Blackleg, caused by Leptosphaeria maculans, is one of the most destructive diseases in Brassica species in Canada and worldwide. Information on variability in virulence is essential for the development of effective control strategies. To characterize the virulence structure of the L. maculans population in western Canada, 262 Leptosphaeria isolates collected from Brassica napus and Brassica rapa (canola) fields between 1998 and 2000 were evaluated for virulence on two sets of B. napus differentials, each with three lines. The isolates were classified into two Leptosphaeria species based on the differential reaction on 'Westar'. Sixty-nine isolates (28.3%) avirulent on 'Westar' were identified as Leptosphaeria biglobosa and 175 isolates (71.3%) virulent on 'Westar' as L. maculans. The L. maculans isolates were classified into three pathogenicity groups (PGs) based on their differential reactions to lines in set A. Eighteen of the field isolates were not classifiable because of inconsistent differential reactions. In western Canada, PG2 was predominant, comprising 81.7% of L. maculans isolates. A new pathotype virulent on 'Westar' and 'Quinta' and avirulent on 'Glacier' was identified and characterized as PGT. Isolates with this virulence pattern increased from 9.7% in 1998 to 22.5% in 2000 and were more prevalent in Manitoba (30.7%) than in Saskatchewan (15.4%) or Alberta (11.6%). A single PG3 isolate was detected in southern Manitoba. Further characterization of the L. maculans isolates on lines in differential set B allowed discrimination of eight pathotypes from 143 PG2 isolates and five pathotypes from 31 PGT isolates. Over one-half of the L. maculans isolates were virulent on 'Quantum' with the resistance gene Rlm4 that has been extensively used in Canadian canola cultivars. Selection pressure on the pathogen from race-specific resistance genes in canola cultivars was probably the cause of the changes in virulence observed. Key words: blackleg resistance, gene-for-gene interactions, oilseed rape, Phoma lingam. La jambe noire, causée par le Leptosphaeria maculans, est une des maladies les plus destructrices chez les espèces de Brassica au Canada et à travers le monde. Des connaissances sur la variabilité de la virulence sont essentielles pour le développement de moyens de lutte efficaces. Afin de caractériser la structure de la virulence de la population de L. maculans dans l'Ouest du Canada, la virulence de 262 isolats de Leptosphaeria obtenus de champs de Brassica napus and Brassica rapa (canola) entre 1998 et 2000 fut évaluée sur deux séries de populations différentielles de Brassica napus, chacune composée de trois lignées. En se fondant sur leur réaction différentielle sur 'Westar', les isolats furent classés en deux espèces de Leptosphaeria. Soixante-neuf isolats (28,3 %) non virulents sur 'Westar' furent identifiés comme L. biglobosa et 175 isolats (71,3 %) virulents sur 'Westar', comme L. maculans. Les isolats de L. maculans furent classés en trois groupes de pathogénicité (GP) en fonction de leur réaction différentielle sur les lignées de la série A. Dix-huit des isolats du champ n'étaient pas classables à cause de réactions différentielles variables. Dans l'Ouest du Canada, le groupe GP2 était prédominant avec 81,7 % des isolats de L. maculans. Un nouveau pathotype virulent sur 'Westar' et 'Quinta' et non virulent sur 'Glacier' fut identifié et caractérisé sous le nom de GPT. Les isolats possédant ce patron de virulence augmentèrent de 9,7 % en 1998 à 22,5 % en 2000 et furent plus prévalents au Manitoba (30,7 %) qu'en Saskatchewan (15,4 %) ou qu'en Alberta (11,6 %). Un seul isolat du groupe GP3 fut détecté dans le sud du Manitoba. La caractérisation supplémentaire des isolats de L. maculans sur les lignées différentielles de la série B a permis la discrimination de huit pathotypes parmi les 143 isolats du groupe GP2 et cinq pathotypes parmi les 31 isolats du groupe GPT. Plus de la moitié des isolats de L. maculans étaient virulents sur 'Quantum' qui possède le gène de résistance Rlm4 largement utilizé dans les cultivars canadiens de canola. La pression de sélection sur l'agent pathogène due à la présence de gènes de résistance spécifique à la race chez les cultivars de canola fut probablement la cause des changements observés dans la virulence. Mots-clés : résistance à la jambe noire, interactions gène pour gène, colza oléagineux, Phoma lingam.
In the Canadian prairies, current recommendations allow growing of canola or pea once every 4 years on a particular field to effectively mange diseases, insects, and weeds, but producers are interested in increasing frequency of these crops to optimize economic returns. A 4-year (from 1999 and 2002) field experiment, with treatments consisting of rotations of monoculture canola and pea to rotations that contained these crops every 2, 3, and 4 years with wheat and flax, was conducted on a Black Chernozem (Udic Boroll) silty clay at Melfort, Saskatchewan, to determine the impact of frequency of broad-leaf crops canola and pea in various crop rotations on accumulation and distribution of nitrate nitrogen (N) and extractable phosphorus (P) in the soil profile after 4 years. Two cultivars of canola, an herbicide-tolerant blackleg- resistant variety (hybrid) and a conventional (not herbicide tolerant) open-pollinated, blackleg-susceptible variety (OP), were included. Mean effects of crop rotation or rotation length on soil nitrate N were not significant, though the amount of soil nitrate N in different soil layers tended to be greatest with monocultures and least in the 4-year rotation with flax. Effects of crop phase (i.e., individual crops that make up the rotation) × crop rotation interactions on soil nitrate N were significant for all layers in the soil profile. The amounts of nitrate N in soil after canola, especially hybrid canola, were lowest in most crop rotations, suggesting the importance of canola in minimizing downward movement of nitrate N in the soil profile. Soil extractable P in the 0- to 15-cm layer was least with monocultures and greatest in the 4-year rotation with flax. There was a significant effect of crop phase on soil extractable P, but soil P levels varied with crop phase in different rotations. In conclusion, residual nitrate N in soil can be reduced by extending crop rotations and using high-yielding disease-resistant canola cultivars, most likely by improving crop yields.
Leptosphaeria maculans is a serious concern for canola production worldwide. For effective disease management, knowledge of the pathogen's genetic variability and population structure is a prerequisite. In this study, whole-genome sequencing was performed for 162 of 1590 L. maculans isolates collected in the years 2007-2008 and 2012-2014 in Western Canada. DNA variants in genome-wide and specific regions including avirulence (Avr) genes were characterized. A total of 31,870 high-quality polymorphic DNA variants were used to study L. maculans genetic diversity and population structure. Cluster analysis showed that 150 isolates were clustered into 2 main groups and 4 subgroups by DNA variants located in either Avr or small secreted protein-encoding genes and into 2 main groups and 6 subgroups by genome-wide variants. The analysis of nucleotide diversity and differentiation also confirmed genetic variation within a population and among populations. Principal component analysis with genome-wide variants showed that the isolates collected in 2012-2014 were more genetically diverse than those collected in 2007-2008. Population structure analysis discovered three distinct sub-populations. Although isolates from Saskatchewan and Alberta were of similar genetic composition, Manitoba isolates were highly diverse. Genome-wide association study detected DNA variants in genes AvrLm4-7, Lema_T86300, and Lema_T86310 associated with the years of collection.
Irvine, B. R., Lafond, G. P., May, W., Kutcher, H. R., Clayton, G. W., Harker, K. N., Turkington, T. K. and Beres, B. L. 2013. Stubble options for winter wheat in the Black soil zone of western Canada. Can. J. Plant Sci. 93: 261–270. Winter wheat (Triticum aestivum L.) production has yet to reach its full potential in the Canadian prairies. Alternative stubble types are needed to help overcome the challenge of timely planting of winter wheat in late-maturing canola (Brassica napus L.) fields. A study was conducted in the prairie provinces of Canada to determine ideal stubble types for winter wheat and select spring cereals grown in the Black soil zone. Spring wheat (Triticum aestivum L.), canola, pea (Pisum sativum L.), barley grain or silage (Hordeum vulgare L.), and oat (Avena sativa L.) stubbles were established at four locations in western Canada. A new study area was established at each location for 3 yr. In the year following establishment, winter wheat, hard red spring wheat, barley, and oats were grown on each stubble type at each study area. Winter wheat and spring cereal crops often yielded best and had greater grain protein concentration on barley silage, pea, and canola stubbles relative to other stubble types. The yield and grain protein concentration of spring cereals was best when grown on pea stubble. Winter wheat production attributes varied most among site by crop combinations, and further investigation indicated the source of this variability may be from winter wheat plantings on canola and pea stubble. Among the optimal stubbles, less variable results were observed when winter wheat was grown on barley silage stubble, suggesting proper crop residue management would reduce the variability observed in canola and pea stubble. Our results suggest stubble alternatives to canola are available for winter wheat plantings in western Canada.
AbstractThe fungus Pyrenophora teres Drechs. occurs as two morphologically similar but genetically distinct forms, P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), which cause the net form and spot form of net blotch of barley, respectively. A collection of 220 isolates from the Canadian prairie provinces (Alberta, Saskatchewan and Manitoba) was evaluated for mating type (MAT) idiomorph distribution and frequency. Fungal isolates were classified as Ptt or Ptm using form-specific polymerase chain reaction (PCR) primers. PCR analysis with MAT-specific primers indicated that the MAT1 and MAT2 idiomorphs of Ptt and Ptm could be identified within the same field, on the same plant, and on the same leaf. There was no significant departure from the expected 1:1 MAT1/MAT2 ratio for both forms in all three provinces or in the Canadian prairies population as a whole. Polymorphic simple sequence repeat primers were used to detect evidence of possible recombination between the two forms. Cluster analysis revealed that all P. teres isolates, including 30 isolates causing intermediate symptoms, clustered in two distinct groups conforming to either Ptt or Ptm. Therefore, hybridization was not detectable from the 220 isolates collected in western Canada. Pyrenophora teres f. teres is still the dominant form (58%) of the net blotch pathogen, and the data suggest both Ptt and Ptm go through regular cycles of sexual reproduction in the Canadian prairies.RésuméLe champignon Pyrenophora teres Drechs. exixte sous deux formes morphologiquement similaires, mais génétiquement différentes, P. teres f. teres (Ptt) et P. teres f. maculata (Ptm), qui causent, respectivement, la forme réticulée et la forme localisée de la tache réticulée de l'orge. Une collection de 220 isolats provenant des Prairies canadiennes (Alberta, Saskatchewan et Manitoba) a été utilisée pour analyser la distribution et de la fréquence des types sexuels (MAT) idiomorphes. Les isolats fongiques ont été classés en tant que Ptt ou Ptm à l'aide d'amorces spécifiques pour la réaction en chaîne de la polymérase (PCR). L'analyse par PCR avec amorces spécifiques du MAT a indiqué que les idiomorphes MAT1 et MAT2 de Ptt et de Ptm pouvaient être décelés dans un même champ, sur une même plante et sur une même feuille. Il n'y avait pas de déviation significative du ratio attendu de 1:1 des MAT1 et MAT2 quant aux deux formes, et ce, dans les trois provinces ou dans l'ensemble de la population des Prairies canadiennes. Des amorces spécifiques des microsatellites ont été utilisées pour détecter une possible recombinaison entre les deux formes. L'analyse typologique a révélé que tous les isolats de P. teres, y compris 30 isolats causant des symptômes atypiques, étaient regroupés en deux différentes grappes conformes à Ptt ou à Ptm. Par conséquent, il a été impossible de détecter de l'hybridation chez les 220 isolats collectés dans l'Ouest canadien. Pyrenophora teres f. teres demeure la forme dominante (58 %) de l'agent pathogène causant la tache réticulée, et les données suggèrent Ptt et Ptm amorcent régulièrement des cycles de reproduction sexuée sur les Prairies canadiennes.Keywords: barleymating typemolecular detectionnet blotchPyrenophora teresMots-clés: détection moléculaireorgePyrenophora terestache réticuléetype sexuel AcknowledgementsThe authors would like to thank Mr Meconnen Beyene, Ms Noryne Rauhala, and Ms Jackie Busaan (Agriculture and Agri-Food Canada) for assistance with the collection of isolates, and Ms Ileana S. Strelkov, Ms Kelley Dunfield, Dr Reem Aboukhaddour and Dr Tiesen Cao (University of Alberta) for technical advice and insight. The constructive suggestions of two anonymous reviewers also are gratefully acknowledged.Additional informationFundingThe authors thank the Western Grains Research Foundation, Alberta Barley Commission, Rahr Malting Inc., Canadian Wheat Board, Agriculture and Agri-Food Canada and the University of Alberta for financial support of this research.
Differences in response to nitrogen (N) fertilizer will affect the production economics of field crops. Currently, there is limited information comparing the agronomic and economic performance of juncea canola (Brassica juncea L.) and sunflower (Helianthus annuus L.) to napus canola (Brassica napus L.) and flax (Linum ustitatissimum L.) in Saskatchewan under no-till practices. A study of these species was carried out at five Saskatchewan locations over 3 yr and included eight nitrogen rates. All four species had a curvilinear increase in grain yield as N rate increased with the largest yield response observed in napus canola to as much as 200 kg N ha -1 . The majority of the increase in flax grain yield occurred as the N rate increased from 10 to 90 kg ha -1 , while most of the increase in grain yield of juncea canola and sunflower occurred as N increased from 10 to 70 kg ha -1 . Biplot analysis indicated that grain yield variation was reduced at and above 50 kg N ha -1 in flax, napus canola and juncea canola, but not in sunflower. Analysis indicated that a wide range of N rates would provide a similar adjusted gross return within each crop with the exact N range being determined by crop price and nitrogen cost. The N rate affected the kernel weight of sunflower but not the kernel weight of other crops. The protein concentration of all the species increased as N rate increased. Seed oil concentration tended to decrease as the N rate increased, but this was not consistent. In conclusion, higher yielding cultivars of sunflower and juncea canola are needed before they will replace a large acreage of flax or napus canola; however, in the drier regions of the Saskatchewan there is potential to expand sunflower production.Key words: Brassica juncea, Helianthus annuus, Brassica napus, Linum usitatissimum, nitrogen, economic analysis
Differential sets used by plant pathologists for race typing experiments to compare stripe rust populations over space and time should be expanded to provide useful information to plant breeders. All the data associated with the paper is available with the paper.
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