Canola Cultivars Research Articles

SNP and Haplotype Variability in the BnP5CR2 Gene and Association with Resistance and Susceptible Cultivars for Sclerotinia sclerotiorum in Brassica napus

Sclerotinia sclerotiorum is a serious disease of oil crop. The P5CR gene is the first gene reported to be associated with resistance to Sclerotinia infection in soybeans, and its closest homologs are located on chromosomes A10 and C09 of Brassica napus. We named these BnP5CR1 and BnP5CR2, respectively. The purpose of this study was to examine the single-nucleotide polymorphism (SNP) and haplotype diversity (Hd) of BnP5CR2 among canola cultivars with different levels of resistance to S. sclerotiorum as well as the expression patterns of BnP5CR2 via an association analysis using resistant and susceptible cultivars of B. napus. The results can thus provide information for future research on the mechanisms of disease resistance to S. sclerotiorum and the breeding of resistant canola cultivars. A total of 95 and 12 polymorphic sites were detected in 1870 and 678 SNP sites in 16 BnP5CR2 and their coding DNA sequence (CDS) population, respectively. A total of six different haplotypes (H1–H6) were inferred from the 16 BnP5CR2 gene-CDS that contributed to the high level of polymorphism. Hd was equal to 0.617, and H1 shared by 10 cultivars was the dominant haplotype, suggesting that H1 is an ancient haplotype among the BnP5CR2 genes. H6 and H5 haplotpypes were present in Nan12R and ZhongYou821, respectively. The expression level in vitro of the BnP5CR2 between Nan12R and ZhongYou821 was significantly different. The upregulated expression of BnP5CR2 in resistant cultivars was higher than that of susceptible cultivars under 6 h, 12 h, 24 h, and 36 h treatments of pathogen stress, among which the expression level was significantly increased at 6 h, 12 h and 36 h in resistant cultivars, and the difference reached a highly significant level at 6 h (p < 0.01). The two cultivars with clear differences in expression features possessed different BnP5CR2 gene-CDS-haplotypes, indicating that gene-CDS-haplotype diversity may have greater power than SNPs for the detection of causal genes for quantitative traits.

Weed Pressure, Nutrient Content, and Seed Yield in Field Grown Sulfonylurea-Resistant Camelina sativa and Brassica napus

Camelina [(Camelina sativa (L.) Crantz], an oilseed species of Brassicaceae, does not have approved herbicides for weed control, which limits its expansion as a commercial crop. To evaluate agronomic traits and ecosystem services of non-transgenic cultivars of sulfonylurea-resistant camelina and canola (Brassica napus L.), a field study was conducted near Fargo, North Dakota. Two replicated locations (NDSU and NW22) were set up in a randomized complete block design including four blocks of camelina, canola, and fallow per location. Camelina and canola were seeded (18 May) at 4.9 and 2.9 kg ha−1, respectively, using 19-cm row spacing. Data was collected mid- and late-season (29 June and 22 July 2020 respectively) for crop and weed stem count (no. m−2), biomass dry matter (kg m−2), and nutrient (N, P, K, S) content (kg ha−1), as-well-as final season (7 August) seed yield (kg ha−1) for camelina and canola treated with and without sulfonylurea. Using Prefer 90 (NIS) at 0.25% v/v, camelina was treated with thifensulfuron at 6.3 g a.i. ha−1, and canola was treated with thifensulfuron at 10.5 g a.i. ha−1 and tribenuron at 5.3 g a.i. ha−1. Sulfonylurea-resistant camelina and canola reduced late-season dry weight biomass of weeds by >75% and ≥60%, respectively, compared with fallow plots. Application of sulfonylurea herbicides to camelina or canola prior to mid-season analyses was not a significant factor (p ≤ 0.05) for reducing weed pressure and generally had little impact on altering crop biomass, seed yield, and nutrient retention. However, in some cases, herbicide treatment had an additive effect of reducing weed pressure over that of camelina or canola alone. Depending on the rotational cropping system, sulfonylurea-resistant camelina and canola should provide additional options for integrated weed management approaches and reducing nutrient leaching in the upper Midwest and northern Great Plains of the USA.

Pydiflumetofen: An SDHI seed‐applied fungicide, a potential tool for the canola‐blackleg management toolbox

AbstractBlackleg is a major fungal disease of canola caused by Leptosphaeria maculans. Due to the breakdown of current host resistance, having an effective fungicide to avoid seedling infection is important to avoid disease. Pydiflumetofen is a newly developed broad‐spectrum seed treatment fungicide in the succinate dehydrogenase inhibitor (SDHI) group. We evaluated the separate and combined application of pydiflumetofen and Vibrance Flexi on early‐season control of blackleg using moderately resistant canola cultivar SY4135 and susceptible cultivar Westar. In the greenhouse, seedlings inoculated with green fluorescent protein (GFP)‐tagged L. maculans showed lesion development and apoplastic mycelial growth in cotyledons in control and Vibrance Flexi treatments but no lesion development or in planta mycelial growth was observed in pydiflumetofen‐treated seedlings, in Westar or SY4135, 14 days postinoculation. SY4135 and Westar plants with pydiflumetofen‐treated seeds inoculated with L. maculans isolate D3 had significantly lower disease severity. Both host genotypes treated with pydiflumetofen showed lower disease severity estimates than the other treatments. Statistically significant disease severity reduction was cultivar dependent in the field. Canola is most susceptible to blackleg as a seedling, from the cotyledon to two‐ to four‐leaf stage. Pydiflumetofen protects the plant at the critical window for infection. Therefore, pydiflumetofen could be a potential tool that farmers can add to their blackleg management toolbox.

Effect of different seed priming agents on chromium accumulation, oxidative defense, glyoxalase system and mineral nutrition in canola (Brassica napus L.) cultivars

The present experiment was conducted to appraise the role of different seed priming agents in circumventing the negative impact of chromium (Cr) toxicity on canola plants. Chromium toxicity resulted in significant decline in photosynthetic pigments and growth attributes of two canola cultivars (Puriga and MS-007). Cr toxicity also resulted in higher oxidative stress mirrored as greater accumulation of hydrogen peroxide (H2O2) superoxide radical (O2•‒), electrolyte leakage (EL) and malondialdehyde (MDA). Further, lipoxygenase enzyme activity that catalyzes the peroxidation of membrane lipids was also enhanced due to Cr toxicity. Canola plants also manifested impaired methylglyoxal (MG) detoxification due to the downregulation of glyoxalase enzymes (GlyI and II) under Cr stress. Seed priming treatments viz. osmo-priming with calcium chloride (CaCl2) and hormonal priming with salicylic acid (SA) remarkably improved growth and chlorophyll content in both canola cultivars under Cr toxicity as compared to other priming treatments such as hydro-priming, redox priming (H2O2) and chemical priming (Se; selenium). Moreover, CaCl2 and SA seed priming also resulted in lower oxidative stress and improved enzymatic (SOD, POD, CAT, APX, GR, GST) and non-enzymatic (GSH, phenolics, flavonoids, proline) antioxidant system of both cultivars under Cr toxicity. Further, hormonal and osmo-priming strengthened glyoxalase and antioxidant systems, thus improving reactive oxygen species (ROS) and MG detoxification. In this background, the cultivar Puriga is considered Cr tolerant as it exhibited better growth and lesser oxidative stress in both seed priming and non-primed conditions under Cr toxicity than cv. MS-007.

Canola as a potential forage.

The nutritive quality of four cultivars of canola forage (Brassica napus L.), Orient, Midas, Global, and Hybrid (Cobra × Regent), which were harvested in the early-spring period, were compared with green-winter barley (GWB) in terms of their yields, chemical composition, in vitro gas production variables, in situ crude protein (CP) degradation, and predicted dry matter intake (PDMI). Data were statistically analyzed using a completely randomized design with four replications and three samples per replication. The study was based on a randomized complete block design, and data were analyzed using SAS, general linear model procedure for normal distribution. The canola dry matter (DM) yield was highest in Orient cultivar and lowest in Midas (P < 0.05). Organic matter (OM), CP, neutral detergent fiber (NDF), and lignin(sa) concentration of the four cultivars ranged from 862 to 865, 218 to 247, 295 to 340, and 35 to 53 g/kg DM, respectively. The estimated OM disappearance (OMD), effective degradability of CP, effective rumen degradable protein (ERDP), digestible undegradable protein, and metabolizable protein (MP) of the forages were from 636 to 671 g/kg, 878 to 910, 172 to 193, 1.9 to 3.4, and 112 to 126 g/kg DM, respectively. Compared to Global and Hybrid cultivars, Orient and Midas contained higher CP, OMD, ERDP, MP concentration, and PDMI, but lower NDF, acid detergent fiber (ADF), and lignin(sa) concentrations (P < 0.05). The level of glucosinolates in the forages ranged from 0.38 to 1.51 µmol/g DM, which is below the detrimental level for ruminants. Compared to winter canola cultivars, GWB had higher DM yield (P < 0.003), NDF, lignin(sa), PDMI (P < 0.01), and digestible undegradable protein (P < 0.04), but had lower OMD (P < 0.03), ERDP (P = 0.01), and MP (P < 0.009). Based on the obtained results, the variation in the nutritive quality among the canola cultivars is relatively small, and the Orient cultivar, which is most comparable to GWB, was judged to be nutritionally the best among the cultivars.

PRODUCTION MUTANT LINES OF TURNIP RAPE (BRASSICA RAPA) AND ITS INTERSPECIFIC HYBRIDS IN THE ISOLATED MICROSPORE CULTURE

This article presents the results of research on the production of mutant doubled haploids of turnip rape (Brassica rapa L.ssp.Oleifera), as well as its interspecies hybrids with rapeseed (Brassica napus). An&nbsp; immature embryo culture&nbsp; was used to increase the productivity of inter-specific hybridization. Studies have obtained interspecific hybrids of turnip rape with rapeseed. The largest number of plants was observed in hybrids where the mother plant was rapeseed. Furthermore, chemical mutagenesis was used to increase the genetic diversity of studied materials. Ethyl methanesulfonate (EMS) has been applied to the treatment of embryos produced in the isolated microspores culture&nbsp; of turnip rape and its interspecies hybrids. Results of embryo regeneration against mutagen on a nutrient medium B5 with gibberellic acid showed that the concentration of 8 mM EMS stimulated the regeneration process in turnip rape cultivars (Zolotistaya - 72% and Yantarnaya - 88%) and showed superior results compared to a low concentration (4 mM). For hybrids compared to high concentration (8mM), a low concentration of 4mM EMS showed superior results. New mutant lines have been obtained as the starting material for selection in the creation of new domestic canola cultivars.

Responses of Canola Morphological and Agronomic ‎Characteristics to Potassium Sulfate Fertilization under ‎Drought Stress

ABSTRACT In order to reduce the damage caused by late-season drought stress of canola, a factorial split plot experiment was performed on the basis of the randomized complete blocks design with three replications in Karaj, Iran. The treatments were Potassium sulfate in two levels, including application and non-application of potassium sulfate, irrigation at three levels including normal irrigation (control), restricted irrigation from the flowering and pod formation stage, as factorial were in main plots and winter canola cultivars including Opera, L72, KR1, GKH3705, GKH0224 were in subplots. The interaction effect of potassium sulfate × irrigation × cultivar on plant height, number of pods per the main stem, number of pods per branch, number of pods per plant, seed yield, and seed oil yield was significant at the 1% level. In conditions of applying potassium sulfate and irrigation interruption from the flowering stage, Opera cultivar had the highest seed yield with a mean of 3715 kg ha−1. In conditions of not applying potassium sulfate and under normal irrigation (control), the promising line of L72 with a mean of 6169 kg ha−1, and in the late season drought stress (irrigation interruption from the pod formation and flowering stages), the opera cultivar with the means of 4763 and 3468 kg ha−1 had the highest seed yield.

Phosphorus Fractionation Affected by Root Induced Changes of Two Canola Cultivars

Phosphorus Fractionation Affected by Root Induced Changes of Two Canola Cultivars

Effects of nitrogen rate on growth and quality of rapeseed blanket seedling for mechanized transplanting

Cultivating a high quality rapeseed blanket seedling is crucial if the mechanized transplant of rapeseed is to become an effective part of oilseed production in China. Nitrogen (N) strongly affects the growth and quality of the rapeseed seedling. This study investigated the agronomic traits, physiological indexes, the surviving number of blanket seedlings, and the survival rate after transplanting two canola (Brassica napus L.) cultivars (Ningza 1838 and Yangyou 9) treated with five N rates (0, 0.5, 1.0, 1.5 and 2.0 g N per tray). Plant height, leaf age, leaf area, collar length, fresh and dry weights, moisture content, and N concentration in root and shoot all increased as the N rate increased. The survival number, collar diameter, root to shoot ratio at the 30th day after sowing and the survival rate at the 10th day after transplanting increased at first then decreased as N rate consecutively increased. The survival number and survival rate under the 1.0 and 1.5 g N per tray treatments were most improved amongst N treatments, although there was no significant difference between these two N treatments. This suggests that to achieve high-quality blanket seedling needed for mechanized transplanting, the application of N at rates of 1.0 to 1.5 g N per tray at the one-leaf and one-heart stages is recommended.

A Proteome-Level Investigation Into Plasmodiophora brassicae Resistance in Brassica napus Canola.

Clubroot of Brassicaceae, an economically important soil borne disease, is caused by Plasmodiophora brassicae Woronin, an obligate, biotrophic protist. This disease poses a serious threat to canola and related crops in Canada and around the globe causing significant losses. The pathogen is continuously evolving and new pathotypes are emerging, which necessitates the development of novel resistant canola cultivars to manage the disease. Proteins play a crucial role in many biological functions and the identification of differentially abundant proteins (DAP) using proteomics is a suitable approach to understand plant–pathogen interactions to assist in the development of gene specific markers for developing clubroot resistant (CR) cultivars. In this study, P. brassicae pathotype 3 (P3H) was used to challenge CR and clubroot susceptible (CS) canola lines. Root samples were collected at three distinct stages of pathogenesis, 7−, 14−, and 21-days post inoculation (DPI), protein samples were isolated, digested with trypsin and subjected to liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis. A total of 937 proteins demonstrated a significant (q-value < 0.05) change in abundance in at least in one of the time points when compared between control and inoculated CR-parent, CR-progeny, CS-parent, CS-progeny and 784 proteins were significantly (q < 0.05) changed in abundance in at least in one of the time points when compared between the inoculated- CR and CS root proteomes of parent and progeny across the three time points tested. Functional annotation of differentially abundant proteins (DAPs) revealed several proteins related to calcium dependent signaling pathways. In addition, proteins related to reactive oxygen species (ROS) biochemistry, dehydrins, lignin, thaumatin, and phytohormones were identified. Among the DAPs, 73 putative proteins orthologous to CR proteins and quantitative trait loci (QTL) associated with eight CR loci in different chromosomes including chromosomes A3 and A8 were identified. Proteins including BnaA02T0335400WE, BnaA03T0374600WE, BnaA03T0262200WE, and BnaA03T0464700WE are orthologous to identified CR loci with possible roles in mediating clubroot responses. In conclusion, these results have contributed to an improved understanding of the mechanisms involved in mediating response to P. brassicae in canola at the protein level.

Cabbage‐centre grub (Hellula hydralis Guenée) (Lepidoptera: Pyralidae): a new pest challenge to long‐season canola grown for forage and grain in southern Australia

AbstractCanola crops grown across southern Australia are subject to damage from more than 40 invertebrate species. Shifts within this invertebrate pest complex have evolved due to changing management practices. The latest change is the sowing of winter canola cultivars in the proceeding spring (September–November), grazing during late summer to early winter (February–June) and then ‘locking up’ for grain harvest in December/January. Complementary to this practice is the sowing of longer‐season spring cultivars in early autumn, also for grazing. Do long‐growing‐season crops create green bridges for insects and diseases? In the autumn of 2016, significant damage to forage canola caused by Hellula hydralis Guenée, 1854 was reported. The widespread occurrence of H. hydralis moths across south‐east Australia is expected due to it migrating on southerly airflows from where it is a pest in subtropical vegetable crops. Previously, H. hydralis had been considered as an occasional pest in forage turnips grown over the summer–autumn period. However, the occurrence of multiple larval instars in winter canola for a prolonged period in late summer and early autumn of 2016 across the high‐rainfall zones of south‐east Australia causing substantial loss of dry matter has not been reported previously. Little is known about this native species, but international literature exists for related pest species. The likely factors and implications of the unusually high occurrence of H. hydralis in forage canola are discussed. Pest report data indicate that H. hydralis continues to cause damage, suggesting that the growing of long‐season forage canola is providing another, more suitable, over‐summer breeding ground in southern Australia for this native species. Long‐term research on crop and non‐crop hosts is necessary to understand, hence manage, H. hydralis as a pest of canola.

Evaluation of Host Resistance, Hydrated Lime, and Weed Control to Manage Clubroot in Canola

Plasmodiophora brassicae Wor. is a soilborne parasite causing clubroot of canola (Brassica napus L.), a serious disease managed mostly by planting clubroot-resistant (CR) cultivars. Recently, new pathotypes of P. brassicae have emerged that overcome resistance, highlighting the need for a greater understanding of resistance stewardship and an integrated approach to clubroot management. Replicated field experiments were conducted in Edmonton, AB, in 2018 and 2019, to evaluate the effect of lime application and weed management on clubroot severity, crop yield and various growth parameters in clubroot-susceptible (CS) and CR canola cultivars. P. brassicae resting spore densities were also monitored by quantitative PCR for each treatment. When hydrated lime was applied to increase the soil pH from initial values of 5.2–5.5 to 7.2, clubroot severity decreased by 34–36% in the CS canola cultivar, while seed yield increased by 70–98%. The application of hydrated lime also resulted in resting spore densities that were 48–80% lower, relative to untreated controls, in plots where the CS cultivar was grown. Lime application or management of weeds did not significantly affect spore densities in plots with the CR cultivar. The results from the field trial suggest that the application of hydrated lime may be a useful strategy to manage clubroot, when used in combination with genetic resistance to reduce disease pressure.

Identification of Arabidopsis Phospholipase A Mutants With Increased Susceptibility to Plasmodiophora brassicae.

Clubroot, caused by the obligate parasite Plasmodiophora brassicae, is one of the most devastating diseases of canola (Brassica napus) in Canada. The identification of novel genes that contribute to clubroot resistance is important for the sustainable management of clubroot, as these genes may be used in the development of resistant canola cultivars. Phospholipase As (PLAs) play important roles in plant defense signaling and stress tolerance, and thus are attractive targets for crop breeding. However, since canola is an allopolyploid and has multiple copies of each PLA gene, it is time-consuming to test the functions of PLAs directly in this crop. In contrast, the model plant Arabidopsis thaliana has a simpler genetic background and only one copy of each PLA. Therefore, it would be reasonable and faster to validate the potential utility of PLA genes in Arabidopsis first. In this study, we identified seven homozygous atpla knockout/knockdown mutants of Arabidopsis, and tested their performance following inoculation with P. brassicae. Four mutants (pla1-iiα, pla1-iγ3, pla1-iii, ppla-iiiβ, ppla-iiiδ) developed more severe clubroot than the wild-type, suggesting increased susceptibility to P. brassicae. The homologs of these Arabidopsis PLAs (AtPLAs) in B. napus (BnPLAs) were identified through Blast searches and phylogenic analysis. Expression of the BnPLAs was subsequently examined in transcriptomic datasets generated from canola infected by P. brassicae, and promising candidates for further characterization identified.

Antioxidant Response and Calcium-Dependent Protein Kinases Involvement in Canola (Brassica napus L.) Tolerance to Drought

Canola is an important temperate oil crop that can be severely affected by drought. Understanding the physiological and molecular mechanisms involved in canola tolerance to water deficit is essential to obtain drought-tolerant productive cultivars. To investigate the role of antioxidant response and the possible involvement of calcium-dependent protein kinases (CDPKs) in canola tolerance to drought, we analyzed four genotypes with different sensitivity to water stress. Leaf relative water content, canopy temperature, PSII efficiency, electrolyte leakage index and lipid peroxidation were used as indicators to classify the cultivars as drought-tolerant or drought-sensitive. Antioxidant enzymes superoxide dismutase, guaiacol peroxidase and catalase displayed significantly higher activities in drought-tolerant than in drought-sensitive cultivars subjected to water deficit, suggesting that the efficiency of the antioxidant response is essential in canola drought tolerance. The increased expression of genes BnaCDPK6 and BnaCDPK14 under drought conditions, their differential expression in drought-tolerant and drought-sensitive genotypes, and the presence of multiple cis-acting stress-related elements in their promoter regions suggest that CDPKs are part of the signaling pathways that regulate drought response in canola. We propose the BnaCDPK genes and their regulator elements as potential molecular targets to obtain drought-tolerant productive canola cultivars through breeding or genetic transformation.

Effect of winter canola cultivar on seed yield, oil, and protein content

AbstractWinter canola (Brassica napus L.) production has increased in the United States over the past several decades; however, there is little research in the southeastern United States on its agronomic production and growth characteristics under different nitrogen (N) fertilizer rates. The objectives of this study were to determine the effects of N rates on winter mortality, yield, oil and protein content, and seedpod shatter resistance across cultivars. Canola was grown in a randomized split complete block design with four replicates under five different N rates (0, 56, 112, 168, and 224 kg N ha−1) with four different cultivars (Hekip, Inspiration, and Edimax CL or Phoenix CL). Seed yield was very low for the 2017–2018 season, likely due to extreme cold conditions in winter and/or frost at flowering. There was high winter mortality during this period, but Edimax CL had significantly lower mortality (79.7%) than Inspiration (85.7%) and Hekip (83.9%). In the following year, more mild temperatures led to low mortality and greater yields, where rates of 112, 168, and 224 kg N ha−1 had the greatest yields (1,612–1,857 kg ha−1) with no significant differences according to cultivar. In 2018, shatter resistance was greatest for the rates of 112, 168, and 224 kg N ha−1 and was positively related to N rate. Across both years, Inspiration had greater shatter resistance. In 2019, the lowest N rate (0 kg N ha−1) and Phoenix CL had significantly greater oil contents (48.4 and 47.3%, respectively), whereas the highest N rate (224 kg N ha−1) with no particular cultivar had a significantly greater protein content (21.0%).

INFLUNCE OF CULTIVARS, PLANT GEOMETRY, HUMIC ACID AND THEIR INTERACTIONS ON GROWTH AND YIELD OF NIGER (Guizotia abyssinicia Cass.) CROP

INFLUNCE OF CULTIVARS, PLANT GEOMETRY, HUMIC ACID AND THEIR INTERACTIONS ON GROWTH AND YIELD OF NIGER (Guizotia abyssinicia Cass.) CROP

Principal component analysis and comprehensive evaluation on drought tolerance difference of canola cultivars at germination and emergence stages

Principal component analysis and comprehensive evaluation on drought tolerance difference of canola cultivars at germination and emergence stages

Comparison of non-subjective relative fungal biomass measurements to quantify the Leptosphaeria maculans\u2014Brassica napus interaction

BackgroundBlackleg disease, caused by the fungal pathogen Leptosphaeria maculans, is a serious threat to canola (Brassica napus) production worldwide. Quantitative resistance to this disease is a highly desirable trait but is difficult to precisely phenotype. Visual scores can be subjective and are prone to assessor bias. Methods to assess variation in quantitative resistance more accurately were developed based on quantifying in planta fungal biomass, including the Wheat Germ Agglutinin Chitin Assay (WAC), qPCR and ddPCR assays.ResultsDisease assays were conducted by inoculating a range of canola cultivars with L. maculans isolates in glasshouse experiments and assessing fungal biomass in cotyledons, petioles and stem tissue harvested at different timepoints post-inoculation. PCR and WAC assay results were well correlated, repeatable across experiments and host tissues, and able to differentiate fungal biomass in different host-isolate treatments. In addition, the ddPCR assay was shown to differentiate between L. maculans isolates.ConclusionsThe ddPCR assay is more sensitive in detecting pathogens and more adaptable to high-throughput methods by using robotic systems than the WAC assay. Overall, these methods proved accurate and non-subjective, providing alternatives to visual assessments to quantify the L. maculans-B. napus interaction in all plant tissues throughout the progression of the disease in seedlings and mature plants and have potential for fine-scale blackleg resistance phenotyping in canola.

Yield Components and Fatty Acids Variation of Canola Cultivars Under Different Irrigation Regimes and Planting Dates

Yield Components and Fatty Acids Variation of Canola Cultivars Under Different Irrigation Regimes and Planting Dates

Genetic Structure of Plasmodiophora brassicae Populations Virulent on Clubroot Resistant Canola (Brassica napus).

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.