Prevalence and virulence of stripe rust in southern Alberta. E. AMUNDSEN, K. MCCORMACK, H. RANDHAWA AND R. ABOUKHADDOUR. Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403-1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Stripe rust, caused by Puccinia striiformis f. sp. tritici Erikss., is a destructive wheat disease worldwide. Disease incidence and severity was assessed in commercial wheat fields in southern Alberta in November 2016 through August 2017. In total, 74 commercial wheat fields were surveyed in 2016–2017 growing seasons. The pathogen overwintered in Alberta over that time. In November 2016, seven fields out of 10 were rated severe or moderate, but during 2017, only one field out of 64 was reported to have severe infection, and 75% of the surveyed fields were reported symptomless. The hot dry weather throughout the summer coupled with fungicide applications may have resulted in low levels of stripe rust in 2017. A set of wheat differentials included 20 near-isogenic lines in the Avocet background with various stripe rust resistance genes, including the null, were seeded in two locations in southern Alberta and in one location in British Columbia. Under natural infection it was determined that Yr5, and Yr15 were still effective against existing races, however, Yr17 and YrSP were partially defeated in Lethbridge and Yr18 was defeated in Creston. Genetic resistance to stripe rust is precarious and the need for genetic resistance in new wheat cultivars depends on reliable knowledge of the pathogen populations.
The identification of new pathotypes among single-spore isolates of Plasmodiophora brassicae derived from field populations that can overcome resistance in canola (Brassica napus). H. ASKARIAN, S. F. HWANG, A. AKHAVAN, V. P. MANOLII, T. CAO AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin, is an important soilborne disease of canola (Brassica napus L.) in Canada. Field populations of P. brassicae can be a mixture of pathotypes, making assessments of the genetics of host–pathogen interactions challenging. Thirty-four single-spore isolates were purified from nine populations of the pathogen collected from clubroot resistant (CR) canola cultivars. The virulence patterns of these 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. Eleven pathotypes were identified on the CCD Set, while the hosts of Williams and Somé et al. enabled identification of seven or three pathotypes, respectively. In some cases, pathogen populations were mixtures of isolates virulent or avirulent on CR canola. Pathotype H, as defined on the CCD Set, was predominant. This pathotype cannot overcome resistance and corresponded to the original pathotypes P2 and 3, respectively, as per Somé et al. and Williams. In contrast, the CCD pathotypes A, D, Q, R, S, T, U and X all were virulent on CR canola. Various new pathotypes, not reported in Canada previously, were identified among the isolates tested. The results suggest that genetically homogeneous single-spore isolates provide a more complete picture of the P. brassicae pathotype structure.
Efficacy of chemical fungicides against white mould of dry edible bean in southern Alberta. D. A. BURKE, M. W. HARDING, G. C. DANIELS, C. A. PUGH AND T. B. HILL. Crop Diversification Centre South, Alberta Agriculture and Forestry, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
Relative efficacy of foliar fungicide treatments against white mould (sclerotinia rot) caused by Sclerotinia sclerotiorum (Lib.) de Bary in dry edible bean (Phaseolus vulgaris L.) were evaluated in replicated field experiments in southern Alberta from 2014˗16. Fungicide was applied at 50% bloom. White mould incidence and severity were determined on subplots prior to senescence and seed yield was subsequently determined. Disease levels varied with each site-year, but based on the incidence and severity of disease, as well as seed yield, a number of registered products performed equal to or better than the industry standard fungicides. A cost per hectare analysis based on current retail prices, indicated a relatively significant price difference between some products.
Diseases of field pea in Alberta in 2017. S. CHATTERTON, M. W. HARDING, R. BOWNESS, C. VUCUREVICH, T. DUBITZ AND J. NIELSON. Crop Diversification Centre South, Alberta Agriculture and Forestry, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (S.C., C.V.) Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403-1 Avenue South, Lethbridge AB T1J 4B1, Canada; and (R.B., T.D.) Alberta Agriculture and Forestry, Lacombe Research Centre, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Diseases of field pea were evaluated in 169 fields across Alberta in 2017. Mycosphaerella blight and bacterial blight were rated in 1 m of row at each location. Root rot ratings were performed on five plants at each location. Mycosphaerella blight, bacterial blight and root rot were present in 67%, 60% and 95% of fields respectively. Incidence and severity of blights were approximately 45% and 0.4, while root rot incidence and severity were 75% and 3 respectively. When compared with 2016, a nominal 3% increase in root rot prevalence was observed in 2017 while incidence and severity each increased by 13%. One encouraging statistic was that a 25% drop in roots with high disease severity (>3) has occurred since 2014. Therefore, while prevalence and incidence may not be dropping, the number of fields with severe economic loss appears to be on the decline.
Evaluation of species composition and fungicide resistance in Fusarium populations causing dry rot in Alberta potato storages. G. C. DANIELS, D. JOHNSON, K. HAILE, D. A. BURKE, C. A. PUGH AND M. W. HARDING. Crop Diversification Centre South, Alberta Agriculture and Forestry, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; and (D.J., K.H.) Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, AB T1K 3M4, Canada
Dry rot on potato (Solanum tuberosum L.) tubers, caused by Fusarium spp. is a common problem in stored potatoes. At least 10 species of Fusarium can cause dry rot on wounded tubers, and many of them vary in their sensitivity to post-harvest fungicides. This project was initiated to characterize the species causing dry rot that are common to Alberta potato storages, and to evaluate their fungicide sensitivities. Over 320 Fusarium isolates were collected between 2011 and 2015 and have been identified to species, and evaluated for their sensitivities to thiabendazole, fludioxonil and difenoconazole. Results from a subset of the most recently collected 15 isolates are presented here. Fusarium sambucinum Fuckel remained the most commonly occurring species causing dry rot in Alberta. Based on IC50 values, insensitivity to thiabendazole was more common in the 15 isolates while most or all were sensitive to fludioxonil and difenoconazole.
The evaluation of lime products as a clubroot management tool in canola. N. M. FOX, S. F. HWANG, V. P. MANOLII, G. TURNBULL AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (S.F.H., G.T.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Clubroot (Plasmodiophora brassicae Woronin) is a soilborne disease that has become a constraint to canola (Brassica napus L.) production in Alberta, Canada. The disease is managed primarily by the planting of clubroot resistant cultivars, but this resistance already has been overcome in over 60 fields in the province. Disease development is known to favour acidic soils; therefore, increasing soil pH could reduce clubroot severity in infested soils and serve as another management tool. The efficacy of hydrated lime products in reducing clubroot severity was assessed in replicated field plot experiments in central Alberta in 2017. The addition of moderate to high rates of hydrated lime significantly reduced clubroot severity and increased above-ground biomass in a susceptible canola cultivar at 8 weeks after planting. At the highest application rate, lime treatment reduced the clubroot disease severity index by 35–91%, while increasing above-ground plant biomass by 58–116%. A greenhouse study currently is underway to assess the efficacy of hydrated lime in reducing clubroot severity in susceptible and moderately resistant canola cultivars, under different application rates and concentrations of inoculum.
Rapid decline in the sensitivity to pyraclostrobin fungicide in Mycosphaerella pinodes. B. D. GOSSEN AND M. R. MCDONALD. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N OX2, Canada; and (M.R.M.) Department of Plant Agriculture, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
Mycosphaerella blight, caused by Mycosphaerella pinodes (Berk. & Blox.) Vestergr., is a destructive disease of field pea on the Canadian prairies that occurs in almost every field in most years. Genetic resistance is not available, so severity is managed primarily with application of foliar fungicides. Strobilurin fungicides have been used for management of mycosphaerella blight since their introduction to western Canada in 2003. Sensitivity of baseline isolates to pyraclostrobin (a widely used strobilurin) has been assessed previously, with EC50 values for mycelial growth ranging from 0.03 to 0.3 mg L−1 and a discriminatory dose of 5 mg L−1. Of the 324 isolates collected in Canada and the northern USA in 2010 and 2011, 8% (all from Alberta or Saskatchewan) were insensitive to pyraclostrobin using that discriminatory concentration. In isolates of M. pinodes collected in 2013–2016 from sites across the field pea production region of Saskatchewan, 72% (46 of 64) were insensitive. This observation, taken together with concurrent studies that demonstrated a high degree of cross-sensitivity between pyraclostrobin and azoxystrobin, indicated that effective management of mycosphaerella blight with solo applications of these two widely used fungicides is likely no longer possible in Saskatchewan.
Monitoring Fusarium graminearum in Alberta: looking back 20 years. M. W. HARDING, R. J. HOWARD, J. FENG, P. LAFLAMME, T. K. TURKINGTON, T. GRÄFENHAN AND G. C. DANIELS. Crop Diversification Centre South, Alberta Agriculture and Forestry (AAF), 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (R.J.H.) RJH Research Solutions, P.O. Box 1456, Brooks, AB T1R 1C3, Canada; (J.F.) Crop Diversification Centre North, AAF, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; (T.K.T.) Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; and (T.G.) Canadian Grain Commission, Grain Research Laboratory, 196 Innovation Drive, Richardson Centre, Winnipeg, MB R3T 6C5, Canada
Fusarium graminearum Schwabe is a major pathogen of small grain cereals and corn. Infections causing head blight in cereals reduce yield, grade and market acceptance. The pathogen was first reported in Alberta in 1989 and in 1999 it was added to Alberta’s Agricultural Pests Act. Efforts to monitor its presence and spread in Alberta have been conducted every three to 5 years since 1995. A total of six surveys for F. graminearum have been conducted over the past 20 years. The pathogen was not reported in a 1995–97 survey, and only in five or six contiguous counties in southern Alberta in 2001–03 and again in 2006. After 2006, changes in F. graminearum prevalence, incidence and distribution were documented in 2010 and 2015 surveys, and by 2016 the pathogen was present in over 45% of counties and over 25% of fields sampled. Additionally, the pathogen was detected in central and northern Alberta in 2015 and 2016. These survey data show that over this 20-year period the risk and threat of F. graminearum progressed from non-detectable, to a southern Alberta problem, to a widely distributed issue for Alberta cereal and corn producers.
Survey for blackleg on canola in southern Alberta in 2017. T. B. HILL, G. C. DANIELS, D. A. BURKE, C. A. PUGH, J. FENG, K. ZUZAK, D. RENNIE, J. MACDONALD AND M. W. HARDING. Crop Diversification Centre South, Alberta Agriculture and Forestry (AAF), 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (J.F., K.Z., D.R.) Crop Diversification Centre North, AAF, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; and (J.M.) Agricultural Research and Extension Council of Alberta, #2 5304 50 Street, Leduc, AB T9E 6Z6, Canada
A survey for blackleg disease on canola caused by Leptosphaeria maculans (Sowerby) P. Karst. was performed in Alberta in 2017 targeting 1% of canola fields in each county. A total of 421 canola fields in 65 counties were surveyed. Within each field surveyed, a total of 100 stems were collected from five locations. Disease was characterized visually based on discolouration within the stem at the crown and/or the presence of basal stem cankers or stem lesions. Disease severity was rated using a 0 to 5 scale where a plant was rated 0 when it had no symptoms through to 5 when the plant was dead due to infection. Blackleg symptoms were observed in 80% of fields at an average incidence of 14.1% and average severity of 0.05. The 2017 growing season was very dry across much of the province and blackleg prevalence, incidence and severity were reduced when compared with the survey results in 2016, a year which generally had higher rainfall than 2017.
Historical distribution of populations of Plasmodiophora brassicae able to overcome clubroot resistance in Alberta. M. D. HOLTZ, S. F. HWANG, V. MANOLII AND S. E. STRELKOV. Field Crop Development Centre, Alberta Agriculture and Forestry, 5030–50 Street, Lacombe, AB T4L 1W8, Canada; (S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; and (V.M., S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin, was first identified as a disease of canola (Brassica napus L.) in Alberta in 2003. Initially, clubroot was localized around the Edmonton region, but has since spread to more than 30 counties in the province. Clubroot resistant (CR) canola varieties were first released in 2009. Highly virulent P. brassicae strains able to overcome this resistance, however, were found in 2013 in Westlock County, north-west of Edmonton. Initial analysis of these strains indicated that they belonged to a population that was genetically distinct from other P. brassicae strains. Using molecular markers developed to distinguish members of the pathogen population virulent on CR canola from the more common population, samples of P. brassicae collected in Alberta from 2005–2016 were examined to determine the historical occurrence and distribution of these virulent strains. Root galls from 219 samples were examined. Ten samples were found to have been infected with members of the population virulent on CR canola. These samples were found in Flagstaff County starting in 2008, Westlock County starting in 2009, the County of Vermillion River in 2011 and Red Deer County in 2014. Although relatively uncommon, members of this population were relatively widespread, occurring at locations 170 km apart prior to the release of CR canola. This widespread distribution may have helped hasten the breakdown of CR canola varieties.
Understanding the role of auxin in clubroot of crucifers. C. P. JAYASINGHEGE, V. P. MANOLII, J. A. OZGA, S. F. HWANG AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Infection by the obligate parasite Plasmodiophora brassicae Woronin, the causal agent of clubroot disease of crucifers, results in the development of root galls. These galls reduce water and nutrient uptake by the affected plants, stunting above-ground growth. The plant hormone auxin is believed to be among the hormones utilized by this pathogen in gall development. Therefore, it may be possible to suppress gall development by modulating auxin signalling in the plant host. Members of the TIR1/AFB family of F-box proteins act as plant auxin receptors. Of a total of six TIR1/AFB family members in Arabidopsis thaliana (L.) Heynh. (TIR1 and AFB1 to AFB5), only TIR1 and AFB2 are primarily responsible for auxin sensitivity in roots. A previous report indicated that the mutants tir1, afb1-3 and afb1-3afb2-3 have increased clubroot susceptibility. In this study, clubroot susceptibility was tested in tir1-10, afb2-3 and afb4-8 mutants of Arabidopsis. The tir1-10 and afb2-3 mutants exhibited reduced auxin sensitivity in root-growth assays with the synthetic auxin 2,4-D. All three of the mutants, however, developed levels of clubroot similar to the wild-type following inoculation with 6 × 104, 6 × 105 or 6 × 106 P. brassicae resting spores/mL. Accordingly, the inactivation of single auxin receptors does not appear to be sufficient to suppress root gall development in P. brassicae-infected plants, possibly as a result of the complementary action of other auxin receptors.
Stripe rust management in winter wheat using cultivar resistance and fungicide. K. KUMAR, K. XI, T. K. TURKINGTON, M. ALJARRAH AND F. CAPETTINI. Field Crop Development Centre, Alberta Agriculture and Forestry, 5030–50 Street, Lacombe, AB T4L 1W8, Canada; and (K.T.) Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Under natural infection conditions in central Alberta during two winter wheat seasons (years), field tests were conducted to determine the effect of winter wheat cultivars with different levels of resistance, seed treatment and foliar fungicide application on management of stripe rust (Puccinia striiformis f. sp. tritici Erikss.). In the check plots containing susceptible AC Bellatrix and CDC Buteo, relatively high levels of stripe rust developed, while lower stripe rust severity was observed on the resistant cultivar AC Emerson. Similar levels of powdery mildew (Blumeria graminis (DC.) Speer f. sp. tritici) developed on all cultivars in check plots evaluated at Olds in 2015–16. Foliar application of the fungicide Caramba (metconazole) at the early flowering stage reduced severity of both diseases. Reduction in disease severity by the fungicide treatments resulted in significant yield increases for the susceptible cultivars. There was a limited yield response to the same fungicide treatments for the resistant cultivar ‘AC Emerson’ due to low levels of stripe rust observed on this cultivar. Seed treatment alone had a limited effect on stripe rust severity and no yield increases were observed for all cultivars. Similar trends were observed for other yield components such as thousand kernel weight (TKW) and test weight (kg hL−1) in response to fungicide treatments. Combination of seed treatment and foliar treatment yielded the same effect as the application of Caramba.
Tsn1 in Canadian winter and durum wheat germplasm. K. MCCORMACK, T. DESPINS, E. AMUNDSEN, R. GRAF, Y. RUAN AND R. ABOUKHADDOUR. Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada (AAFC), 5403-1 Avenue South, Lethbridge, AB T1J 4B1, Canada; and (Y.R.) Swift Current Research and Development Centre, AAFC, P.O. Box 1030, Swift Current, SK S9H 3X2, Canada
The wheat Tsn1 gene on chromosome 5B confers sensitivity to the ToxA-producing wheat pathogens Pyrenophora tritici-repentis (Ptr) and Stagonospora nodorum that cause the diseases tan spot and stagonospora nodorum blotch (SNB), respectively. Both are destructive foliar diseases of wheat worldwide and in Canada. ToxA is the necrosis inducing effector (protein) that contributes considerably to necrosis development in sensitive wheat genotypes carrying the Tsn1 gene. In this study, Canadian durum and winter wheat germplasm were evaluated for their reaction to Ptr and its ToxA-producing isolate and for the presence of Tsn1 and therefore sensitivity to ToxA. Bioassay with ToxA-producing isolate followed by PCR amplification of Tsn1 different domains revealed that 65 and 67% of winter and durum wheat respectively amplified the Tsn1 gene. While bioassay results need further confirmation, the high level of Tsn1 amplification indicates that ToxA-sensitivity is widespread in the Canadian winter and durum wheat and is consistent with the prevalence of ToxA-producing Ptr isolates in Canada.
Stripe rust on wheat and barley in central Alberta during 2015 and 2016. K. XI, K. KUMAR, T. K. TURKINGTON AND F. CAPETTINI. Field Crop Development Centre, Alberta Agriculture and Forestry, 5030–50 Street, Lacombe, AB T4L 1W8, Canada; and (K.T.) Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Wheat stripe rust caused by Puccinia striiformis f. sp. tritici Erikss. (Pst) is widespread, while barley stripe rust resulting from P. striiformis f. sp. hordei (Psh) has regularly been observed in central Alberta. Cross infection between wheat and barley by the two pathogens has been observed. The objective of this study was to differentiate the two pathogens and identify virulence in each pathogen. Sixty-four isolates were purified from diseased leaf samples that had been collected from wheat, barley, foxtail barley and triticale in central Alberta during 2015 and 2016. Based on phenotyping on barley and wheat differentials, 21 of the 23 isolates sampled from barley and foxtail barley were classified to be Psh and two were Pst; all 41 isolates from wheat and triticale were classified to be Pst. Temporal changes in virulence frequency were apparent when Psh and Pst collected during 2015 to 2016 were compared with those collected during 2009 to 2011. Current Psh and Pst pathotypes from the 2015 to 2016 collection exhibited substantial increases in virulence frequency on a number of wheat differentials when inoculated at the seedling stage, compared with previous isolates from the 2009 to 2011 collection. Current Psh pathotypes showed substantial decreases in virulence frequency on seven of the 12 barley differentials, while current Pst pathotypes exhibited similar virulence frequency on 12 barley differentials compared with those collected from 2009–2011.
Three SNPs in a CCHC-type zinc finger protein gene are linked to a net form net blotch resistance 3H QTL in Shyri. S. XUE, M. D. HOLTZ, J. BUSAAN, T. K. TURKINGTON AND J. ZANTINGE. Field Crop Development Centre, Alberta Agriculture and Forestry, 5030–50 Street, Lacombe, AB T4L 1W8, Canada; and (J.B., T.K.T.) Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Net form net blotch (NFNB), caused by Pyrenophora teres f. teres (Ptt), is one of the major barley leaf diseases in North America. Identifying diagnostic molecular markers linked to NFNB resistance QTLs/genes is necessary for improving popular barley varieties which contain insufficient resistance to NFNB. Through genotyping by sequencing (GBS), we found three SNPs in one CCHC-type zinc finger (zinc knuckle) family protein gene that are linked to a QTL for adult plant NFNB resistance on chromosome 3H in ‘Shyri’. Physical mapping indicated that this shyri_QRptt3 QTL is different from the 3H QTLs previously reported. The QTL shyri_QRptt3 accounted for up to 20.6% of phenotypic variations in NFNB severity, and the lines containing this QTL showed an average of 51% less NFNB than the lines without this QTL. This QTL is an additional major QTL for adult plant NFNB resistance after the two adult plant resistance 6H QTLs reported previously by two research groups. Whether the CCHC-type zinc finger (zinc knuckle) family protein gene is involved in the resistance remains a question for investigation.
Using the dimorphic sequences in Plasmodiophora brassicae genes as markers for pathotype differentiation. Y. YANG, K. ZAHR, K. ZUZAK, M. HARDING, S. F. HWANG, S. E. STRELKOV, D. FEINDEL AND J. FENG. Crop Diversification Centre North, Alberta Agriculture and Forestry (AAF), 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; (M.H.) Crop Diversification Centre South, AAF, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; and (S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Genetic markers for Plasmodiophora brassicae Woronin pathotype differentiation would be extremely useful, but are not currently available. An attempt to discover pathotype markers was undertaken by screening sequence polymorphisms on 85 P. brassicae protein coding genes. Sequences from 85 expressed sequence tag (EST) of a New Zealand strain were compared with their corresponding sequences in the two released whole genomes. Of the identified differences in all genes, approximately 80% were dimorphisms falling into two distinct groups: Group 1 was formed by the New Zealand strain and Group 2 included the two whole genome sequenced strains. Two genes with a high density of dimorphism were selected and their partial sequences were PCR amplified from the original Alberta pathotypes 2, 3, 5, 6 and 8 (based on the Williams’ differential set) and the new virulent pathotypes 3x and 5x. For each of the two genes, the sequences of the original pathotypes were identical to those of Group 2 and the sequences of the new virulent pathotypes were identical to those of Group 1. Based on the dimorphisms on the sequences of these two genes, an RNase H-dependent PCR protocol was developed. This protocol was demonstrated to be useful for virulent pathotype identification and may also be used to study the population dynamics of P. brassicae.
Pathogenicity and genetic diversity of Rhizoctonia solani isolates from field pea and other crops in Alberta, Canada. H. T. YU, Q. ZHOU, H. T. FU, K. F. CHANG, S. F. HWANG AND S. E. STRELKOV. Institute of Food Crops, Yunnan Academy of Agricultural Science, Kunming, Yunnan, 650 205 China; (Q.Z., H.T.F., K.F.C., S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, 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
Root rot is a major constraint to the production of field peas (Pisum sativum L.) and other pulse crops around the world. In Western Canada, Rhizoctonia solani Kuhn was identified as one of the major pathogens of the root rot complex that causes the disease. In the summer of 2016 and 2017, a total of 66 isolates of R. solani were isolated from diseased pea and soybean plants and soil samples in central Alberta. The isolates could be classified based on their anastomosis behaviour against tester isolates (AG grouping). When tested on the field pea cv. ‘Midas’, five isolates showed no aggressiveness (disease severity of 0.00) while nine isolates were highly aggressive to pea with disease severity ranging from 3.0–3.7. The remaining 52 isolates resulted in disease severity ratings between 0.03 and 2.50. A phylogenetic analysis based on the rDNA ITS sequences among the isolates was also carried out. The differential pathogenicity of the identified isolates showed the existence of a wide spectrum of R. solani in Alberta.
A molecular marker for specific detection of new pathotype 5-like strains of Plasmodiophora brassicae in canola. Q. ZHOU, S. F. HWANG, S. E. STRELKOV, R. FREDUA-AGYEMAN AND V. P. MANOLII. Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; and (S.E.S., V.P.M.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Clubroot of canola (Brassica napus L.), caused by Plasmodiophora brassicae Woronin, is primarily managed by the deployment of resistant cultivars in Alberta, Canada. Recently, however, new strains of P. brassicae have been detected, which can overcome this resistance. Some of these strains are classified as pathotype 5 based on the differential system of Williams, but are distinguished by their ability to overcome resistance in cultivars which were previously resistant to pathotype 5. In order to expedite the identification of these new pathotype 5-like strains, three primer sets were developed based on the 18S-ITS region of the pathogen. With one of the primer sets (P5XF3 and P5XR3), a 127-bp product was amplified from all new pathotype 5-like strains following optimized PCR analysis. Together with a TaqMan probe (P5XP3) and primer set (P5XF3/P5XR3), a quantitative assay also was developed. Host infection could be detected as early as 4 days after inoculation. Samples containing ≤ 500 fg of P. brassicae DNA, and as few as 1 × 104 mL−1 pathogen resting spores could be consistently detected using these primers and PCR protocol. The PCR and qPCR assays described in this study represent useful tools for the rapid and reliable diagnosis and quantification of new pathotype 5-like strains of P. brassicae.
Evaluation of qPCR primers for clubroot diagnosis. K. A. ZUZAK, D. C. RENNIE, Y. YANG, M. W. HARDING, D. FEINDEL AND J. FENG. Crop Diversification Centre North, Alberta Agriculture and Forestry (AAF), 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada; and (M.H.) Crop Diversification Centre South, AAF, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
To select a quantitative PCR (qPCR) protocol for routine diagnosis of the clubroot pathogen Plasmodiophora brassicae Woronin in the Alberta Plant Health Lab, 12 primer sets were evaluated for their specificity and sensitivity. Ten of these primer sets were developed in this study based on the sequences of the ribosomal DNA (rDNA) region or single-copy protein coding genes of P. brassicae, while the other two primer sets were selected from literature. Sensitivity was tested using serial dilutions of the P. brassicae DNA. Specificity was tested against the DNA extracted from organisms commonly associated with canola roots in the field conditions, including fungi, bacteria and other protists. The data indicated an inverse relationship between the sensitivity and the specificity of the primers. In general, primers targeting a single-copy gene have higher specificity but lower sensitivity than the primers targeting the rDNA region (multiple copies). Based on these data, we recommend using at least one pair of the single-copy gene primers to confirm the results from rDNA-based primers in the diagnosis of clubroot.