Adaptation to Brassica Host Genotypes by a Single-Spore Isolate and Population of Plasmodiophora brassicae (Clubroot)

Plasmodiophora brassicae, the cause of clubroot of crucifers, is an increasingly important pathogen of canola (Brassica napus) in Alberta, Canada. In response, clubroot-resistant canola genotypes are being deployed to help reduce yield losses. Two experiments were conducted to examine the effect on P. brassicae virulence of repeated exposure of a population and single-spore isolate of the pathogen to the same host. The first experiment examined changes in the index of disease over five cycles of infection on seven Brassica hosts (European Clubroot Differential [ECD] 02, ECD 04, ECD 05, ECD 15, ‘45H26’, ‘45H29’, and 08N823R). The second experiment tested the virulence of five cycled populations (‘45H29’, 08N823R, ECD 05, and ECD 15) and three cycled single-spore isolates (‘45H29’, 08N823R, and ECD05) on four resistant canola genotypes (‘73-77’, ‘73-67’, VT-SD-09, and ‘9558C’). The results from these experiments clearly demonstrate the ability of both single-spore isolates and populations of P. brassicae to rapidly erode the resistance present in the two canola genotypes, ‘45H29’ and 08N823R. Although the index of disease increased on these two genotypes, the four resistant canola genotypes remained resistant to all the cycled populations and single-spore isolates in the second experiment. These results underscore the importance of crop rotation in the management of clubroot in Alberta.

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Genetic structure of Plasmodiophora brassicae populations virulent on clubroot resistant canola (Brassica napus)

Plant Disease ◽

10.1094/pdis-09-20-1980-re ◽

2021 ◽

Author(s):

Homa Askarian ◽

Alireza Akhavan ◽

Leonardo Galindo González ◽

Sheau-Fang Hwang ◽

Stephen Ernest Strelkov

Keyword(s):

Brassica Napus ◽

Genetic Structure ◽

Plasmodiophora Brassicae ◽

Single Spore ◽

Specific Primers ◽

Brassica Napus L ◽

Before And After ◽

Differential Hosts ◽

And Migration ◽

Simple Sequence

Clubroot, caused by Plasmodiophora brassicae Woronin, is a significant threat to the canola (Brassica napus L.) industry in Canada. Clubroot resistance has been overcome in more than 200 fields since 2013, representing one of the biggest challenges to sustainable canola production. The genetic structure of 36 single-spore isolates derived from 12 field isolates of P. brassicae collected before and after the introduction of clubroot resistant (CR) canola cultivars (2005-2014) was evaluated by simple sequence repeat (SSR) marker analysis. Polymorphisms were detected in 32 loci with the identification of 93 distinct alleles. A low level of genetic diversity was found among the single-spore isolates. Haploid linkage disequilibrium and number of migrants suggested that recombination and migration were rare or almost absent in the tested P. brassicae population. A relatively clear relationship was found between the genetic structure and virulence phenotypes of the pathogen as defined on the differential hosts of Somé et al., Williams and the Canadian Clubroot Differential (CCD) set. Although genetic variability within each pathotype group, as classified on each differential system, was low, significant genetic differentiation was observed among the pathotypes. The highest correlation between genetic structure and virulence was found among matrices produced with genetic data and the hosts of the CCD set, with a threshold index of disease of 50% to distinguish susceptible from resistant reactions. Genetically homogeneous single-spore isolates provided a more complete and clearer picture of the population genetic structure of P. brassicae, and the results suggest some promise for the development of pathotype-specific primers.

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Virulence Spectrum of Single-Spore and Field Isolates of Plasmodiophora brassicae Able to Overcome Resistance in Canola (Brassica napus)

Plant Disease ◽

10.1094/pdis-03-20-0471-re ◽

2021 ◽

Vol 105 (1) ◽

pp. 43-52 ◽

Cited By ~ 2

Author(s):

Homa Askarian ◽

Alireza Akhavan ◽

Victor P. Manolii ◽

Tiesen Cao ◽

Sheau-Fang Hwang ◽

...

Keyword(s):

Brassica Napus ◽

Confidence Interval ◽

Plasmodiophora Brassicae ◽

Large Collection ◽

Single Spore ◽

Brassica Napus L ◽

Clubroot Resistance ◽

Field Isolates ◽

Virulence Spectrum ◽

Important Disease

Clubroot, caused by Plasmodiophora brassicae Woronin, is an important disease of canola (Brassica napus L.) that is managed mainly by planting clubroot-resistant (CR) cultivars. Field isolates of P. brassicae can be heterogeneous mixtures of various pathotypes, making assessments of the genetics of host–pathogen interactions challenging. Thirty-four single-spore isolates were obtained from nine field isolates of the pathogen collected from CR canola cultivars. The virulence patterns of the single-spore and field isolates were assessed on the 13 host genotypes of the Canadian Clubroot Differential (CCD) set, which includes the differentials of Williams and Somé et al. Indices of disease (IDs) severity of 25, 33, and 50% (±95% confidence interval) were compared as potential thresholds to distinguish between resistant and susceptible reactions, with an ID of 50% giving the most consistent responses for pathotype classification purposes. With this threshold, 13 pathotypes could be distinguished based on the CCD system, 7 on the differentials of Williams, and 3 on the hosts of Somé et al. The highest correlations were observed among virulence matrices generated using the three threshold IDs on the CCD set. Genetically homogeneous single-spore isolates gave a clearer profile of the P. brassicae pathotype structure. Novel pathotypes, not reported in Canada previously, were identified among the isolates. This large collection of single-spore isolates can serve as a reference in screening and breeding for clubroot resistance.

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Characterization of a Single-Spore Isolate Population of Plasmodiophora brassicae Resulting from a Single Club

Journal of Phytopathology ◽

10.1111/j.1439-0434.2004.00868.x ◽

2004 ◽

Vol 152 (7) ◽

pp. 438-444 ◽

Cited By ~ 23

Author(s):

M. Fahling ◽

H. Graf ◽

J. Siemens

Keyword(s):

Plasmodiophora Brassicae ◽

Single Spore ◽

Single Spore Isolate

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Variation for virulence on Brassica napus L. amongst Plasmodiophora brassicae collections from France and derived single‐spore isolates

Plant Pathology ◽

10.1046/j.1365-3059.1996.d01-155.x ◽

1996 ◽

Vol 45 (3) ◽

pp. 432-439 ◽

Cited By ~ 87

Author(s):

A. SOME ◽

M. J. MANZANARES ◽

F. LAURENS ◽

F. BARON ◽

G. THOMAS ◽

...

Keyword(s):

Brassica Napus ◽

Plasmodiophora Brassicae ◽

Single Spore ◽

Brassica Napus L

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Plasmodiophora brassicae (club root).

10.1079/cpc.41865.20210102194 ◽

2021 ◽

Author(s):

Graham McGrann

Keyword(s):

Crop Rotation ◽

Plasmodiophora Brassicae ◽

Brassica Species ◽

Infested Soil ◽

Yield Losses ◽

Varietal Resistance ◽

Weed Species ◽

Clubroot Disease ◽

Local Spread ◽

Resting Spores

Abstract Plasmodiophora brassicae is a root-infecting protist pathogen that causes clubroot disease in brassica species. The organism is soil-borne and has long-lived resting spores that can survive in soil for more than 15 years. Local spread of motile zoospores can be facilitated by wet conditions but most dispersal of the pathogen is through the movement of infested soil. P. brassicae has a wide host range in the brassica family including numerous weed species. Control of the disease is difficult but clubroot can be managed by a combination of crop rotation, varietal resistance, improved agronomic practice such as improved drainage and the application of lime of related products to raise pH which can limit the effects of the disease. There are currently no effective fungicides for the widespread control of clubroot. Yield losses range from 10 to 15% but can exceed 50% under disease conducive environmental conditions.

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Reaction of Lines of the Rapid Cycling Brassica Collection and Arabidopsis thaliana to Four Pathotypes of Plasmodiophora brassicae

Plant Disease ◽

10.1094/pdis-08-12-0752-re ◽

2013 ◽

Vol 97 (6) ◽

pp. 720-727 ◽

Cited By ~ 6

Author(s):

Kalpana Sharma ◽

Bruce D. Gossen ◽

David Greenshields ◽

Gopalan Selvaraj ◽

Stephen E. Strelkov ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Plasmodiophora Brassicae ◽

Field Isolate ◽

Strongly Correlated ◽

Rapid Cycling ◽

Single Spore ◽

Single Spore Isolate ◽

Wide Range ◽

Intermediate Response ◽

Highly Correlated

The clubroot reaction of five Rapid Cycling Brassica Collection (RCBC) lines (Brassica carinata, B. juncea, B. napus, B. oleracea, and B. rapa) and 84 lines of Arabidopsis thaliana to pathotypes 2, 3, 5, and 6 of Plasmodiophora brassicae (as classified on William's system) was assessed. Also, the reaction of the Arabidopsis lines to a single-spore isolate of each of pathotypes 3 and 6 was compared with that of a field isolate. Seedlings were inoculated with resting spores of P. brassicae, maintained at 25 and 20°C (day and night, respectively), and assessed for clubroot incidence and severity at 6 weeks after inoculation. Several lines of A. thaliana and RCBC exhibited a differential response to pathotype but none of the lines were immune. Among the RCBC lines, B. napus was resistant to all of the pathotypes; B. oleracea was resistant to pathotypes 2, 3, and 5; B. carinata and B. rapa were resistant to pathotypes 2 and 5; and B. juncea was susceptible to pathotypes 5 and 6 and had an intermediate response to pathotypes 2 and 3. Line Ct-1 of A. thaliana was highly resistant to pathotype 2, Pu2-23 was highly resistant to pathotype 5, and Ws-2 and Sorbo were highly resistant to pathotype 6. These results indicate that the lines of RCBC and A. thaliana have potential for use as model crops for a wide range of studies on clubroot, and could be used to differentiate these four pathotypes of P. brassicae. The reaction of the RCBC lines to pathotype 6 was highly correlated with response under field conditions but the reaction to the single-spore isolates of pathotypes 3 and 6 was not strongly correlated with reaction to the field collections in the Arabidopsis lines.

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The Rlm13 Gene, a New Player of Brassica napus–Leptosphaeria maculans Interaction Maps on Chromosome C03 in Canola

Frontiers in Plant Science ◽

10.3389/fpls.2021.654604 ◽

2021 ◽

Vol 12 ◽

Author(s):

Harsh Raman ◽

Rosy Raman ◽

Yu Qiu ◽

Yuanyuan Zhang ◽

Jacqueline Batley ◽

...

Keyword(s):

Brassica Napus ◽

Genetic Linkage ◽

Leptosphaeria Maculans ◽

Genotyping By Sequencing ◽

Gene Interaction ◽

Nucleotide Polymorphisms ◽

Single Spore ◽

Brassica Napus L ◽

Single Spore Isolate ◽

Trait Locus

Canola exhibits an extensive genetic variation for resistance to blackleg disease, caused by the fungal pathogen Leptosphaeria maculans. Despite the identification of several Avr effectors and R (race-specific) genes, specific interactions between Avr-R genes are not yet fully understood in the Brassica napus–L. maculans pathosystem. In this study, we investigated the genetic basis of resistance in an F2:3 population derived from Australian canola varieties CB-Telfer (Rlm4)/ATR-Cobbler (Rlm4) using a single-spore isolate of L. maculans, PHW1223. A genetic linkage map of the CB-Telfer/ATR-Cobbler population was constructed using 7,932 genotyping-by-sequencing-based DArTseq markers and subsequently utilized for linkage and haplotype analyses. Genetic linkage between DArTseq markers and resistance to PHW1223 isolate was also validated using the B. napus 60K Illumina Infinium array. Our results revealed that a major locus for resistance, designated as Rlm13, maps on chromosome C03. To date, no R gene for resistance to blackleg has been reported on the C subgenome in B. napus. Twenty-four candidate R genes were predicted to reside within the quantitative trait locus (QTL) region. We further resequenced both the parental lines of the mapping population (CB-Telfer and ATR-Cobbler, > 80 × coverage) and identified several structural sequence variants in the form of single-nucleotide polymorphisms (SNPs), insertions/deletions (InDels), and presence/absence variations (PAVs) near Rlm13. Comparative mapping revealed that Rlm13 is located within the homoeologous A03/C03 region in ancestral karyotype block “R” of Brassicaceae. Our results provide a “target” for further understanding the Avr–Rlm13 gene interaction as well as a valuable tool for increasing resistance to blackleg in canola germplasm.

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Isolation and Variation in Virulence of Single-Spore Isolates of Plasmodiophora brassicae from Canada

Plant Disease ◽

10.1094/pdis-92-3-0456 ◽

2008 ◽

Vol 92 (3) ◽

pp. 456-462 ◽

Cited By ~ 81

Author(s):

S. Xue ◽

T. Cao ◽

R. J. Howard ◽

S. F. Hwang ◽

S. E. Strelkov

Keyword(s):

British Columbia ◽

Brassica Napus ◽

Efficient Method ◽

Plasmodiophora Brassicae ◽

Breeding Strategy ◽

Single Spore ◽

Susceptible Host ◽

Significant Difference ◽

Resting Spores ◽

Important Disease

Clubroot of crucifers, caused by Plasmodiophora brassicae, is emerging as an important disease of canola (Brassica napus) in Alberta, Canada. Populations of the pathogen often consist of a mixture of different pathotypes. Therefore, a simple and efficient method to isolate single resting spores of P. brassicae was developed, based on serial dilution of spore suspensions. The virulence of 24 single-spore isolates, representing five populations of the pathogen from Alberta, Ontario, and British Columbia, was characterized on the differentials of Williams and Somé et al. Symptoms were rated 6 weeks after inoculation and Fisher's least significant difference (P < 0.05) was used to differentiate resistant from susceptible host reactions. The pathotype composition of P. brassicae in Canada appeared more diverse when single-spore isolates were examined rather than populations of the pathogen. In Alberta, at least three and possibly four pathotypes were identified among the 14 isolates tested, whereas a maximum of only two pathotypes had been reported previously when populations of the pathogen were examined. Pathotype 3 or P2, as classified on the differentials of Williams and Somé et al., respectively, was found to be predominant in the province. The occurrence of other pathotypes at lower frequencies suggests that caution should be used in any breeding strategy, because rare pathotypes of P. brassicae may quickly become predominant if susceptible host genotypes are continuously grown.

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