Propagation and reintroduction of Caladenia

Abstract

Many Caladenia species have been reduced to extremely small and/or fragmented populations, and reintroduction/translocation into natural or rehabilitated habitats, by using ex situ propagated plants or via direct seeding, represents an important adjunct in conservation planning. However, Caladenia species are some of the most difficult terrestrial orchid taxa to propagate, in part because of the specificity of the mycorrhizal associations and the need to provide growing conditions that suit both the mycorrhizal fungi and Caladenia plants. The present paper reviews recent advances in Caladenia propagation and reintroduction methods, including in vitro seed germination, transferral from in vitro to nursery environments, ex vitro symbiotic germination (germination in inoculated nursery media), nursery cultivation, the use of nurse plants and reintroduction of Caladenia into natural habitats by using seed, dormant tubers or growing plants. Techniques discussed in the present paper increase the options for future Caladenia conservation programs, especially for those species currently on the brink of extinction.

Effects of mycorrhizal fungi on symbiotic seed germination of Pecteilis susannae (L.) Rafin (Orchidaceae), a terrestrial orchid in Thailand

“…Although P. bellatulum and S. affinis were obtained from local market, but these two terrestrial orchid species were collected from forests and replanted in forest soil before sold in the market. This confirms that terrestrial orchids depend upon mycorrhizal associations in nature ( McKendrick et al 2002;Smith and Read 2008;Wright et al 2009). …”

“…Many orchids have been shown to have symbiotic relationships with specific fungi in their environment. It has been estimated that when a wild terrestrial orchid is dug up and transplanted from a natural source, most of them will die or become unhealthy because the new environment lacks the correct fungi to keep it alive (Withner 1974;Rasmussen 1995). In addition, some orchids may depend upon fungi which also associate with the roots of specific nearby trees and shrubs in a microenvironment that is of value to all the plants (Roy et al 2009).…”

“…This is the main problem for propagation and conservation of wild terrestrial orchids. In nature, most orchid seeds cannot germinate or are able to start germinating but will not grow unless they are infected with mycorrhizal fungi which supplies young plants with a carbon source and inorganic nutrients (Brundrett et al 1996;Swarts and Dixon 2009;Wright et al 2009). …”

Asymbiotic in vitro germination and seed quality assessment of Australian terrestrial orchids

“…The advantages of this method are that it produces rapid germination and growth (Rasmussen et al 1991;Markovina and McGee 2000), seedlings are often superior to those grown asymbiotically (Clements 1981) and it allows co-introduction of the appropriate mycorrhizal fungus if the orchid is to be grownon or reintroduced into the wild (Clements 1981;Wright et al 2009). Disadvantages include the extreme mycorrhizal-specificity of some orchids (Clements 1981;Brundrett 2007), the requirement for time-consuming fungal isolation, culture and maintenance, and the need for specialist mycological skills and facilities (Wright et al 2009). …”

“…Seeds are cultured on nutrient rich media containing minerals, carbohydrates (typically sucrose) and organic compounds. It can yield relatively high germination rates and produce seedlings with a long in vitro flask life (Wright et al 2009). Unfortunately, this method has proven difficult for many Australian terrestrial species (Clements 1982;Oddie et al 1994).…”