APS Abstract of Presentation

Resistance to Cronartium ribicola in whitebark pine – family variation and effect of inoculum density
R. A. SNIEZKO (1), A. Kegley (1), R. Danchok (1), J. Hamlin (2), S. Long (1)
(1) USDA FS/Dorena Genetic Resource Center, Cottage Grove, OR, USA; (2) USDA FS/Umpqua NF, Roseburg, OR, USA
Phytopathology 99:S122

Whitebark pine (Pinus albicaulis) is a keystone forest species in many high elevation ecosystems in western North America. Its viability in many areas is threatened by several factors, including white pine blister rust, caused by the non-native, invasive pathogen C. ribicola. A petition in December 2008 by NRDC to list the species under the Endangered Species Act is pending. Genetic resistance offers the best option for survival and restoration of this species. For resistance testing, seedling progeny from field selections in natural stands are artificially inoculated with basidiospores by placing infected leaves of the alternate host, Ribes spp., above the pines. Sets of progenies from 18 field selections from OR and WA and one bulk seedlot from WY were inoculated at two spore densities (~1000 and ~5000 spores/cm²) with a local OR population of rust. Needle infection and subsequent stem infection (SI) and mortality levels were very high at both spore densities, but variation in the latter two was evident among families. Survival four years after inoculation was similar across the inoculum densities (19.0 and 14.4%), and families varied from 0 to >50% survival. Families with higher survival generally displayed fewer stem infections, a lower percentage of trees with SI, and a higher percentage of trees alive with SI. Screening of hundreds of additional families of whitebark pine is now underway, and restoration plantings are being planned.