Genetic variation and parameter estimates in Taxusbrevifolia (Pacific yew)

Abstract

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.

High differentiation among populations of the woody legume Sesbania sesban in sub-Saharan Africa: Implications for conservation and cultivation during germplasm introduction into agroforestry systems

“…RAPD data are, however, in contrast to molecular studies on other woody perennials sampled across a similar geographic scale, which generally indicate relatively little variation among populations for nuclear-encoded molecular markers (e.g., Leonardi and Menozzi, 1995;Wheeler et al, 1995;Zanetto and Kremer, 1995;Bodénès et al, 1997; for reviews, see Hamrick et al, 1992;Hamrick and Godt, 1989;Nybom and Bartish, 2000).…”

High variation and strong phylogeographic pattern among cpDNA haplotypes in Taxus wallichiana (Taxaceae) in China and North Vietnam

“…1996), populations of T. wallichiana seem to maintain large differentiation values between populations, probably because of its habitat as part of the undergrowth in forests. There, wind velocities are greatly reduced and the temperature inversions negatively affect pollen dispersal (Tauber 1967; Levin & Kerster 1974; Wheeler et al . 1995).…”

“…Despite its dioecy, wind-pollination and endozoochorous seed dispersal (DiFazio 1996;Wilson et al 1996), populations of T. wallichiana seem to maintain large differentiation values between populations, probably because of its habitat as part of the undergrowth in forests. There, wind velocities are greatly reduced and the temperature inversions negatively affect pollen dispersal (Tauber 1967;Levin & Kerster 1974;Wheeler et al 1995). The significant population structuring and high population differentiation recorded for T. wallichiana would fit a very limited range of wind-mediated pollen flow, as indicated earlier for Taxus by Allison (1990) who reported that the efficiency of dispersal of T. canadensis pollen drops significantly after a few metres under natural conditions, this is despite the small size of Taxus pollen (17-21.5 µm, Xing et al 2000).…”

FINE-SCALE GENETIC STRUCTURE OF WHITEBARK PINE (PINUS ALBICAULIS): ASSOCIATIONS WITH WATERSHED AND GROWTH FORM

“…Since the 1980s, abundant allozyme studies of widespread, open-pollinated, coniferous species in the western United States and elsewhere-most of which have wind-dispersed seed-s-have composed a rather consistent pattern of genetic architecture for this taxonomic group (e.g., Dancik and Yeh 1983;Hiebert and Hamrick 1983;Li and Adams 1989;Wheeler et al 1995). For such species, genetic differences among populations are low and within populations are high (e.g., Hamrick and Godt 1990).…”