Crop residues influence Rhizoctonia solani population dynamics and reduce canola seedling blight. H. U. AHMED, S. F. HWANG, G. D. TURNBULL, Q. X. ZHOU, S. E. STRELKOV AND B. D. GOSSEN. Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada; (S.E.S.) Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Seedling blight of canola (Brassica napus L. and B. rapa L.), caused by Rhizoctonia solani Kühn, is an important disease that reduces crop stand establishment. Seed treatment chemicals are used to control seedling blight, but can have a negative impact on the environment. The effects of previous crop residues on soil R. solani populations and canola seedling blight severity were examined. Field plots were established in 2010 following a split-plot design with inoculum (Rhizoctonia and no Rhizoctonia) as the main plots and crop residue (barley, canola, oat, and pea) as the sub-plots. Following harvest, the crop residues were ploughed down in the fall of 2010. In the spring of 2011, soil samples were collected from each experimental unit. The effect of crop residue on Rhizoctonia populations was assessed by growing canola in these soils in a replicated greenhouse trial following the same design as was used in the field. Populations of Rhizoctonia were estimated by soil dilution plating onto selective medium. Canola seedling emergence was greater, while damping off and disease severity were less severe, in soil with barley or oat residues compared to soil with canola or pea residues. Similar results were obtained in both inoculated and non-inoculated plots. A plate assay also revealed reduced Rhizoctonia populations in plots with barley or oat residues. Crop rotation and residue incorporation with barley or oat between canola crops may be a useful strategy to manage seedling blight of canola.
Quantitative PCR as a tool to evaluate resistance to Plasmodiophora brassicae in Brassica hosts. T. CAO, 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 Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin (Pb), is an emerging canola disease in Alberta. In an attempt to rapidly identify canola lines carrying clubroot resistance, quantitative PCR (qPCR) analysis was employed to measure the amount of Pb DNA in the roots of susceptible, moderately susceptible, moderately resistant and resistant hosts, as well as in a non-host genotype (wheat), at 5, 10, 15, 20, and 42 days post-inoculation (dpi). Results indicated that Pb biomass, as estimated by Pb DNA, showed an overall upward trend in clubroot susceptible hosts from 5 to 42 dpi, in contrast to an overall downward trend in clubroot resistant hosts and wheat. Disease severity was positively correlated with the amount of Pb DNA in roots sampled at 42, 20, 15, and 5 dpi. The amount of Pb DNA in the roots sampled at 20, 15, and 5 dpi was also positively correlated with the amount of Pb DNA in the roots sampled at 42 dpi. These results suggest that the in planta quantification of Pb DNA at 20, 15, and 5 dpi could be used as an early indicator of the final disease reaction of the host to the pathogen.
Effect of host resistance on infection by Plasmodiophora brassicae in canola. A. DEORA, B. D. GOSSEN AND M. R. MCDONALD. Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada; and (B.D.G.) Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada
Little is known about how and when resistance to clubroot [Plasmodiophora brassicae Woronin] is expressed in canola (Brassica napus L.). Time series assessments of root hair infection and cortical infection were made in inoculated seedlings of four commercial cultivars that differed in reaction to two pathotypes (P3 and P6) of P. brassicae: cvs. ‘45H29’ (resistant), ‘Invigor 5030’ (partially resistant), ‘46A76’ (susceptible), and ‘45H21’ (susceptible to P3, resistant to P6). For assessment of root hair infection (RHI), seedlings were harvested at 4, 8, and 12 days after inoculation (DAI). For assessment of cortical infection (CI), plants were harvested at 16, 22, and 28 DAI. RHI occurred quickly in compatible (susceptible cultivar × pathotype) combinations and more slowly in incompatible combinations. The maximum RHI for both reactions was about 65%, except on ‘Invigor 5030’ where RHI was >60%. At 28 DAI, CI was high in the susceptible cv. ‘46A76’ (P3 = 45%, P6 = 35%), intermediate in ‘Invigor 5030’ (P3 = 23%, P6 = 16%), and no CI (0%) was observed for either pathotype in the resistant ‘45H29’. In ‘45H21’, CI caused by P3 was high (35%), but P6 resulted in no CI (0%). CI caused by P3 was consistently higher than for P6 in compatible reactions. Although there were small differences in the pattern of RHI associated with resistance, the largest impact of resistance was on CI.
Effect of soil type on assessment of biofungicide efficacy against clubroot under controlled conditions. B. D. GOSSEN, H. KASINATHAN, G. PENG AND M. R. MCDONALD. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; and (H.K., M.R.M.) Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
Three studies were conducted under controlled conditions to examine the effect of soil type on the efficacy of two biofungicides, Serenade (Bacillus subtilis) and Prestop (Gliocladium catenulatum), against clubroot caused by Plasmodiophora brassicae Woronin. Combinations of three factors were examined: soil type (muck soil, pH 6.2; mineral soil, pH 6.8; non-calcareous sand, pH 6.5; soil-less mix, pH 6.0), pathotype (P3, P6), and biofungicide. Seedlings of canola (Brassica napus L.‘46A76’) and Shanghai pak choy (B. rapa L. subsp. Chinensis (Rupr.) var. communis Tsen and Lee ’Mei Quing Choi’) were treated with Serenade (5% v/v) and Prestop (7.5 g L-1 of water) at 5 days after germination inoculated with 5 × 105 resting spores of P. brassicae per seedling 3 days later. Clubroot severity was assessed at 6 weeks after inoculation. Each experiment consisted of four replicates and 12 plants per experimental unit, and each was repeated. Clubroot levels (incidence and severity) in Shanghai pak choy were consistently higher than in canola, and inoculation with P3 resulted in slightly higher clubroot levels than P6. Clubroot levels in soilless mix were substantially lower than in the other soil types, but there was little or no difference among the other soil types. Application of the biofungicides often reduced clubroot incidence and severity, but the reduction was generally small. Also, the relative impact of the two biofungicides was not consistent; Prestop was the more effective agent in two trials, but Serenade was more effective in the third trial. There was also a small interaction of soil type with biofungicide, associated primarily with low levels of clubroot in the soilless mix treatment. These results indicate that growing medium is an important factor in evaluation of clubroot under controlled conditions, and that soil type will likely influence the efficacy of biofungicide in field situations.
Wisconsin Fast Plants as model crops for studies of clubroot. B. D. GOSSEN, K. SHARMA, K. K. C. ADHIKARI AND M. R. MCDONALD. Saskatoon Research Centre, Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada; and (K.S., K.K.C.A., M.R.M.) Department of Plant Agriculture, Crop Science Building, University of Guelph, 50 Stone Road East, Guelph, ON N1G 2W1, Canada
The acreage affected by clubroot [Plasmodiophora brassicae Woronin] on canola (Brassica napus L., B. rapa L.) in western Canada is expanding rapidly. Arabidopsis is widely used as a model crop for studies of clubroot, but a model crop with a plant architecture more similar to susceptible crop species would be useful for many kinds of studies. Wisconsin Fast Plants are small, short-generation selections that represent a wide range of Brassica species, which might be very useful as model crops for such studies. Field assessments of the reaction of selected lines were conducted from 2008–2010 on naturally infested soil at the Muck Crops Research Station in Ontario, where pathotype 6 is predominant. B. carinata and B. juncea were highly susceptible, several lines of B. napus were moderately susceptible, and B. napus and R. sativus were resistant, and their response was consistent over years. Also, these selected lines were tested against pathotypes 2, 3, 5, and 6 under controlled conditions. The response to pathotype 6 under controlled conditions was strongly correlated with those from the field. In addition, a strong interaction in response to several of the pathotypes was observed for several of the lines. We conclude that Wisconsin Fast Plants have potential for use as model crops for clubroot research, e.g., under controlled conditions and other situations where space is limited.
Genetics of clubroot resistance in rutabaga (Brassica napus var. napobrassica). M. J. HASAN AND H. RAHMAN. Department of Agricultural, Food and Nutritional Science, 410 Agriculture/Forestry Centre, University of Alberta, Edmonton, AB T6G 2P5, Canada
Development of canola (Brassica napus L.) cultivars resistant to clubroot disease, caused by Plasmodiophora brassicae Woronin, is an important objective for breeders and researchers. Several resistant canola cultivars have been developed and marketed by private companies in Canada, in which resistance is conferred by single gene. However, there are reports of the breakdown of monogenic resistance in Europe. Therefore, it is important to have multiple resistance genes in canola for durability in resistance to clubroot disease in this crop. The objective of this research is to introgress clubroot resistance from rutabaga into canola and to develop molecular marker(s) for use in marker-assisted breeding. Two rutabaga genotypes, Rutabaga-BF and Rutabaga-PL, inbred for resistance to multiple P. brassicae pathotypes including pathotype 3, were crossed with two clubroot susceptible spring canola lines, A07-29NI and A05-17NI. Double haploid (DH) populations were produced from the F1 plants through the application of microspore culture technique, and were evaluated for resistance to pathotype 3. Segregation in the DH population of Rutabaga-BF × A07-29NI followed a simple Mendelian 1:1 segregation for resistant and susceptible phenotypes; while, segregation in the DH population of Rutabaga-PL × A05-17NI cross deviated significantly from a 1:1 ratio, suggesting a more complex genetic control of this trait in this population. Molecular mapping of resistance in these two populations is in progress.
Recent shifts in the stripe rust [Puccinia striiformis] populations in central Alberta. M. D. HOLTZ, K. KUMAR, L. LANGFORD, J. ZANTINGE AND K. XI. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
Puccinia striiformis Westend. f. sp. tritici Eriks. (Pst) and P. striiformis f. sp. hordei Eriks. (Psh), the causal agents of stripe rust of wheat and barley, respectively, have been common in Alberta for the past 10 years. Isolates collected during 2010 and 2011 were tested for virulence on a series of differential lines and genotyped with 11 simple-sequence repeat (SSR) markers. Results for both formae speciales indicated that recent shifts have occurred in the pathogen populations present in central Alberta. In 2010, Pst isolates showed few differences from Pst of previous years although pathotypes virulent on the Yr10 gene increased in frequency. During 2011, a new Pst genotype, matching that of a pathotype first detected in the Pacific States during 2007, was detected. During 2010, the Psh pathotypes that were common previously were rare. Most 2010 Psh isolates belonged to two distinct groups. Isolates in the first group were similar in virulence to those previously detected. Isolates in the second group were virulent on fewer barley differentials, but were highly virulent on several wheat and triticale differentials. All of these isolates also contained SSR alleles that had previously been found only in Pst isolates. These results indicate that new races continue to migrate to central Alberta and contemporary gene flow may occur between the two formae speciales.
Transformation of Pyrenophora teres with the ToxB gene causes altered infection phenotypes on wheat and barley. Y. M. KIM, R. ABOUKHADDOUR, T. K. TURKINGTON 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
Ptr ToxB, a 6.6 kDa proteinaceous molecule, is a host-specific toxin (necrotrophic effector) produced by some races of Pyrenophora tritici-repentis (Died.) Drechs., the causal agent of tan spot of wheat. The toxin is encoded by the ToxB gene and induces extensive chlorosis on Ptr ToxB-sensitive wheat genotypes. A sister species of P. tritici-repentis, Pyrenophora teres Drechs., causes net blotch of barley, an economically important foliar disease of cultivated barley worldwide. In order to gain further insights into the function of Ptr ToxB, we transformed the ‘wild-type’ ToxB gene from P. tritici-repentis into P. teres by PEG-mediated protoplast transformation. Integration of the ToxB gene in the transformed P. teres strains was evaluated by PCR and Southern blotting analyses, while production of Ptr ToxB was assessed via Western blotting. The transformed P. teres strains were then tested for virulence on their original barley host as well as on Ptr ToxB-sensitive and insensitive wheat genotypes. Transformants expressing functional Ptr ToxB caused significantly increased levels of disease on a net blotch-resistant barley cultivar and an altered infection phenotype on a Ptr ToxB-sensitive wheat genotype, compared with the un-transformed strain. These results suggest that Ptr ToxB or ToxB-like proteins may contribute to virulence in pathosystems other than tan spot.
Effect of a wide range of pH values on resting spore germination and clubroot [Plasmodiophora brassicae] severity in canola. A. RASHID, H. U. AHMED, 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 soilborne disease of cruciferous crops. Disease development is associated with the formation of large root galls, which reduce water and nutrient uptake by infected plants. Liming of the soil to increase its pH is often recommended as an effective strategy to reduce clubroot severity. In order to evaluate the effectiveness of this approach to manage clubroot in canola (Brassica napus L.), root hair infection and clubroot severity over a range of soil pH values (pH 5.0 to 9.0) were assessed. Significant levels of root hair infection and gall formation were observed at neutral and alkaline pH (6.5 to 9.0), although these declined at pH <6.0. The germination rates of P. brassicae resting spores were also assessed after treatment with host root exudates, the pH of which also had been adjusted from pH 5.0 to 9.0. Germination of the spores was significantly higher in all treatments that contained root exudates, relative to a control in which the spores were treated with a nutrient solution alone. However, the highest spore germination rates were observed at pH 5.0 to 7.0 and gradually declined at pH >7.5 in both the presence and absence of root exudates. The implications of these results were discussed.
Oxidized silvers - experimental fungicides for control of white mold on dry bean. M. J. UNRUH, S. LEPP, R. J. HOWARD AND M. W. HARDING. Innovotech Inc., Suite 101-2011 94 Street, Edmonton, AB T6N 1H1, Canada; and (R.J.H.) Crop Diversification Centre South, Alberta Agriculture and Rural Development, 301 Horticultural Station Road East, Brooks, AB T1R 1E6, Canada
White mold, caused by Sclerotinia sclerotiorum (Lib.) de Bary, routinely causes destructive disease outbreaks in dry bean fields in Southern Alberta. Oxidized silver compounds are fungicidal, and have been demonstrated to control diseases such as Ascochyta blight (Ascochyta rabiei (Pass.) Labr.) on chickpea (Cicer arietinum L.). In this study, we evaluated the potential of oxidized silver compounds to control, or reduce, white mold symptoms on dry edible bean (Phaseolus vulgaris L.). We report reductions in white mold disease incidence and severity on bean after foliar applications of silver-based compounds, such as oxysilver nitrate and sodium diperiodatoargentate (III), when applied independently, and as tank mixes with registered, commercially formulated fungicides. Taken together with previous findings, these data suggest that oxidized silver compounds are effective, broad-spectrum fungicides that are frequently compatible with existing, commercially available, fungicide formulations. The use of oxidized silvers in fungicide tank mixes may provide more versatile disease management tools, particularly in areas such as fungicide resistance management, broad-spectrum activity and efficacy enhancement.
Rhynchosporium secalis virulence and genetics in relation to barley cultivar resistance. K. XI, J. ZANTINGE, J. MEADUS, J. NYACHIRO AND K. TURKINGTON. Field Crop Development Centre, Alberta Agriculture and Rural Development, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada; and (J.M., K.T.) Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C & E Trail, Lacombe, AB T4L 1W1, Canada
The use of resistant barley cultivars is a primary strategy for the management of scald caused by Rhynchosporium secalis (Oudem.) Davis in central Alberta. The objective of the present study was to determine R. secalis pathotype virulence in relation to cultivar resistance. Field plots consisting of barley scald differentials with resistance genes and local commercial cultivars were set up across central Alberta during 2007 to 2011 to monitor scald development in relation to changes in pathotype virulence. The scald reactions of a few barley differentials and commercial resistant cultivars were found to change substantially during the test period. Inoculation at the seedling stage demonstrated that virulent pathotype E#2 and weakly virulent pathotype H#2 were generally separated based on virulence spectra. DNA microsatellites showing polymorphism did not reveal a clear pattern in grouping of isolates collected from central Alberta. Analysis of molecular variance showed a small but significant genetic difference accounting for 12% of total variation between the early (1997-2004) and the more recently (2009-2010) collected isolate groups. A higher degree of genetic similarity was found between other chronological groups. Sequence comparison of a 1.4 kb DNA band designated ‘OPX7’, previously found to be polymorphic between E#2 and H#2, was able to separate the pathotypes according to virulence in relation to barley cultivar resistance.
Evaluation of primary and secondary infection by Plasmodiophora brassicae in both resistant and susceptible canola genotypes. Q. XIAO, J. FENG, 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 (J.F., S.F.H.) Crop Diversification Centre North, Alberta Agriculture and Rural Development, 17 507 Fort Road N.W., Edmonton, AB T5Y 6H3, Canada
Clubroot, caused by Plasmodiophora brassicae Woronin, has emerged as a major disease of canola (Brassica napus L.) in Alberta, Canada. The deployment of resistant cultivars is an important aspect of an integrated control strategy. To better understand resistance mechanisms, primary and secondary infection of resistant (‘73-77RR’) and susceptible (‘45H26’) canola genotypes was investigated in two experiments, by inoculation with resting spore (primary zoospore) and secondary zoospore suspensions. Over an 8-day time course, the level of primary infection was lower in the resistant genotype than in the susceptible genotype, following inoculation with either resting spores or secondary zoospores. However, a greater number of secondary plasmodia (indicative of secondary infection) were observed in the resistant genotype. These results suggest that resistance in ‘73-77RR’ is expressed during primary infection.
Pathogenicity and genetic variation in Rhizoctonia spp. isolated from canola in central Alberta. Q. X. ZHOU, 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
Canola is an important oilseed crop grown worldwide. In western Canada, Rhizoctonia spp. represents one of the major pathogens causing canola seedling blight and damping off, which result in significant yield losses. In 2009, 2010 and 2011, 98 isolates of Rhizoctonia spp. were isolated from fields in central Alberta. The pathogenicity of these isolates on canola was tested, with 58% causing high disease severity, 26% causing low disease severity, and 5% causing no disease. Genetic variability among the isolates was assessed by analysis of the internal transcribed spacer (ITS) 1, 5.8S, and ITS 2 regions of the rDNA repeat, from which a neighbor-joining tree was constructed using the PAUP software. Isolates of Rhizoctonia were separated into four groups (Groups I – IV) with strong bootstrap support. Isolates in Groups I and IV tended to be weakly virulent, while those in Group II caused the highest disease severity.