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Variability of Leptosphaeria maculans in Relation to Blackleg of Oilseed Rape. D. C. McGee, Plant Pathologist, Dept. of Agriculture, Victorian Plant Research Institute, Victoria, Australia, Present address of senior author: Dept. of Botany and Plant Pathology, University of Maine, Orono, ME 04473; G. A. Petrie, Plant Pathologist, Research Station, Research Branch, Agriculture Canada, 107 Science Cres., Saskatoon, Saskatchewan, Canada, S7N 0X2. Phytopathology 68:625-630. Accepted for publication 7 October 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-625.

Virulent and avirulent strains of Leptosphaeria maculans isolated from rapeseed plants in Saskatchewan were differentiated on the basis of cultural characteristics and virulence to rapeseed (“rapeseed” here refers to rape plants grown for oil extraction from the seed). Surveys of field populations showed that the avirulent strain was more prevalent. An isolate from cabbage in Wisconsin was identical to the virulent strain. Several isolates from rapeseed in Australia all were virulent on rapeseed but showed variability in culture. There was a significant correlation between disease rankings on one set of Brassica sp. seed lines tested against the Wisconsin isolate and an Australian isolate. Similar results were obtained with a second set tested against the Wisconsin isolate and a field population of L. maculans in Australia. A strain of L. maculans also was detected on stinkweed (Thlaspi arvense L.) collected from fields in Saskatchewan. This strain could be distinguished from others by the differential reactions of rapeseed and stinkweed in pathogenicity tests. Blackleg was more severe in rapeseed field plots containing residues of rapeseed infected with blackleg than in those containing infected residues of stinkweed.

Additional keywords: Phoma lingam, cruciferous crops, oilseeds.