SEEDLING AND ADULT-PLANT REACTIONS OF BRASSICA-NAPUS BRASSICA-JUNCEA RECOMBINANT LINES TOWARDS A-GROUP AND B-GROUP ISOLATES OF LEPTOSPHAERIA-MACULANS

The Brassica napus-B. juncea recombinant Lines MX and MXS carrying a B . juncea major gene (JLm1) in the genetic background of a spring-or a winter-type B. napus cultivar, respectively, were tested for their res istance level to Leptosphaeria maculans under controlled conditions. I noculation with three A- and four B-group individual isolates and with different mixtures of isolates realised within or between these group s was performed on cotyledons, leaves and stems. Cotyledons and leaves of the two recombinant lines were more resistant to A-group isolates than those of B. napus cultivars, except for one isolate recovered fro m the MX line. The recombinant lines were susceptible at cotyledon sta ge and resistant on leaves to B-group isolates,; as were B. napus cult ivars. On stems, severe cortical damage was usually produced on B. nap us cultivars by some A-group isolates, whereas B-group isolates induce d pith blackening on all genotypes. Stems of the MX line and the resis tant donor species (B. juncea cv. Picra) were more resistant than thos e of the susceptible B. napus (cv. Westar) to the individual A-group i solates. Cultivar Picra was the most susceptible genotype to pith infe ction caused by the B-group isolates. The consequence of the host-path ogen differential interactions on the durability of the monogenic resi stance to L. maculans introduced from B. juncea into B. napus is discu ssed.