When plants of R. ussuriense Jancz. and two R. nigrum var. sibiricum E. Wolf. cultivars Rus and Narjadnaja were exposed to infestation by the black currant gall mite (Phytoptus ribis Nal.) typical galled buds were not formed but damage was caused to meristematic tissues of the buds. Mites were not found in buds during the winter and the plants also remained free from symptoms of reversion virus. Progenies from crosses between these mite-resistant forms and susceptible cultivars indicated that resistance is controlled by a single dominant gene designated P.
The above species readily form fertile hybrids with cultivars of black currant and should be useful sources of mite resistance in a breeding programme.