Screening for resistance to canker (Leptosphaeria maculans) in winter oilseed rape (Brassica napus ssp. oleifera)

A test involving infection of seedlings in a glasshouse was evaluated for potential use in screening breeding material by comparing the results with those of field tests. The two tests correlated well for some resistant selections, particularly those closely related to Jet Neuf, and for very susceptible selections. However, two small groups of selections were resistant in the field but consistently susceptible in the glasshouse. Inoculation of mature plants in the glasshouse resulted in similar discrepancies and therefore gave no advantage over the seedling test. These discrepancies limit the usefulness of glasshouse techniques for routine resistance screening. A very high correlation was found overall between internal and external canker symptoms of the crown in nine field trials. Significant differences were found, however, between selections and cultivars in the relative severity of these two symptoms. Upper stem canker and crown canker were found to be very poorly correlated for individual plants, but highly correlated for eultivar means. The significance of these observations is discussed with respect to scoring canker in the field.