This special issue is dedicated to the in vitro tools and methods used to conserve the genetic diversity of rare and threatened plant species from around the world. Species that are on the brink of extinction because of the rapid loss of genetic diversity and habitat come mainly from resource-poor areas of the world and from global biodiversity hotspots and island countries. These species are unique because they are endemic, and only a few small populations or sometimes only a few individuals remain in the wild. Therefore, the challenges to support conservation by in vitro measures are many and varied. The editors of this invited issue solicited papers from experts from Asia, Africa, Europe, Australia, and North and South America. This compilation of articles describes the efforts in these diverse regions toward saving plants from extinction, and details the direct application of in vitro and cryopreservation methods. In addition, these contributions provide guidance on propagation of rare plants, including techniques for large-scale propagation, storage, and reintroduction. The in vitro techniques for conserving plant biodiversity include shoot apical or axillary-meristem-based micropropagation, somatic embryogenesis, cell culture technologies and embryo rescue techniques, as well as a range of in vitro cold storage and cryopreservation protocols, and they are discussed in depth in this issue.

Continuing loss of native orchid habitat has lead to an increased emphasis on orchid conservation. Major obstacles in the production of native orchid seedlings for use in conservation have been: (1) development of efficient and reliable seed germination protocols and (2) an understanding of early seedling growth and development. Effects of six asymbiotic media (Modified Lucke, Murashige & Skoog, Lindemann, Vacin & Went, Malmgren Modified, Knudson C), four exogenous cytokinins (BA, Zea, Kin, 2-iP), and three photoperiods (0/24, 16/8, 24/0 h L/D) were examined on seed germination and early protocorm development of Habenaria macroceratitis, a rare native Florida terrestrial orchid. Finally, the effects of three photoperiods (8/16, 12/12, 16/8 h L/D) on in vitro seedling development were examined. Percent seed germination was highest on both LM and KC after seven weeks culture (LM = 89.1%, KC = 89.2%); however, protocorm development was enhanced on MM after both seven and 16 weeks. Both zeatin and kinetin at 1 lM enhanced seed germination (Zea = 58.1%, Kin = 47.2%). Final percent seed germination (91.7%) and protocorm development (Stage 4) was increased in the absence of light (0/24 h L/D). In vitro seedlings cultured under 8/16 h L/D conditions produced the highest number of tubers per seedling (1.06) with the greatest tuber (42.7 lg) and shoot (fwt = 69.5 lg) biomass and tuber diameter (3.1 mm).

Procedures for asymbiotic seed germination and seedling acclimatization were developed for

A major obstacle to native orchid production is difficulty in seed germination. Culture media and light effects on seed germination of Calopogon tuberosus var. tuberosus, a native orchid with horticultural potential, were studied. Culture media included Knudson C, Malmgren modified terrestrial orchid, and PhytoTechnology orchid seed sowing. Effects of 8 weeks continual darkness, 8 weeks 16-h photoperiod, 2 weeks dark followed by 6 weeks 16-h photoperiod, 4 weeks dark followed by 4 weeks 16-h photoperiod, and 6 weeks dark followed by 2 weeks 16-h photoperiod were examined. Percent seed germination was highest on Knudson C after 8 weeks culture; however, seedling development was enhanced on PhytoTechnology seed sowing medium during 8 weeks culture under a 16-h photoperiod. This suggests that while KC and darkness promoted seed germination, P723 and light enhanced further seedling development. Seedlings of C. tuberosus readily acclimated to greenhouse conditions. Abbreviations: KC -Knudson C; MM -Malmgren modified terrestrial orchid medium; NAD -nicotinamide adenine dinucleotide; NADP -nicotinamide adenine dinucleotide phosphate; P723 -Phyto Technology orchid seed sowing medium

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