Elliottia racemosa, classified within the group of the Ericaceae family, is one of the rarest native small trees or large shrubs in Georgia and is a state threatened shrub (Chafin, 2007). Elliottia racemosa, commonly called Georgia plume, derives its name from the beautiful plume-like clusters of slightly aromatic white flowers that appear in early summer (Elliott, 1971). Georgia plume is a beautiful deciduous shrub reaching heights of 20 feet tall with leaves that are elliptic, alternate, 2.5 to 12.7 cm long by 1.3 to 5 cm wide, and tapering at both ends. Flowers have four or five curved white petals each growing up to 14 mm long, which appear between the middle of June and end of July (Patrick et al., 1995). The flowers develop into small round capsules, which can contain up to ≈40 seeds.
Georgia plume was first discovered by William Bartram in 1773 and not collected again until it was found by South Carolina botanist Stephen Elliot 35 years later (Ewan, 1968; Patrick et al., 1995). Attesting to the rarity of the species, no wild populations were known to science after ≈1875 until it was rediscovered in 1901. Many of the known populations are now destroyed or very reduced with few on conservation land (Chafin, 2007). Today, E. racemosa is found only in ≈36 locations in the state of Georgia (Patrick et al., 1995). The best habitats generally seem to be sunny to partially shady conditions on well-drained sand ridges, oak ridges, evergreen hammocks, acid soil, and sandstone outcrops. Although this plant is very rare and localized, it grows in a broad variety of sandy soil conditions ranging from moist to extremely dry (Patrick et al., 1995).
Bozeman and Roger (1983) reported that natural seed set in Georgia plume is limited or nonexistent. Recent seedling recruitment has not been documented in any populations (Godt and Hamrick, 1999). Contributing factors may include self-incompatibility, low pollen viability, and limited numbers of clones within locations (Godt and Hamrick, 1999; Thompson and Spira, 1991). Some plants show multiple trunks owing to vegetative root sprouting after injury such as cutting or fire indicating extensive clonal growth occurs. However, the biological cycle and life history of Georgia plume is not well reported or understood.
Efforts to propagate Georgia plume using conventional methods have been generally ineffective. Fordham (1969) obtained limited success with seed germination. The problem was that only a small percentage of seed was sound. Seed stratification removed a cold requirement, but only if given to seed treated within a few months of collection. Old seed acquired secondary dormancy and unpredictable behavior (Fordham, 1969). Fordham (1991) determined that Georgia plume's seed dormancy mechanism required a prolonged chilling period (42 to 64 d) for germination. Propagation by root cutting methods can produce shoots, but in a limited number.
Tissue culture methods can be an excellent option for the propagation and conservation of threatened or endangered species because small amounts of tissues can be used for mass propagation without damage to the donor (Varadaragan, 1993). A large number of plants may be produced in a given time, and little space is required for tissue culture compared with other propagation methods (Fay, 1992). It is also possible to maintain large genotypic libraries of selected species for plant conservation.
The Ericaceae contains a number of economically important plants such as blueberry, cranberry, and rhododendron. This has led to the development of efficient plant regeneration protocols achieved through organogenesis from cultures derived from leaf tissue, shoot tips, and axillary buds. Plants regenerated from this family include blueberry (Billings et al., 1988; Callow et al., 1989; Cao and Hammerschlag, 2000; Hruskoci and Read, 1993), cranberry (Debnath and McRae, 2001b; Qu et al., 2000), lingonberry (Debnath, 2003; Debnath and McRae, 2002), blackberry (Gonzalez et al., 2000), and rhododendron (Iapichino et al., 1992; Meyer, 1982).
A number of endangered species have been successfully regenerated using in vitro culture methods. For example, rapid multiplication of Blue Vanda of Asia (Vanda coerulea Griff ex. Lindl.) was accomplished using shoot tips, leaves, and leaf bases (Seeni and Latha, 2000). After plant regeneration, plantlets were successfully reintroduced into alien forest habitats. Mass propagation protocols for Vaccinium cylindraceum Smith (Ericaceae) (Pereira, 2006), Maclura tinctoria (Gomes et al., 2003), Vanda coerulea (Malabadi et al., 2004), and Daphne cneorum (Mala and Bylinsky, 2004) were successfully achieved.
In vitro plant regeneration of Georgia plume has not been previously reported and may be a method for the conservation and propagation of this threatened species. The overall goal of this study was to develop tissue culture protocols for the mass propagation of Elliottia racemosa, Georgia plume, applicable for conservation purposes. Objectives of the work include the development of efficient sterilization conditions for initiation of cultures and the development of protocols for shoot proliferation, rooting, and acclimatization of plants.
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