Canadian Journal of Plant Pathology (2007) 29, 388-393

H.R. Kutcher, M. Keri, D.L. McLaren and S.R. Rimmer (2007)
Pathogenic variability of Leptosphaeria maculans in western Canada
Canadian Journal of Plant Pathology 29 (4), 388-393
Abstract: 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.
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Link to article at publishers website
Database assignments for author(s): H. Randy Kutcher, S. Roger Rimmer

Research topic(s) for pests/diseases/weeds:
general biology - morphology - evolution
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Plenodomus lingam	Rape/canola (Brassica napus)	Canada (west)
	Plenodomus biglobosus	Rape/canola (Brassica napus)	Canada (west)