Development of light leaf spot and phoma stem canker on a range of current and historical oilseed rape cultivars at Rothamsted in 2003/4 and 2004/5 growing seasons

Field trials in successive growing seasons (2003/04 and 2004/05) were monitored for light leaf spot (Pyrenopeziza brassicae), phoma leaf spot and phoma stem canker (Leptosphaeria maculans) infection. Each experiment included 42 current, historical or exotic cultivars/breeding lines. Weekly assessments examined leaf, stem and pod disease as % plants affected and % area affected. Significant differences were found between resistant and susceptible cultivars, suggesting resistance to be under discrete genetic control. Many of the cultivars that were susceptible or resistant in the 2003/04 season gave similar responses in 2004/05. However, material gave a range of responses to the two pathogens; for example, cv. Aviso was very resistant to L. maculans in both seasons whilst Bronowski was the most susceptible cultivar in both seasons. For Pyrenopeziza brassicae, cv. Tapidor was consistently susceptible whilst the line PR45W05 was consistently resistant, when % leaf area affected was assessed. The results are discussed in relation to current knowledge of the reported oilseed rape resistance gene mediated response to L. maculans and the suggested resistance mechanism of oilseed rape to P. brassica