A survey of pea diseases in Alberta in 2018. D. A. BURKE, G. C. DANIELS, S. CHATTERTON, C. VUCUREVICH, R. BOWNESS, T. DUBITZ AND M. W. HARDING. Crop Diversification Centre South, Alberta Agriculture and Forestry (AAF), 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.) Lacombe Research Centre, AAF, 6000C & E Trail, Lacombe, AB T4L 1W1, Canada
A survey of diseases on field pea (Pisum sativum L.) was performed in Alberta in 2018. Disease prevalence, incidence and severity was recorded for root rot, mycosphaerella blight and bacterial blight in 74 fields. Within each field, 100 plants were examined for foliar diseases and 25 to 50 roots were evaluated for root rot symptoms. Diseases were characterized visually based on root discolouration and foliar lesions. Disease severities were estimated using published disease rating scales ranging from 1 to 7 where a rating of ‘1ʹ represented no visible disease symptoms, through to a rating of ‘7ʹ which represented extreme disease severity, and often plant death. Root rots were present in 90% of fields with average disease incidence and severity of 55% and 2.0, respectively. Mycosphaerella blight was present in 66% of fields with average incidence and severity of 53% and 2.0, respectively. Bacterial blight was observed at trace levels in two fields. These results represent a slight decline in root rot and mycosphaerella blight and an extreme decline in bacterial blight when compared with survey results reported in 2017.
Seasonal and regional variability of pea root rot and yield in field trials naturally infested with Aphanomyces euteiches in Alberta. S. CHATTERTON, R. BOWNESS AND M. W. HARDING. Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403-1 Avenue South, Lethbridge, AB T1J 4B1, Canada; (R.B.) Lacombe Research Centre, Alberta Agriculture and Forestry (AAF), 6000C & E Trail, Lacombe, AB T4L 1W1, Canada; and (M.W.H.) Crop Diversification Centre South, AAF, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
Aphanomyces root rot, caused by Aphanomyces euteiches Drechs., was first detected in pea (Pisum sativum L.) fields in Saskatchewan and Alberta in 2012 and 2013, respectively, and has caused significant crop loss in both provinces. Currently, extending the cropping interval between susceptible crops and avoiding infested fields are the only root rot management recommendations. Field trials were conducted in four locations in Alberta from 2015–2018 to determine the effects of various seed treatments. Trial sites were located in producers’ fields that last had peas in 2014 and were identified to have high levels of natural inoculum of A. euteiches and Fusarium spp., based on root rot ratings during the 2014 growing season. Trials were conducted in the same fields but research plots were placed at unique sites within the naturally infested fields every year, with some exceptions due to producer practices. Some seed treatment products provided early season suppression of root rots at some locations, but did not result in significant yield differences. Average yields across all treatments varied from 0 to > 4000 kg ha−1 at different locations, regardless of disease pressure, emphasizing the seasonal and regional variability of root rot severity, and difficulties assessing impacts of root rots on pea yields. At some locations yields improved slightly as the length of time out of peas increased, but root rot severity did not, except at one location. Results highlight the long-term impact of A. euteiches on yield loss, and the lack of effective management options for this destructive pathogen.
Prevalence and distribution of Fusarium graminearum chemotypes in Alberta corn fields from 2015 to 2017. G. C. DANIELS, C. A. PUGH, M. KUNDU, C. L. MCCONNELL, K. ZUZAK, J. FENG AND M. W. HARDING. Crop Diversification Centre South, Alberta Agriculture and Forestry (AAF), 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; and (K.Z., J.F.) Alberta Plant Health Laboratory, AAF, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Fusarium graminearum Schwabe causes stalk and ear rot of corn (Zea mays L.). From 2015 through 2017, samples consisting of 100 lower-stem nodes were collected from ~1% of Alberta corn fields. Over the three years, 37, 43 and 135 samples were collected, respectively. Nodes were surface sterilized, dissected and cultured on acidified potato dextrose agar. The fungal colonies obtained were sub-cultured to fresh plates and single-spore isolates were generated, identified to species by multiplex PCR, and tested to determine their chemotypes. The prevalence of F. graminearum within the province was 70.3%, 73.8% and 46.6% over the three seasons. The 15-ADON chemotype was present in 92.3%, 87.1% and 92.7% of the fields where F. graminearum was identified, while the 3-ADON chemotype was present in 26.9%, 35.5% and 18.2% of these fields, respectively. Overall, the disease prevalence for the province dropped in 2017 due to large increases in corn acreage reported in the 2016 agricultural census. Many areas with increased corn production do not yet display a high prevalence of the pathogen. F. graminearum prevalence remains highest in southern Alberta, but this report, and others, demonstrate that it is becoming more prevalent in other areas of the province. This report also highlights that while the incidence of head blight in wheat may fluctuate dramatically from year to year due to weather, F. graminearum stalk rot on corn does not.
Identification of the durable blackleg resistance loci in Chinese and Canadian canola germplasm through genome-wide association analysis. F. FU, X. ZHANG, F. LU, G. PENG, F YU AND W. D. G. FERNANDO. Department of Plant Science, 222 Agriculture Building, 66 Dafoe Road, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; and (G.P., F.Y.) Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
The fungal pathogen Leptosphaeria maculans (Desmaz.) Ces. & De Not. causes blackleg disease on canola in many parts of the world. It is important to use resistant cultivars to manage the disease and minimize yield losses. In this study, a total of 13 L. maculans isolates from western Canada were used to identify and map resistance genes in a collection of 243 canola/rapeseed germplasm from Canada and China. These isolates showed different complements of avirulence genes, and the investigation was based on a genome-wide association study (GWAS) and genotype-by-sequencing (GBS). A total of 5 583 338 variants were identified using the CROP-SNP pipeline, including 5 102 201 SNPs and 481 137 InDels. GWAS was performed using the TASSEL 5.0 with GLM + Q model. Thirty-two and 13 SNPs tightly associated with blackleg resistance were identified respectively from the Canadian and Chinese germplasm with a P value < 1 × 10−4. These SNP loci were distributed on chromosomes A03, A05, A08, A09, C01, C04, C05 and C07, with the majority of them on A08 followed by A09 and A03. Those significant SNPs identified on A08 were all located in a 2010-kb region and associated with the resistance to 12 of the L. maculans isolates. This study provides insights into potentially new regions for discovery of additional blackleg resistance genes. Resistance loci identified in this study may provide new resistant resources for blackleg resistance breeding in canola.
Adapting agronomic practices to changing climates through ‘System Integration’. Y. GAN AND H. CUTFORTH. Swift Current Research and Development Centre, Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, SK S9H 3X2, Canada
Agriculture in western Canada faces significant challenges with changing climates, variable weather patterns, increased production costs and threats of various biotic stresses. For example, in southwestern Saskatchewan, the maximum air temperature has increased from 9.0°C in 1950 to 10.2°C in 2017 and the minimum temperature increased from −3.2°C to −0.7°C. Accumulated January–April precipitation decreased by 26 mm while May–August precipitation increased by 54 mm. These changes may have direct or indirect impacts on cropping systems with various consequences. Effective strategies/practices are needed to alleviate these challenges. Here, we discuss one of the promising approaches – adapting ‘system integration’ to increase crop productivity and improve resource use efficiency but without extra cost to the environment. Decades of research at Agriculture and Agri-Food Canada Swift Current Research and Development Centre reveal that the following practices are key to achieving significant, positive outcomes: (i) managing microclimates under field conditions through stubble height and straw management to improve WUE and water productivity; (ii) comparing rooting systems (root length, volume, diameter, etc.) of different crops to define crop rotation sequences; (iii) promoting uniform seedling establishment to improve resource use efficiencies (land area, soil water and nutrients); (iv) diversifying crop rotations to buffer biotic risks; (v) including N2-fixers in rotation to convert atmospheric N2 to plant available N and thus reducing synthetic fertilizer input; and (vi) exploring intercropping, relay-cropping and ‘gene-mixing’ cropping opportunities to enhance system resilience.
Rhynchosporium commune and Pyrenophora teres: screening for resistant barley varieties at the Lacombe Research and Development Centre. K. C. GARLAND, N. E. RAUHALA, J. L. BUSAAN AND T. K. TURKINGTON. Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Leaf diseases in barley can affect the overall yield of the crop by 20–40% in a single field. This decrease in yield is due to reduced photosynthetic area on the leaves. Scald and net blotch are particularly prominent leaf diseases on the Canadian prairies, caused by the fungi Rhynchosporium commune and Pyrenophora teres respectively. Resistant varieties are an economic and environmentally friendly solution to combat leaf disease. To test new varieties for resistance, three disease nurseries were set up at the Lacombe Research and Development Centre, each independently testing for scald, net-form net blotch and spot-form net blotch reactions. There were 6000–8000 hill plots in the scald nursery, and 1000–1500 hill plots in each net blotch nursery. Hill plots were hand seeded in the spring and inoculated twice in early and mid-June. Diseased straw was spread over the nursery sites to provide a source of infection. Additionally, the scald nursery was sprayed with a suspended R. commune isolate solution, while the net blotch nurseries were inoculated with autoclaved winter wheat grain infested with either P. teres f. teres, or P. teres f. maculata. In July, each hill plot was rated using a 0–9 scale: where 0 = no disease symptoms and 9 = 50+% infection level of lower, middle and upper canopy. Results and recommendations from these ratings were sent back to breeders for use in assessing levels of resistance and for consideration when determining which lines to advance.
Disease trends in wheat, canola and pea in Alberta from 2015 to 2018. M. W. HARDING, S. CHATTERTON, R. ABOUKHADDOUR, H. BENNYPAUL, S. E. STRELKOV AND T. GRÄFENHAN. Alberta Agriculture and Forestry, Crop Diversification Centre South, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (S.C., R.A.) Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403-1 Avenue South, Lethbridge, AB T1J 4B1, Canada; (H.B.) Centre for Plant Health, Canadian Food Inspection Agency, 8801 East Saanich Road, North Saanich, BC V8L 1H3, Canada; (S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (T.G.) Canadian Grain Commission, 1404-303 Main Street, Winnipeg, MB R3C 3G8, Canada
Diseases on cultivated crops can fluctuate significantly from one season to another. The amount of disease seen in a given year changes due to variables such as introduction or loss of host resistance, pesticide applications, pesticide resistance, and crop rotation and sequence. In addition, crop disease risks can change dramatically due to weather-related parameters such as temperature, rainfall and relative humidity which exhibit high spatio-temporal variability. These weather parameters varied significantly in Alberta each year between 2015 and 2018. Some crop diseases such as fusarium head blight and white mould benefited from the above-average rainfall and humidity in 2016, whereas clubroot detections were greater in years with higher temperatures. Finally, for diseases such as stripe rust and wheat streak mosaic, overwinter survival was affected by winter weather. This presentation reported disease trends for the 2015–2018 period for eight diseases on four crops; fusarium head blight, wheat streak mosaic and stripe rust on wheat, clubroot, blackleg and sclerotinia on canola, root rot on pea and white mould on dry bean. Disease levels were correlated with historical weather information that may have played a role in the annual increases or decreases in disease incidence or severity.
Survey for blackleg on canola in southern Alberta in 2018. T. B. HILL, C. A. PUGH, C. MCCONNELL, G. C. DANIELS, D. A. BURKE, J. FENG, K. ZUZAK 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.) Crop Diversification Centre North, AAF, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
A survey for blackleg disease on canola, caused by Leptosphaeria maculans (Desmaz.) Ces. & de Not., was performed in Alberta in 2018. A target of 1% of canola fields in the province, or 385 canola fields in 65 counties, were to be surveyed. Within each field surveyed, 20 stems were collected from five locations for a total of 100 stems per field. 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. At the time this abstract was prepared, data from 136 fields were available. Blackleg symptoms were observed in 77.9% of fields at an average incidence of 13.27% and average severity of 0.24. These results were very similar to those reported in 2017 for blackleg prevalence and incidence in Alberta which were 80%, 14.1%, respectively. Interestingly, the average severity of blackleg in 2018 from the 136 fields available was nearly five times greater than the severity reported in the 2017 survey.
Assessing the potential of managing root rot with nitrogen fertilizer and an arbuscular mycorrhizal fungal product in three Saskatchewan environments. M. HUBBARD, Y. GAN, G. PENG, W. MAY AND L. D. BAINARD. Swift Current Research and Development Centre (SCRDC), Agriculture and Agri-Food Canada (AAFC), P.O. Box 1030, Swift Current, SK S9H 3X2, Canada; (G.P.) Saskatoon Research and Development Centre, AAFC, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; and (W.M.) SCRDC, Indian Head Research Farm, AAFC, P.O. Box 760, Indian Head, SK S0G 2K0, Canada
Root rot is a major constraint to the production of pea and lentil. The disease is often caused by Aphanomyces euteiches Drechsler. It is not effectively controlled by synthetic fungicide seed treatments and genetic resistence is not available in pea or lentil. Currently, the only management recommendation is extended rotations away from susceptible crops. Thus, assessment of other approaches for reducing losses from Aphanomyces is urgently needed. Field studies, conducted at three sites in Saskatchewan with differing climates and soil types, were used to evaluate whether the application of nitrogen fertilizer or a commercial arbuscular mycorrhizal fungal (AMF) product could reduce root rot severity in pea. A greenhouse study, using soil from the three field sites, was conducted in parallel to the field trials. In two of the three field sites, nitrogen fertilization at seeding reduced one of the two disease severity metrics, without impacting nodulation. In the greenhouse, application of nitrogen fertilizer failed to reduce root rot. However, it increased root and shoot biomass in some of the field soils, without decreasing nodulation. The AMF inoculant did not alter any of the parameters measured in the field or greenhouse, relative to untreated controls. These results suggest that the AMF inoculant is not an effective tool for Aphanomyces root rot management. However, under some conditions, nitrogen fertilization may reduce root rot severity and/or ameliorate yield losses. Further study is merited to better understand the conditions in which nitrogen application to pulse crops in Aphanomyces-infested soils might be advantageous.
The roles of auxin, ethylene and abscisic acid in clubroot development in Brassica napus. C. P. JAYASINGHEGE, V. P. MANOLII, J. A. OZGA, S. F. HWANG AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, 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
The manipulation of plant hormones by the obligate parasite Plasmodiophora brassicae Woronin, causal agent of clubroot of crucifers, is believed to drive the formation of root galls in susceptible plants. The activation of plant defence mechanisms and disease-associated plant stress responses also modulate the hormone profile and hormone action in infected plants. To improve understanding of the roles of auxin, ethylene and abscisic acid (ABA) in clubroot development, the levels of these hormones and associated catabolites and precursors were investigated in susceptible and resistant canola (Brassica napus L.) cultivars. No clear association between pathogen infection and the root hormone profiles was observed in either canola cultivar at 4 and 14 days after inoculation (DAI) with P. brassicae. By 21 DAI, however, the level of ABA and its catabolites phaseic acid (PA) and dihydrophaseic acid (DPA) was increased in susceptible inoculated plants relative to non-inoculated controls. The level of ethylene precursor 1-aminocyclopropane-1-carboxylic acid also was higher in both the susceptible and resistant cultivars following inoculation, suggesting an increase in root ethylene biosynthesis in response to P. brassicae infection. Despite being considered an important player in root gall development, no change was detected in root auxin levels, except for a decline in inoculated susceptible plants by 21 DAI. This suggests that gall formation is not directly triggered by an increase in root auxin.
Virulence of Puccinia striiformis on wheat and barley in central Alberta during 2015–2017. K. KUMAR, K. XI, T. K. TURKINGTON AND F. CAPETTINI. Field Crop Development Centre, Alberta Agriculture and Forestry, 5030-50 Street, Lacombe, AB T4L 1W8, Canada; and (T.K.T.) Lacombe Research and Development Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Stripe rust of wheat and barley, caused by Puccinia striiformis f. sp. tritici (Pst) and P. striiformis f. sp. hordei (Psh), respectively, has devastated cereal production worldwide. Over the last decade, virulent pathotypes have shown up more often, and spread more aggressively on Alberta farms. The objective of this study was to differentiate the two pathogens and identify virulence in each forma specialis. From 2015–2017 in central Alberta 140 isolates collected from wheat, barley, foxtail barley and triticale were phenotyped on wheat and barley differentials. Based on this phenotyping, 48 of the 55 isolates sampled from barley were classified to be Psh and seven were Pst; all 85 isolates from wheat were classified to be Pst using cluster analysis. These results indicate the occurrence of cross-infection between wheat and barley by the two pathogens. Fifty-four Pst and 26 Psh pathotypes were identified and a few new Psh and Pst pathotypes were also identified from the 140 isolates. Temporal changes in virulence frequency were apparent when Psh and Pst isolates collected from the period of 2007–2017 were compared. From 2015–2017, the virulence frequency increased on six barley differentials with the current Psh isolates, but from 2007–2014 there was less virulence on five of the 12 barley differentials. The Psh isolates from the 2015–2017 collection exhibited an increased virulence frequency in 24 of the 26 wheat differentials, as compared with the 2007–2014 collection.
Developing a droplet-digital PCR-based protocol for rapid screening of quantitative resistance against blackleg of canola. L. MCGREGOR, X. LIU, E. LEMKE AND G. PENG. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Blackleg, caused by Leptosphaeria maculans (Desmaz.) Ces. & De Not, is a serious disease of canola in western Canada. Cultivar resistance, including quantitative resistance (QR), is the key for blackleg management. The current methods of screening QR rely mostly on extensive field trials, which can be laborious and sometimes give inconsistent results. In earlier work, we used droplet-digital PCR (ddPCR) to quantify L. maculans DNA in inoculated petioles and stems of canola, and found that the amounts correlated well with the severity of stem infection on four cultivars with variable levels of QR under greenhouse conditions. The aim of this project was to assess the relevance of pathogen colonization and development in canola stem (based on ddPCR) to blackleg resistance, especially QR, in commercial canola cultivars/lines based on multi-year field trial data. Cotyledon or petiole (1 cm from the stem) was inoculated with a L. maculans isolate carrying AvrLm6,7 at 7 days (cotyledon) or 14 days post seeding (petiole). The resistance gene Rlm6 or Rlm7 was generally absent in these canola cultivars/lines. Stem tissues close to the inoculated cotyledon or petiole were sampled 14 days post inoculation for fungal DNA quantification using ddPCR. About 50 lines were tested and the data were compared against the resistance performance in field trials using correlation and regression analyses. Preliminary results have shown a positive correlation between the amount of L. maculans DNA in stem tissues and the average field disease ratings against the standard susceptible control ‘Westar’.
Climate change and its impact on diseases of winter wheat in the northwestern USA. T. D. MURRAY. Department of Plant Pathology, P.O. Box 646430, Washington State University, Pullman, WA 99164-6430, USA
Washington State has the fourth highest wheat production in the USA. Wheat is the third most valuable crop produced in the state. High yields result from moderate temperatures and favourable distribution of rainfall during the growing season. Regional climate is strongly influenced by the Pacific Ocean, which results in relatively mild winter temperatures for this latitude and is transitional between southerly temperate climates. Consequently, changes in climate have potential to impact wheat production through its impact on biotic stresses. More than eight diseases regularly impact wheat production in Washington. Among these is speckled snow mould, caused by Typhula ishikariensis. Snow mould is prevalent in the north-central wheat-producing area of Washington where snow falls on unfrozen or lightly frozen soil and persists for 100 days or more. Persistent snow cover does not occur every year in this area; therefore, increasing winter temperatures and decreasing snow cover resulting from climate change will result in less frequent occurrence of snow moulds. Other chronic diseases in the Pacific North West including Cephalosporium stripe (Cephalosporium gramineum), eyespot (Oculimacula yallundae, O. acuformis), and stripe rust (Puccinia striiformis) are also strongly influenced by winter weather and will likely become more prevalent in areas where snow moulds now occur as winter temperatures increase. Interactions between plant diseases and environmental conditions are complex; shifts in geographic distribution, frequency of occurrence, and severity of other diseases should be expected in response to changes in winter climate. Anticipating changes and developing varieties with effective resistance are important strategies to prevent future losses.
Detection and evaluation of the residual effect of defeated stripe rust resistance genes (Yr genes) in wheat. K. NABETANI, K. WIEBE, C. J. POZNIAK, R. ABOUKHADDOUR AND H. R. KUTCHER. Department of Plant Sciences, University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada; and (R.A.) Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada, 5403 1st Ave South, Lethbridge, AB T1J 4B1, Canada
Race-specific stripe rust resistance genes (Yr genes) have been deployed into wheat cultivars against stripe rust caused by Puccinia striiformis f. sp. tritici Eriks. (Pst); however, in many cases the resistance has broken down only a few years after its introduction. Near isogenic lines (NILs) with defeated Yr genes in the susceptible cv. Avocet background were used in this study to evaluate residual effects of these genes. The parental NILs with the single Yr genes, Yr10, Yr26 and Yr32, the NILs with gene combinations of Yr32/Yr10, Yr32/Yr26 and Yr26/Yr10 and ‘Avocet’ were inoculated under controlled conditions with Pst isolates, W020, W049 and mixture of T034/W052, all virulent to all three Yr genes. The infection type (IT), infection area (IA) and latent period (LP) were recorded. The same NILs were tested in stripe rust nurseries at Saskatoon, SK and Lethbridge, AB in 2018 and disease incidence and severity were recorded. Under the controlled conditions the range of IT scores tended to be lower in NILs with Yr32/Yr10 and Yr32/Yr26 gene combinations with the isolate combination T034/W052. The IA was reduced more often in the NILs carrying Yr32/Yr10 and Yr32/Yr26 gene combinations than the Yr26/Yr10 gene combination. Increased LP was negatively correlated with reduced IA. In field disease nurseries, genotypically identical NILs varied in resistance level; however, NILs with Yr32/Yr10 and Yr32/Yr26 combinations usually had lower disease incidence and severity than NILs with Yr26/Yr10. These data suggest that there may be a residual effect of defeated Yr genes in wheat.
Managing blackleg of canola in western Canada:an integrated approach. G. PENG, W. SOOMRO, M. HUBBARD, C. ZHAI, X. LIU, L. MCGREGOR, W. G. D. FERNANDO, R. LANGE, F. YU AND D. MCLAREN. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada (AAFC), 107 Science Place, Saskatoon, SK S7N 0X2, Canada; (D.W.G.F.) Department of Plant Science, 222 Agriculture Building, 66 Dafoe Road, University of Manitoba, Winnipeg, MB R3T 2N2, Canada; (R.L.) InnoTech Alberta, P.O. Bag 4000, Vegreville, AB T9C 1T4, Canada; and (D.M.) Brandon Research and Development Centre, AAFC, 2701 Grand Valley Road, Brandon, MB R7C 1A1, Canada
Blackleg of canola (Brassica napus L.), caused by the fungal pathogen Leptosphaeria maculans (Desmaz.) Ces. & de Not. increased noticeably in western Canada in the past several years. While most canola cultivars are registered as resistant to blackleg, Rlm1 and Rlm3 have been the only specific resistance (R) genes found in commercial varieties. Field monitoring has found that the avirulent genes AvrLm1 and AvrLm3 are at very low levels in most areas, while AvrLm4, AvrLm6 and AvrLm7 are relatively abundant at about 60–100% in pathogen populations. This indicates additional resistant mechanisms at works in commercial fields. When inoculated with L. maculans isolates carrying no AvrLm1 and AvrLm3, most canola cultivars showed a moderate level of resistance to infection relative to ‘Westar’ (susceptible); pathogen spread from infected cotyledons to stem was limited and infection development in stem was also reduced. This indicates quantitative resistance (QR) for these cultivars. RNA-seq data indicate that the resistance mediated by Rlm1 showed that jasmonic-acid and salicylic-acid pathways were activated, whereas QR or race-nonspecific resistance seemed to be related to genes involved in programmed cell death and ROS. QR was also stable under high temperature conditions (~32°C daytime high). Due to a much shorter growing season (75–100 days), relative to many other canola-growing regions in the world, early infection is probably the key to causing severe blackleg impact in western Canada. This underscores the importance of fungicide timing for blackleg management. These issues were discussed in light of new data.
The impact of barley variety rotation, mixtures and intercropping on leaf disease and silage production. T. K. TURKINGTON, K. XI, H. KLEIN-GEBBINCK, K. N. HARKER, J. T. O’DONOVAN, R. BLACKSHAW, T. MCALLISTER AND N. LUPWAYI. Lacombe Research and Development Centre, Agriculture and Agri-Food Canada (AAFC), 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; (K.X.) Field Crop Development Centre, Alberta Agriculture and Forestry, 5030-50 Street, Lacombe, AB T4L 1W1, Canada; and (R.B., T.M., N.L.), Lethbridge Research and Development Centre, AAFC, 5403-1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Western Canadian barley silage producers, whether they are meeting on-farm needs or local market opportunities, will often look at continuous barley production, which leads to productivity issues related to leaf disease development. Although fungicides can be used, they represent an added input cost for silage producers. The objective of the current study was to determine the effects of monocultures, mixtures, intercropping and rotational diversity on crop health and productivity in a cereal silage production system. Three year rotational treatments were established in 2008 at Lacombe, Alberta with a final combined comparison for 2010, 2013 and 2016. 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, 2013 and 2016, all treatments had the six-row barley variety ‘Sundre’. Leaf disease severity on ‘Sundre’ was highest for continuous ‘Sundre’, and lowest for mixtures or intercrops with different varieties. Silage yields were lowest for continuous ‘Sundre’, highest for the intercropping treatments with the same or different varieties each year, and intermediate for barley mixtures where the variety components changed each year. Results suggest that adding diversity in crop types and/or barley genetics may reduce leaf disease and improve silage productivity.
Screening of Brassica species for resistance to Plasmodiophora brassicae (clubroot) pathotype 5X. J. WANG, Y. ZHANG, M. KEHLER, A. DAKOURI, S. E. STRELKOV, S. F. HWANG, B. D. GOSSEN, G. PENG AND F. YU. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; (S.E.S.) 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 Rural Development, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Clubroot, caused by the soil-borne parasite Plasmodiophora brassicae Woronin, is associated with the formation of clubs or galls on the roots of susceptible hosts. The disease is a significant problem on Brassica crops worldwide, and is most commonly managed by planting resistant cultivars. In recent years, however, new pathotypes of P. brassicae have been identified that can overcome the resistance in most cultivars. A screening study was conducted to identify sources of resistance to one of these new pathotypes, 5X. Two hundred and eighty-six B. napus lines, 43 B. oleracea lines and 57 B. nigra lines were tested for resistance by inoculation with resting spores of pathotype 5X under controlled environmental conditions. A total of 15 B. napus, three B. oleracea and three B. nigra lines were found to be resistant, with a disease severity index (DSI) < 20%. Further research is being carried out to determine the genetic basis of this resistance, while additional lines and accessions are being screened.
Yield losses of canola caused by blackleg and pyraclostrobin sensitivity in populations of Leptosphaeria maculans. Y. WANG, S. F. HWANG, A. AKHAVAN, H. AHMED, G. D. TURNBULL AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, Edmonton, AB T6G 2P5, Canada; and (S.F.H., H.A., G.D.T.) Crop Diversification Centre North, Alberta Agriculture and Forestry, 17507 Fort Road NW, Edmonton, AB T5Y 6H3, Canada
Blackleg of canola (Brassica napus L.), caused by Leptosphaeria maculans (Desm.) Ces. & de Not., is an important disease worldwide. In Canada, blackleg is managed mainly by the cultivation of resistant or moderately resistant canola hybrids and fungicide application. A field experiment was conducted in central Alberta to determine the relationship between blackleg severity and yield in two moderately resistant hybrids ‘73-15RR’ and ‘1950RR’. Seed yield per plant was found to decrease as a consequence of L. maculans infection, with regression analysis showing that the relationship between yield and disease severity was best explained by second degree quadratic equations. Sensitivity to the fungicide pyraclostrobin, a strobilurin that is commonly applied as a foliar and seed treatment for blackleg and other diseases, was evaluated in 12 and 250 isolates of L. maculans collected in Alberta in 2011 and 2016. The half-maximal effective concentration (EC50) of pyraclostrobin was determined, and two discriminatory doses of the fungicide were used to identify highly insensitive isolates in the collection. The mean EC50 value was significantly higher for the isolates collected in 2016 (0.28 mg L−1) versus those collected in 2011 (0.07 mg L−1). Nonetheless, while all isolates were still sensitive to pyraclostrobin, the increase in mean EC50 observed in the more recent L. maculans collections suggests that proper fungicide stewardship is warranted.
Transcriptome analysis of Brassica napus lines carrying single and double clubroot resistance genes against the Plasmodiophora brassicae pathotype X-LG2 (5X). R. WEN, J. LEE, K. HORNADAY, N. TONU, T. SONG, F. YU AND G. PENG. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Clubroot, caused by the obligate biotrophic pathogen Plasmodiophora brassicae Woronin, is one of the most important diseases of Brassica crops worldwide. Growing cultivars carrying clubroot resistance (CR) genes is the most effective and practical approach to managing clubroot disease on canola, but the CR sources are limited. Transcriptome analysis was carried out of three Brassica napus L. lines carrying a single CR gene located in (i) chromosome A03 (Rcr1, line 16), (ii) A08 (similar to Crr1, line 20) or (iii) carrying both CR genes (line 15) against P. brassicae pathotype X-LG2 (previously 5X). Bioassay results showed that line 16 was susceptible, while both lines 15 and 20 were moderately resistant to the X-LG2. Functional annotation of the differentially expressed genes (DEGs) involved biological processes such as response to stress, biosynthesis and signal transduction. Venn diagram analysis showed that lines 15 and 20 shared many DEGs, but these DEGs often were not found in line 16. Enrichment analysis revealed that 286 DEGs were involved in defence responses, including those associated with pathogen-associated molecular patterns (PAMPs), activation of innate immunity, hormone signalling, transcription factors, and cell wall modification. These results indicate that the intermediate level of resistance against pathotype X-LG2 conferred by the CR gene on A08 may function via activated PAMPs and effector trigged immunity. Interestingly, the transcription levels for the most DEGs involved in defence responses were much higher in line 15 than in line 20, indicating that the two CR genes together trigger a stronger defence response than either gene alone.
Genome-wide association studies on the resistance of rutabaga accessions to Plasmodiophora brassicae isolates from Alberta, Canada. Z. YU, R. FREDUA-AGYEMAN, S. F. HWANG AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, Edmonton, AB T6G 2P5, Canada; and (R.F.-A., 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 a devastating soil-borne disease of Brassica crops worldwide. In this study, genomic regions associated with resistance to five single-spore isolates (classified as pathotypes 2F, 3H, 5I, 6M and 8N) and 12 field isolates (classified as pathotypes 2B, 3A, 3O, 5C, 5G, 5K, 5L, 5X, 8E, 8J and 8P) were investigated using 125 Brassica napus L. spp. napobrassica (swede or rutabaga) accessions. The accessions were screened for resistance in greenhouse inoculation experiments, while genotyping was carried out with a 15 K Brassica SNP array. The rutabaga accessions exhibited differential reactions towards the 17 isolates with 4.8–67.2% found to be resistant, 4.0–16.8% moderately resistant and 22.4–86.4% susceptible. About 32% of the 13 714 SNP markers used for genotyping were included in the association studies, while those that did not meet specific filtering criteria were discarded. One hundred and twenty SNPs (78 on A01–A10 and 42 on C genome scaffolds) were found to be significantly (P = 0.05) associated with resistance to the 17 P. brassicae isolates. The largest number (34) of SNPs associated with clubroot resistance was found on the A03 chromosome, which is consistent with the identification of at least four clubroot resistance genes on this chromosome. Between 3–10 SNPs were found on chromosomes A01, A02, A06 and A08, which also have mapped CR genes. The SNPs identified in this study will be important in the marker-assisted breeding of clubroot-resistant canola.
Introgression of disease resistance from Brassica nigra into canola. Y. ZHANG, J. WANG, M. KEHLER, G. PENG, B. D. GOSSEN AND F. YU. Saskatoon Research and Development Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Brassica nigra L. (genome BB) lines were identified to carry resistance to two important diseases of canola (B. napus L., genome AACC); clubroot caused by Plasmodiophora brassicae Woronin, and blackleg caused by Leptosphaeria maculans (Desmaz.) Ces. & De Not. Current sources of resistance to clubroot in Canadian canola cultivars were derived mostly from B. rapa L. (genome AA). Resistance genes from the A-genome of B. rapa or B. napus have also been used to develop canola cultivars resistant to blackleg. New sources of clubroot and blackleg resistance are required to manage these important diseases because virulent pathogen populations have been reported in western Canada that are able to overcome the resistance of canola cultivars for both diseases. In this study, a total of 497 F1 or BC1 embryos from interspecific crosses between the resistant B. nigra line CR2716 and the susceptible B. napus line DH 16156 were rescued by tissue culture to overcome pre-fertilization issues. Clubroot resistance genes against pathotype 2, 3, 5, 6, 8 and 5X were identified in this B. nigra line. Four SNP markers tightly linked to the resistance genes were developed and used for marker-associated selection in the backcross population. For blackleg, cotyledon inoculation was used for resistance assessment. To date, BC4 populations with putative resistance to clubroot (17 lines) and blackleg (nine lines) have been developed and additional analyses are in progress.