Cytological investigation of resistance to Leptosphaeria maculans conferred to Brassica napus by introgressions originating from B. juncea or B. nigra B genome

Introgressions into Brassica napus from the B genome, either the B. nigra c hromosome B4 or the B. juncea fragment carrying the Jlm1 gene, have given r ise to the B. napus-B. nigra addition line (LA4+) and the B. napus-B, junce a recombinant line (MXS), respectively. The resistance of these two lines t o Leptosphaeria maculans is characterized by a hypersensitive reaction (HR) on both the cotyledons and leaves, while the collar displays a high degree of resistance. Responses induced in cotyledons of the two lines by L macul ans inoculation were investigated with emphasis on cytological events under lying the HR and on host defense reactions. Features of host cell changes i ncluding condensation and lobing of nuclei, fragmentation of chromatin, dis ruption of the nuclear membranes, and plasma membrane withdrawal were remin iscent of KR cell death in MXS and LA4+ plants. Restriction of pathogen gro wth to the infection areas in LA4+ was correlated to reinforcement of cell wall barriers, including wall apposition papillae, and vessel plugging. In MXS, the lower expression of resistance was associated with a delay in plan t responses. These results indicate that mechanisms underlying the HR in th e B, napus recombinant and addition lines are differently controlled accord ing to the introgressed genes.