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POSTERS: Mycology I

P-389 - Contemporary Status of White Pine Blister Rust on Naturally Regenerated Western White Pine (Pinus monticola) in Interior, Northwestern USA

Monday, August 4, 2025
4:30 PM - 5:15 PM HST
Location: Exhibit Hall 3
Abstract Text: In temperate, moist forests of western North America, western white pine (WWP; Pinus monticola) is a keystone species adapted to a range of site conditions and with relatively high tolerance to native root diseases. WWP was dramatically reduced after Cronartium ribicola, causal agent of white pine blister rust (WPBR), became established in western North America in the early 1900s. Because it appeared that recent naturally regenerated WWP in the inland northwestern USA had less WPBR incidence, we compared historical and contemporary disease rates. Disease progress curves for WPBR were compared for 15-year infection data for historical (1942-1966) and contemporary (2006-2020) periods in 17 naturally regenerated WWP stands of similar age and location. WPBR incidence (percentage of trees infected) and severity (number of WPBR cankers per tree) were dramatically lower for the contemporary vs historical time. At the end of the 15-year monitoring periods across all sites, 48% of the trees in the historical period were infected with C. ribicola, whereas 5% of the trees in contemporary stands were infected. Additionally, the average number of cankers at the end of the historical period (1.14 per tree) was 16 times higher than at the end of the contemporary period (0.07 per tree). Based on these results, WWP can be re-established to fulfill its key ecological roles in forests of this region. When mature WWP are sufficiently abundant, natural regeneration should be encouraged to increase forest resilience and local adaptation to biotic and environmental factors.