When progenies of the cross Ribes dikuscha x R. nigrum were exposed to field infection by Pseudopeziza ribis a proportion bore only restricted, non-sporulating lesions on their leaves and rarely showed premature defoliation. The segregation observed is explained if resistance is controlled by two complementary genes, Pr2 and Pr2, the R. dikuscha parent being heterozygous for both of them and some of the R. nigrum parents carrying one, also in the heterozygous state.