Gene‐for‐gene resistance is expressed in cotyledons, leaves and pods, but not during late stages of stem colonization in the Leptosphaeria maculans–Brassica napus pathosystem

Abstract The blackleg fungus, Leptosphaeria maculans, interacts with canola (Brassica napus) in a gene‐for‐gene manner. These major resistance genes are well characterized in the seedling stage of development, but not in other plant organs. Cotyledons, leaves, pods and stems of plants of two cultivars of B. napus, each harbouring a different major resistance gene (Rlm1 and Rlm4), were inoculated with two individual L. maculans isolates with different alleles of the corresponding avirulence genes (AvrLm1, avrLm4 and avrLm1, AvrLm4), and the disease phenotype in terms of lesion development was determined. Major gene resistance was expressed in cotyledons, all leaves and during pod set, but not in the stems of the adult plant. This is the first time major gene resistance has been shown to be effective in B. napus pods.