Abstract

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.