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The use of western white pine (Pinus monticola) has declined to very low levels due to its susceptibility to white pine blister rust and silvicultural guidelines recommending extremely conservative guidelines for reforestation with this species.
The decline of the native population, combined with the lack of regeneration, has driven white pine down to a small fraction of the total forest composition despite its ecological and commercial values and usefulness as a substitute for Douglas-fir in areas subject to laminated root rot. Heritable natural resistance has been noted in some individuals and populations, and a program involving selection and seedling screening for blister rust resistance involving both the Ministry of Forests and Range and Canadian Forest Service is underway. Trees from this program have been selected and been established in seed orchards. Although increased resistance has been achieved in progeny, it is considered only “partial resistance” based mainly on slow canker growth. Silvicultural interventions such as pruning are still advised. Another type of resistance that originates from near the USDA Forest Service seed orchard in Dorena, Oregon can confer total resistance. This trait provides resistance to blister rust that is based on a single gene known as Cr2, and is often referred to as MGR (Major Gene Resistance) white pine. This gene activates a recognition mechanism that prevents the rust from entering the host completely. The dark cloud behind the silver lining is that this MGR resistance will likely fail at some point in the future. This is due to the inherent dynamics of disease resistance that is based on a single host gene that can be overcome by the pathogen, as the generation time of the pathogen is an order of magnitude faster than that of the host tree, allowing it to evolve more rapidly. Predictions suggest MGR resistance may last about 40 years. The white pine tree improvement program is concentrated on improving the partial resistance by a recurrent selective breeding program. By combining resistance mechanisms in MGR pedigrees we may be able to extend the duration of MGR protection. A major research component supports finding other types of strong resistance similar to the MGR. The breeding program has been guided by Dr. Rich Hunt of the CFS who has screened over 300 families. The best parents were designated as either Slow Canker Growth (SCG) or Difficult to Infect (DI). SCG trees occur more frequently than DI. Also included as parents were some of the best of the Texada Island trees and some Idaho, Interior B.C., and Dorena (Oregon) trees. Most of the crossing for this program was conducted in the CanFor Seed Orchard in Sechelt by Patti Brown, who is also the chair of the White Pine species committee of the Coastal Technical Advisory Committee supporting the Forest Genetics Council of B.C. To date, we have over 200 F1 families in this recurrent selection program tested in sites on Texada Island, the Sunshine Coast and Vancouver Island. Measurements of these trials including survival, infection rates, resistance mechanism, and growth is ongoing. Recent publications from the white pine program include: Hunt, R.S. 2004a. Blister-rust-resistant western white pine for British Columbia. Natural Resources Canada, Canadian Forestry Service Information Report BC-X-397. Hunt, R.S. 2004b. Environmental and inoculum source effects on resistance of Idaho F2 western white pine in British Columbia. Can. J. Plant Pathol. 26:351-357. Hunt, R.S., G.D. Jensen, and A. K. Ekram. 2004. Confirmation of dominant gene resistance (Cr2) in the U.S. white pine selections to white pine blister rust growing in British Columbia. Pp: 227-229 in Richard A. Sniezko, Safiya Samman, Scott E. Schlarbaum,and Howard B. Kriebel, eds. Breeding and genetic resources of five-needle pines: growth, adaptability, and pest resistance: 2001 July 23-27; Medford, OR, USA. IUFRO Working Party 2.02.15. Proceedings RMRS-P-32. Fort Collins, CO, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 259 p. King J.N. and R. Hunt. 2004. Five-needle pines in British Columbia, Canada: Past present and future. Pp: 12-19 in Richard A. Sniezko, Safiya Samman, Scott E. Schlarbaum,and Howard B. Kriebel, eds. Breeding and genetic resources of five-needle pines, growth, adaptability, and pest resistance, 2001 July 23-27; Medford, OR, USA. IUFRO Working Party 2.02.15. Proceedings RMRS-P-32. Fort Collins, CO, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 259 p. King J.N. and A. David. Genetic approaches to the management of blister rust in white pines. For. Ecol. Manage. (submitted)
Ministry Contact: Alvin Yanchuk |
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