Field isolates of Leptosphaeria maculans from Western Australia overcome a single dominant resistance gene in Brassica napus cv. Surpass 400

In 2001, in experimental field rows of cultivar (cv.) Surpass 400 at Mount Barker in Western Australia, a small proportion of the lower stem lesions observed were typical of those observed in susceptible cultivars but containing fewer pycnidia. Approximately 80 % of isolates obtained from those plants with stem lesions showing pycnidia induced a hypersensitive response on cv. Surpass 400 cotyledons. The remaining 20 % of isolates developed characteristic disease lesions with pycnidia on cv. Surpass 400 cotyledons. These isolates were able to infect cv. Surpass 400 such that characteristic blackleg cotyledon necrotic lesions and crown cankers in the field with pycnidia developed, confirming the ability of these isolates to overcome the single dominant resistance gene present in cv. Surpass 400