Propagation In Action: Avon Park Harebells

Erica SmithBlog Tower Garden, HorticultureLeave a Comment

Crotolaria avonensis is a federally listed endangered species and a rare endemic to the Lake Wales Ridge. Its common names include Avon Park rattlebox, Avon Park harebells, and Avon Park rabbit-bells. It is known from only three sites. It flowers in the spring and then lies dormant the rest of the year, relying on a long taproot to help sustain it during the dormant period. C. avonensis is primarily threatened by development and fire suppression. However, there are plants that are being preserved in the Rare Plant Conservation Program’s (RPCP) National Collection Beds at Bok Tower Gardens to help prevent extinction. Many of these plants are the result of tissue culture propagation.

Tissue culture techniques were developed in the 1950s, and have aided research, conservation, and agriculture. Plant tissue culture involves culturing sterile pieces of plants in a lab, similar to how scientists grow bacteria in a lab on a petri dish.

Pieces of plant tissue must be sterilized with a dilute solution of bleach or alcohol. The test tube and growing media must also be thoroughly sterilized before use to prevent the bacteria or fungi from growing on the plant tissue. The plant tissue is then placed in the prepared test tube with the growing media. The media contains required vitamins, minerals, and sugars, along with plant growth regulating hormones selected to induce rooting or shooting as desired, mixed into an agar substrate. With careful techniques, good incubating conditions, and some luck, one initial small piece of plant tissue may grow into a new, whole plant.

The new tissue cultured plant (called a “plantlet”) can then be carefully removed from the test tube and acclimatized into potted conditions. This is done by carefully washing off agar from the roots, preparing a special soil mix, maintaining moisture by use of a protective dome, and keeping the plant in an environment to protect it from the harsh outdoor environment.

For species for which few seeds are available or for which propagation by cuttings is not feasible, tissue culture propagation can greatly benefit conservation efforts and dramatically increase the number of plants in existence, even when their biology is not completely understood. Because tissue culture produces clones of the parent plant, propagation via tissue culture, as with propagation from cuttings, needs to done for numerous individuals of a population in order to maintain the genetic diversity of a species.

For over a decade, the Rare Plant Conservation Program (RPCP) has partnered with the Cincinnati Zoo on tissue culture propagation of C. avonensis. Scientists at the plant tissue culture lab at the Center for Conservation and Research of Endangered Wildlife at the Zoo propagate new plants from fresh cuttings supplied by the RPCP, then send the new plants back to Bok Tower Gardens for acclimatization, growth, and transplanting into either the National Collection Beds or into a wild population. In May, inventories of the National Collection revealed that many of the tissue culture propagated C. avonensis currently in the Beds are healthy and flowering.

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