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Conservation genetics of whitebark pine (Pinus albicaulis Engelm) in British Columbia Krakowski, Jodie

Abstract

Pinus albicaulis Engelm. is a keystone subalpine species found throughout mountainous regions of western North America. Population genetic investigations in British Columbia using isozymes (17 populations, 12 loci) extracted from bud tissue revealed that the species has high levels of observed and expected heterozygosity compared to other pine species (0.213 and 0.262, respectively). Isozyme analysis (two populations, ten loci) using maternal gametopyte tissue and embryos extracted from seed elucidated that biparental inbreeding, and possibly selfing, is common (mean multilocus outcrossing rate = 0.73, mean single-locus outcrossing rate = 0.69). There is moderate population substructuring (FST = 0.061), typified by the clumped distribution of trees, influencing gene flow, although seed distribution by Clark's nutcracker appears to be the overriding factor influencing genetic patterns. There were few rare alleles found and genetic distances between populations were small (Nei's 1978 distance ranged from 0.006 to 0.134 and Cavalli-Sforza and Edwards' (1967) chord distance from 0.086 to 0.297). Genetic distances were weakly related to physical distances between populations (Mantel test, p = 0.036). Observed heterozygosity was significantly negatively correlated with longitude (R² = 0.295) and latitude (R² = 0.357). Population genetic parameters were consistent with other studies suggesting northerly postglacial recolonization from refugia in the Washington and Oregon Cascades and several more northern refugia in the Rockies, including the possiblity of a refugium near Roger's Pass, BC. Nearly all populations were observed to have Cronartium ribicola Fisch. (white pine blister rust) infections, mortality of trees of all ages was often present (due to various causes), and regeneration was often sparse or absent. A conservation strategy was developed based on the results of these investigations, concurrent with the priorities and recommendations of other agencies involved with whitebark pine conservation. Priorities included continuing surveys of natural stands in order to identify and monitor putatively resistant trees, collecting seed from all available seed sources and especially these selected individuals, establishing common garden tests to assess adaptive variation and screen for disease resistance, establishing field trials in natural habitats with a variety of hazard ratings for blister rust, developing appropriate seed and scion transfer guidelines, and maintaining a cooperative exchange in terms of materials and research with other jurisdictions involved in whitebark pine conservation. Future research may involve isolation of any specific resistance mechanisms, genetic transformation or cross-breeding of susceptible individuals, and bulk propagation of resistant individuals or families via rooting cuttings or somatic embryogenesis. In the longer term, breeding strategies involving controlled crosses of putatively restitant parents in order to produce hardy and disease resistant planting stock for a variety of hazard-rated sites should be instituted. Due to the extremely long generation time of this species, it is critical that conservation measures begin immediately.

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