radicum) and clubroot (Plasmodiophora brassicae) in winter oilseed rape crops in the Czech Republic

Abstract

Hlavjenka V., Seidenglanz M., Dufek A., Šefrová H. (2017): Spatial distribution of cabbage root maggot (Delia radicum) and clubroot (Plasmodiophora brassicae) in winter oilseed rape crops in the Czech Republic. Plant Protect. Sci., 53: 159-168.The amount and spatial distribution of plants afflicted with cabbage root maggot (Delia radicum; CRM) and clubroot (Plasmodiophora brassicae) in winter oilseed rape crops were assessed in the Olomouc region (Northern Moravia, Czech Republic) over the course of 2012-2014. A total of 16 commercial rape fields were included in the assessments. Plants with tumours showed a significantly lower (P < 0.001) level of infestation induced by CRM (24% of plants infested) compared to plants without tumours (37% of plants infested). According to a generalised linear mixed model, plants with thicker hypocotyls are predisposed to significantly higher levels (P < 0.001) of root surface damage induced by CRM. The correlation analysis indicates rather weak or intermediate levels of correlation between the two variables (hypocotyls thickness × root surface damage induced by CRM). Both CRM and clubroot symptomatic plants showed a significant tendency for aggregation in rape crops, but not in all cases. Distributions of CRM and clubroot symptomatic plants were either significantly spatially dissociated or not associated in crops. Ovipositing D. radicum females showed some tendency to avoid zones with higher number of plants infected by P. brassicae. Distributions of CRM and hypocotyl thickness levels were significantly spatially associated in crops in several cases.

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

“…Maximum P. brassicae inoculum densities varied from 1.7 × 10 3 to 3.2 × 10 7 resting spores/g soil in the fields evaluated. These values are similar to inoculum densities previously observed in commercial fields in Alberta and Europe where canola or rapeseed, respectively, was grown [15,[46][47][48]. It has been reported that inoculum densities between 1 × 10 3 and 1 × 10 5 resting spores/g soil are sufficient to cause clubroot symptoms under field conditions [57], and that concentrations between 3 × 10 3 and 1.3 × 10 5 resting spores/g soil caused yield losses in susceptible hosts [48].…”

“…A few studies have investigated the spatial patterns of P. brassicae at a field level, but (to our knowledge) none has evaluated changes in these patterns over time, nor their relationship with soil chemical properties. A patchy spatial pattern has been described for the pathogen in fields in Canada, Sweden and the Czech Republic, based on anecdotal observations, descriptive statistics [45,48] and Spatial Analysis by Distance Indices (SADIE) [46,47]. Clubroot also occurs more frequently at field entrances [45,46] and margins [47].…”

“…A patchy spatial pattern has been described for the pathogen in fields in Canada, Sweden and the Czech Republic, based on anecdotal observations, descriptive statistics [45,48] and Spatial Analysis by Distance Indices (SADIE) [46,47]. Clubroot also occurs more frequently at field entrances [45,46] and margins [47]. Similarly, in the current analysis, a patchy pattern was found with respect to P. brassicae inoculum density in the evaluated fields, with most patches located at the field edges adjacent to the entrance.…”

“…Soilborne diseases are characterized by aggregated spatial patterns, with dynamic patches that vary in size over time, and which may reflect local soil conditions that favor the disease or inhibit crop growth [39,43,44]. Observations of in-field clubroot spatial patterns have indicated that disease incidence is higher at the field entrances [45,46] or field margins [47,48], suggesting that disease spread occurs mainly through the movement of infested soil on farm machinery [45]. However, while it is widely known that clubroot tends to have a patchy spatial pattern [45,46,48], detailed evaluations of within field spread over time or the effect of soil properties on inoculum density have not been conducted.…”