Assessment of Genetic Variation Among Leptosphaeria maculans Isolates Using Pathogenicity Data and AFLP Analysis

Increased production of rapeseed in the north central and southeastern regions of the United States has been accompanied by an increase in the incidence of blackleg disease caused by Leptosphaeria maculans. In order to assess the genetic variability and relatedness of isolates from these regions to others from around the world, we analyzed 49 aggressive isolates representing three pathogenicity groups (PG2, 3, and 4) of L. maculans from North Dakota, Georgia, Ontario, Western Canada, the United Kingdom (UK), France, Germany, and Australia using pathogenicity data and amplified fragment length polymorphism (AFLP). Approximately 10% of the 400 amplified fragments were polymorphic, scored as discrete characters and analyzed by cluster analysis. The isolates from North Dakota, Western Canada, Georgia, and PHW1252 from the UK formed one tightly clustered group and were mostly of the same pathogenicity group; whereas isolates from Ontario, Australia, France, Germany, and the remaining isolates from the UK formed a second group, which exhibited greater variation and consisted of three pathogenicity groups. The similarity between North Dakota isolates collected in 1995-96 and Western Canadian isolates collected in the 1980s suggests that L. maculans was introduced into North Dakota from Western Canada, and that the populations have remained relatively unchanged over the past 10 years.