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The demand for taxol, a promising cancer chemotherapeutic agent, far exceeds supply. Presently, taxol is derived from the bark of the Pacific yew, Taxus brevifolia, a small, slow-growing evergreen tree native to the northwestern United States. Knowledge of the distribution and magnitude of genetic and non-genetic sources of variation in taxol content in the genus Taxus is necessary if supply issues are to be met through plant harvesting. Analytical determinations of taxol, cephalomannine, and baccatin III in more than 200 trees representing several populations of T. brevifolia and other yew taxa indicate that (1) significant variation in taxane content exists among and within populations and species, (2) taxol levels exceeding those reported for T. brevifolia bark were found in shoots of individual trees from most taxa studied, and (3) the season in which samples are collected and handling procedures can influence taxane content.

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Pacific yew (Taxusbrevifolia Nutt.) is a shade-tolerant gymnosperm native to the western United States and Canada. It recently gained attention as the source of Taxol® (paclitaxel), a promising new anticancer drug. Large-scale harvest of mature Pacific yew trees for the extraction of paclitaxel has resulted in the need for improved forest management practices and an increased understanding of the amount and distribution of genetic variation in the species. We partitioned estimates of genetic variance for allozyme, metric, and taxane traits into region, population, family, and within family components in seedling common-garden tests. Genetic diversity, genetic distance, and Nei's Gst values were estimated based on gene frequencies for 22 isozyme loci. Concentrations of taxanes were determined for needles and roots using HPLC. Populations of Pacific yew are more distinct from one another than is typical of long-lived, wind-pollinated conifers in western North America, but there is little regional differentiation. Yew populations have notably less allozyme diversity than most other gymnosperms with similar life-history characteristics. Most genetic variation in all traits occurs within the population, and much of that is within family. Heritabilities for growth and taxane traits ranged from low to moderately high. Gene conservation or management strategies should include broad sampling among and within populations of Pacific yew. Opportunities for genetic selection to develop improved lines or cultivars for the production of paclitaxel exist, but use of currently domesticated yew species is more time and cost efficient.

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Gene flow is a critical determinant of population genetic structure, playing an important role in forest tree improvement, conservation genetics, and the potential for the escape of engineered genes. A review of gene flow among plant populations yields the following generalization: although gene flow varies substantially among species, populations, seasons, and even individual plants, at physical isolation distances of hundreds to thousands of meters, gene flow levels are frequently sufficient to counteract genetic drift and moderate levels of directional selection. Gene flow will be hard to predict a priori. Therefore, any project or management plan depending on a given level of gene flow or reproductive isolation should include a genetically-based method to measure the actual gene flow among the populations involved.Abstract.Biochemical markers are ideally suited for addressing questions concerning genetic or parental identity. For production seed orchards, such questions are common as a consequence of the uncertainty of paternity in non-controlled cross situations. During the last decade, electrophoretic procedures have been used extensively to investigate issues such as:-clonal identification, -pollen contamination levels, -mating systems, -supplemental mass pollination (SMP) verification, -patterns of gene flow, and -levels of pollen competition.A number of patterns have emerged from this work. Most notable, contamination rates are disturbingly high, clonal phenology and pollen application methodology influence SMP success, and phenology and proximity are important in determining paternal success. Results are discussed with reference to orchard management prescriptions.This paper was distibuted within Weyerhaeuser Company as an internal research report.