New Strains of Blackleg in the Canadian Prairies and the North Central Plains of the United States: a Potential New Threat to the Canola Industry?

W.G. Dilantha Fernando and Yu Chen

Department of Plant Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.

Blackleg disease is the most destructive disease of canola/rapeseed (Brassica napus) worldwide. Pathogenicity group (PG) PG-2 has been the predominate group in the Canadian Prairies and North Central Plains of the USA for almost two decades. However, new pathogenicity groups PG-3, PG-4 and PGT of the Blackleg pathogen (Leptosphaeria maculans) were isolated from Manitoba, Saskatchewan, and Alberta Canada, and North Dakota, USA in 2002, 2003 and 2004. Ninety five percent of the commercially grown cultivars in Canada do not have resistance to the new strains at the seedling stage. To understand whether these isolates are introduced, they were compared to isolates from Brazil, Australia and United Kingdom using the sequence-related amplified polymorphism (SRAP) technique to determine their genetic diversity and population structure. Extensive diversity was detected from those geographic populations. The number of polymorphic loci varied from 26.2 to 78.6% based on 42 polymorphic fragments. Fifty to 100% of isolates in the geographic populations and 93.0 to 100% in PG populations sampled from different geographic regions represented unique genotypes. Values of heterozygocity (H) varied from 5.8 to 13.1% in the geographic populations and 6.9 to 13.4% in the PG populations. The populations from Western Canada and North Dakota showed a higher genetic diversity than those collected from Australia and United Kingdom. The populations from Canada, North Dakota and Brazil had closer genetic distance to each other compared to those from Australia and United Kingdom. The new strains may become a threat to the North American Canola industry with a change in population structure.