Whitebark pine (Pinus albicaulis) resistance to white pine blister rust : a cost-effective approach to progeny testing for restoration

Endangered whitebark pine (Pinus albicaulis Engelm.), native to high elevation forests of western North America, is declining mainly due to the introduced pathogen Cronartium ribicola J.C. Fisch, causing the disease white pine blister rust. This decline is compounded by the impacts of climate change, mountain pine beetle, and fire suppression. Low levels of genetic resistance to blister rust are present in whitebark pine. Traditional methods of inoculating seedlings to determine family-level resistance to the rust are costly, labour and time intensive. Due to the need for resistant material for planting, this presents a bottleneck in the process of restoring whitebark pine stands that have been heavily infected by the rust. In this study I tested an alternative approach to controlled inoculations that would be an effective way to screen large numbers of families without as many costs and limitations. A large genetic sample comprising 214 open-pollinated families from 44 provenances were screened at Skimikin Nursery, British Columbia, to determine: (1) the effectiveness of natural rust inoculation from Ribes nigrum L. in a common garden; (2) family and provenance level resistance to blister rust; and (3) climate variables related to height and rust resistance. Eighty-one families previously screened in Dorena, Oregon using artificial inoculation methods were also planted at Skimikin to compare with the natural inoculation. The natural inoculation was effective, with 73% of seedlings displaying stem symptoms of the disease, and 95% showing rust infection. A clear relationship was found between distance from the Ribes and severity of blister rust. Linear mixed models with spatial correlations were fitted to height and rust data using ASReml-R to estimate breeding values, heritability, and among-population differentiation (QST). Resistance was highest in the Cascade Mountains of Washington, while the most susceptible families were located mainly in the BC Coast Mountains. QST values revealed low genetic differentiation for height (0.07) and moderate differentiation for rust (0.28) while heritability was higher for height (0.42) than for rust resistance (0.23). This method of screening should be used more widely to determine families resistant to white pine blister rust and increase the availability of resistant seedlings for restoration.Forestry, Faculty ofGraduat