Micropropagation of endangered plants of the American interior Northwest

John L. Edson and David L. Wenny, Dept of Forest Resources, University of Idaho Moscow, Idaho, 83844-1133, USA

Abstract

A micropropagation unit was established at the University of Idaho in 1991 to undertake propagation studies of plants native to the interior Pacific Northwest of the United States. The unit aims to help reduce endangerment to threatened restricted endemic and coastal disjunct species in the region. Current projects involve a diverse group of species from a variety of habitats.

Introduction

The University of Idaho Forest Research Nursery established a tissue culture laboratory in 1987. In 1991 a fog propagation room and an acclimatization house were added to create an operational micropropagation unit.

Until recently, our micropropagation research concentrated on multiplying valuable clones for native tree and shrub improvement projects and mass propagating common native species for habitat rehabilitation. However, as rare plant inventories and endangerment assessments have become available (Moseley & Groves, 1990), we have increasingly focused on conserving threatened and endangered plants of the montane forests, the subalpine and alpine zones, and the basin rangelands of the interior Pacific Northwest of the USA.

Endemics and disjuncts

The complex geography, geology, and climate history of the interior Northwest have probably influenced the distribution of not only the restricted endemic species but also the small disjuncts isolated since pre-glacial times from larger populations on the Pacific coast (Daubenmire, 1956). The crest of the northerly trending Cascade Ranges of the Pacific coast forms the western boundary of the region. The Cascades intercept the prevailing moist westerly winds from the Pacific to create a rain shadow in the semi-arid lowlands of the Columbia Basin, where the steppe communities include a number of rare restricted endemics. Over 350 km to the east, the Northern Rockies rise to form the region's eastern boundary. Here, subalpine communities on mountaintops of lower elevation have become ecological islands with numerous restricted endemics. Here also, in a few relatively warm and wet low-elevation valleys, are isolated plant communities with strong coastal affinities. The Snake River plain defines the region's southern border.

The species selected for propagation have satisfied one or more of the criteria recommended by Falk & Holsinger (1991) for initiating a high priority conservation effort. The selections are either naturally rare species or small coastal populations disjunct to northern Idaho. The rare species are at risk from proximity to human activity, widespread and irreversible changes in land use, and the possible threat of rapid climate change.

Projects

A highly endangered endemic

Showy stickseed, Hackelia venusta (Boraginaceae), is a biennial herb native to the low-rainfall eastern-slope forests of the Washington Cascades. The species exists at three known sites. The surface-sterilized explants consisted of nodal segments excised from the basal sections of flower stalks, embryos dissected from immature seed, and shoot tips from basal rosettes. After incubation for a week on ˝MS medium (Murashige & Skoog, 1962), + 0.1 mg/l BAP, axillary shoots began to elongate. Several microshoots have rooted after transfer to hormone-free media. Although tissue blackening currently slows multiplication, we aim to plant out several thousand plantlets at four sites.

H4>A threatened coastal disjunct Pacific dogwood, Cornus nuttallii (Cornaceae), an understory tree with large showy white bracts, is a unique coastal disjunct to the coniferous montane forests of northern Idaho. The dogwood population has declined rapidly since 1988 with fewer than 700 individuals remaining in their former Pleistocene Rocky Mountain refugium. Seed crops have failed since 1990 and most trees exhibit disease symptoms (Lichthardt, 1991). However, representative seed collections made in 1986 and 1990 form the basis of an ongoing conservation effort (Guerrant, 1991).

From the first seed collection, we produced 400 greenhouse seedlings for vegetative propagation. Since stem cuttings failed to root and the success rate with rooted layers was low, we micropropagated shoot-tip and nodal explants on WPM medium (Lloyd & McCown, 1980) + 0.1 mg/l BAP. We maintain over 500 microshoots in a clone bank (representative of the cultivated seedlings). We have rooted some of these shoots ex vitro using 4.5% IBA in a dry talc powdered dip.

Endangerment from urban expansion

Three species of southern Idaho, Allium aasae (Alliaceae), Astragalus mulfordiae (Leguminosae), and Lepidium papilliferum (Cruciferae), are restricted endemics in the foothills of the ranges immediately to the north of the rapidly growing metropolitan city of Boise. The impending habitat loss threatens with extinction these rare but otherwise genetically stable populations. Seed and shoot-tip explants of these species are currently in culture.

Plant adaptability studies with a rare steppe species

Astragalus columbianus, once thought extinct, was rediscovered by Sauer et al. (1979) on several benches and sandy slopes in the basalt flow terrain of the Columbia basin. Seed has germinated in vitro, and propagation systems are being studied. The on-site performance of plantlets and natural germinants from the soil bank will be compared.

Pre-empting the threat of global climate change

Douglasia idahoensis (Primulaceae) is a rare, highly ornamental ground cover plant found in several subalpine communities on ridges and peaks of the Northern Rockies. The dependence of this species on elevation-specific conditions would putthis plant at risk if the climate were to warm rapidly. An incubation and multiplication protocol being developed with commoner closely related taxa will be applied to D. idahoensis.

Conclusion

Updated inventories and endangerment assessments have identified rare flora of the American interior Northwest in need of conservation. In response, the Forest Research Nursery at the University of Idaho has initiated micropropagation projects to help conserve the species diversity of the region.

References

Daubenmire R. (1956) Climate as a determinate of vegetation distribution. Ecol. Monographs 26:231.

Falk D.A. & Holsinger K.E. (1991) Genetics and conservation of rare plants. OUP.

Guerrant E.O. (1991) Ex situ conservation collection of Pacific dogwood (Cornus nuttallii) from Idaho, at the Berry Botanic Garden. Report to the State of Idaho Natural Heritage Program, Department of Fish and Game, Boise. 6 pp. Moseley R. & Groves C. (1990) Rare, threatened, and endangered plants and animals of Idaho. Report to the State of Idaho Natural Heritage Program, Department of Fish and Game, Boise. 33 pp.

Murashige T. & Skoog F. (1962) A revised medium for rapid growth and bio-assays with tobacco tissue cultures. Phys. Plant. 15:473-497.

Sauer R.H., Mastrogiuseppe J.D., & Smookler R.H. (1979) Astragalus columbianus (Leguminosae) - rediscovery of an "extinct" species. Brittonia 31:261-264