Scott L. Stewart

Symbiotic germination of three semi-aquatic rein orchids (Habenaria repens, H. quinquiseta, H. macroceratitis) from Florida

The destruction of wetlands in populated areas (e.g. Florida) has prompted interest in habitat restoration. We describe a symbiotic technique to germinate seeds of three semi-aquatic rein orchid species from Florida (Habenaria repens, H. quinquiseta, H. macroceratitis) and to cultivate H. repens seedlings on soil ex vitro. Seeds of all three Habenaria spp. germinated within 21 days of inoculation. Leaf-bearing seedlings of H. repenswere obtained using two fungal isolates (Epulorhiza spp.) recovered from Florida orchids Spiranthes brevilabrisand Epidendrum conopseum . Seedlings infected with the S. brevilabris fungus that were transferred to peat in a greenhouse had the highest (88.9%) survival (>159 days ex vitro). One H. repens seedling initiated anthesis 18 months after seed sowing. The methods outlined by this study have the potential to be adopted by wetland restoration projects seeking to include an orchid ( H. repens) and mycorrhizal fungi as biotic agents.

Water requirements of terrestrial and epiphytic orchid seeds and seedlings, and evidence for water uptake by means of mycotrophy.

The use of endomycorrhizal fungi as an energy source (=mycotrophy) initiates seedling development and supplements or replaces photosynthesis in all orchids in nature. Fungus-infected and non-infected seeds of the monkey face orchid, Platanthera integrilabia, a US Federally-threatened terrestrial species, had a different set of water relations than seeds of the green fly orchid, Epidendrum conopseum, a subtropical epiphyte. Seeds of the terrestrial species had lower water loss rates, smaller activation energies for water loss and absorbed water from lower relative humidities. Thus, the epiphyte lacks the enhanced water retention capacity associated with the terrestrial species, implying that epiphytic orchids are capable of germinating quickly given an adequately moist substrate. After germination, water content of fungus-infected seeds was higher. These results provide first time fundamental information related to habitat preference by analyzing seed. Germination is considerably enhanced with mycorrhizal fungi that facilitate the absorption of free water by their orchid seed hosts.

Mycorrhizal Fungi and Cold-assisted Symbiotic Germination of the Federally Threatened Eastern Prairie Fringed Orchid, Platanthera leucophaea (Nuttall) Lindley

Abstract The 70% decline of the Federally threatened eastern prairie fringed orchid, Platanthera leucophaea (Nuttall) Lindley, has prompted concern for its recovery through artificial propagation. We describe a technique to germinate seeds and cultivate seedlings of P. leucophaea in vitro using cold treatments (=stratification) and mycorrhizal fungi (=symbiotic seed germination). Five fungal isolates were recovered from mature P. leucophaea plants in Illinois and Michigan and were identified as members of the anamorphic genus Ceratorhiza Moore. Stratified seeds inoculated with mycorrhizal fungi germinated within 25 d of sowing. Leaf-bearing seedlings were obtained by chilling young seedlings (protocorms) for 107 d. Our successful culture of leaf-bearing seedlings with a presumed mycotrophic capability may make it possible for this threatened orchid to be propagated in soil ex vitro, followed by reintroduction into suitable habitats.

EFFECTS OF CARBOHYDRATE SOURCE ON THE IN VITRO ASYMBIOTIC SEED GERMINATION OF THE TERRESTRIAL ORCHID HABENARIA MACROCERATITIS

The effects of the carbohydrates fructose, sucrose, and dextrose on the seed germination and protocorm development of the terrestrial orchid Habenaria macroceratitis were assessed in the presence or absence of banana powder. Malmgren Modified Terrestrial Orchid Medium was used as the basal medium. Each carbohydrate was screened at 50 mM with and without banana powder (15 g L−1). No significant differences in germination or protocorm development among all treatments were observed after seven weeks. There were no significant differences in advanced development among carbohydrate treatments without banana powder after 21 weeks. However, the presence of banana powder in the medium suppressed advanced protocorm development in the fructose, dextrose, and control treatments. These data support the wide suitability of simple exogenous carbohydrates in supporting the germination and protocorm development of H. macroceratitis, and suggest that a wide range of carbohydrates are suitable for the culture of often difficult-to-germinate terrestrial orchids.