Severity of phoma leaf spotting and stem canker on Brassica napus cultivars with Rlm7 resistance against Leptosphaeria maculans in the UK

摘要

Leaves with phoma leaf spots were sampled from established winter oilseed rape field trials at 10 different sites in the UK. The number of lesions per leaf caused by Leptosphaeria maculans and Leptosphaeria biglobosa and the area of lesions were scored to assess the disease severity on cultivars carrying the Rlm7 gene (Excel and Roxet) and the susceptible cultivar Drakkar. Leaf samples were incubated for single pycnidial isolation and pathogen identification was done by visual observation on potato dextrose agar. It was difficult to distinguish between lesions caused by L. maculans or L. biglobosa on leaves of Rlm7 cultivars. Stem pieces from each of cultivars were obtained in summer 2012 before harvest from nine different sites in the UK and basaland upper stem cankers were scored on a 0-6 scale.