Poplar clones and rusts interact both at the qualitative and the quantitative level. Qualitative resistance (immunity) was assessed in a factorial mating design, composed of two intraspecific progenies (P. trichocarpa x P. trichocarpa and P. deltoides x P. deltoides) and three interspecific families (P. trichocarpa x P. deltoides and P. deltoides x P. trichocarpa). Parents and full-sibs were inoculated in the laboratory with three races of M. larici-populina and also observed in nursery trials after natural infection. All the P. trichocarpa genotypes were susceptible, but segregation was detected in P. deltoides and within the interspecific progenies. Bulked segregant analysis were performed on resistant and susceptible individuals of the segregating families. No recombinant phenotype was observed between the resistance and marker OPM03/04.480 on 189 individuals of four families, involving 6 different parents. This fragment has been cloned and is currently being sequenced. Specific primers will be synthesized and used to reveal SCARS. Quantitative resistance has been evaluated through laboratory tests, measuring three epidemiological components, number of uredia, latent period and sporulation. Mapping of QTLs for these components is underway in our genetic linkage map, composed of 150 RAPD markers and based on a pseudo-test cross strategy in an INRA FI interspecific pedigree.