AGNR HOME

Elaine M. Shea, Plant Physiologist, Loyola College in Maryland

Since the origins of agriculture, humans have propagated plants.  The most familiar method is propagation by seed which involves sexual recombination. The plants produced from seed are related to, but not identical to the parent plant.  Vegetative propagation methods take advantage of the natural tendency of a plant to reproduce asexually.  The plants produced are genetically identical to the parent plant.  Traditional methods include rooting cuttings, division, air-layering, and grafting. 

Plant tissue culture is a more recent and highly technical method for propagating plants.  The phrase 'plant tissue culture' refers to a variety of techniques that permit the growth and development of plant fragments in vitro (meaning, literally, 'in glass').  The fragments may be as large as a 1/4 inch diameter leaf disk or as small as a single cell.  The success of tissue culture is due the ability of specialized plant cells to return to an unspecialized state and begin dividing.  This commonly occurs at the site of injury in wounded plants.  Cells at the edges of the injury are stimulated to divide, they form a mass of unspecialized cells called a callus and seal the wound.  In tissue culture, callus cells are stimulated to form shoots and roots.

The idea of tissue culture was first proposed in 1902.  The first successful tissues grown in culture were in the 1930's.  The first whole plants regenerated from culture were carrots in 1958.  The number of species that can now be propagated by tissue culture techniques is beyond count.  In general, the procedure involves sterilizing the surfaces of the source tissue (root, stem, or leaf) with bleach.  The tissue is rinsed in sterile water, cut into small pieces and placed on culture medium.  The culture medium contains all of the mineral nutrients, hormones, vitamins and sugars needed for the cells to divide and grow.  By changing the amounts and types of hormones in the medium, the cells can be stimulated to develop into shoots or roots.

Micropropagation is the use of plant tissue culture techniques to generate high quality, genetically uniform plants.  It is the only way to produce virus free clones of infected plants.  The first plants to be commercially propagated in this manner were Cymbidium orchids, but the method is used for most plants that are commonly propagated vegetatively.  Familiar examples include tulips, potatoes, & lilies.  Micropropagation is also useful for reproducing copies of plants with ideal (forestry and fruit trees) or unique (introductions of a new rose or orchid hybrid) characteristics for commercial distribution.   With a limited amount of materials and laboratory space, millions of plants can be produced.  From miniature African Violets to the tallest California redwoods, the variety of plants that can be propagated in vitro is almost unlimited.

The newest outcome of micropropagation in the green industry can be seen through plug production technology.  Currently the greenhouse and nursery industry rely on micropropagation technologies to mass produce high quality, uniform plants.  As we move into the millennium we will see several benefits of micropropagation emerge for the green industry such as more production space will become available to growers and producers will be better able to schedule production needs.