Variation in resistance to white pine blister rust among 43 whitebark pine families from Oregon and Washington - Early results and implications for conservation

Conference Paper

Transfer Guideline: Recommendation

All nine North American species of white pines are susceptible to the introduced, invasive pathogen Cronartium ribicola, the cause of white pine blister rust. Whitebark pine is considered one of the most susceptible species. Genetic resistance is considered a cornerstone for survival to this pathogen. Fortunately, all of the native species of white pines have some level of resistance. Evaluation of resistance in Oregon and Washington families of whitebark pine has only recently begun; currently over 150 seedlots collected from individual parent trees are in resistance testing. This report summarizes differences in responses among 43 seedling families and one bulked seedlot through two years after artificial inoculation with blister rust. Initial infection after inoculation of three-year-old seedlings was very high in the first set of trials; 100% of the seedlings developed needle lesions in the two trials reported in this paper. There were large differences among families in several traits, including percentage of trees with stem symptoms and survival two years after inoculation. The level of resistance present in some families and the frequency of resistance among the 43 families reported here is encouraging. A possible geographic trend in resistance is also noted. It is recommended that at least a subset of families be field planted to validate resistance ratings from this short-term screening. The collection and use of seed from putative resistance parent trees identified through this testing would be a good starting point for restoration efforts.