Somatic Embryogenesis and Organogenesis of Rare Woody Species in Georgia, Stewartia and Franklinia

Propagation of rare and endangered plant species via seed is often challenging due to difficulties with seed collection, low seed yields and viability, and sometimes complicated requirements for germination. Also, sites for collection are few and the amounts of seed and plant material are limited. As an alternative to propagation by seed, this research investigated the use of plant tissue culture methods, specifically somatic embryogenesis and organogenesis, to enhance the populations of two rare and one extinct woody plant species in Georgia, Stewartia malacodendron Linnaeus (Silky camellia), Stewartia ovata (Mountain camellia), and Franklinia alatamaha (Franklinia), respectively. At present, only 40 populations of S. malacodendron are known to exist and they are currently located on three state conservation lands, military bases, and a few on private lands in Georgia. Franklinia has not been seen in the wild since 1804. Seeds from immature fruit capsules for each species were surface-disinfested and zygotic embryos were aseptically excised and cultured on sterile semisolid culture media supplemented with various types and concentrations of plant growth regulators (PGRs). Adventitious shoot organogenesis was induced on embryo explants of F. alatamaha and S. ovata using 0.1 mg/L Indole-3-butyric acid (IBA) and 1 mg/L 6-Benzylaminopurine (BAP). Somatic embryogenesis was induced at a very low frequency in the presence of 2 mg/L 2, 4-Dichlorophenoxyacetic acid (2, 4-D) on excised embryos with endosperm explants of S. malacodendron and S. ovata. Propagation of Stewartia and Franklinia using plant tissue culture methods demonstrates the ability to increase the populations of rare woody plant species to support conservation and restoration efforts.

Keywords: Somatic embryogenesis, organogenesis, plant growth regulators (PGRs), Indole-3-butyric acid (IBA), 6-Benzylaminopurine (BAP), 2, 4-Dichlorophenoxyacetic acid (2, 4-D), restoration, conservation.