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Etiology of Canola Blackleg in Kentucky and Seasonal Discharge Patterns of Leptosphaeria maculans Ascospores from Infested Canola Stubble. D. E. Hershman, Department of Plant Pathology, University of Kentucky, Princeton 42445. D. M. Perkins, Department of Plant Pathology, University of Kentucky, Princeton 42445. PLANT DIS. 79:1225. Accepted for publication 21 September 1995. This article is in the public domain and not copyrightable. It may be (freely reprinted with customary crediting of the source. The American Phytopathological Society, 1995. DOI: 10.1094/PD-79-1225.

A limited survey was conducted to determine the pathogenicity groupings (PG) of Leptosphaeria maculans associated with canola (Brassica napus var. oleifera) blackleg in south central Kentucky. In addition, multiyear ascospore discharge patterns were determined for infested canola stubble from seven fields. Strains PG3 and PG4 of L. maculans were most commonly associated with blackleg in Kentucky (18.4 and 79% of the isolates tested, respectively). One weakly virulent PG1 isolate (2.6%) and no PG2 isolates were found. L. maculans-infested canola stubble discharged ascospores within 1 week of harvest in 1990 and 1991. Early discharge patterns were not determined in 1989. Stubble collected each year released significant quantities of ascospores in the fall and winter months following crop harvest. However, few ascospores were released from infested stubble after the first year following crop production. The implications of these data in blackleg management are discussed.