GENETIC-VARIATION AND PARAMETER ESTIMATES IN TAXUS-BREVIFOLIA (PACIFIC YEW)

Pacific yew (Taxus brevifolia Nutt.) is a shade-tolerant gymnosperm na tive to the western United States and Canada. It recently gained atten tion as the source of Taxol(R) (paclitaxel), a promising new anticance r drug. Large-scale harvest of mature Pacific yew trees for the extrac tion of paclitaxel has resulted in the need for improved forest manage ment practices and an increased understanding of the amount and distri bution of genetic variation in the species. We partitioned estimates o f 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 G(st) val ues were estimated based on gene frequencies for 22 isozyme loci. Conc entrations of taxanes were determined for needles and roots using HPLC . Populations of Pacific yew are more distinct from one another than i s typical of long-lived, wind-pollinated conifers in western North Ame rica, but there is little regional differentiation. Yew populations ha ve notably less allozyme diversity than most other gymnosperms with si milar life-history characteristics. Most genetic variation in all trai ts occurs within the population, and much of that is within family. He ritabilities for growth and taxane traits ranged from low to moderatel y high. Gene conservation or management strategies should include broa d sampling among and within populations of Pacific yew. Opportunities for genetic selection to develop improved lines or cultivars for the p roduction of paclitaxel exist, but use of currently domesticated yew s pecies is more time and cost efficient.