Effect of inoculum concentration on growth of clubroot-resistant canola and Napa cabbage. J. A. DALTON, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin, reduces yield in canola (Brassica napus L.) and Brassica vegetables such as Napa cabbage (B. rapa L. ssp. pekinensis). Genetic resistance is essential for clubroot management. However, studies indicate that high spore loads may reduce growth and delay development in clubroot-resistant cultivars of canola and Napa cabbage. Area under the growth stairs (AUGS) was calculated using weekly measurements of height for canola and leaf length for Napa cabbage. Inoculation with 1 × 106 spores mL−1 of P. brassicae reduced plant height by 11% (± 5%) in three resistant canola cultivars, but leaf length of Napa cabbage cultivars was only reduced by 3% (± 1%). A field trial was conducted in 2014 to compare the growth of clubroot-resistant canola cultivars at two adjacent sites at the Muck Crops Research Station, University of Guelph, Kingston, ON, selected based on a field history differing only in spore loads of P. brassicae (estimated at 5 × 108 vs.7 × 107 spores g−1 dry soil). There were no symptoms of clubroot in the resistant cultivars, but severe clubroot developed in the susceptible control at both sites. At the location with a higher inoculum concentration, plant height of the resistant canola cultivars was reduced by 36% (± 6%) and leaf length of Napa cabbage was reduced by 18% (± 3%) relative to the lower inoculum concentration. These results support previous reports that the growth of resistant cultivars of canola and Napa cabbage is reduced when resting spore populations are high.
Expression patterns of selected Plasmodiophora brassicae genes in resistant and susceptible canola. W. X. FEI, S. RONG, J. FENG, S. F. HWANG AND S. E. STRELKOV. Crop Research Institute, Anhui Academy of Agricultural Sciences, Hefei, Anhui, 230031,China; (J.F., S.-F.H.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada; and (S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Plasmodiophora brassicae Woronin causes clubroot disease in cruciferous plants, and is an emerging threat to Canadian canola (Brassica napus L.) production. The in planta expression patterns of 12 P. brassicae genes were analysed by quantitative PCR over a time-course following inoculation of resistant and susceptible canola genotypes. For all 12 genes, a single expression peak was observed in the resistant genotype at 5 or 7 days after inoculation (dai), indicating the involvement of these genes in the early stages of infection. In the susceptible genotype, the 12 genes were classified into three groups: two genes showed a single expression peak at 14 dai, three showed two expression peaks at 14 and 35 dai, and the remainder showed a single expression peak at 35 dai. The genes specifically up-regulated during the early stages of infection in the resistant genotype are probably responsible for causing a similar amount of primary infection in the susceptible genotype. Furthermore, if the molecular interaction between canola and P. brassicae follows the traditional gene-for-gene model, any effort to search for Avr genes should focus on candidates that have an expression pattern with a specific up-regulation in the resistant genotype at the early stages of infection.
Sensitivity of Leptosphaeria maculans isolates from canola to pyraclostrobin fungicide in Alberta, Canada. M. C. FRASER, S. F. HWANG, H. U. AHMED, W. BARTON AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; (S.-F.H., H.U.A.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 7000–113 Street, Edmonton, AB T5Y 6H3, Canada; and (W.B.) BASF, Research & Commercial Development, 100 Milverton Drive, Mississauga, ON L5R 4H1, Canada
Blackleg disease, caused by Leptosphaeria maculans (Desmaz.) Ces. & De Not, poses a serious risk to canola production in Canada. Pyraclostrobin is commonly used to manage blackleg disease, but as a strobilurin fungicide, it has the potential to select for fungicide intensive isolates within the L. maculans population. In 2011, infected canola stubble was collected from Camrose, Ponoka, Lacombe, Lethbridge, Strathcona, and Wetaskiwin, Alberta. From these samples, 117 single-spore isolates of L. maculans were prepared and their sensitivity to Headline EC fungicide (pyraclostrobin) was evaluated through a growth plate assay. The mean EC50 value of 13 reference isolates was determined to be 0.25 mg L−1. The 117 isolates were then screened with the EC50 dose. Two thirds of the isolates were highly sensitive (>50% growth inhibition relative to the non-amended control), while one third was moderately sensitive (<50% inhibition). Lethbridge had a greater proportion of moderately sensitive isolates, while Camrose, Strathcona, and Ponoka had a greater proportion of highly sensitive isolates. Further research will include testing of the isolates with a discriminatory dose to determine if any insensitive isolates are present in the sample population. Preliminary results of this study show that the sensitivity of isolates to pyraclostrobin in Alberta varies.
Genetic diversity of the wheat pathogen Zymoseptoria tritici in Alberta, Canada. M. D. HOLTZ, T. K. TURKINGTON AND K. XI. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada; (T.K.T.) Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Zymoseptoria tritici (Desm.) Quaedvlieg & Crous, comb. nov. (Synonyms: Septoria tritici and Mycosphaerella graminicola) is a member of the leaf spot complex of wheat. Eighty-nine isolates were collected from central and southern Alberta. The species population genetic structure was analysed by examining the mating type and 13 microsatellite loci. Both mating types were detected in approximately equal proportions in both central and southern Alberta. At each microsatellite locus, 2–5 alleles were detected, for a total of 35 alleles. A high level of genotypic diversity was found, with a clonal fraction of only 4.5%. There was no evidence of linkage disequilibrium between the loci. Cluster analysis using the shared allele distances between the isolates showed no differentiation between regions and all clusters had low bootstrap support. Based on these results, Z. tritici in Alberta appears to be one large panmictic population. The equal mating type ratios, lack of linkage disequilibrium, and high genetic variation suggest that frequent and ongoing sexual recombination occurs.
A QTL for all-stage resistance to stripe rust [Puccinia striiformis f. sp. hordei] in the barley cultivar ‘Seebe’. M. D. HOLTZ, S. XUE, P. JUSKIW, K. XI, K. KUMAR AND J. ZANTINGE. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada
Barley stripe rust caused by Puccinia striiformis Westend f. sp. hordei is an important disease of barley in Central America and parts of the USA. There is concern the disease may become more severe within Canada. Genetic resistance is the best approach for controlling the disease. The 2-row barley cultivar ‘Seebe’ possesses all-stage resistance to barley stripe rust. To determine the source of the resistance, Seebe was crossed with the cultivar ‘Harrington’ and from the resultant F1 seeds a population of recombinant inbreed lines (RILs) was developed by single-seed descent. The parents and RILs were screened for stripe rust resistance at the seedling stage under controlled conditions. Eighty-two lines were analysed with Diversity array technology (DArT) and simple sequence repeat (SSR) markers. Single marker analysis and confidence interval mapping indicate that this all-stage resistance is controlled by a single QTL located on chromosome 5H. This QTL has the potential to be incorporated into breeding lines by marker assisted breeding at the Field Crop Development Centre.
Plant pathogen interaction enzyme expression (PPIEE) assay for linking enzymes to fusarium head blight resistance in barley. K. KUMAR, J. ZANTINGE, K. XI, K. STEENBERGEN, P. JUSKIW, S. WATERMAN AND M. D. HOLTZ. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada
Fusarium head blight (FHB) of barley, primarily caused by the fungus Fusarium graminearum Schwabe, has become a major production problem in the humid and semi-humid areas of the world. This disease has well established in Manitoba and has been moving westward and northward in western Canada. In addition to yield losses, FHB is detrimental to grain quality due to the mycotoxin contamination. This has resulted in grain unsuitable for malting or feed. The objective of the present study is to develop an in vitro assay to screen barley germplasm for FHB resistance. In this Petri dish assay, the seed of barley cultivars/lines inoculated with F. graminearum were incubated on growth medium amended with a specific enzyme substrate to measure 1–3 β-glucanase, an enzyme previously identified to increase plant resistance to pathogens. Enzyme activity was visible in the growth medium and could be measured with a simple optical density (OD) reading. The blue colour and OD readings were significantly higher in resistant cultivars/lines compared with susceptible ones. Some lines showed variation in both lab and field data, this variation emphasized the complex nature of the pathogen–plant relationship. Further research is planned to reduce variability by identifying the optimal test conditions and standardizing the assay measurements.
Does drought stress affect the resistance reaction of wheat and triticale to different pathogens? A. LAROCHE, M. M. FRICK, S. VERMA, N. GAUDET, G. DHARIWAL, M. SCHUSSLER, M. J. FRICK, S. WOGSBERG, K. KUNDRIK AND D. GAUDET. Lethbridge Research Centre, Agriculture and Agri-Food Canada, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Whether abiotic stress interacts positively or negatively with the plant responses to different pathogens has important implications to cereal production. The induction of the stress signalling pathway mediated by abscisic acid (ABA) following a drought treatment is well documented in the literature. It is less clear how the developmental hormones auxin, cytokinins (CKs) or defence signalling hormones jasmonic acid (JA), salicylic acid (SA), ethylene (ET), and brassinosteroids, interact with drought stress to finally determine the outcome of the plant–pathogen interactions. Additionally, numerous plant resistance genes are known to be effective only at the adult plant stage. Our goal is to understand the interaction between drought stress and resistance expression to stripe rust and powdery mildew in wheat and triticale during several seedling and adult developmental stages. Numerous defence- and stress-related plant transcripts were profiled during infection of drought-stressed wheat and triticale at the Zadoks’ Z12, Z21, Z42 and Z59 stages. Results suggest that the regulations of specific key genes regulating stress response are under the control of regulatory processes that control plant developmental stages. Furthermore, the response to pathogen inoculation was different in root and leaf tissues. Up-regulation of different WRKY transcription factors previously associated with the drought stress response were also up-regulated following inoculations with the pathogens.
The role of pollen in the development of blossom blight of seed alfalfa caused by Botrytis cinerea. J. REICH, D. JOHNSON AND S. CHATTERTON. University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 3M4, Canada; and (S.C.) Lethbridge Research Centre, Agriculture and Agri-Food Canada, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Blossom blight of seed alfalfa, caused by fungal pathogens Botrytis cinerea Pers.:Fr. and Sclerotinia sclerotiorum (Lib.) de Bary, is an economically important disease in the Canadian Prairies. Both B. cinerea and S. sclerotiorum readily infect alfalfa pollen in vitro, though the extent to which infection occurs under field conditions is unknown. Leafcutter bees (Megachile rotundata) are intensively managed to pollinate the florets and may transmit the pathogens if pollen infection is common. A greenhouse study was conducted to investigate the role of pollen in the development of blossom blight caused by B. cinerea. Racemes of alfalfa plants were tripped or not tripped, inoculated with conidia applied in a suspension (wet) or dry dusted (dry), and placed in a humidity chamber at 100% relative humidity for 24 h. Florets were harvested at 0, 24, 48 and 96 h post-inoculation and subsamples were tested for pollen and floret infection, pollen viability, and used for histopathological analysis. No infection of pollen was observed and there were no significant effects of tripping or harvest time on floret infection (P > 0.1). However, wet-inoculated florets had a higher percentage of blossom blight than dry-inoculated florets (P ≤ 0.005). These results suggest that infected pollen does not play a significant role in pathogen transmission, though trials are ongoing.
Metam-sodium and chloropicrin soil treatments reduce resting spore populations of Plasmodiophora brassicae, 2014. J. ROBSON, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Clubroot [Plasmodiophora brassicae Woronin] is an important disease of canola (Brassica napus L.) and other Brassica crops. The efficacy of metam-sodium (trade name Vapam HL or Busan 1236) and chloropicrin (Pic Plus) fumigants against P. brassicae was assessed in growth room and field studies. Efficacy was assessed in a bioassay of severity (disease severity index, DSI) on Shanghai pak choi (B. rapa L. subsp. chinensis var. communis) under controlled conditions. In a growth room study, severity was low (< 2 DSI) on infested muck soil treated by drenching with Vapam (146, 292, 585 L a.i. ha−1) or Busan (145, 290, 581 L a.i. ha−1) in air-tight plastic bags, but high (70 DSI) in the non-treated control. In soil from treatments on a muck soil (~70% organic matter) site, a low rate of chloropicrin (89 L) covered with an impermeable plastic film reduced subsequent clubroot severity compared with the check (45 vs. 89 DSI), but moderate to high rates of Vapam (292, 585 L) that was packed but not tarped were much less effective (78 DSI). In soil from treatments on mineral soil, severity in the control was low (3 DSI) and no symptoms developed from treatment that received metam-sodium (Vapam and Busan) or chloropicrin. There was no difference between Vapam and Busan at any application rate in any study. Chloropicrin was more effective than metam-sodium in the field, but sealing the soil surface (as used with chloropicrin) may improve the efficacy of metam-sodium.
Prevalence of avirulence genes in Leptosphaeria maculans isolates from Alberta, Canada. S. B. RONG, J. FENG, W. X. FEI, S. F. HWANG AND S. E. STRELKOV. Anhui Academy of Agricultural Sciences, Hefei, Anhui, China; (J.F., S.-F.H.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada; and (S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Blackleg, caused by the species complex of Leptosphaeria maculans (Desmaz.) Ces. & de Not. and Leptosphaeria biglobosa, is a severe disease of canola or oilseed rape (Brassica napus L.) worldwide. In this study, 121 single-spore isolates of L. maculans were obtained from infected canola plants collected from six locations in Alberta. Race structure was investigated by PCR amplification of five avirulence genes. Among these, AvrLm1 was found to be absent in all isolates while AvrLm4-7 and AvrLm6 were present in all isolates. AvrLmJ1 and AvrLm11 were present in most isolates but absent in isolates 334, 437 and 491. AvrLm11 was absent in isolates 235 and 245. This result suggests a low level of race diversity in the L. maculans populations from Alberta. The absence of AvrLm1 suggests that the corresponding resistance gene Rlm1 may be well distributed in Alberta’s canola cultivars. The prevalence of the other four Avr genes in most isolates is consistent with the race structure of L. maculans found in Ontario and in other countries, such as Mexico and Chile. The absence of AvrLmJ1 and AvrLm11 in a few isolates suggests that the corresponding resistance genes may have limited effectiveness in Alberta.
The impact of barley variety rotation, mixtures, and intercropping on leaf disease and silage production. T. K. TURKINGTON, K. XI, K. N. HARKER, J. T. O’DONOVAN, R. BLACKSHAW, T. McALLISTER AND N. LUPWAYI. Lacombe/Beaverlodge Research Centre, Agriculture and Agri-Food Canada (AAFC), 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada; (K.X.) Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada; and (R.B, T.M., N.L.) Lethbridge Research Centre, AAFC, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Three year rotational treatments were established in 2008 at two Alberta locations with comparisons made in 2010 and 2013. Treatments included: continuous barley, same variety; a mixture of the same three barley varieties each year; a mixture of three different barley varieties each year; an intercrop of barley, oat and spring triticale with the same or different crop varieties each year; and an intercrop of barley, oat and winter triticale with the same or different crop varieties each year. In 2010 and 2013, all treatments had the six-row barley variety Sundre. For both locations leaf disease, primarily net-form net blotch, was generally highest for continuous Sundre, and lowest for mixtures or intercrops with different varieties. At Lacombe in 2010 and 2013, silage yields were lowest for the continuous Sundre, highest for the intercropping treatments with the same or different varieties, and intermediate for barley mixtures. At Lethbridge in 2010 and 2013, continuous Sundre tended to have the lowest silage yield, although the intercrop treatments with winter triticale also had lower yields. Barley variety mixtures and intercropping with spring triticale tended to have higher, but similar yields. Results suggest that adding diversity in crop types and barley genetics may reduce leaf disease and improve silage productivity.
The impact of seed treatment, foliar fungicide timing, and plant growth regulator on leaf-disease severity and productivity of barley. T. K. TURKINGTON, K. XI, K. N. HARKER, J. T. O’DONOVAN, G. PENG, R. A. MARTIN, B. BERES, W. E. MAY AND R. M. MOHR. Lacombe/Beaverlodge Research Centre, Agriculture and Agri-Food Canada (AAFC), 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada; (K.X.) Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C and E Trail, Lacombe, AB T4L 1W1, Canada; (G.P.) Saskatoon Research Centre, AAFC, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; (B.B.) Lethbridge Research Centre, AAFC, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada; (W.E.M.) Indian Head Research Farm, AAFC, P.O. Box 760, Indian Head, SK S0G 2K0, Canada; (R.M.M.) Brandon Research Centre, AAFC, 2701 Grand Valley Road, Brandon, MB, R7A 5Y3; and (R.A.M.) Crops and Livestock Research Centre, AAFC, 440 University Avenue, Charlottetown, PE C1A 4N6, Canada
At Lacombe and Lethbridge, AB, Melfort and Indian Head, SK, Brandon, MB, and Charlottetown, PE, the impact of seed treatment, foliar fungicide timing (flag leaf versus head emergence), and plant growth regulator (PGR) on leaf disease severity and crop productivity of barley was assessed in 2013. InsureTM (triticonazole + pyraclostrobin + metalaxyl) seed treatment was used at two times the recommended rate, while TwinlineTM (metconazole + pyraclostrobin) and Prosaro (tebuconazole + prothioconazole) fungicides were applied at recommended rates at flag leaf and head emergence, respectively. The PGR EthrelTM (Ethephon) was applied between flag leaf emergence and just prior to head emergence. Preliminary results suggest a negative effect of seed treatment on emergence at most sites. Reduced emergence due to seed treatment may have also led to slightly later maturity at some locations. The most significant treatments impacting leaf disease severity at the late milk/early dough, were between the two fungicide applications. Yields tended to be highest at most sites when a fungicide was applied, especially at the head emergence stage. Smaller yield increases were observed with seed treatment, but only at Lethbridge, Melfort, and Indian Head. The application of PGR also increased yields, especially at sites where significant lodging occurred.
Immunofluorescent detection of clubroot resting spores. T. VUCUREVICH, C. SHEEDY, G. DUKE AND L. KAWCHUK. Lethbridge Research Centre, Agricultural and Agri-food Canada, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Clubroot caused by the pathogen Plasmodiophora brassica Woronin is becoming an important disease in Alberta, affecting plants of the Brassica family such as canola. Purified clubroot resting spores and 45 μm cross-sections of infected canola root tissue were examined under a confocal microscope following specific labelling with a polyclonal antibody and a fluorochrome for immunofluorescent detection. This method shows that binding is occurring as we see highly fluorescing clubroot spores under confocal imagery when the spores are antibody-labelled, as opposed to the negative controls. The antibodies were highly specific to clubroot resting spores and did not exhibit cross-reactivity to closely related spores of the powdery scab causing agent, Spongospora subterranea (Wallr.) Lagerh. These findings support results obtained by other detection methods being developed in our laboratory (rt-iPCR, proximity ligation assay and enzyme-linked immunoassay) and are being used to develop a rapid on-farm detection method of clubroot disease for Alberta’s producers.
Detection of stripe rust spores through self-assembly antibody conjugations by rt-IPCR. F. WANG, M. FRICK, E. AMUNDSEN, D. A. GAUDET, A. LAROCHE AND C. SHEEDY. Lethbridge Research Centre, Agricultural and Agri-Food Canada, 5403–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Stripe rust, caused by Puccinia striiformis f. sp. tritici Westend./Eriks., is one of the most important diseases of wheat. In this report, we describe the development of a rapid and sensitive real time immuno-PCR (rt-IPCR) assay for the detection of stripe rust spores. The general scheme of this assay is similar to that of an enzyme-linked immunoassay (ELISA); however, rt-IPCR employs oligomeric reagents for signal amplification by PCR rather than colorimetric reagents. Antibody conjugates are widely used as diagnostics and imaging reagents but many such conjugates suffer losses in sensitivity and specificity due to non-specific labelling techniques. Here, we used a rabbit polyclonal antibody raised against spores isolated in 2006. A 60-mer oligonucleotide sequence was covalently bound to a secondary antibody with S-4FB and S-HyNic protein cross-linkers. The rt-IPCR assay increases the sensitivity of the analogous ELISA by as much as 25-fold, with a limit of detection of 40 spores so far. The assay can quantify from 40 to 5000 stripe rust spores per sample. This assay strategy is highly adaptable, and any antigen of interest can be quantified providing a sensitive and specific primary antibody is available.
SNP markers for clubroot resistance gene CR01 based on RNA sequencing. F. YU, X. ZHANG, Z. HUANG, T. SONG, M. CHU, K. C. FALK, B. D. GOSSEN, A. DEORA, M. R. MCDONALD AND G. PENG. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N OX2, Canada; and (A.D., M.R.M.) Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
A clubroot resistance gene CR01, effective against pathotype 3 of Plasmodiophora brassicae Woronin, was previously mapped to chromosome A03 of Brassica rapa L. in pak choy cv. ‘Flower Nabana’ (FN). A number of differentially expressed genes associated with this gene were identified using RNA sequencing. In the current study, genetic mapping demonstrated that resistance to pathotypes 2, 5 and 6 co-segregate with CR01, indicating that the CR01 locus may confer broad resistance against P. brassicae. About 350 M short sequences were identified from resistant (FNR) bulks and 320 M from susceptible (FNS) bulks. The sequences were assembled, and SNP (85% of total) and Indel (15%) variants were identified, about 80% of which were homozygous. Unique FNR, unique FNS and heterozygous variants were below 10%, 9% and 4%, respectively. The frequency of homozygous variants in chromosome A03 was only 66%, but unique FNR, unique FNS and heterozygous variants were identified on A03, at about 14%, 12% and 8%, respectively. Four closely linked genes on A03 that carried the highest numbers of variants, including unique FNR in the CR01 region, were used to confirm the presence of SNPs. Seven SNP markers identified in these genes co-segregated with 12 recombinants obtained from a segregating population consisting of 1600 plants, indicating these gene-specific SNP markers are completely linked to CR01. These markers are polymorphic between the resistant donor and three B. napus canola lines, indicating they can be used for marker-assisted selection during the introgression of CR01 into canola.
Study of resistance to clubroot [Plasmodiophora brassicae] in a canola (Brassica napus) doubled haploid population. H. ZHANG, J. FENG, S. F. HWANG, S. E. STRELKOV, I. FALAK, X. Q. HUANG AND R. F. SUN. Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing, 100081, China; (H.Z., S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; (J.F., S.-F.H.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada; and (I.F., X.Q.H.)Pioneer Hi-Bred Production Ltd, 12111 Mississauga Road, Caledon, ON L7C 1X1, Canada
Currently, most of the identified clubroot [Plasmodiophora brassicae Woronin] resistance genes are derived from turnip (Brassica rapa L. ssp. rapifera). In this study, a population of 134 doubled haploid (DH) lines derived from a cross between a resistant and a susceptible canola (Brassica napus L.) was subjected to phenotypic and genotypic studies to determine the inheritance and location of the resistance gene(s). The resistance was originally derived from B. rapa spp. rapiferea. After inoculation with pathotype 3 of P. brassicae, the lines showed a 1:1 segregation ratio for resistance, indicating that resistance in this population is controlled by a single gene. Twelve markers linked to known resistance genes in the A genome were screened. Marker GC1680 linked to CRa was found to be polymorphic between the parents as well as the resistant and susceptible bulks. Several CRa-specific primers were screened against the parents and the sequences of the amplified nucleotide binding site domain were compared. A high sequence similarity between the parents was found and no insert fragment could be identified in the susceptible parent. In contrast, polymorphisms were detected between sequenced leucine rich repeat domains from the parents. Based on these results, we conclude that the resistance gene in this population is CRa or is tightly linked to CRa.