Genetic structure of Pyrenophora teres f. teres (net form of net blotch of barley) populations from the Canadian Prairies as revealed by simple sequence repeats analysis. A. AKHAVAN, T. K. TURKINGTON, B. KEBEDE, A. TEKAUZ, K. XI, R. KUTCHER, J. TUCKER, C. KIRKHAM, K. KUMAR, D.RENNIE AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; (T.K.T.) Lacombe Research Centre, Agriculture and Agri-Food Canada (AAFC), 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; (A.T.) Cereal Research Centre, AAFC, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada; (K.X., K.K.) Field Crop Development Centre, Alberta Agriculture, Food and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; (R.K.) Crop Development Centre, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada; (J.T.) Brandon Research Centre, AAFC, 18th Street North and Grand Valley Road, P.O. Box 1000A, R.R. #3, Brandon, MB R7A 5Y3, Canada; and (C.K.) Melfort Research Farm, AAFC, P.O. Box 1240, Melfort, SK S0E 1A0, Canada
A collection of 126 Pyrenophora teres Drechs. f. teres Smedeg. isolates from the Canadian Prairies were analysed to determine the genetic structure of pathogen populations from this region. A total of 94 alleles were detected among the isolates at 13 polymorphic simple sequence repeat loci, with 3–11 alleles per locus. High levels of diversity were found among the isolates with a clonal fraction of approximately 12%. Following clone-correction, a significant genetic differentiation (PhiPT = 0.038, P = 0.001) was detected among populations collected from Alberta, Saskatchewan and Manitoba, although analysis of molecular variance showed that 96% of the genetic variation occurred within populations and only 4% between populations. Employing the unweighted pair group method with arithmetic mean procedure and Jaccard’s similarity coefficient, cluster analysis revealed that isolates clustered in two main clades. Most isolates collected from Alberta (69%) grouped in the first clade, while most isolates collected from Saskatchewan (67%) grouped in the second clade. Isolates collected from Manitoba grouped in either clade in statistically equal numbers. The clonal fraction observed within the population, combined with an equal ratio of both pathogen mating types, suggests that P. teres f. teres goes through regular cycles of sexual recombination on the Prairies.
Genetic diversity of the spot form of the net blotch pathogen of barley (Pyrenophora teres f. maculata) on the Canadian Prairies as revealed by simple sequence repeats analysis. A. AKHAVAN, T. K. TURKINGTON, B.KEBEDE, A. TEKAUZ, K. XI, R. KUTCHER, J. TUCKER, C.KIRKHAM, K. KUMAR, D. RENNIE AND S. E. STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; (T.K.T.) Lacombe Research Centre, Agriculture and Agri-Food Canada (AAFC), 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; (A.T.) Cereal Research Centre, AAFC, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada; (K.X., K.K.) Field Crop Development Centre, Alberta Agriculture, Food and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; (R.K.) Crop Development Centre, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada; (J.T.) Brandon Research Centre, AAFC, 18th Street North and Grand Valley Road, P.O. Box 1000A, R.R. #3, Brandon, MB R7A 5Y3, Canada; and (C.K.) Melfort Research Farm, AAFC, P.O. Box 1240, Melfort, SK S0E 1A0, Canada
Microsatellite DNA markers were employed to investigate genetic variation among 82 isolates of Pyrenophora teres Drechs. f. maculata Smedeg. (causal agent of the spot form of net blotch) collected from barley on the Canadian Prairies. A total of 35 alleles were detected among the isolates at 13 polymorphic simple sequence repeat loci, with an average of 2.7 alleles per locus and a range of 1–5. High levels of diversity were found among the isolates with a clonal fraction of approximately 11%. Following clone-correction, both pairwise population PhiPT values and analysis of molecular variance showed no significant genetic differentiation (PhiPT = 0.010, P = 0.177) among populations collected from Alberta, Saskatchewan and Manitoba, with 99% of the total genetic diversity found within populations and only 1% between populations. Cluster analysis using the unweighted pair group method with arithmetic mean procedure and Jaccard’s similarity coefficient also resulted in no obvious clustering based on geographical origin of the isolates. These results combined with a high level of gene flow among the provinces suggest the occurrence of one singular panmictic Prairies population. Furthermore, the high number of distinct haplotypes combined with an equal ratio of both pathogen mating types indicates extensive sexual recombination in the Prairie P. teres f. maculata population.
Reaction of Tillage Radish (Raphanus sativus var. longipinnatus) to clubroot. T. CRANMER, B. D. GOSSEN AND M. R. McDONALD. Plant Agriculture, University of Guelph, 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
Tillage Radish (Raphanus sativus var. longipinnatus (Bailey) ‘Tillage Radish’) is a cruciferous crop that can enhance the yield of subsequent crops by building up top soil, increasing earthworm populations, and improving soil and plant health. Plasmodiophora brassicae Woronin, the causal agent of clubroot of crucifers, is an important pathogen of canola (Brassica napus L.) in Canada. There was a concern that resting spore populations of P. brassicae might build up on crops of ‘Tillage Radish’, to the detriment of subsequent canola crops. Therefore, the reaction of ‘Tillage Radish’ to Canadian pathotypes (pathotypes 2, 3, 5 and 6) of P. brassicae was assessed in a replicated growth room study. Shanghai pak choy (B. rapa subsp. chinensis var. communis) was included as a highly susceptible control. Plants were harvested at 6 weeks after seeding and were rated for clubroot severity using a standard 0–3 scale and a disease severity index (DSI) was calculated. ‘Tillage Radish’ remained free of symptoms throughout the study. Shanghai pak choy had a mean of 95.0% incidence (range 93–98%) and 91.7 DSI (range 88–95). These results indicate that ‘Tillage Radish’ will not contribute to the resting spore concentration of P. brassicae, and has potential for use as a cover crop in fields infested with P. brassicae.
Study on the interaction between clubroot resistant and susceptible cultivars. J. FENG, S. F. HWANG AND S. E. STRELKOV. 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
Clubroot, caused by Plasmodiophora brassicae Woronin, is an important root disease of crucifers worldwide. Without a host, the resting spores of the pathogen can persist in the soil for as long as 20 years, until suitable environmental factors induce their germination. These factors include not only the physical and chemical components of the soil environment, but also biological signals from the host, which are components of the root exudates. To study the interactions of resistant and susceptible canola genotypes on the development of the pathogen during clubroot infection, experiments were conducted by seeding resistant and susceptible canola cultivars together in the same pots. The data indicated that mixed seeding could reduce clubroot severity and single-gall weight on the susceptible cultivar compared with the seeding of the susceptible cultivar alone, and that on the resistant genotype, the severity and gall weight remained unchanged. This result suggests that the resistant cultivar could change the environment in the vicinity of the roots, making it unsuitable for P. brassicae germination or infection and that the negative effect of the resistant cultivar on the pathogen could overwhelm the positive effect of the susceptible cultivar.
Assessment of fungicidal treatments for control of blackleg [Leptosphaeria maculans] in canola. M. C. FRASER, S.F.HWANG, G. D. TURNBULL, 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.W., G.D.T., 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
Levels of blackleg disease, caused by Leptosphaeria maculans (Sowerby) Karst., are increasing in Canadian canola fields. This disease can cause serious yield losses due to seedling death and stem cankers. The purpose of this study was to evaluate the performance of fungicide treatments as a tool in managing blackleg. Field experiments were conducted in 2012 and 2013 in Edmonton, Camrose and Namao, Alberta; a greenhouse experiment was also conducted in 2013. The experiment was designed as a randomized complete block, and included a susceptible and moderately resistant canola cultivar. The seed treatments consisted of Prosper FX (carbathiin, trifloxystrobin and metalaxyl), and an experimental treatment (pyraclostrobin and fluxapyroxad) at the half and full rates. Foliar treatments included Priaxor (pyraclostrobin and fluxapyroxad) and Tilt 250 EC (propiconazole), which were applied in combination with the experimental seed treatment. All plots were inoculated with L. maculans. In 2012, Priaxor significantly reduced stem infection compared with the inoculated control in the susceptible cultivar. In Edmonton in 2013, Priaxor significantly reduced stem infection compared with the experimental seed treatment (half rate) in the susceptible cultivar, and yielded significantly more than the control and seed treatments. These preliminary results suggest a potential for combining seed and foliar treatments to manage blackleg, particularly when a susceptible cultivar is grown.
Longevity and ploidy of secondary zoospores of Plasmodiophora brassicae. B. D. GOSSEN, K. SHARMA, A. DEORA AND M. R. McDONALD. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; and (K.S., A.D., M.R.M.) Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
The disease cycle of Plasmodiophora brassicae Woronin consists of a primary phase in root hairs, initiated by primary zoospores from resting spores, and a secondary phase in the root cortex, initiated by secondary zoospores from root hairs. Primary and secondary zoospores are visually indistinguishable, but primary zoospores infect only root hairs, while secondary zoospores infect root hairs and the root cortex. A study was conducted to determine how long secondary zoospores survived in the absence of a host, based on infection success. Healthy 5-day-old canola seedlings (five seedlings/replicate, four replicates) were transplanted into soil at 0, 1, 2, 3 and 4 days after inoculation of the soil with 1 × 105 secondary zoospores. After 5 days, the seedlings were transplanted into much larger pots of non-infested soil and assessed for clubroot severity at 37 days after transplanting. The trial was repeated. The viability of secondary zoospores decreased rapidly and no symptoms developed when seedlings were introduced later than 2 days after inoculation. To determine if secondary zoospores fuse prior to secondary infection, pure suspensions of secondary zoospores were collected, fixed in glutaraldehyde, stained with DAPI (4‘-6-diamidino-2-phenylindole), and the number of nuclei in each zoospore was assessed using epifluorescence microscopy. At least 25 flagellated and 25 encysted zoospores were examined, and the study was repeated. All of the secondary zoospores were uni-nucleate. This observation does not support previous reports that secondary zoospores fuse to form bi-nucleate zoospores prior to infection of the root cortex.
Mechanisms of spread of clubroot of canola on the Canadian prairies. B. D. GOSSEN, S. E. STRELKOV AND M. R. McDONALD. Saskatoon Research 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 (M.R.M.) Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
On the Canadian prairies, clubroot [Plasmodiophora brassicae Woronin] was discovered on canola (Brassica napus L.) for the first time in 2003 on 12 infested fields in a localized area in Alberta. Since then, clubroot has been confirmed in > 1000 fields across large areas of Alberta, and could eventually affect much of the > 8 M ha of canola in the Prairie region each year. Movement of infested soil on farm (and other) equipment is an important mechanism of short-distance dispersal. Clubroot has recently been identified from widely separated sites in Saskatchewan and Manitoba, which demonstrates that long-distance dispersal is also occurring. Transmission of spores on seed produced in infested fields has been demonstrated previously, but is likely not an important mechanism of dispersal. Long-distance dispersal likely occurs primarily via movement of infested machinery or wind erosion of infested fields. Heavily infested canola fields represent a potential source of trillions of spores per erosion event. Also, endemic susceptible weeds can function as hosts even where a canola crop is not present. As a result, there is potential for establishment of clubroot at previously clean sites whenever moisture and other environmental conditions are conducive for the pathogen. The risk of clubroot establishment is lower on dry, alkaline soils high in calcium or boron (unfavourable for infection), compared with wet, acidic soils that drain slowly (favourable). Once the pathogen is established at a new site, short-distance dispersal could quickly result in a new focus of infection.
Evaluations of plant resistance activators for management of Sclerotinia diseases in edible bean and canola. M.W. HARDING, D. A. BURKE, S. L. I. LISOWSKI, C.A.PUGH AND R. J. HOWARD. Alberta Agriculture and Rural Development, Crop Diversification Centre South, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
Resistance priming in plants refers to the ability of a molecule, or signalling compound, to enhance the readiness of basal plant defences. Some priming compounds have been used as seed treatments to reduce the impact of subsequent disease challenges by priming the host’s resistance mechanisms Priming compounds described in peer-reviewed articles include β-aminobutyric acid (BABA), jasmonic acid (JA) and acibenzolar-S-methyl (ASM). A product discovered and developed in western Canada (Heads Up®) also claims to have resistance priming qualities when applied to seed. The product label lists the active ingredient as extract from Chenopodium quinoa that contains triterpene bidesmosidic glycosides, hederagenin and phytolaccagenic acid. In this study we evaluated the ability of Heads Up® seed treatment to reduce sclerotinia diseases in edible bean and canola in replicated, small-plot field trials. Our evaluations also compared Heads Up® with other resistance priming compounds (BABA, JA and ASM), and evaluated the compatibility of Heads Up® with two registered fungicidal seed treatment formulations. The results showed that dry bean seed treated with Heads Up® consistently had significantly lower disease incidence and severity than the untreated check treatments. The compatibility of Heads Up® with other fungicidal seed treatments varied with concentration and formulation. Additionally, preliminary results at one of two locations showed that Heads Up® may reduce stem rot severity on canola.
Aggressiveness and temperature adaptation in distinct genetic groups of Puccinia striiformis in North America. M. D. HOLTZ, K. KUMAR AND K. XI. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Puccinia striiformis Westend., the cause of stripe rust, is a major pathogen of wheat and a regular occurrence on barley. The increased severity of stripe rust on wheat in North America has been attributed to the introduction of a more aggressive strain adapted to a wider range of temperatures that replaced the pre-existing wheat stripe rust population. This study attempted to determine if there were differences in aggressiveness and adaptation to higher temperatures in additional genetic groups of stripe rust. Twenty-four isolates were selected, four from each of six groups. Four groups were wheat stripe rust and two were barley stripe rust. Components of pathogen aggressiveness including latent period, infection efficiency and disease severity were examined on wheat and barley seedlings at two different temperatures (15 °C and 21 °C). Urediniospore germination was also determined at the same temperatures in vitro. Assessment of aggressiveness on seedlings did not consistently produce clear evidence of adaptation to higher temperatures. Urediniospores of the lineages responded differently to the temperature regimes, however. The two most common wheat stripe rust groups germinated well at both temperatures, one of the barley stripe rust groups was intermediate with the remaining groups germinating poorly at 21 °C.
Distribution and frequency of mating types of Rhynchosporium commune in central Alberta. M. D. HOLTZ AND K. XI. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Scald of barley is caused by the fungus Rhynchosporium commune Zaffarano et al. (formerly R. secalis (Oudem.) J.J. Davis). The species is heterothallic where individuals contain one of two mating types and the presence of individuals with alternative mating types would be necessary for sexual reproduction. The sexual state of R. commune has never been detected, but population analyses from other countries suggest that it does occur. In this study, the presence and distribution of R. commune’s mating types was determined in central Alberta by multiplex PCR. Ten field sites were sampled. Four hundred and ten scald lesions from 297 leaves were successfully tested for mating type. Mating type 1–2 was more common than mating type 1–1 with five of the ten locations significantly deviating from a 1 : 1 ratio, based on Chi-square tests. Both mating types did occur at all locations though. Additionally, 23% of leaves which had multiple lesions assessed had lesions of different mating type and 11% of all lesions contained both mating types. The results of this study suggest it is possible that R. commune could be reproducing sexually in the field.
Root diseases in greenhouse production in Alberta. R. J. HOWARD. Crop Diversification Centre South, Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
Root diseases, both infectious and non-infectious, can have a major negative impact on the yield, quality and saleability of greenhouse crops and their products. Historically, these diseases have been a major limiting factor in the production of greenhouse crops grown in soil in Alberta. This situation has considerably improved with the adoption of modern production practices, including the use of soilless media and hydroponic culture, disinfestation of water and nutrient solutions, application of biofungicides, enhanced monitoring and control of the greenhouse environment, and the availability of experienced crop consultants and advisors to help growers monitor plant health and implement effective disease management strategies. The successful management of root diseases depends upon the integration of several key cultural practices, such as providing optimal growing conditions for crops, reducing or eliminating pathogens from greenhouses, planting resistant varieties, and using biological and chemical controls. Some examples of research trials aimed at improving disease management strategies for greenhouse vegetables, which were conducted at CDC South, Brooks over the past two decades, will be discussed.
Goss’s wilt of field corn – a new disease for Alberta. R. J. HOWARD, M. W. HARDING, N. M. RASMUSSEN, S.L.I. LISOWSKI, C. A. PUGH AND L. M. KAWCHUK. Crop Diversification Centre South, Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (N.M.R.) DuPont Pioneer, 4233-56 Avenue, Taber, AB T1G 0A8, Canada; and (L.M.K.) Lethbridge Research Centre, Agriculture and Agri-Food Canada, 5401–1 Avenue South, Lethbridge, AB T1J 4B1, Canada
Goss’s wilt, caused by Clavibacter michiganensis subsp. nebraskensis (Vidaver and Mandel) Davis et al. (Cmn), was detected in irrigated field corn in southern Alberta in August 2013. This is believed to be the first confirmed record of this disease in the province. Goss’s wilt can cause systemic wilt and foliar blight, eventually leading to plant death. It was first reported in Nebraska, USA in 1969 and has since spread to many Great Plains and Corn Belt states, where heavy yield losses have sometimes occurred in susceptible hybrids. The disease was discovered in Manitoba in 2009, and surveys in 2011 revealed that it occurred in 224 (83%) of 270 fields examined. The initial discovery of Goss’s wilt in Alberta was by field representatives of DuPont Pioneer, and subsequent surveys of 45 silage and grain corn fields showed that it was present in five of them. In addition, a positive sample was detected in a corn research plot near Edmonton. The presence of Cmn was confirmed using the Agdia ImmumoStrip® test kit and Gram staining technique on symptomatic leaf tissues. DNA extraction and sequencing was also used to verify Cmn in some of the leaf samples. The origin of the disease remains unknown, but possibilities include infected corn seed, infested machinery and long-distance airborne dispersal of Cmn.
Evaluation of seed assay to screen barley for fusarium head blight resistance. K. KUMAR, P. JUSKIW, K. XI, S.LOHR, K. STEENBERGEN, J. ZANTINGE AND M. HOLTZ. Field Crop Development Centre, Alberta Agriculture Food, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; and (P.J., S.L.) Field Crop Development Centre, Alberta Agriculture Food, 5030 50 St., Lacombe, AB T4L 1W8, Canada
Fusarium graminearum Schwabe is the major causal agent of fusarium head blight (FHB) of barley. Two experiments were conducted to evaluate FHB resistance in barley lines from the FCDC breeding programme using a seed assay. Seeds were inoculated in vitro with a F. graminearum macroconidia suspension and incubated for 6 days at 15°C with a 12 h light period. Seedling weight, seed germination percentage and in vitro DON content were measured. The resistant checks had heavier seedling weight and higher seed germination percentage than susceptible checks. As well, the in vitro DON rankings for the susceptible checks were higher compared with the resistant checks. The lines evaluated were found to rank between the resistant and susceptible cultivars in seedling weight and seed germination percentage. In Experiment 1, of the five lines tested in the field to have low DON, four of the lines would have been selected for resistance using the seed assay based on low in vitro DON. Of the 21 lines tested in Experiment 2, eight were identified as high DON and four as low DON that agreed with field assessments. In conclusion, the seed assay has potential to rapidly screen barley lines for FHB resistance.
Alberta greenhouse crops industry – How diseases have shaped its past, present and future. M. MIRZA AND R. J. HOWARD. Alberta Greenhouse Growers Association, 200, 10331–178 Street, Edmonton, AB T5S 1R5, Canada; and (R.J.H.) Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
The Alberta greenhouse crops industry grew from 16 ha in 1980 to 128 ha in 2013, and from $40 million gross revenues to $170 million. The industry employs over 1600 full-time and 3000 part-time people and represents an investment of over $280 million in Alberta’s economy. The major factor influencing this growth has been root diseases, which created pressure to change from soil cultivation to soilless methods. In the 1980s, cucumber was the main vegetable crop being grown in soil and root knot nematodes and pythium wilt caused significant economic losses to some growers. A research programme was started at the Alberta Horticulture Research Centre, Brooks in which disease control strategies were developed by using different soilless growing media, e.g. straw bales, peat moss, sawdust, rockwool and perlite. By 1984, most vegetable growers were using soilless cultivation systems and economic integrity was restored. Research into the production of tomatoes, peppers and lettuce using these alternative media was initiated. Regular surveys identified diseases such as internal fruit rot of pepper, fusarium wilt on tomato, and grey mould and gummy stem blight on cucumber. Research projects were developed and results were provided to growers. The bedding plant and ornamentals industry also adopted soilless growing media and were able to reduce the prevalence of damping-off and other root diseases. However, foliar diseases, such as powdery mildew, became more prevalent. Adoption of strict environmental controls has helped growers to manage crop diseases in a more efficient manner, thus reducing crop losses.
Continued dissemination of Plasmodiophora brassicae (clubroot) on Canadian canola. S. E. STRELKOV, V. P. MANOLII AND S. F. HWANG. 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, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada
Clubroot, caused by the obligate parasite Plasmodiophora brassicae Woronin, is an important soilborne disease of the Brassicae family. In Alberta, Canada, clubroot was first identified in canola (Brassica napus L.) in 2003, when 12 clubroot infested crops were found near the City of Edmonton. Annual surveys have since revealed a rapid increase in the number of clubroot infestations in Alberta, with the occurrence of P. brassicae confirmed in >1400 fields as of 2013. To document spread, 25 fields in each of three municipalities where clubroot is highly prevalent (Sturgeon County), moderately prevalent (Wetaskiwin County) or rare (Lac Ste. Anne County), and which had been found to be free of the disease in surveys conducted from 2006–2009, were surveyed again in 2013. In Sturgeon County, 19 of 25 re-surveyed fields were found to be clubroot infested; in Wetaskiwin County, 8 of 25 fields were now infested; and in Lac Ste. Anne County, 6 of 25 previously non-infested fields were infested in 2013. Clubroot symptoms in the newly infested fields were most severe in Sturgeon County. These results indicate continued dissemination of P. brassicae, most likely as the result of movement of infested soil on machinery, but possibly also through the movement of spores via wind and water erosion.
The impact of seed treatment, foliar fungicide and variety resistance on barley productivity. T. K. TURKINGTON, K. XI, G. PENG, K. N. HARKER AND J.T. O’DONOVAN. Lacombe/Beaverlodge Research 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 Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; and (G.P.) Saskatoon Research Centre, AAFC, 107 Science Place, Saskatoon, SK S7N 0X2 Canada
Fungicides are becoming a key strategy for barley disease management. However, little information exists regarding this practice when using seed treatments and resistant varieties. At Lacombe, AB and Melfort, SK, the impact of seed treatment and foliar fungicide (treated versus untreated), and variety resistance (susceptible, intermediate and resistant) on barley productivity was assessed. The focus of the trial at Lacombe was scald, while at Melfort net-form net blotch was the main disease issue. InsureTM (triticonazole + pyraclostrobin + metalaxyl) seed treatment was used at two times the recommended rate, while TwinlineTM (metconazole + pyraclostrobin) fungicide was applied at the recommended rate at flag leaf emergence. Disease assessments using leaf samples collected during the summer are underway for both sites. Variety had a significant impact on yield at Melfort, with the susceptible variety having lower yield compared with varieties with net blotch resistance. In contrast, no effect of variety was observed at Lacombe. Seed treatment alone increased grain yield at Lacombe, while fungicide increased yield at both sites. At Melfort, there was an interaction of fungicide and variety resistance, where the susceptible variety had similar yields to both resistant varieties when a fungicide was applied, but not for the check treatments. In addition, fungicide response was greatest for the susceptible variety, intermediate for the moderately resistant variety, but limited for the resistant variety.
Studies on internal fruit rot of greenhouse sweet pepper caused by Fusarium lactis. J. YANG, Y. YANG, P. D. KHARBANDA, R. J. HOWARD, M. MIRZA AND S.E.STRELKOV. Alberta Innovates Technology Futures, Bag 4000, Vegreville, AB T9C 1T4, Canada; (Y.Y., S.E.S.) Department of Agriculture, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; (R.J.H.) Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; and (M.M.) Alberta Greenhouse Growers Association, 200, 10331–178 Street, Edmonton, AB T5S 1R5, Canada
Internal fruit rot of sweet pepper was found in Alberta greenhouses in 2003. Research was conducted to study the aetiology, histopathology, mycotoxins, epidemiology and control of this new disease. Fungi were isolated and identified, and pathogenicity of representative isolates was confirmed. Fusarium spp., mainly F. lactis (Pirotta & Riboni) Bilai, was isolated from infected tissues and was identified based on its morphology and DNA sequence analysis. All 11 pepper cultivars screened were susceptible to F. lactis and the susceptibility varied among cultivars. The infection process on pepper was initiated through infested pollen grains on the stigma, which infected the style during anthesis. Bee pollinators could be vectors and spread the pathogen in a greenhouse. Infected seed may contribute to disease spread between greenhouses. Seventeen isolates of Fusarium lactis produced the mycotoxins moniliformin and beauvericin in culture and in infected fruits as detected using HPLC methods. An epidemiological study showed that the monthly pattern of airborne Fusarium spores fitted a polynomial model. Airborne Fusarium spore populations in a greenhouse had a high peak in June–July in both 2006 and 2007. Disease control practices can be applied before this time to prevent the disease development. Several fungicides were evaluated for controlling F. lactis and Pristine was the most effective product. Seed treatment, use of tolerant cultivars, sanitation and biocontrol are recommended for disease management.
Update on Cucumber green mottle mosaic virus on greenhouse cucumber crops in Alberta. W. ZHANG, K. LING AND R. CRAMER. Greenhouse Branch, Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada; (K.L.) USDA- ARS U.S. Vegetable Laboratory, 2700 Savannah Highway, Charleston, SC 29414, USA; and (R.C.) County Fresh Farms, 12118 Range Road 63, Medicine Hat, AB T1A7H3, Canada
On 16 January 2013, Cucumber green mottle mosaic virus (CGMMV) was reported on greenhouse cucumber plants (cv. ‘Picowell’) in a commercial greenhouse near Medicine Hat, Alberta. A systematic disease survey was subsequently carried out at this location on 15 April. Distinctive symptoms resembling those caused by CGMMV were observed on the upper leaves of several cucumber plants. Affected leaves showed light to dark green mosaic mottling symptoms and were sometimes blistered, wrinkled and deformed. CGMMV symptoms on some infected plants were compounded with other infections caused by Melon necrotic spot virus and Erwinia carotovora pv. carotovora. The disease was observed to spread primarily along the rows of plants. Yield losses ranged from 10–15%. Symptomatic leaves were collected from nine cucumber plants for laboratory analysis. Molecular testing methods revealed the presence of CGMMV in all of these samples. Partial genome sequence analysis showed a 99% sequence identity to CGMMV isolates identified in Asia, suggesting that the CGMMV isolate from Alberta was likely of Asian origin. Virus infectivity was confirmed in greenhouse bioassays.
Evaluation of resistance to Canadian Plasmodiophora brassicae pathotypes in Brassica rapa and B. juncea varieties in China. H. ZHANG, R. F. SUN, S. F. HWANG, S. E. STRELKOV, S. J. ZHANG, S. F. ZHANG AND F. LI. Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing, 100081, China; (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
Clubroot disease, caused by the protist Plasmodiophora brassicae Woronin, has become a major problem in cruciferous vegetable crops around the world. Chinese cabbage, pak-choi (Brassica rapa) and mustard (B. juncea) are among the most important vegetable crops in China. Development of clubroot-resistant cultivars of these crops is urgently needed. The objective of this study was to screen and evaluate the resistance of 75 B. rapa and B. juncea genotypes (divided into five groups) to three P. brassicae pathotypes (pathotypes 3, 5 and 6). A highly significant interaction (P < 0.001) was observed between P. brassicae pathotypes and Brassica genotypes. Pathotype 3, which is the most virulent pathotype on canola in Alberta, showed the weakest virulence among the pathotypes on all plant materials. On the other hand, pathotypes 5 and 6 were both highly virulent in regular lines. Nine out of 13 of the resistant cultivars in group 1 were resistant to all three pathotypes, while four were resistant only to a specific pathotype. Ten genotypes in group 2 derived from resistant cultivars showed only partial resistance, especially to pathotypes 5 and 6; three turnip cultivars showed resistance to all pathotypes. Regular inbred lines of Chinese cabbage and pak-choi, (groups 3, 26 and group 4, 11), were susceptible to all three pathotypes, but their susceptibility was lower to pathotype 3 and higher to pathotypes 5 and 6. No resistance was found in the regular mustard group 5 (12).
Initial validation of a quantitative PCR-based system for detection of Sclerotinia sclerotiorum on canola. B. R. ZIESMAN, T. K. TURKINGTON, U. BASU AND S.E.STRELKOV. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (T.K.T.) Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Sclerotinia sclerotiorum (Lib.) de Bary is a ubiquitous ascomycete fungus that causes numerous diseases including stem rot of canola (Brassica napus L.). Stem rot is a sporadic disease that can cause devastating yield losses and is primarily managed with routine fungicide application. Fungicides are often applied without any indication of disease risk, highlighting the need for a reliable risk prediction system. This study looks at using a S. sclerotiorum-specific Taqman® quantitative (q) PCR assay to estimate stem rot risk in canola fields. Canola petals were collected from 10 commercial fields in central Alberta in 2013 on two different sampling dates. The amount of S. sclerotiorum DNA on canola petals was determined for each sampling date. Regression analysis was used to investigate the relationship between qPCR estimates of petal infestation and final disease incidence. A relationship was observed between qPCR-based estimates of petal infestation and final stem rot incidence, but additional analyses are underway to test the strength of this correlation. Preliminary analyses also indicate that seeding date may play a role in stem rot development, suggesting that additional factors may need to be considered to fully understand the relationship between the amount of S. sclerotiorum inoculum, as determined via qPCR, and final stem rot incidence in the field.
Managing clubroot [Plasmodiophora brassicae] in canola (Brassica napus) using Vapam as a soil fumigant. K. A. ZUZAK, S. F. HWANG, G. D. TURNBULL, V. P. MANOLII 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.D.T.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada
The soilborne pathogen clubroot [Plasmodiophora brassicae Wor.] poses a serious threat to the Canadian canola (Brassica napus L.) industry. As of 2013, over 1400 fields in Alberta were confirmed to be clubroot-infested. Clubroot is also spreading to previously non-infested regions, as isolated cases of the disease have been identified in Saskatchewan and Manitoba. It is important to consider alternative control measures, such as soil fumigation, to mitigate the disease. The soil fumigant Vapam is a metam sodium solution applied to the soil to suppress weeds, nematodes, insects and soil-borne diseases in various cropping systems. In 2012, two heavily infested field locations in Edmonton, Alberta, were selected to analyse the efficacy of various Vapam application rates for the control of clubroot of canola. A clubroot-susceptible canola cultivar was sown into treated soil to assess the impact on a number of traits including clubroot severity, plant height, plant weight and gall weight. In 2013, the experiment was repeated at two new sites at the same locations, while the sites from 2012 were sown to the same canola cultivar to assess any residual action by the fumigant. Preliminary results suggest significant differences between treatment and control plots for above ground canopy weights and pod numbers at one of the field sites.