Cronartium ribicola
White Pine Blister Rust - Cronartium ribicola J.C. Fisch
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White pine blister rust
White pine blister rust is a disease that rivals chestnut blight for impact on North American ecosystems. The fungus attacks five-needle pine species (Pinus) in both eastern and western forests, causing galls that eventually girdle branches and stems. Gooseberry and currant species (Ribes) serve as alternate hosts. The fungus thrives in a cool, wet-weather environment, so climate is a major factor in determining rust hazard areas. The rust fungus was introduced in multiple shipments of nursery stock from Europe to Kansas in 1892, eastern Canada and New York in 1906, and western Canada in 1910 (Mielke, 1938; Tainter & Baker, 1996). After introduction, the fungus quickly spread west and north to eastern white pine (P. strobus) populations in the Great Lakes region and northeast and subsequently southward, to high-elevation eastern white pine populations in North Carolina. In western forests, the disease rapidly spread through western white and sugar pines (P. monticola and P. lambertiana), as well as impacting whitebark and southwestern white pines (P. albicaulis and P. strobiformis; USDA Forest Service, 1991; Hoff & Hagel, 1989). Mortality in western white pine stands can approach 94% (Hirt, 1948). More recently, infection of limber pine (Pinus flexilis) has been observed in one stand in the central Rocky Mountains (G. I. McDonald pers. comm. to S. Schlarbaum). Limber pine is a five-needle pine species that is not commonly harvested for timber or pulp, but it is a common component of western forest ecosystems. Devastation of this species would have significant impacts on the structure and function of these ecosystems as well as to recreational use of the forests. In Idaho, scientists have found three sites at which the white pine bister rust pathogen is hybridizing with a native rust, C. comandrae, on limber pine. The hybridization is occurring despite a lack of shared hosts. Scientists have not yet determined whether this event is widespread or whether it demonstrates a new hybridization mechanism. Such a mechanism might be synchronized sporulation at these high elevations, or insect transmission of the spores (Hamelin, 2004).
Different approaches have been used to address white pine blister rust. In eastern forests, a massive gooseberry and currant eradication program reduced populations of the alternate host for the pathogen. This strategy was particularly effective for intermediate hazard areas (Tainter & Baker, 1996). Exploiting natural resistance, long-term breeding programs were initiated by the USDA Forest Service (Bingham, 1983). Rust-resistant western white, sugar pine and eastern white pine seedlings are available for planting (Bingham, 1983; Garrett, 1986). This is a dramatic change from the late 1960s, when planting of western white pines was generally discontinued (Ketcham et al., 1968). Rust-resistance breeding programs continue today in the United States and Canada (Hunt, 2002; Neuenschwander et al., 1999; Sniezko et al., 2000).
Whitebark pine is not a commercially important species for timber and, therefore, has not received much attention in terms of resistance breeding. This is unfortunate, as Schmidt (1992) estimated that 80-90% of the whitebark pines in Montana's Glacier National Park and the Bob Marshall Wilderness area have blister rust. In British Columbia, a sampling of 54 stands revealed 21% of the trees were dead and as high as 44% of the remaining trees had blister rust (Campbell & Antos, 2000). Other whitebark pine populations have similar mortality and infection percentages. Whitebark pine occupies a critical niche in western ecosystems by producing large seeds that are extremely nutritious and important in food chains of 110 animals. Whitebark pine seeds are especially important diet components of grizzly bear, black bear, red squirrel, and Clark's nutcracker (Kendall & Arno, 1989; Schmidt, 1992; Reinhart et al., 2001).
Sources
Bingham, R. T. 1983. Blister rust resistant western white pine for the Inland Empire: the story of the first 25 years of the research and development program. USDA Forest Service General Technical Report INT-146. 45 pages.
Campbell, E. M., and J. A. Antos. 2000. Distribution and severity of white pine blister rust and mountain pine beetle on whitebark pine in British Columbia. Can. J. For. Res. 30: 1051-1059.
Garrett, P. W. 1986. Role of tree improvement in providing pest-resistant eastern white pine (Pinus strobus L.). In Eastern White Pine: Today and Tomorrow Symp. Proc., U.S. Dep. Ag. For. Serv. Gen. Tech. Rep. WO-51, pp. 75-88.
Hamelin, R.C. 2004. Exotic and native rust pathosystems: A population genomics approach. Presentation given at the American Phytopathological Society annual meeting August 2, 2004 - Special Sessions: Co-Evolutionary Processes of Introduced Pathogens and Hosts in Natural Ecosystems.
Hirt, R. R. 1948. Evidence of resistance to blister rust by eastern white pine growing in the Northeast. J. For. 46: 911-913.
Hoff, R. and S. Hagle. 1989. Diseases of whitebark pine with special emphasis on white pine blister rust. In Proceedings - Symposium on Whitebark Pine Ecosystems: Ecology and Management of a High-Mountain Resource. Bozeman, MT. March 29-31, 1989. Schmidt, W. C., and K. J. McDonald, Compilers. pp. 179-190.
Hunt, R. S. 2002. Relationship between early family-selection traits and natural blister rust cankering in western white pine families. Can. J. Plant Path. 24: 200-204.
Kendall, K. C. and S. F. Arno. 1989. Whitebark pine - an important but endangered wildlife species. In Proceedings - Symposium on Whitebark Pine Ecosystem: Ecology and Management of a High-Mountain Resource. Bozeman, Mt. March 29-31, 1989. Schmidt, W. C. and K. J. McDonald, Compilers. pp. 264-273.
Ketcham, D. E., C. A. Wallner, and S. S. Evans, Jr. 1968. Western white pine management programs realigned on northern Rocky Mountain National Forests. J. Forestry 6: 329-332.
Mielke, J. L. 1938. Spread of blister rust to sugar pine in Oregon and California. J. For. 36: 695-701.
Neuenschwander, L. F., J. W. Byler, A. E. Harvey, G. I. McDonald, D. S. Ortiz, H. L. Osborne, G. C. Snyder, and A. Zack. 1999. White pine in the American West: a vanishing species - can we save it? Gen. Tech. Rep. RMRS-GTR-35. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 20 p.
Reinhart, D. P., M. A. Haroldson, D. J. Mattson, and K. A. Gunther. 2001. Effects of exotic species on Yellowstone's grizzly bears. Western N. Amer. Naturalist 61: 277-288.
Schmidt, W. C. 1992. Effects of White Pine Blister Rust on Western Wilderness. In Society of American Foresters 1992 Annual Meeting, Proceedings. SAF Publication 92-01.
Sniezko, R. A., A. Bower, and J. Danielson. 2000. A comparison of early field results of white pine blister rust resistance of sugar pine and western white pine. HortTechnology 10: 519-522.
Tainter, F. H., and F. A. Baker. 1996. Principals of Forest Pathology. John Wiley & Sons, Inc., New York. 805 pp.
United States Department of Agriculture Forest Service. 1991. Pest Risk Assessment of the Importation of Larch from Siberia and the Soviet Far East, Miscellaneous Publication No. 1495, September, 1991.
