Abstract
BackgroundPlasmodiophora brassicae is a soilborne pathogen of the family Brassicaceae and the causal agent of clubroot disease. In Canada, P. brassicae is now one of the most important constraints to canola (Brassica napus) production, and is managed mainly by the deployment of resistant cultivars. In recent years, however, new strains of the pathogen have emerged that are capable of overcoming host resistance, posing new challenges for disease management. Despite its economic significance, molecular studies of P. brassicae are rare, mainly because this microorganism cannot be cultured outside of its host.ResultsRestriction site-associated DNA sequencing (RADseq) was used to examine the genetic diversity within P. brassicae single-spore and field isolates collected from across Canada. The isolates included individuals that were either capable or incapable of causing disease on clubroot resistant canola cultivars. Over 8750 variants were identified through RADseq. Population analysis indicated that most isolates belonged to one of two distinct populations, corresponding with the ability of isolates to cause disease on resistant cultivars. Within each population, there were low levels of genetic diversity. One thousand and fifty of the genetic variants that distinguished the two populations were nonsynonymous, altering the coding sequences of genes.ConclusionThe application of RADseq revealed two distinct populations of P. brassicae in Canada, suggesting multiple introductions of the pathogen into the country. The genetic variation found here will be important for future research and monitoring of the pathogen.
Highlights
Plasmodiophora brassicae is a soilborne pathogen of the family Brassicaceae and the causal agent of clubroot disease
This study examined the relationship between recently detected P. brassicae isolates virulent on CR canola and other P. brassicae isolates from Alberta and the rest of Canada
When dealing with clonal species it has been found that Restriction site-associated DNA sequencing (RADseq), very capable of distinguishing clonal populations, can introduce noise that makes it difficult to infer fine-scale population structure [29].The rBarD values for the pathogen population virulent on CR canola were nonsignificant, indicating that recombination may occur
Summary
Plasmodiophora brassicae is a soilborne pathogen of the family Brassicaceae and the causal agent of clubroot disease. Clubroot is an important disease of Brassica crops worldwide. The causal organism, Plasmodiophora brassicae Woronin, is a member of the eukaryotic super group Rhizaria [2]. It is a soilborne, obligate parasite with a complex lifecycle, the majority of which is spent intracellularly within host roots or as dormant resting spores in the soil [3]. Reports of clubroot in Canada date back at least 100 years [4], its importance was considered relatively minor until the disease was found on canola (Brassica napus L., B. rapa L.) on the Canadian prairies in 2003 [5]. Canola is one of the major crops grown in this region, with the canola industry valued at approximately $15.5 billion
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