White pine blister rust (WPBR), Cronartia ribicola Fischer, causes economic damage to white pines, Pinus strobus L., and infects leaves of some Ribes late in the summer after harvest. Susceptible Ribes and Pinus serve as obligate alternate hosts for this disease. The objective of this study was to determine the response of Ribes species and cultivars to WPBR under field conditions at Corvallis, OR, where inoculum is naturally present. In 1995 and 1996, 54 Ribes taxa from North and South America, Europe, and Asia visually evaluated August through October for the presence of uredia on the abaxial leaf surfaces. Plants with no observable uredia for the duration of the study were considered resistant. WPBR infection varied by year, within taxonomic sections, and between and within species. Uredia of WPBR were present on 22 Ribes taxa in one or both years, while 32 others were resistant, i.e., had no uredia. Some of the resistant Ribes species were native outside of eastern Russia, which is the native range of the rust. Resistant species may contain new sources of genes for developing additional rust-resistant commercial Ribes cultivars. The cultivation of resistant Ribes is an alternative to consider where state statutes banning the genus are under review.
