Effect of rotation of canola (Brassica napus) cultivars with different complements of blackleg resistance genes on disease severity

Abstract

Blackleg disease (phoma stem canker) caused by the fungus Leptosphaeria maculans is a major disease of canola (oilseed rape, Brassica napus) worldwide. Canola plants in pots were exposed to blackleg-infested stubble of canola with different complements of resistance genes and then assessed for disease. Plant mortality was reduced when plants were exposed to stubble from a cultivar with a different complement of resistance genes compared to stubble of a cultivar with the same resistance gene. These findings were consistent with 7years of field surveys, which showed that changes in selection pressure as a result of extensive sowing of cultivars with major-gene resistance, termed 'sylvestris re..