Adventitious shoot-based propagation of Franklinia alatamaha for commercial horticulture and restoration

Franklinia is a monotypic genus of the family Theaceae that is now extinct in the wild. F. alatamaha Bartram ex Marshall has been maintained in cultivation for nearly 250-y because of the ornamental appeal of its flowers and foliage. The goal of this research was to develop an in vitro propagation system to increase the availability of this rare tree for commercial horticulture and restoration. Immature zygotic embryos were cultured on semi-solid Woody Plant Medium containing 34 different plant growth regulator treatments. Shoot organogenesis was induced from dark-grown explants with indole-3-butyric acid in combination with 6-benzylaminopurine. Shoot organogenesis was also obtained with thidiazuron, N-(2-Chloro-4-pyridyl)-N′-phenylurea, and indole-3-butyric acid in combination with meta-Topolin, although shoot development was abnormal. Adventitious buds were produced on the epidermal surfaces of immature zygotic embryos while exposed to the above plant growth regulator treatments. Once the adventitious buds elongated into shoots, these adventitious shoots were further multiplied by axillary shoot production. Elongated shoots from axillary shoot production were rooted on Woody Plant Medium supplemented with 0.25 g L−1 activated charcoal, but no plant growth regulators. The resulting plantlets were transferred to soil and acclimatized to the greenhouse and outdoor environments. Tissue culture-derived trees flowered within one and a half years in the greenhouse under an extended photoperiod.